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  • Leväsaari, Antti (2013)
    In the standard model of competitive labor markets, an influx of immigrants increases the labor market prospects of native workers whose labor is complementary to the immigrants' labor and decreases that of those native workers whose labor is substitutable with immigants' labor. The standard model cannot, however, explain how vacancies and unemployment exist at the same time, or allow the job creation to respond to the arrival of new workforce. This master's thesis studies the effects of immigration on the wages, employment and welfare of native workers when firms and workers have to spend resources to find a suitable job match. In this environment, search frictions produce unemployment and the job creation is allowed to respond to an influx of immigrants. Matching model with three different settings is used to study these effects. In the first one immigration is introduced to a two-country matching model to see how an influx of immigration affects wages, unemployment rate and welfare of natives through probabilities of finding a job and finding a worker for an open vacancy. By Pareto ranking the three equilibria the model produces it is shown that immigration is beneficial to all parties involved. The second setting is a one-country model with two sectors and examines how an influx of immigrants to one of the sectors affects natives' welfare in that sector. The effect is ambiguous and comprises of an impact through matching probabilities and an impact though relative prices. Finally, the impact of low-skilled immigration on both high-skilled and low-skilled native workers is studied. It will be shown that an influx of low-skilled immigrants has a positive impact on the wages and employment rate of high-skilled natives but an ambiguous impact on those of low-skilled natives. When the education choice is endogenized, however, more natives decide to acquire education and the overall effect is positive. While these results do not perfectly fit the empirical findings on the subject, they offer one mechanism to understand the behavior of labor markets with immigration, and help to understand the empirical results that contradict the predictions by the standard model.
  • Yukhtenko, Anna (2014)
    In this paper I develop an endogenous growth model with labor market frictions and spillover effects of physical capital stock on human capital accumulation. Using this instrument, I study the effects of labor market frictions on the balanced growth path of the economy, accounting for possible substitutability or complementarity between the two types of capital. I find out that severe labor market frictions impede economic growth, lower workers’ wage, educational and work effort. Faster human capital accumulation process caused by improved market conditions, enhanced importance of work experience or exogenous positive shocks benefits economic growth. I prove that if human and physical capital are complements (positive externality), the process of on-the-job learning increases the speed of human capital accumulation, resulting in higher work effort and economic growth rate. Substitutability between the two factors of production (negative externality) leads to inability of workers to adjust to rapid technological progress, causing economic inefficiencies, invalid usage of capital and, in the end, lower growth rate of the economy.
  • Siljander, Eero (2004)
    This thesis deals with labour demand, the elasticises of labour demand and adjustment through the theory of labour economics, an econometric model and its application to panel data set of finnish firms. First a continues and discrete time model of labour demand are specified with strictly convex or quadratic adjustment costs. In the econometric part of the study a model for labour demand with firm and time specific elasticises and adjustment are specified. The adjustment parameter is also explicitly modeled. From the econometric model for labour demand the wage-, output-, capital- and trend elasticity are calculated for each observation in time. Then these elasticities are averaged according to the factor of interest which in this thesis are 1.time, 2.industry and 3.size of firm. The same applies for the adjustment parameter. Especially the wage elasticity is of special interest as it describes the effects of the tax wedge of labour on labour demand. In the econometric part of the thesis the elasticises and adjustment of labour demand are estimated from an unbalanced panel data set of the 500 largest enterprises in Finland as measured by turnover. The data covers the years from 1986 to 2003 and has a total of 8185 observations. As an econometric research method a fixed effects nonlinear seemingly unrelated regressions (SUR) algorithm is used to estimate labour demand. The results indicate that the wage and output elasticity of labour demand have increased during the observed period from 1986 to 2003. The wage elasticity has increased from -0.6 to -0.75 and the output elasticity from 0.8 to 0.9 in the long run during the data period. The same pattern is observed for these elasticises in the short run as well. Technical change has decreased labour demand by approximately two percent p.a. in the short and long run. These results confirm that finnish labour markets have become more flexible due to increased competition and integration of product markets which in turn are due to the single market policies of the EU and the effects of globalization on labour markets. The only surprise in the results is that the adjustment parameter has decreased slightly during the end of the observation period which points to mounting adjustment costs of labour demand and rigidities in the adjustment of labour markets. The results also show that the elasticises and adjustment of labour demand vary strongly with the industry of the firm. This points to the heterogeneity across firms and industries which validates the research strategy and methodology used here and should not be overlooked in empirical research in general. On the other hand firm size is not found to be a significant factor in determining the elasticises or adjustment. Therefore the explicit modeling of firm and time specific adjustment should be taken into account in future research on labour demand and its elasticises.
  • Roppola, Juha (2008)
    Vuonna 1968 Neuvostoliitto halusi mukaan nopean tietokoneistumisen aikakauteen ja ostaa brittiyritys International Computersin (ICL) uusia tehokkaita digitaalisia tietokoneita. ICL:n lupaavan liiketoiminnan päänavaus törmäsi kuitenkin amerikkalaisten vastustukseen. Koska kyse oli kolmannen sukupolven tietokoneista eli kauppasaarron alaisesta strategisesta kaupasta, se vaati USA:n hyväksynnän. Britannian pääministeri Harold Wilson, joka oli ymmärtänyt tietokoneiden merkityksen kasvun, henkilökohtaisesti antoi kaiken tukensa tietokoneiden idänkaupalle. Lopulta amerikkalaiset taipuivat kompromissiin. Tässä tutkielmassa väitetään, että ICL oli erityisen tärkeä Harold Wilsonin Labour-hallitukselle, mikä korosti myös tietokoneiden idänkaupan merkitystä. Ilman hallituksen tukea ICL ei olisi menestynyt Neuvostoliiton markkinoilla länsiyrityksistä parhaiten. Tutkimuksessa on uutta arkistolähteisiin perustuvaa tietoa tapauksesta ja monitasoinen lähestymistapa, jota aikaisemmassa tutkimuksessa ei ole käytetty. Tässä tutkitaan tarkemmin neljän tietokoneen viennin vaiheita, jotka hiersivät eniten USA:n ja Britannian välejä. Amerikkalaiset asettuivat vastustamaan tiukasti tietokoneiden vientiä Neuvostoliittoon strategisin perustein ja asiassa jouduttiin vetoamaan suoraan presidentti Richard Nixoniin. Yhdysvallat piti läheistä liittolaistaan tiukemmin kiinni lännen Neuvostoliittoa kohtaan asettamasta kauppasaartopolitiikasta, jota valvoi yhteistyöjärjestö Cocom, kun Britannia puolestaan painotti idänkaupassa enemmän taloudellisia intressejään. Brittien pahimmaksi kilpailijaksi idänmarkkinoilla nousikin Ranska, joka suhtautui teknologian vientikieltoihin välinpitämättömästi. Britannian taloudellinen teollinen kehitys olivat jääneet jälkeen sen tärkeimmistä kilpakumppaneista, mikä alkoi herättää kasvavaa huolta 60-luvulla. Vuonna 1964 valtaan noussut Britannian työväenpuolue Labour syytti konservatiiveja kestämättömästä "stop-go" -taloudenpidosta ja tarjosi tilalle teknologista vallankumousta. Vienninedistämisellä pyrittiin korjaamaan suurta vaihtotaseen vajetta, joka nähtiin keskeisenä taloudellisena ongelmana. Labourin uudessa teknologiapolitiikassa näkyvimpään rooliin nousi tietokoneteollisuus. ICL muodostettiin juuri vuonna 1968 Labour-hallitukselle tärkeässä fuusiossa, jota se tuki avokätisesti, kilpailemaan amerikkalaisen markkinajohtaja IBM:n kanssa. IBM ei vielä vaikuttanut Neuvostoliiton markkinoilla, mikä teki niistä ICL:lle vieläkin houkuttelevammat. Merkittävästä tietokoneteollisuuden 1960-luvun kilpailusta, josta IBM selvisi voittajana, ei ole kunnon tutkimusta. Tämä tutkielma valottaa asetelmaa idänkaupan kautta. Idänkauppaan ladattiin odotuksia myös Amerikassa ja monet yritykset tutkivat mahdollisuuksia idän markkinoilla. Juuri suuret odotukset alleviivasivat idänkaupan merkitystä. Vaikka taloudellisen kylmän sodan ja kauppasaartotutkimuksen piirissä viitataan usein "taloudellisiin intresseihin" tai kansalliseen politiikkaan, tämä tutkielma nostaa ne uudella tapaa keskeisiksi lähtökohdiksi. Tämä on tutkimus pikemminkin vienninedistämisestä ja teknologian poliittisuudesta kuin vientikielloista.
  • Erholm, Juha (2006)
    The European Union has taken down internal borders in Europe to allow for the free movement of people, companies, goods and services. Yet EU member states retain great liberty in setting their own tax levels and public systems. As mobility causes public economies to take the external situation into consideration when setting tax and public expenditure policies, this new setting can encourage fiscal competition between EU member states and lower income redistribution levels in the EU. This thesis examines this setting from the perspective of how labour mobility can cause fiscal competition. In recent decades, labour mobility in Europe has been quite low. This can be expected to change, however, partly because of the May 2004 enlargement of the EU. Wildasin (1991) models a combined federal and local system with federal subsidies and local income redistribution, with only the poor being allowed to move. In equilibrium local jurisdictions end up with the same income redistribution as all other local jurisdictions. Hindriks (1999) examines a setting where independent jurisdictions compete fiscally, attracting the rich and deterring the poor. Particularly the mobility of the rich is detrimental to income redistribution. Also the mobility of the poor has in most cases a negative effect. Jurisdictions can compete either in taxes, transfers or both in taxes and transfers, with competition in transfers having the strongest effect on income redistribution. Tax and income redistribution reasons are not currently the biggest cause to migrate in the EU. Despite this, expecting labour mobility levels to go up European nations will have to consider labour mobility induced fiscal competition as possibly limiting public policy in the future.
  • Kylmä, Tarja (1993)
    Tähän tutkielmaan kuuluu sekä kirjallisuuskatsaus että tutkimusosa. Kirjallisuuskatsauksessa käsitellään verkkokalvon anatomian ja fysiologian perusteiden sekä koiran verkkokalvon kehityksen lisäksi lyhyesti fototransduktiota (valoenergian muuttumista näköaistinsoluissa sähköisiksi impulsseiksi), koiran verkkokalvosurkastumia ja elektroretinografiaa. Tutkimuksessa mitattiin pimeäadaptoidun verkkokalvon DC-elektroretinogrammi yhdeksältä labradorinnoutajalta. Koirien molemmat vanhemmat sairastavat perinnöllistä verkkokalvosurkastumaa (yleistynyt sauva-tappi -dystrofia). Rekisteröinneissä koirat olivat 1, 2, 3, 4 ja 18 kuukauden ikäisiä. Kontrolliryhmän koirat olivat terveitä, vastaavanikäisiä labradorinnoutajia. Xenon-salamalampulla annetut ärsykkeet kolmella eri intensiteetillä (alkaen 2 log yksikköä b-aallon kynnysarvon alapuolelta) aiheuttivat negatiivisia vasteita, jotka tunnistettiin kynnysherätevasteiksi (scotopic threshold response, STR). STR:n oletetaan olevan postreseptoriaalinen kynnysvaste. Vasteiden latenssiajat vaihtelivat 37-78 ms:iin. Vasteen voimakkuuteen vaikuttivat valon intensiteetti ja koiran ikä. Latenssiaika, vasteen alkamiseen kulunut aika, lyheni koiran vanhetessa sekä kontrolleilla että dystrofisilla. Amplitudien huippuarvot vaihtelivat 0-70 mikroV:iin, eikä kummassakaan ryhmässä amplitudeilla ollut merkitsevää eroa. 18 kuukauden iässä ei kuitenkaan yhdeltäkään dystrofiselta mitattu STR:ää, vaikka kontrolleilla se oli. Ero oli merkitsevä (P=0.028). Vasteen huippuarvon saavuttamiseen kulunut aika (implicit time)lyheni terveen koiran vanhetessa. Dystrofisilla lyhenemistä ei tapahtunut. Kolmen kuukauden iässä ero oli tilastollisesti merkitsevä. Tutkimus osoittaa, että STR:ää voidaan käyttää avuksi, kun tutkitaan perinnöllistä verkkokalvosurkastumaa sen varhaisvaiheessa.
  • Mikkonen, Maria (Helsingfors universitet, 2014)
    Tutkimus osoittaa kerronnan trooppien, sääntöjen kääntämisen ja useamman asteen maailmojen yhteyden fantasiakirjallisuudessa. Tutkimuksen kohteena on Ilkka Auerin fantasiateos Sysilouhien sukua (2004), joka aloittaa Lumen ja jään maa -sarjan. Teoksen juoni mukailee fantasiakirjallisuudelle tyypillistä quest-tarinatyyppiä, jossa henkilöhahmon tulee suorittaa tiettyjä tehtäviä voidakseen päästä päämääräänsä. Tämä päämäärä on usein konkreettinen, mutta siihen liittyy myös henkilöhahmon kasvutarina. Kerronnan troopit ovat Margaret Anne Doodyn The True Story of the Novel -teoksessaan (1997) erittelemiä kerronnan hetkiä, joiden yhteyteen juonenkulun kannalta tärkeät elementit keskittyvät. Tutkimukselle erityisen tärkeitä kerronnan trooppeja ovat rikkomisen, korjaamisen, luolan, unen, labyrintin, Minotauroksen, Eroksen ja jumalattaren troopit, joiden yhteyden useamman asteen maailmoihin ja sääntöjen kääntämiseen tutkimus selvittää. Lisäksi tutkimus keskittyy erityisesti reunan trooppiin, joka on fantasiakirjallisuudessa tärkeä useamman asteen maailmoihin liittyvä trooppi, jonka yhteydessä esiintyy toistuvia fantasiakirjallisuudelle tyypillisiä motiiveja. Sääntöjen kääntämisellä tarkoitetaan teoksen sisäisten tosiasioiden ja sääntöjen muuttamista niin, että niistä tulee teoksen maailmassa epätavallisia. Sääntöjen kääntämisen teoriaa on eritellyt Eric S. Rabkin teoksessaan The Fantastic (1976). Tutkimus erittelee teoksen maailmojen rakennetta ja nostaa yksityiskohtaisesti esille useamman asteen maailmojen tunnuspiirteitä. Useamman asteen maailmojen teoreettisena lähtökohtana on Maria Nikolajevan väitöskirja The Magic Code : the use of magical patterns in fantasy for children (1988), joka käsittelee erilaisia useamman asteen maailman ilmentymiä lasten fantasiakirjoissa. Tutkimus osoittaa, että kerronnan troopeilla, useamman asteen maailmoilla ja sääntöjen kääntämisellä on selvä yhteys, mikä tekee fantasiasta juonen kannalta hyvin tärkeän elementin. Kerronnan trooppien ympärille keskittyy useamman asteen maailmojen merkkejä, sääntöjen kääntämisiä sekä quest-tarinatyypille tyypillisiä juonen kannalta tärkeitä tehtäviä.
  • Korhonen, Kalle (Helsingin yliopisto, 2003)
  • Zavaleta Ochoa, Eugenia (Helsingin yliopisto, 2013)
    During the decade of 1970, in Costa Rica started more often to appear state and private exhibition spaces; and commercialization of the artistic creations began to develop on a regular basis. This scenario was set by the interference of the welfare state; without this intervention the cultural development of Costa Rica would have been slower and weaker. Since 1950, began a series of economic, political and social changes that allowed the definition of cultural policies, which permitted state actions that resulted in museums, contests, awards and public collections, among others. Thus, cultural policies became the driving force that impulsed the culture and, specifically, the art market in the country. In other words, the welfare state created a primary substrate from which cemented the country's cultural life and, therefore, the commodification of art. So, this research focuses on the primary substrate that led to the flowering of an art market. In the process of building the art market, we consulted the Collection of Laws, Decrees and Resolutions, and The Gazette. Furthermore, we used databases such as the Costa Rican Legal Information System. The Costa Rican Art Museum (MAC) has albums, files, documents and databases that were fundamental in determining the country's cultural life, in other words, -for example- the identification of national and foreign artists, public collections, exhibitions, awards, contests, art reviews, comments and auctions. From these documents, databases were developed to process the extracted information. Other databases that were consulted were the catalogs of the National Insurance Institute, the Central Bank of Costa Rica, the Social Security Fund and the Museum of Contemporary Art and Design.
  • Lehtinen, Mari (Helsingin yliopisto, 2009)
    "The contextualization of radio discourse by prosodic means. The example of five great French philosophers of the 20th century" This PhD thesis treats the contextualization of radio discourse by prosodic means. More precisely, the work is focussed on seven “marked figures”, which consist of the salient changes of one or more prosodic parameters. The phenomena are studied here both from the angle of their acoustic forms and from the angle of their typical contexts of occurrences and discursive functions. The data comes from six radio broadcasts transmitted by different French radio stations between 1948 and 1973. The speakers of the broadcasts are famous French 20th–century philosophers: Jean-Paul Sartre, Albert Camus, Michel Foucault, Maurice Merleau-Ponty and Gaston Bachelard. The total duration of the data is 162’32. In addition to a general presentation of the phenomena, the thesis includes contrastive studies in which the two main phenomena of the work (the so-called “figure HB” and the so-called “undulating figure”) are compared with a melodic figure occurring in classical piano music and with a prosodic phenomenon of Finnish (the so-called “figure of familiarity”). One part of the thesis is also devoted to a contrastive study discussing the prosodic interpretation of punctuation (the full stop and the comma) in The Stranger (L’Étranger) by Albert Camus, as read by the author. Methodologically, the work falls within the scope of conversation analysis (CA), and it is inspired by the interaction-based approach to prosody, the “theory of contextualization” of Gumperz and by numerous linguistic and phonetic works directed towards French. The results of this work, based on seven original publications, suggest that the “marked figures” constitute multidimensional phenomena of speech having an important and a complex role in the contextualization of radio discourse. The acoustic forms of these phenomena are very different, and their functions reach several discursive levels. In addition to presenting the phenomena under consideration, the work includes some methodological and theoretical discussion concerning the study and the nature of the process of the contextualization of speech.
  • Arffman, Johanna (Romaanisten kielten laitos, 2007)
    Coordination and juxtaposed sentences The object of this study is the examination of the relations between juxtaposed clauses in contemporary French. The matter in question is sentences which are composed of several clauses adjoined without a conjunction or other connector, as in: Je détournai les yeux, mon c ur se mit à battre. The aim of the study is to determine, which quality is the relation in these sentences and, on the other hand, what is the part of the coordination there. Furthermore, what is this relation of coordination, which, according to some grammars, manifests through a conjunction of coordination, but which, according to some others is marked in juxtaposed sentences through different features. The study is based on a corpus of written French from literary and journalistic text sources. Syntactic, semantic and textual properties in the clauses are discussed. The analysis points to differences so, it has been noted, in each case, if one of the clauses is affirmative and the other negative and if in the second clause, the subject has not been repeated. Also, an analysis has been made on the ground of the tense, mode, phrase structure type, and thematic structure, taking into account, in each case, if the clauses are identical or different. Punctuation has been one of the properties considered. The final aim has been to eliminate gradually, based on the partition of properties, subordinate sentences, so that only the hard core of coordinate sentences remains. In this way, the coordination could be defined similarly as the phoneme is defined as a group of distinctive features. The quantitative analyses have led to the conclusion that the sentences which, from a semantic point of view, are interpreted as coordinating, contain the least of these differences, while the sentences which can be considered as subordinating present the most of these differences. The conditions of coordination are, in that sense, hierarchical, so that the syntactic constraints have to make room for semantic, textual and cognitive factors. It is interesting to notice that everyone has the ability to produce correct coordinating structures and recognize incorrect coordinating structures. This can be explained by the human ability to categorize which has been widely researched in the semantic of prototype. The study suggests that coordination and subordination could be considered as prototypical cognitive categories based on different linguistic and pragmatic features.
  • Abbas Hilmi, Hanan (2010)
    Bacteriocin-producing lactic acid bacteria and their isolated peptide bacteriocins are of value to control pathogens and spoiling microorganisms in foods and feed. Nisin is the only bacteriocin that is commonly accepted as a food preservative and has a broad spectrum of activity against Gram-positive organisms including spore forming bacteria. In this study nisin induction was studied from two perspectives, induction from inside of the cell and selection of nisin inducible strains with increased nisin induction sensitivity. The results showed that a mutation in the nisin precursor transporter NisT rendered L. lactis incapable of nisin secretion and lead to nisin accumulation inside the cells. Intracellular proteolytic activity could cleave the N-terminal leader peptide of nisin precursor, resulting in active nisin in the cells. Using a nisin sensitive GFP bioassay it could be shown, that the active intracellular nisin could function as an inducer without any detectable release from the cells. The results suggested that nisin can be inserted into the cytoplasmic membrane from inside the cell and activate NisK. This model of two-component regulation may be a general mechanism of how amphiphilic signals activate the histidine kinase sensor and would represent a novel way for a signal transduction pathway to recognize its signal. In addition, nisin induction was studied through the isolation of natural mutants of the GFPuv nisin bioassay strain L. lactis LAC275 using fl uorescence-activated cell sorting (FACS). The isolated mutant strains represent second generation of GFPuv bioassay strains which can allow the detection of nisin at lower levels. The applied aspect of this thesis was focused on the potential of bacteriocins in chicken farming. One aim was to study nisin as a potential growth promoter in chicken feed. Therefore, the lactic acid bacteria of chicken crop and the nisin sensitivity of the isolated strains were tested. It was found that in the crop Lactobacillus reuteri, L. salivarius and L. crispatus were the dominating bacteria and variation in nisin resistance level of these strains was found. This suggested that nisin may be used as growth promoter without wiping out the dominating bacterial species in the crop. As the isolated lactobacilli may serve as bacteria promoting chicken health or reducing zoonoosis and bacteriocin production is one property associated with probiotics, the isolated strains were screened for bacteriocin activity against the pathogen Campylobacter jejuni. The results showed that many of the isolated L. salivarius strains could inhibit the growth of C. jejuni. The bacteriocin of the L. salivarius LAB47 strain, with the strongest activity, was further characterized. Salivaricin 47 is heat-stable and active in pH range 3 to 8, and the molecular mass was estimated to be approximately 3.2 kDa based on tricine SDS-PAGE analysis.
  • Lyhs, Ulrike (Helsingin yliopisto, 2002)
  • Laurikkala, Sini (Helsingin yliopisto, 2015)
    The literature review presents general information on fungi and mycotoxins and then deals with aflatoxins, in particular aflatoxin B1 and M1, their occurrence, significance, and current methods for controlling the risk of aflatoxin. Particular emphasis was given to studies on lactic acid bacteria (LAB) in controlling the growth of aflatoxigenic molds and binding of aflatoxins. The aim of the experimental work was to assess the ability of 171 LAB isolates originating from Kenyan naturally fermented traditional milk and maize samples (1) to inhibit the growth of Aspergillus and (2) to bind aflatoxin M1 in vitro. All the LAB isolates (n=171) were screened for their antifungal activity against A. flavus by an overlay method with 100 µl LAB culture on potato dextrose agar (PDA) plate. Out of 171 LAB isolates, mold growth was reduced by 33 isolates, of which 19 isolates were confirmed to retain their activity. These 19 LAB isolates were tested against A. flavus with three different amounts of LAB culture (50 µl, 100 µl and 200 µl). Three LAB isolates performed best against A. flavus by inhibiting the growth with all the tested amounts of LAB culture. The three LAB isolates were identified as Lactobacillus plantarum first by 16S rDNA sequence analysis and later confirmed by recA derived primers and multiplex PCR assay. The ability of 171 LAB isolates to bind AFM1 from phosphate-buffered saline (PBS) in vitro was carried out. LAB isolates were incubated with an amount equivalent to 50 ng AFM1 /ml for 4 h and then centrifuged (10 000 rpm, 10 °C) for 15 min to obtain supernatant containing unbound AFM1. The amount of unbound aflatoxin was analysed by HPLC chromatography from 51 samples. Binding ability of the analyzed isolates varied from 15,4 % to 51,5 %, and six LAB isolates were shown to bind more than 42,4 % of AFM1. The results showed that all tested indigenous LAB isolated from fermented milk and maize products manufactured in Kenya had variable ability to control the growth of A. flavus and bind AFM1 in vitro. It is suggested that such LAB strains could be used for reduction of the risk of aflatoxin contamination in food and feed chains.
  • Wikman, Helena (Helsingfors universitet, 2010)
    Surface (S-) layers, structural entities that surround the cell envelope of various bacteria, are comprised of a porous lattice of identical protein or glycoprotein subunits. Interestingly, the S-layer is able to promote adherence to host epithelial cells in a variety of Lactobacillus species. L. amylovorus DSM 16698, a strain of porcine origin, encodes at least three putative types of S-layer proteins in its genome sequence. In this study the surface structure of L. amylovorus DSM 16698 strain and the adhesion properties of its S-layer proteins to porcine intestinal epithelial IPEC-1 cell line were examined based on preliminary results. In addition, host receptors potentially specific for S-layer proteins were isolated from IPEC-1 cells. Cloned recombinant S-layer proteins rSlpA and rSlpB of DSM 16698 were reassembled onto fluorescent-labeled L. amylovorus cell wall extracts as a means to mimic the native S-layer lattice structure. Adhesion between the reassembled recombinant S-layer complexes and IPEC-1 cells was assessed qualitatively by microscopy and quantitatively by measuring fluorescence intensity. Results from in vitro adhesion assays indicate that the rSlpA and rSlpB proteins both mediated the adherence of the L. amylovorus DSM 16698 strain to porcine intestinal epithelial cells. Antibodymediated adhesion inhibition experiments were also performed, in which the two rSlps were pretreated with their specific anti-rSlp serum, and showed that adhesion between the rSlps and IPEC-1 cells could be inhibited by the antibody treatment. Moreover, by using fluorescent-labeled rSlp-specific antibody, the surface structure of L. amylovorus cells was microscopically examined. With this immunofluorescent technique, the SlpA and SlpB proteins were both observed to localize on the cell surface and exhibit a similar distribution pattern. Putative S-layer host cell receptors were isolated from the interaction between the reassembled rSlp/cell wall complexes and IPEC-1 derived membrane proteins using a SDS-PAGE-based system. Receptor isolation experiments resulted in repeatedly the same protein profile. It has previously been shown that L. amylovorus DSM 16698 attaches to IPEC-1 cells, but the identities of surface-localized components that mediate this microbe-host interaction had yet to be determined. In this present study, S-layer proteins were found to be an important mediator in the interaction between L. amylovorus DSM 16698 and a porcine epithelial cell line. Additionally, it was shown how S-layer proteins are localized on the surface of L. amylovorus DSM 16698 cells.
  • Salminen, Minna (Yliopistopaino, 2006)
    Lactobacilli are gram positive rods, which belong to normal oropharyngeal, gastrointestinal and urogenital flora. They are widely used in food industry and as food additives. Although their virulence is presumed to be very low, opportunistic bacteremic infections, especially in immunocompromised hosts, have been detected. In the present study, the possible effects of increasing probiotic use of Lactobacillus rhamnosus GG (LGG) on the occurrence of bacteremia due to lactobacilli was evaluated on population level. In Finland, 90 Lactobacillus bacteremia cases were reported to the National Infectious Disease Register maintained by National Public Health Institute, during 1995-2000. Their proportion of all bacteremia cases was on average 0.24%, corresponding to 0.3 cases/100 000 inhabitants annually. In the Helsinki University Central Hospital district the corresponding proportion of all bacteremia cases was observed during 1990-2000. Despite LGG intake increased six folded no increasing trend in the occurrence of lactobacilli bacteremia was seen. A total of 85 Lactobacillus sp. blood isolates collected from different human bacteremic cases were characterised and compared with the commercial probiotic LGG strain. In species characterisation 46 L. rhamnosus strains, 12 L. fermentum and L. casei strains each, three each of L. gasseri, L. salivarius and L. jensenii species, two L. curvatus, and one each of L. plantarum, L. sakei, L. zeae and L. reuteri species were detected. Nearly half of the L. rhamnosus findings turned out to be indistinguishable from the probiotic LGG strain. Common predisposing factors to Lactobacillus bacteremia were immunosuppression, prior prolonged hospitalisation and prior surgical interventions. Severe or fatal comorbidities were found in 82% of the patients. Mortality at one month was 26% and severe underlying diseases were a significant predictor of death (OR 15.8). Antimicrobial susceptibility of Lactobacillus strains was species dependent. The Lactobacillus isolates were generally susceptible to imipenem, piperacillin-tazobactam, clindamycin and erythromycin, whereas all other than L. gasseri and L. jensenii species were not at all susceptible to vancomycin. The susceptibility to cephalosporin varied greatly even within species why they might not be recommended for treatment of Lactobacillus infections. The effect and safety of probiotic LGG preparation in amelioration of gastric symptoms and diarrhea in HIV-infected patients was evaluated. No significant differences in gastrointestinal symptoms or diarrhoea in LGG treated patients compared to placebo could be found. LGG was well tolerated with no adverse effects including bacteremic outbreaks could be observed. The use of probiotic LGG can be regarded safe in this immunocompromised patient group.
  • Ojala, Teija (Helsingin yliopisto, 2016)
    Modern DNA sequencing technologies have opened up new possibilities to study bacteria. These methods have not only enabled the characterization of the genetic capacities of bacteria at previously unseen scale but have also provided a wealth of information about bacterial transcriptomes. In this thesis, sequencing and subsequent analysis approaches were applied to study Lactobacillus crispatus and Propionibacterium freudenreichii. Specifically, the aim was to uncover how these two Gram-positive species of human relevance can live in and interact with their environments. L. crispatus is a prominent member of the human vaginal flora and important for urogenital health. In this thesis, an annotated genome sequence was produced for L. crispatus ST1 and analyzed in conjunction with publicly available genome sequences of nine vaginal L. crispatus isolates. The common ortholog groups of the ten isolates captured approximately 57% of the ortholog groups of each isolate and provided a good estimation of the final set of core features of this central urogenital species. Notably, several of the detected L. crispatus core features were of putative relevance to vaginal health. Among these features was a previously characterized adhesin, which was in this thesis identified as a likely antagonist to the harmful vaginal bacterium Gardnerella vaginalis. Altogether, the study revealed a notable functional similarity between the L. crispatus strains and established the role of L. crispatus core proteins in maintaining vaginal health. P. freudenreichii, in turn, is an industrially important dairy culture. In this thesis, the cheese starter P. freudenreichii ssp. shermanii JS was subjected to transcriptome and genome sequencing to gain a deeper understanding of the role of this bacterium in industrial cheese ripening. The genome of strain JS encoded several enzymes and metabolic pathways involved in the formation of flavor compounds and was highly similar to those of the other P. freudenreichii strains. Transcriptome analysis of industrial cheese samples revealed nearly 15% of the 2,377 protein-coding genes of strain JS to be significantly differentially expressed between the warm and cold room ripening of cheese. Several of the flavor-associated genes exhibited higher expression levels in the warm compared to the cold room samples, corroborating the hypothesis that P. freudenreichii contributes more to the cheese flavor development during warm than cold room ripening. Automated function prediction of bacterial protein sequences greatly facilitated the genomics investigations of L. crispatus and P. freudenreichii in this thesis, providing functional descriptions for a majority of the predicted coding sequences of strains ST1 and JS. Moreover, re-annotation of the coding sequences of the nine publicly available vaginal L. crispatus isolates significantly increased the portion of the L. crispatus coding sequences with functional descriptions in the comparative genomics study of L. crispatus. The different methods varied in their prediction capabilities and were often complementary, supporting the use of more than one function prediction method in a bacterial genome project. Moreover, extremely strict thresholds in the homology searches were noted to unnecessarily restrict the pool of hits available for annotation transfer, hampering both the annotation quality and the fraction of coding sequences with a functional classification. Taken together, the utilized sequencing approaches coupled with suitable downstream analyses proved effective in deciphering the physiology of lactobacilli and propionibacteria and offered novel insights into the health-promoting properties of L. crispatus and flavor-forming capabilities of P. freudenreichii.
  • Vikberg, Riitta (1997)
    Helsingin yliopiston eläinlääketieteellisen tiedekunnan elintarvike- ja ympäristöhygienian laitoksella on kuvattu pilaantuneesta tomaattiketsupista eristetty Lactobacillus fructivorans -kanta. Ko. bakteeri on muihin maitohappobakteereihin verrattuna huomattavan lämpöresistentti ja kestää lisäksi alhaista pH:ta ja korkeita etanolipitoisuuksia. Kyseisen kannan kuumennuskestävyyttä tutkittaessa on todettu eloonjäämiskäyrän loppuosassa nk. häntä. Tällaista bakteeripopulaatiota kuumennettaessa bakteerien kuoleminen hidastuu lyhyen ajan kuluttua selvästi, ja bakteereista jää pieni osa henkiin hyvin pitkänkin kuumennuksen jälkeen. Havaittu lämpöresistenssi voi johtua esim. osapopulaation ominaisuuksista tai kyseessä voi olla indusoituva lämpötoleranssi, joka johtuu nk. lämpöshokkiproteiineista. Useimmat organismit muodostavat lämpöshokkiproteiineja kasvuympäristön lämpötilan noustessa. Ne suojaavat solua kuumennuksen aiheuttamilta vaurioilta. Myös muunlaiset stressitekijät voivat saada aikaan lämpöshokkiproteiinien muodostumista. Tutkimuksessa altistettiin L. fructivorans -bakteereita lyhytkestoisille stressitekijöille (lämpökäsittely ja korkea etanolipitoisuus). Käsitellyistä bakteereista eristettiin proteiineja lysotsyymikäsittelyn avulla ja proteiinit eroteltiin molekyylipainon mukaisesti SDS-PAGE-elektroforeesimenetelmällä. Lisäksi tutkittiin yhden tärkeä lämpöshokkiproteiinin, Escherichia colin hsp60-proteiinin, GroEL:n, vasta-aineiden sitoutumista L. fructivoransin proteiineihin Western blotting -menetelmällä. Lämmölle ja etanolille altistettujen L. fructivorans -bakteereiden ja altistamattomien vertailuerien välillä ei todettu eroja proteiiniprofiileissa. Lämpökäsittelyille altistetun L. fructivoransin proteiinit reagoivat GroEL vasta-aineen kanssa erittäin heikosti. Vertailubakteerina käytetyllä Lactobacillus sakella todettiin SDS PAGE:ssa selvä proteiinien induktio lämpökäsittelyn seurauksena. Erityisesti lisääntyi molekyylipainoltaan n. 70 kDa suuruisen proteiinin synteesi. Tämä proteiini reagoi immunoblottauksessa GroEL-vasta-aineen kanssa. Tulosten perusteella ei voida tehdä johtopäätöksiä L. fructivoransin proteiinien stressi-induktion olemassaolosta. Immunoblottauksella saadut tulokset viittaavat kuitenkin siihen, että L. fructivoransin aiemmissa tutkimuksissa havaittu lämpöresistenssi ei johdu GroEL-proteiinin induktiosta.