Browsing by Subject "mikrobiekologia"

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  • Ruusulehto, Liisa (Helsingin yliopisto, 2018)
    Diverse ecological interactions between populations have a considerable impact on the composition and evolution of microbial communities. Microbial evolution can happen in such short timescales that the evolutionary and coevolutionary events occurring in the populations, in turn, affect the ecological interactions in the communities. Predation and competition are the two most important factors affecting the composition and evolution of microbial communities, and usually they are strongly dependent on each other. The aim of this work was to study the effects of a predatory ciliate, Tetrahymena thermophila, on the composition and activity of a synthetic bacterial community, and to compare the differences between the effects of an ancestral strain and a coevolved strain that had previously coevolved with Pseudomonas fluorescens SBW25. Another aim of this study was to examine whether the rapidly evolving P. fluorescens bacterial strain has any definitive impact on the composition of the synthetic multi-strain bacterial community, and what are the differences between the effects of ancestral, evolved and coevolved populations of the bacterium. The effects of the different treatments were studied by measuring bacterial and ciliate population densities and community activity, and with 16S rRNA gene sequence analysis of different timepoints in the experiment. Predation had a significant effect on community composition, activity and bacterial population densities. The effect of the coevolved predator on the community composition was weaker than the effect of the ancestral predator, which was most likely caused by the smaller population density of the coevolved predator. Possibly because of this, there was no significant difference in community activity, diversity or bacterial population densities between the predator treatments. Thus, for this part, the results were consistent. P. fluorescens had a small effect on the community composition, and the difference in the evolutionary history of the P. fluorescens populations had a significant effect on the metabolic activity of the community. The experimental results indicated that prior coevolution between P. fluorescens and T. thermophila can have possible notable effects on the composition and metabolic activity of a bacterial community. The impact of earlier evolutionary adaptation or possible coevolution between community parties should be taken into consideration when studying ecological interactions and evolutionary changes in microbial communities.
  • Sinkko, Hanna (Helsingin yliopisto, 2013)
    The Baltic Sea has experienced fresh-, brackish, oxic and hypoxic water phases and its deepest bottom areas are naturally hypoxic. Recently, eutrophication has caused spreading of hypoxic areas and internal feedback mechanisms, such as the release of phosphorus (P) and nitrogen (N) nutrients from sediment to water, which sustains hypoxia. Bacteria participate in release of nutrients by mineralizing organic matter or by altering the sediment s ability to retain nutrients. In deeper sediment layers, most microbes are inactive, dead or only their DNA is preserved, representing the remains of the preceding sedimentary communities. This work investigated variation in bacterial communities in the northeastern Baltic Sea sediments along the gradients of chemical forms of P and elements related to its cycling, as well as organic matter and some properties of the upperlying water column such as oxygen concentrations. The results were discussed from the standpoint of nutrient recycling, which sustains the eutrophic conditions of the Baltic Sea. In addition, a sediment core covering the last 8000 years were investigated to determine whether historical phases of the Baltic Sea can be inferred from bacterial community data and this kind of data could be used as a palaeomicrobiological tool. Current and historical bacterial communities were studied using terminal restriction fragments length polymorphism and sequencing of the 16S rRNA genes. The data obtained were examined with sediment properties, using statistics and phylogenetics. Bacterial communities changed mainly along the gradients of chemical forms of P and organic matter. Most importantly, sulphate-reducing bacteria correlated with organic and Fe-bound P as well as redox-sensitive iron (Fe). The correlations indicated that sulphate reducers participated in the release of Fe-bound P, indirectly by producing sulphide, which captures Fe, or directly by reducing Fe oxyhydroxides. The predominance of sulphate reducers in most areas suggests that hypoxia has progressed in the phase where bacteria process most of the benthic energy. The phylum Chloroflexi, typical for organic-rich environments, increased downwards and was common throughout the sediment core spanning the 8000-year history of the Baltic Sea. This indicates that these bacteria were important in terminal mineralization and that the Baltic has been relatively organic-rich throughout its history, which makes it sensitive to external nutrient loading. The bacterial communities of the Early and Late Litorina Sea phase were distinguished from the communities of the Litorina Sea phase, which correlated positively with uranium and strontium, used as palaeooxygen and palaeosalinity proxies. Salinity changes also explained a sudden increase in the heterogeneity of the bacterial communities of Litorina Sea layers, which indicates that a salinity maximum occurred in the central Gulf of Finland 6200 6600 years ago. This study showed that bacterial community data may be used as an additional tool e.g. in ocean-drilling projects, which aim to detect historical environmental events from the sedimentary record.
  • Viitamäki, Sirja (Helsingin yliopisto, 2019)
    Soil microbial communities have a critical role in the biogeochemical processes on Earth, but their response to the ongoing climate change is poorly understood. Arctic permafrost harbors approximately 50% of Earth’s below ground carbon, and warmer climate leads to increased rate of microbial decomposition of soil organic matter in polar regions. Without a comprehensive understanding of the soil microbial ecology, the overall impact of climate change to nutrient cycles and greenhouse gas emissions is difficult to predict. My aim was to improve the knowledge of active microbes and their energy sources in subarctic soil. I studied the activity and functions of soil microbial communities by applying metatranscriptomics to soils along a natural climate gradient in subarctic Kilpisjärvi, northwestern Finland. The gradient represents the possible soil conditions, that microbial communities live in as the climate changes. Additionally, I studied the relationship of microbial activity and various environmental factors, including pH and soil organic matter. Results of the thesis showed that the active microbial communities in subarctic soils are diverse taxonomically and by their energy metabolism, and that pH, soil organic matter content and moisture are the main drivers of soil microbial activity and functions.