Phosphonate degradation by the toxic Baltic Sea cyanobacterium Nodularia spumigena

Show full item record

Title: Phosphonate degradation by the toxic Baltic Sea cyanobacterium Nodularia spumigena
Author: Shrestha, Rashmi
Other contributor: Helsingin yliopisto, Maatalous-metsätieteellinen tiedekunta, Elintarvike- ja ympäristötieteiden laitos
University of Helsinki, Faculty of Agriculture and Forestry, Department of Food and Environmental Sciences
Helsingfors universitet, Agrikultur- och forstvetenskapliga fakulteten, Institutionen för livsmedels- och miljövetenskaper
Publisher: Helsingin yliopisto
Date: 2018
Language: eng
Thesis level: master's thesis
Discipline: Mikrobiologia
Abstract: Inorganic phosphate (Pi) is the only readily utilizable form of phosphorus for toxic diazotrophic cyanobacterium Nodularia spumigena (N. spumigena). Pi is one of the limiting nutrients in the Baltic Sea where surprisingly N. spumigena are highly abundant especially during the summer. This indicates that N. spumigena possibly has an alternative pathway to fulfill its phosphorus requirement. The Baltic Sea, like most aquatic environments, is enriched with organic phosphorus compounds among which phosphonates may constitute a significant fraction. Interestingly, the Baltic Sea N. spumigena strains UHCC 0039 and CCY9414 have been found to carry phosphonate degrading gene cluster (phnC-M) implying that these cyanobacteria could assimilate phosphonates as a phosphorus source. However, the significance of the presence of phn gene cluster in N. spumigena for phosphonate utilization has not been investigated in detail. Here, I aimed to understand how N. spumigena copes with Pi limitation and utilizes phosphonates in laboratory conditions using biochemical assays, PCR-based methods and bioinformatics tools. This would aid in finding a suitable marker for Pi deficiency in cyanobacterial blooms in the Baltic Sea. In this study, bioinformatics and PCR screening showed that phn gene cluster was conserved in the Baltic Sea N. spumigena strains. The studied N. spumigena strains UHCC 0039 and UHCC 0060 were found to utilize naturally produced low molecular weight phosphonates, methylphosphonate (MPn), ethylphosphonate (EPn) and 2-aminoethylphosphonate (2APn). Among these phosphonates, MPn seemed to be the most preferred phosphorus source. Alkaline phosphatase activity, an indicator of Pi limitation, was found to be elevated in the media with Pi and 2APn questioning its suitability as a marker for phosphorus limitation. In addition, growth on MPn released methane indicating that massive blooms of N. spumigena might contribute to an elevated methane supersaturation in the Baltic Sea. Reverse transcriptase quantitative PCR (RT-qPCR) in N. spumigena strains did not show expected upregulation of high-affinity phosphate transporter pstS in Pi limitation. It demonstrated an induction of phosphonate transporter gene phnD in media lacking Pi and supplemented by 2APn. The phosphonate lyase gene phnJ was however, upregulated only in the presence of MPn suggesting that phnJ gene could be used as a marker for phosphonate bioavailability. The findings from this study suggest that the presence of phn gene cluster could provide N. spumigena a competitive advantage in Pi-limited cyanobacterial blooms in the Baltic Sea. The molecular detection methods designed in this study thus could be used in future to monitor the expression of genes induced during Pi limitation and the presence of phosphonates, and the method could be further optimized for screening natural water samples.
Subject: Cyanobacteria
inorganic phosphorus
Baltic Sea
N. spumigena

Files in this item

Total number of downloads: Loading...

Files Size Format View
Shrestha_Rashmi_Pro_gradu_2018.pdf 3.175Mb PDF View/Open

This item appears in the following Collection(s)

Show full item record