Abstract
Planktothrix is a dominant cyanobacterial genus forming toxic blooms in temperate freshwater ecosystems. We sequenced the genome of planktic and non planktic Planktothrix strains to better represent this genus diversity and life style at the genomic level. Benthic and biphasic strains are rooting the Planktothrix phylogenetic tree and widely expand the pangenome of this genus. We further investigated in silico the genetic potential dedicated to gas vesicles production, nitrogen fixation as well as natural product synthesis and conducted complementary experimental tests by cell culture, microscopy and mass spectrometry. Significant differences for the investigated features could be evidenced between strains of different life styles. The benthic Planktothrix strains showed unexpected characteristics such as buoyancy, nitrogen fixation capacity and unique natural product features. In comparison with Microcystis, another dominant toxic bloom-forming genus in freshwater ecosystem, different evolutionary strategies were highlighted notably as Planktothrix exhibits an overall greater genetic diversity but a smaller genomic plasticity than Microcystis. Our results are shedding light on Planktothrix evolution, phylogeny and physiology in the frame of their diverse life styles.
Highlights
Strains P. agardhii Pasteur Culture Collection of Cyanobacteria (PCC) 7805 P. rubescens PCC 7821 P. serta PCC 8927 P. tepida PCC 9214 P. paucivesiculata PCC 9631 Planktothrix sp
A compound previously unrelated to this genus has been recently found in Planktothrix paucivesiculata PCC 963121 leading us to expect more unusual Planktothrix compounds in their various life styles
Using PCC 7805 genome as reference, we identified the scaffolds belonging to the chromosome, the megaplasmid and the plasmid in P. rubescens PCC 7821 (Table 2)
Summary
Strains P. agardhii PCC 7805 P. rubescens PCC 7821 P. serta PCC 8927 P. tepida PCC 9214 P. paucivesiculata PCC 9631 Planktothrix sp. This study aims (i) at better representing the Planktothrix genus diversity and life style at the genomic level and (ii) at investigating the genetic basis behind few common and divergent metabolic features between benthic and planktic strains. In this frame and in complement to the recent genomic data obtained for nine closely related planktic Planktothrix forming blooms in Nordic lakes[22,23], we sequenced the genomes of six strains from the Pasteur Culture Collection of Cyanobacteria (PCC) including four biphasic/benthic strains. We examined their genetic potential for natural products to find the diverse pathways present in this oscillatorialean genus
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