Gene flow , recombination and selection in cyanobacteria : population structure of 1 geographically related

28 Several Planktothrix strains, each producing a distinct oligopeptide profile, have been 29 shown to coexist within Lake Steinsfjorden (Norway). Using nonribosomal peptide 30 synthetase genes (NRPS) as markers, it has been shown that the Planktothrix community 31 comprises distinct genetic variants displaying differences in bloom dynamics, suggesting a 32 Planktothrix subpopulation structure. Here, we investigate the structure of Planktothrix 33 variants inhabiting four lakes in southeast of Norway utilizing both NRPS and non-NRPS 34 genes. Phylogenetic analyses showed similar topologies for both NRPS and non-NRPS 35 genes and the lakes appear to have similar structuring of Planktothrix genetic variants. The 36 structure of distinct variants was also supported by very low genetic diversity within 37 variants, compared to between-variant diversity. Incongruent topologies and split 38 decomposition revealed recombination events between Planktothrix variants. In several 39 strains the gene variants seem to be a result of recombination. Both NRPS and non-NRPS 40 genes are dominated by purifying selection, however, sites subjected to positive selection 41 were also detected. The presence of similar and well-separated Planktothrix variants with 42 low internal genetic diversity indicates gene flow within Planktothrix populations. Further, 43 on Jne 7, 2017 by gest ht://aem .sm .rg/ D