A survey of NRPS genes from Planktothrix in Lake Kolbotnvannet

Abstract

Lake Kolbotnvannet is dominated by the Cyanobacteria Planktothrix. Cyanobacteria produce oligopeptides by nonribosomal peptide synthetases (NRPS), which have unknown biological functions. NRPS genes encoding the NRPS enzymes producing two oligopeptides, microcystin and cyanopeptolin, have been studied in this thesis. These genes have been used as markers for studying recombination events and subpopulation structure of Planktothrix strains in Lake Kolbotnvannet. DNA isolation, amplification and sequencing were carried out, and bioinformatical analyses were performed. Previous obtained DNA sequences from Lake Steinsfjorden and oligopeptide data produced by LC-MSMS were included to get reliable analyses, and to compare Lake Steinsfjorden and Lake Kolbotnvannet genetics. Phylogenetic analyses showed recombination in two strains. Recombination events were also supported by split decomposition analyses and phi-test. A new chemotype in Lake Kolbotnvannet is suggested to be a result of recombination and positive selection. Recombination was observed in the ociB and mcyC regions in this thesis. Correlating chemotypes and genotypes in Lake Kolbotnvannet, and correlation between Lake Steinsfjorden and Lake Kolbotnvannet findings supports a subpopulation differentiation of freshwater cyanobacteria. A higher nucleotide variation between chemotypes and a low nucleotide variation within chemotypes were seen in both Lake Kolbotnvannet and Lake Steinsfjorden. Distinct groupings by the phylogenetic inferences, and selection and diversity analyses results support a NRPS oligopeptide based subpopulation structure among Lake Kolbotnvannet Planktothrix strains.