Chemotype diversity in Planktothrix rubescens (cyanobacteria) populations is correlated to lake depth

The cyanobacterial species Planktothrix rubescens is known to preferably inhabit deep, stratified, oligo- to mesotrophic lakes. It is also known for the production of diverse bioactive peptides, including the hepatotoxic microcystins. A number of studies showed that P. rubescens populations generally consist of multiple distinct genotypes or chemotypes, respectively. In the present study, variability of chemotype diversity was analysed. Filaments of P. rubescens were isolated from water samples originating from 10 European lakes and analysed by MALDI-TOF mass spectrometry. In most of the analysed filaments multiple peptides belonging to multiple peptide classes could be detected. A resulting data matrix of 964 filaments and 37 individual peptides was subjected to correspondence analysis and K-means clustering. From the latter analysis the distribution of chemotypes among the lakes was established and diversity estimated by computing Shannon-Indices. Diversity varied strongly among lakes with the lowest diversity found in non-alpine lakes. Further, chemotype diversity was strongly correlated to the maximum depth of the sampled lakes in alpine and non-alpine lakes. The possible influence of both factors, geographic isolation and water column depth, on the observed patterns of chemotype diversity of P. rubescens populations is discussed.