In Situ Collection and Preservation of Intact Microcystis Colonies to Assess Population Diversity and Microcystin Quotas

Understanding of colony specific properties of cyanobacteria in the natural environmenthas been challenging because sampling methods disaggregate colonies and there are often delaysbefore they can be isolated and preserved. Microcystis is a ubiquitous cyanobacteria that forms largecolonies in situ and often produces microcystins, a potent hepatotoxin. In the present study a newcryo-sampling technique was used to collect intact Microcystis colonies in situ by embedding them ina sheet of ice. Thirty-two of these Microcystis colonies were investigated with image analysis, liquidchromatography-mass spectrometry, quantitative polymerase chain reaction and high-throughputsequencing to assess their volume, microcystin quota and internal transcribed spacer (ITS) genotypediversity. Microcystin quotas were positively correlated to colony volume (R2=0.32; p=0.004).Individual colonies had low Microcystis ITS genotype diversity and one ITS operational taxonomicunit predominated in all samples. This study demonstrates the utility of the cryo-sampling methodto enhance the understanding of colony-specific properties of cyanobacteria with higher precisionthan previously possible.