Benthic survival of Microcystis: Long-term viability and ability to transcribe microcystin genes
Résumé
Microcystis is a microcystin-producing cyanobacterium known to proliferate in the water column of freshwater ecosystems, and to overwinter in the sediment. In this study, we demonstrate that microcystins can remain present in benthic cells buried in the sediment for long periods, and suggest that Microcystis is able to produce microcystins throughout its benthic survival. We investigated the viability and ability to transcribe one microcystin gene (mcyB) in three benthic populations of Microcystis containing microcystins. We chose deeply buried benthic populations that had been trapped in the sediment for periods ranging from several months to more than 6 years. Merely by revealing the presence of mcyB mRNA in every benthic population we investigated, we showed that benthic Microcystis could remain viable and able to initiate microcystin production after more than 6 years of benthic life. This finding also suggests that microcystins could be involved in the benthic survival mechanisms of Microcystis. The quantification of mcyB transcripts by RT-qPCR did not detect any visible influence of the duration of the benthic life stage, although the three populations did display different mcyB transcription levels.