Secondary metabolites are thought to bring about evolutionary advantages for their producer organisms. Among these are small peptides called microcystins (MCs), which are produced by multiple genera of cyanobacteria. Considerable energy and resources are diverged from primary metabolism for MC production; however, their physiological roles remain unclear. Cyanobacteria store large amounts of MCs, which are released upon cell lysis and dense colonies of cyanobacteria can drive MC concentrations to high levels (&gt;1ppm), but how released MCs interact with remaining cyanobacterial cells is not understood. We are studying this interaction between MC-producing cyanobacteria and exogenous MCs using nanoscale secondary ion mass spectrometry (nanoSIMS). In these experiments, cultures of Microcystis aeruginosa (PCC 7806) are grown under various conditions in media supplemented with 15N,13C-labeled MCs. At multiple time points, cells are harvested and the distribution of 15N and 13C in individual cells is resolved via nanoSIMS. Cell extracts are analyzed by high-pressure liquid chromatography paired with tandem mass spectrometry to determine if exogenous MCs remain intact and/or breakdown upon interaction with living cells. This study examines the effects of MCs on the cyanobacteria responsible for their production to better understand the fate and function of released MCs within cyanobacteria dominated blooms.

Investigating the interaction between microcystins and cyanobacterial cells using nanoscale secondary ion mass spectrometry

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ACS Fall 2022

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