Microcystins do not necessarily lower the sensitivity of Microcystis aeruginosa to tannic acid

Different phytoplankton strains have been shown to possess varying sensitivities towards macrophyte allelochemicals, yet the reasons for this are largely unknown. To test whether microcystin (MC) is responsible for strain-specific sensitivities of Microcystis aeruginosa to macrophyte allelochemicals, we compared the sensitivity of 12 MC- and non-MC-producing M. aeruginosa strains, including an MC-deficient mutant and its wild-type, to the polyphenolic allelochemical tannic acid (TA). Non-MC-producing strains showed a significantly higher sensitivity to TA than MC-producing strains, both in Chlorophyll a concentrations and quantum yields of photosystem II. In contrast, an MC-deficient mutant displayed a higher fitness against TA compared to its wild-type. These results suggest that the resistance of M. aeruginosa to polyphenolic allelochemicals is not primarily related to MCs per se , but to other yet unknown protective mechanisms related to MCs.