Phenotypic plasticity and negative allelopathy in Microcystis strains

The importance of microorganism culture collections is undeniable considering the amount of knowledge acquired from them in several areas of microbiology and biotechnology. However, strains that have been subcultured for a long period of time could have changed some of their morphological and biochemical characteristics. The present study assessed the behavior of two Microcystis aeruginosa strains that have been cultured for different time periods. M. aeruginosa (CCIBt 3194) kept in laboratory culture for a 13-year period lost its mucilaginous envelope and no longer formed colonies, whereas M. aeruginosa (CCIBt 3454), isolated in 2011, still maintained its colony morphological features. Both strains were exposed to the lyophilized cellular content of the other, and were observed daily for 17 days for cell growth, morphology and morphometry ( n = 3). Samples for chemical analyses were collected on a daily basis until day 17. We also observed cellular recruitment, mucilage formation and growth inhibition in both strains. Furthermore, an increase in cell diameter was seen only in strain CCIBt 3194, while a reduction of microcystin production was found in both strains. Such reactions are observed only in negative allelopathic events, which typically occur among different cyanobacterial species. The resumption of exopolysaccharide synthesis by CCIBt 3194, inactive for more than 10 years, suggests the occurrence of pleiotropy.