Morphospecies and genospecies of Microcystis during blooms in eutrophic Lake Taihu (China) in autumn

Morphospecies-dependent disaggregation of colonies of the cyanobacterium Microcystis under high turbulent mixing

Preventing formation of large colonies and reducing colony size of the cyanobacterium Microcystis may lead to reductions in bloom formation. Here we investigated the effects of artificial mixing on morphology and disaggregation dynamics of Microcystis colonies in vivo, using a stirring device and a laser particle analyzer. The turbulent dissipation rate (ε) was varied from 0.020 to 0.364 m² s^-3. We hypothesized that colonies of M. aeruginosa and M. ichthyoblabe would be more susceptible to disaggregation from turbulent mixing than colonies of M. wesenbergii. Our results showed that colony size of M. aeruginosa and M. ichthyoblabe decreased with increased turbulence intensity and duration of stirring for ε > 0.094 m² s^-3, while M. wesenbergii showed less obvious changes in colony size with mixing. Spherical M. wesenbergii colonies exposed to high turbulence intensities for 30 min gradually transitioned to colony morphologies similar to M. ichthyoblabe and M. aeruginosa-like colonies (irregular, elongated or lobed, with distinct holes). Our results suggest that turbulent mixing is an important factor driving morphological changes of Microcystis colonies, and artificial mixing may effectively reduce colony size of Microcystis, thereby preventing bloom formation.

Polysaccharide biosynthesis-related genes explain phenotype-genotype correlation of Microcystis colonies in Meiliang Bay of Lake Taihu, China

The 16S rDNA, 16S-23S rDNA-ITS, cpcBA-IGS, mcy gene and several polysaccharide biosynthesis-related genes (epsL and TagH) were analyzed along with the identification of the morphology of Microcystis colonies collected in Lake Taihu in 2014. M. wesenbergii colonies could be distinguished directly from other colonies using espL. TagH divided all of the samples into two clusters but failed to distinguish different phenotypes. Our results indicated that neither morphology nor molecular tools including 16S rDNA, 16S-23S ITS and cpcBA-IGS could distinguish toxic and non-toxic species among the identified Microcystis species. No obvious relationship was detected between the phenotypes of Microcystis and their genotypes using 16S, 16S-23S and cpcBA-IGS, but polysaccharide biosynthesis-related genes may distinguish the Microcystis phenotypes. Furthermore, the sequences of the polysaccharide biosynthesis-related genes (espL and TagH) extracted from Microcystis scums collected throughout 2015 was analyzed. Samples dominated by M. ichthyoblabe (60-100%) and M. wesenbergii (60-100%) were divided into different clade by both espL and TagH, respectively. Therefore, it was confirmed that M. wesenbergii and M. ichthyoblabe could be distinguished by the polysaccharide biosynthesis-related genes (espL and TagH). This study is of great significance in filling the gap between classification of molecular biology and the morphological taxonomy of Microcystis.