Morphological changes of Microcystis aeruginosa colonies in culture

<p>We investigated the changes in the morphology, genetics and photosynthetic characteristics of <em>Microcystis aeruginosa</em> colonies during two months of cultivation. The colonies were collected in Lake Taihu, kept under 25°C on a 12h:12h light/dark cycle at a light density of about 45 μmol m^-2 s^-1. <em>M. novacekii</em>-type colonies were detected on the 10^th day and their percentage of the population tended to increase until the 60^th day. With <em>M. novacekii</em>-like colonies<em> </em>increased, the proportion of <em>M. aeruginosa</em> colonies decreased and reached almost zero by the end of the experiment. <em>M. novacekii</em>-like colony size (D₅₀; this value indicates that particles below D₅₀ accounts for 50%) was greater than 500 μm when<em> </em>these colonies<em> </em>first appeared and was similar to that of <em>M. aeruginosa</em> in the experiment. No differences in cell size were found between these two <em>Microcystis</em> morphotypes either collected from Lake Taihu or cultured in the laboratory. Through molecular tools (16S rDNA, 16S-23S ITS and <em>cpc</em>BA-IGS), there were strong evidences to claim that the original <em>M. aeruginosa</em> colonies isolated from Lake Taihu and the later <em>M. novacekii</em>-like colonies in our cultures were the same species. We suggest that <em>M. aeruginosa </em>colonies consistently changed their colonial morphology to that of a typical <em>M. novacekii</em>.