Isolation of a Flocculent Photosynthetic Bacterium Rhodovulum sp. and Characterization of Nucleic Acids Dependent Flocculation

A marine photosynthetic bacterium (PS88) identified as Rhodovulum sp. with flocculating ability was isolated from the sea sediment mud of a shrimp cultivation farm in Thailand. This bacterium flocculated in glutamate/malate medium during aerobic/dark or anaerobic/light cultivation. The flocculating ability was enhanced with the increase of NaCl concentration to 6% (w/v). Flocculation and growth were promoted by Mg2+ up to 10 mM in culture medium. Kaolin, anionic colloidal particle was flocculated only in the simultaneous presence of extracellular polymeric substance (EPS) derived from bacterial cells, and metal cations. With the advantage of self-flocculation, high density cell cultivation was accomplished by continuous cultivation to 43 g dry matter l–1 with acetate as a substrate consumption at 22.5 g l–1d–1.