Bacterium and Fish-Mediated Morphological Changes of the Toxic Cyanobacterium Microcystis aeruginosa

ABSTRACT

An antialgal bacterium Xanthobacter autotrophicus and two small teleost fishes (Tanichthys albonubes and Oryzias latipes) were examined for their effects on the growth and morphology of the cyanobacterium Microcystis aeruginosa NIES 298 (solitary morph). The X. autotrophicus or its filtrate showed the maximum growth suppression (76.6% or 79.6% of control density, respectively) and colony formation (1.9 or 6.4 colonies/mL) of M. aeruginosa during the one-week experimental period. Colony formation was similar in the presence of low and high densities of the living bacteria, whereas low filtrate concentrations (1% culture filtrate of total volume) promoted colony formation more effectively than high filtrate concentrations (5%). No or few cells or colonial morphs were observed in the presence of either T. albonubes or O. latipes after three-five days of cultivation. Maximum numbers of colonies (27.0 colonies/mL) and cell numbers (104 cells/colony) were induced by 5% culture filtrate of O. latipes. M. aeruginosa colony formation was more obvious in the presence of culture filtrates than living organisms, either bacterium or fish. Bacterial filtrate was dose-negative dependent, while fish filtrate was dose-positive dependent.