藍藻Ｍｉｃｒｏｃｙｓｔｉｓ ａｅｒｕｇｉｎｏｓａと細菌Ｍｏｒａｘｅｌｌａ ｎｏｎｌｉｑｕｅｆａｃｉｅｎｓとの相互関係

Abstract

To investigate blue-green algal/heterotrophic bacterial interactions related to the outbreak of water blooms in eutrophic lakes, heterotrophic bacteria associated with the floc of Microcystis forming the water bloom in Lake Kasumigaura were isolated, and their effects on the growth of an axenic clone of Microcystis aeruginosa K-3A were examined. It was found that many isolated bacteria stimulated the growth of M. aeruginosa K-3A in the presence of a small amount of nutrient broth. One of them, a strain No. 7, was identified as Moraxella nonliquefaciens. When M. aeruginosa K-3A was cultivated with M. nonliquefaciens No. 7 in a medium containing 40 mg·1-1 of nutrient broth, the specific growth rate and the maximum growth yield of this alga increased 1.5-2.0 folds and 3-5 fold, respectively. Although organic nutrients usually inhibited the growth of the pure culture of M. aeruginosa K-3A, these were indispensable to promote the growth in the mixed culture with M. nonliquefaciens No. 7. In the mixed culture, considerable numbers of bacterial cells attached to flocs of the alga, and the floc size and buoyancy increased.