有明海から分離したCytophaga属細菌による珪藻Skeletonema costatumの溶解〔英文〕

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Many heterotrophic bacteria isolated from the coastal waters of the Ariake Sea were screened as to their ability to lyse diatoms. Among them a strain of Cytophaga, which has strong algal-lytic activity against the diatom Skeletonema costatum, was selected. This strain was derived from samples collected during the period of small-scale bloom of S. costatum. Cytophaga sp. could lyse Dytilum brightwellii, S. costatum, Tharassiosira sp., and Chattonella antiqua, but could not lyse Chaetoceros didymum or Gymnodinium nagasakiense. The process of lysis of S. costatum by Cytophaga sp. was examined in coculture. Several days after the bacterium was inoculated to the culture of S. costatum, the cell number of the bacterium increased rapidly without lysing algal cells, and after it reached the order of 106 cells/ml the lysis of algae began to be observed. The bacterial number increased again with the progress of lysis and reached the order of 107 cells/ml. These results suggest that Cytophaga sp. can utilize not only algal cells but also EOC excreted from the algae. A significant increase in the number of protoplasts of diatom was microscopically observed in the process of lysis of the algae, following which these protoplasts were thoroughly lysed and disappeared in the last stage of lysis.
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