Diversity of the Photosynthetic Bacterial Communities in Highly Eutrophicated Yamagawa Bay Sediments

Yamagawa Bay, located in Ibusuki, Kagoshima Prefecture, Japan, is a geographically enclosed coastal marine inlet, and its deteriorating seabed sediments are under an anoxic, reductive, sulfide-rich condition. In order to gain insight into diversity of anoxygenic photosynthetic bacteria (AnPBs) and their ecophysiological roles in the sediments, three approaches were adopted: isolation of AnPBs, PCR-DGGE of 16S rDNA, and PCR-DGGE of pufM. Among the bacterial isolates, relatives of Rhodobacter sphaeroides were most dominant, possibly contributing to transforming organic pollutants in the sediments. Abundance of Chlorobium phaeobacteroides BS1 was suggested by 16S rDNA PCR-DGGE. It could reflect intensive stratification and resultant formation of the anoxic, sulfide-rich layer in addition to extreme low-light adaptation of this strain. Diverse purple non-sulfur or sulfur bacteria as well as aerobic anoxygenic photoheterotrophs were also detected by pufM PCR-DGGE, which could be associated with organic or inorganic sulfur cycling. The outcome of the present study highlights ecophysiologically important roles of AnPBs in the organically polluted marine sediments.