The distribution of dormant cells of the red tide flagellate Heterosigma akashiwo (Raphidophyceae) was investigated by the extinction dilution method in sediments of northern Hiroshima Bay where red tides of H. akashiwo occur almost every year. Densities of the dormant cells in sediment samples ranged from 56 to 5, 950 cells·cm^-3 wet sediment in April 1987, and from 56 to 29, 300 cells·cm^-3 in March 1989. No significant relationship was observed between the number of dormant cells of H. akashiwo and mud content of sediment sample. High density stations of the dormant cells in sediments appeared to coincide with the areas with high concentrations of vegetative cells in water columns during the red tide season.

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The rates of anaerobic respirations, methanogenesis, sulfate reduction, and denitrification were studied for sediments of three sites along the watercourse in the polluted lower Tama River, Japan, in summer and winter. The rate of methanogenesis was high at the upper freshwater site (Site 1) and low in lower sites (Sites 2 and 3) in accordance to the level of sulfate in interstitial water. On the contrary, the rate of sulfate reduction was high at the lower sites. Denitrification was high at Site 1 and the intermediate site (Site 2). The relative importance of anaerobic respirations was estimated on area basis. At Site 1, methanogenesis was the dominant process in summer, but it was slightly lower than denitrification in winter. At Sites 2 and 3, the dominant process was denitrification and sulfate reduction, respectively, in both seasons.

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Cell surface hydrophobicity of Bradyrhizobium japonicum strains 123ET and 138NR was studied as a factor in competition for the attachment to root and the nodulation of soybean. Hydrophobicity of the strains, which was measured by a biphasic water-hydrocarbon system, significantly changed with culture age having a maximum value in mid-log phase. Three days-old soybean (Glycine max cv. Tamahomare) were inoculated with the mixture of two strains, and grown for 3 weeks in sterilized vermiculite tubes. Bradyrhizobia attached to the seedling roots were released at 90 min after the inoculation by sonication and enumerated by plate counting. Two strains were distinguished by the difference in antibiotic resistance. Nodule occupancies by the strains were determined by the ratio of the strains on the seedling root surface, not in the inocula. Logarithm of the ratio of the strains on the root was highly correlated with the difference in hydrophobicity of the strains.

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Rhodobacter sphaeroides NR3 produced significant amounts of inorganic polyphosphates (polyPs) with visible volutin granules when grown phototrophically at external orthophosphate (P_i) concentrations of 10 mM and above with 20 mM malate as the sole carbon source. The maximum level of the accumulated polyPs, amounting to 6.2% of the cell dry weight, was found with 300 mM P_i. On the other hand, the stimulatory effect of excess P_i on polyP accumulation was not so pronounced in the cells grown under aerobic-dark conditions. The fractionation of the cellular phosphorous compounds revealed that the alkali-soluble and cold acid-soluble polyPs were the major polyPs in the high P_i-loaded phototrophic cultures. The phosphorus/carbon ratio in cell growth media was also found as an important factor affecting polyP accumulation in the bacterium. There was an antagonistic relationship between the polyP content and the RNA/DNA ratio during batch phototrophic growth. Ecophysiological implications of polyP accumulation in the phototrophic bacterium were also discussed.

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Sulfur-turf is one of the so-called “sulfureta” which are massive aggregates of colorless sulfur bacteria. Interest in the ecological and physiological aspects of the sulfuretum has strongly increased not only due to the discovery of massive occurrence of colorless sulfur bacteria in an area of hydrothermal vents but also due to the possibility of its significant contribution to the sulfur cycle in the coastal region. Here, I review the types, habitats, and bacterial constituents of the sulfur-turf, and further, reveal the microaerophilic oxidation of elemental sulfur by the sulfur-turf and discuss the possibility of the detoxification of hydrogen sulfide with peroxides. The habitat of the sulfur-turf is regarded as a thermostating, continuous culture enriched with hydrogen sulfide. The massive aggregates including the sulfur-turf are very useful, because they can be harvested directly from their habitats without the need for isolation and mass cultivation. Taking advantage of these massive aggregates, we should design experiments in situ and also in the laboratory to clarify the ecology and physiology of the colorless sulfur bacteria. It is necessary to elucidate the microenvironment caused by bacterial aggregation using microelectrodes, but, on the other hand, more interest should be focused on the bacterial reaction to environmental factors, especially oxygen tension.

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