Akira Hiraishi

Rhodoferax fermentans gen. nov., sp. nov., a phototrophic purple nonsulfur bacterium previously referred to as the “Rhodocyclus gelatinosus-like” group

Strains of the phototrophic bacteria previously referred to as the “rhodocyclus gelatinosus-like (RGL)” group were taxonomically studied in comparison with Rhodocyclus species. Cells of the RGL strains were curved rods and motile by means of polar flagella. They contained bacteriochlorophyll a and carotenoids of the spheroidene series. The intracytoplasmic membrane system was absent. Photoorganotropho with various organic compounds as carbon sources was the preferred mode of growth. Aerobic growth at full atmospheric oxygen tension and fermentative growth under anaerobic-dark conditions were also possible. The major cellular fatty acids were palmitoleic acid and palmitic acid, and 3-hydroxylated fatty acids with octanoic acid predominating were also found. Both ubiquinone-8 and rhodoquinone-8 occurred as major quinones. The mol% guanine plus cytosine of the DNAs varied between 59.8 and 60.3. DNA-DNA hybridization studies showed that the RGL strains were highly related to each other but exhibited low levels of the homology to Rhodocyclus species. These data allow the establishment of the RGL group as a new taxon of the purple nonsulfur bacteria, for which the name Rhodoferax fermentans gen. nov., sp. nov. is proposed.

Fumarate reduction systems in members of the family Rhodospirillaceae with different quinone types

Nineteen established and one undesignated species of the Rhodospirillaceae were examined for fumarate reduction in connection with their quinone systems. The fumarate reductase activity with reduced methyl viologen (MVH) or FMNH2 as electron donor was found in membrane (chromatophore) preparations from phototrophically grown cells of all species containing menaquinone (MK) and/or rhodoquinone. The species having ubiquinone as the sole quinone contained no fumarate reductase activity, except some Rhodobacter species showing the FMNH2-dependent activity. The MVH-fumarate reductase activity of the MK-type species was not inhibited by Triton X-100 or acetone treatment, suggesting the presence of a fumarate reductase reacting directly with MVH, while such an enzyme was absent in the MK-lacking strains, with few exceptions. The FMNH2-fumarate reduction system was abolished by a detergent or acetone extraction in all bacteria but differed much among species with different quinone types as to the response to respiratory inhibitors. These differences in fumarate-reducing properties and quinone systems among the phototrophic bacteria are discussed from evolutionary and taxonomic viewpoints.

Effects of Organic Nutrient Strength on the Purple Nonsulfur Bacterial Content and Metabolic Activity of Photosynthetic Sludge for Wastewater Treatment

Abstract Changes in the purple nonsulfur bacterial content and metabolic activity of photosynthetic sludge in response to wastewater strength in a practical plant and in laboratory-scale batch reactors were investigated. Both plant and laboratory systems yielded large quantities of purple nonsulfur bacteria, as many as 107 viable cells·mg dry sludge−1, when loaded with high biological oxygen demand (BOD) levels of wastewater containing acetate as a major BOD source. Experiments with laboratory reactors showed that the phototrophic bacteria could keep occurring in such large numbers at BOD-loading rates higher than 0.8 kg BOD·kg dry sludge−1·d−1. The loading of high BOD wastewater also enhanced oxygen uptake activity with lower fatty acids used as substrates, as well as the enzyme activities of the tricarboxylic acid cycle of the sludge. However, there was no difference in the enzyme activities of the glyoxylate pathway between high BOD-loaded and low BOD-loaded sludges. The results obtained suggest that wastewater strength, especially a lower fatty acid concentration, is one of the most important factors affecting the viability and activity of purple nonsulfur bacteria in the photosynthetic sludge process.

Vertical distribution in and isolation of bacteria from Lake Vanda: an Antarctic lake

Vertical distribution of bacteria in Lake Vanda, an Antarctic meromictic lake, was examined by the acridine orange epifluorescence direct count method. Total bacteria were 104–105 cells · ml−1 in the water at 55 m depth and above, and increased drastically to 107 cells · ml−1 in the bottom water. Filamentous or long rodshaped bacteria occurred at a high frequency in the upper layers, but in the bottom layers most bacteria were coccoidal or short rods. Mean bacterial cell volume in water of between 10 m and 60 m deep was fairly large compared with common bacterial populations in seawater and lake water. Aerobic heterotrophic bacteria were recovered from the water of a depth of 30 m and above, and were assumed to belong to Caulobacter. Viable heterotrophic bacteria were not recovered from the high salinity deep water by media prepared with the same deep water. Phototrophic purple non-sulphur bacteria were isolated by enrichment cultures from water at 55 m depth.