No abstract

The nucleotide sequences of the genes of 16S rRNAs were determined for the type strain Oscillochloris trichoides DG-6 T and three new strains of Oscillochloris-like mesophilic filamentous green bacteria. Two major clusters have been found within the family Chloroflexaceae by phylogenetic analysis : one cluster includes thermophilic species of Chloroflexus and the second includes mesophilic strains of Oscillochloris. The degree of relatedness of these clusters was below an intergeneric level, having only 825-865 % of 16S rDNA sequence similarity. These phylogenetic data correlate well with the significant physiological, biochemical and chemotaxonomical differences between members of both groups. Therefore, the Oscillochloris and Chloroflexus clusters should be considered as two separate families. The description of the new family, Oscillochloridaceae fam. nov., and emended descriptions of the genus Oscillochloris and the species Oscillochloris trichoides are presented.

The new strain of filamentous green bacterium strain DG-6 was isolated in pure culture from the spring of Caucuses. The study of this bacterium allows to suggest that it is a member of the familyChloroflexaceae and may be considered asOscillochloris trichoides neotype strain. The description of this green bacterium is given.

Studies on autotrophic CO, fixation by the filamentous anoxygenic photosynthetic bacteri um Oscillochloris frichoides strain DG-6 demonstrated that, unlike other green bacteria, this organism metabolized CO, via the reductive pentose phosphate cycle. Both key enzymes of this cycle -ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoribulokinase -were detected in cell extracts. The main product of ribulose 1,5-bisphosphatedependent CO, fixation was 3-phosphoglyceric acid. KCN, which is known to be a competitive inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase, completely inhibited the CO, assimilation by whole cells as well as by cell extracts of 0. frichoides. The I3Ul2C carbon isotope fractionation during photoautotrophic growth of 0. trichoides was -19*7O/io, which is close to that obtained for autotrophic organisms that use ribulose-1,5-bisphosphate carboxylase as the primary carboxylation enzyme. Cell extracts of 0. trichoides contained all the enzymes of the tricarboxylic acid cycle except 2-oxoglutarate dehydrogenase. No activity of isocitrate lyase, a key enzyme of the glyoxylate shunt, was found in cell extracts of 0. frichoides DG-6.

Whole cells, chlorosome-membrane complexes and isolated chlorosomes of the green mesophilic filamentous bacterium Oscillochloris trichoides, representing a new family of the green bacteria Oscillochloridaceae, were studied by optical spectroscopy and electron microscopy. It was shown that the main light-harvesting pigment in the chlorosome is BChl c. The presence of BChl a in chlorosomes was visualized only by pigment extraction and fluorescence spectroscopy at 77 K. The molar ratio BChl c: BChl a in chlorosomes was found to vary from 70:1 to 110:1 depending on light intensity used for cell growth. Micrographs of negatively and positively stained chlorosomes as well as of ultrathin sections of the cells were obtained and used for morphometric measurements of chlorosomes. Our results indicated that Osc. trichoides chlorosomes resemble, in part, those from Chlorobiaceae species, namely, in some spectral features of their absorption, fluorescence, CD spectra, pigment content as well as the morphometric characteristics. Additionally, it was shown that similar to Chlorobiaceae species, the light-harvesting chlorosome antenna of Osc. trichoides exhibited a highly redox-dependent BChl c fluorescence. At the same time, the membrane B805-860 BChl a antenna of Osc. trichoides is close to the membrane B808-866 BChl a antenna of Chloroflexaceae species.