ALBERT

Description: We describe a new species of purple nonsulfur bacteria, which has the ability to grow under photoautotrophic growth conditions with sulfide as an electron donor and shows the characteristic properties of Rhodobacter species (i.e., ovoid to rod-shaped cells, vesicular internal photosynthetic membranes, bacteriochlorophyll a and carotenoids of the spheroidene series as photosynthetic pigments). In its physiological properties this new species is particularly similar to the recently described species Rhodobacter adriaticus, but it shows enough differences compared with R. adriaticus and the other Rhodobacter species to be recognized as a separate species. In honor of Hans Veldkamp, a Dutch microbiologist, the name Rhodobacter veldkampii sp. nov. is proposed.

Description: Sequences of the 16S rDNA from all available type strains of Chromatium species have been determined and were compared to those of other Chromatiaceae, a few selected Ectothiorhodospiraceae and Escherichia coli. The clear separation of Ectothiorhodospiraceae and Chromatiaceae is confirmed. Most significantly the sequence comparison revealed a genetic divergence between Chromatium species originated from freshwater sources and those of truly marine and halophilic nature. Major phylogenetic branches of the Chromatiaceae contain (i) marine and halophilic species, (ii) freshwater Chromatium species together with Thiocystis species and (iii) species of the genera Thiocapsa and Amoebobacter as recently reclassified [Guyoneaud, R. & 6 other authors (1988). Int J Syst Bacteriol 48, 957-964], namely Thiocapsa roseopersicina, Thiocapsa pendens (formerly Amoebobacter pendens), Thiocapsa rosea (formerly Amoebobacter roseus), Amoebobacter purpureus and Thiolamprovum pedioforme (formerly Amoebobacter pedioformis). The genetic relationships between the species and groups are not in congruence with the current classification of the Chromatiaceae and a reclassification is proposed on the basis of 16S rDNA sequence similarity supported by selected phenotypic properties. The proposed changes include the transfers of Chromatium minus and Chromatium violascens to Thiocystis minor comb. nov. and Thiocystis violascens comb. nov., of Chromatium vinosum, Chromatium minutissimum and Chromatium warmingii to the new genus Allochromatium as Allochromatium vinosum comb. nov., Allochromatium minutissimum comb. nov., and Allochromatium warmingii comb. nov., of Chromatium tepidum to the new genus Thermochromatium as Thermochromatium tepidum comb. nov., of Chromatium salexigens and Chromatium glycolicum to the new genus Halochromatium as Halochromatium salexigens comb. nov. and Halochromatium glycolicum comb. nov., of Chromatium gracile and Chromatium purpuratum to the new genus as Marichromatium gracile comb. nov. and Marichromatium purpuratum comb. nov., of Thiocapsa pfennigii to Thiococcus pfennigii gen. nom. rev., of Thiocapsa halophila to the new genus Thiohalocapsa as Thiohalocapsa halophila comb. nov., and of Chromatium buderi to the new genus Isochromatium as Isochromatium buderi comb. nov.

Description: The 16S rDNA sequence of Rhodospirillum mediosalinum was determined and compared with corresponding sequences from other spiral-shaped purple non-sulfur bacteria classified as or related to the genus Rhodospirillum in the α subclass of the Proteobacteria. Sequence similarities separate the currently recognized Rhodospirillum species into five different groups with no more than 91% sequence similarity, clearly indicating the necessity to recognize these groups as different genera. Major diagnostic properties of these bacteria are compared and new genera Phaeospirillum gen. nov., Roseospira gen. nov., Rhodothalassium gen. nov. and Rhodovibrio gen. nov. are described with the species Phaeospirillum fulvum comb, nov., Phaeospirillum molischianum comb. nov., Rhodovibrio salinarum comb. nov., Rhodovibrio sodomensis comb. nov., Rhodothalassium salexigens comb. nov. and Roseospira mediosalina comb. nov. The genus Rhodospirillum is represented by Rhodospirillum rubrum and Rhodospirillum photometricum and an emended description of this genus is also given

Description: Complete nucleotide sequences of the 16S rDNAs were determined from Thiocapsa and Amoebobacter species, including all available type strains and some additional isolates. The distance-matrix analysis and the dendrogram for estimating the genetic relationships revealed that the investigated strains were found in two major clusters within the Chromatiaceae. One cluster comprises all Amoebobacter species, Thiocapsa roseopersicina and several isolates related to Thiocapsa roseopersicina. Representatives of the species Amoebobacter roseus, Amoebobacter pendens and Thiocapsa roseopersicina, the so called ‘Thiocapsa roseopersicina group’, are very closely related, justifying their inclusion into one genus, Thiocapsa, for which an emended description is presented. Amoebobacter purpureus and Amoebobacter pedioformis formed two separate lines of descent with less than 93% (89·6–92·9%) similarity to strains of the ‘Thiocapsa roseopersicina group’. Therefore, they will be considered as two separate genera. As a consequence, an emended description is presented for the genus Amoebobacter, with Amoebobacter purpureus as the new type species and A. pedioformis is transferred to Thiolamprovum pedioforme gen. nov., comb. nov. Two species, Thiocapsa pfennigii and Thiocapsa halophila, which have been classified with the genus Thiocapsa because of their morphological properties, were found within another major cluster of the Chromatiaceae and are only distantly phylogenetically related to the first cluster with 88·4–90·6% and 90·4–92·2% sequence similarity, respectively.

Description: A new purple sulfur bacterium was isolated from microbial films on decaying plant mass in the near-shore area of the soda lake Malyi Kasytui (pH 9.5, 0.2% salinity) located in the steppe of the Chita region of south-east Siberia. Single cells were vibrioid- or spiral-shaped (3-4 microns wide and 7-20 microns long) and motile by means of a polar tuft of flagella. Internal photosynthetic membranes were of the lamellar type. Lamellae almost filled the whole cell, forming strands and coils. Photosynthetic pigments were bacteriochlorophyll a and carotenoids of the spirilloxanthin group. The new bacterium was strictly anaerobic. Under anoxic conditions, hydrogen sulfide and elemental sulfur were used as photosynthetic electron donors. During growth on sulfide, sulfur globules were formed as intermediate oxidation products. They were deposited outside the cytoplasm of the cells, in the peripheral periplasmic space and extracellularly. Thiosulfate was not used. Carbon dioxide, acetate, pyruvate, propionate, succinate, fumarate and malate were utilized as carbon sources. Optimum growth rates were obtained at pH 9.0 and optimum temperature was 30 degrees C. Good growth was observed in a mineral salts medium containing 5 g sodium bicarbonate l-1 without sodium chloride. The new bacterium tolerated up to 60 g sodium chloride l-1 and up to 80 g sodium carbonates l-1. Growth factors were not required. The DNA G + C composition was 56.0-57.4 mol%. Based on physiological, biochemical and genetic characteristics, the newly isolated bacterium is recognized as a new species of a new genus with the proposed name Thiorhodospira sibirica.