Summary auto-generated
This study reorganizes the genus Erythromicrobium based on morphological, physiological, biochemical, and phylogenetic analyses. Researchers examined five Erythromicrobium species and found that two previously classified species—"Erythromicrobium sibiricum" and "Erythromicrobium ursincola"—differed sufficiently from the other three species to warrant elevation to separate genera. Using 16S rDNA sequencing, DNA-DNA hybridization data, and electron transfer carrier analysis, the authors demonstrated these two species had distinct phylogenetic positions within the alpha-4 subclass of Proteobacteria and unique biochemical characteristics. "E. sibiricum" is formally described as Sandaracinobacter sibiricus gen. nov., sp. nov., characterized by thin rod morphology and yellow-orange coloration. "E. ursincola" is described as Erythromonas ursincola gen. nov., sp. nov., distinguished by ovoid cells and budding reproduction. Both genera contain bacteriochlorophyll a and are obligately aerobic, photosynthetic bacteria. The reorganization leaves Erythromicrobium composed of three species: E. ramosum (type species), "E. hydrolyticum," and "E. ezovicum."
Key findings
- Two Erythromicrobium species were reclassified into separate genera based on phylogenetic analysis showing distinct 16S rDNA sequences and low DNA-DNA hybridization homology with the genus type species.
- Sandaracinobacter sibiricus differs from other species in carotenoid composition, cell morphology (thin long rods in chains), photosynthetic apparatus organization (RC-bound cytochrome c), and ubiquinone composition (contains Q9 and Q10).
- Erythromonas ursincola is characterized by unique budding reproduction, ovoid cell morphology, and contains an unusually small soluble cytochrome c of 6.5 kDa rarely found in bacteria.
- Both new genera contain bacteriochlorophyll a and light-harvesting antenna complexes but differ from remaining Erythromicrobium species in electron transfer carrier composition and organization.
- All five species studied belong to the alpha-4 subclass of Proteobacteria and are obligately aerobic photosynthetic bacteria isolated from freshwater environments.
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Abstract
The results of investigations on the morphology, physiology, pigment composition, light-harvesting antenna and reaction center organization, and electron carriers of five Erythromicrobium representatives, and on phylogenetic relations among them, are summarized. On the basis of clear phenotypic differences and distinct phylogenetic positions shown by 16S ribosomal DNA analysis, the tentative species "Erythromicrobium sibiricum" and "Erythromicrobium ursincola" are formally described as the type species of two new genera: Sandaracinobacter sibiricus gen. nov., sp. nov., and Erythromonas ursincola gen. nov., sp. nov., respectively. The genus Erythromicrobium is at present composed of the type species, E. ramosum, and two species, "E. hydrolyticum" and "E. ezovicum," whose nomenclature is yet to be validated. All species studied group within the alpha-4 subclass of Proteobacteria.