NOTEReclassification of some species of Thiobacillus to the newly designated genera Acidithiobacillus gen. nov., Halothiobacillus gen. nov. and Thermithiobacillus gen. nov.
The complete genome sequence of Thiobacillus denitrificans ATCC 25259 is the first to become available for an obligately chemolithoautotrophic, sulfur-compound-oxidizing, -proteobacterium. Analysis of the 2,909,809-bp genome will facilitate our molecular and biochemical understanding of the unusual metabolic repertoire of this bacterium, including its ability to couple denitrification to sulfur-compound oxidation, to catalyze anaerobic, nitrate-dependent oxidation of Fe(II) and U(IV), and to oxidize mineral electron donors. Notable genomic features include (i) genes encoding c-type cytochromes totaling 1 to 2 percent of the genome, which is a proportion greater than for almost all bacterial and archaeal species sequenced to date, (ii) genes encoding two [NiFe]hydrogenases, which is particularly significant because no information on hydrogenases has previously been reported for T. denitrificans and hydrogen oxidation appears to be critical for anaerobic U(IV) oxidation by this species, (iii) a diverse complement of more than 50 genes associated with sulfurcompound oxidation (including sox genes, dsr genes, and genes associated with the AMP-dependent oxidation of sulfite to sulfate), some of which occur in multiple (up to eight) copies, (iv) a relatively large number of genes associated with inorganic ion transport and heavy metal resistance, and (v) a paucity of genes encoding organic-compound transporters, commensurate with obligate chemolithoautotrophy. Ultimately, the genome sequence of T. denitrificans will enable elucidation of the mechanisms of aerobic and anaerobic sulfurcompound oxidation by -proteobacteria and will help reveal the molecular basis of this organism's role in major biogeochemical cycles (i.e., those involving sulfur, nitrogen, and carbon) and groundwater restoration.Thiobacillus denitrificans, first isolated by Beijerinck over a century ago (4), was one of the first nonfilamentous bacteria ever described to be capable of growth on inorganic sulfur compounds as sole energy sources (47, 49). Characterized by its ability to conserve energy from the oxidation of inorganic sulfur compounds under either aerobic or denitrifying conditions, T. denitrificans is the best studied of the very few obligate chemolithoautotrophic species known to couple denitrification to sulfur-compound oxidation (Thiomicrospira denitrificans and Thioalkalivibrio thiocyanodenitrificans also have this ability [76,85]). Despite many years of work on the biochemistry of inorganic sulfur-compound oxidation by Thiobacillus thioparus and T. denitrificans, the mechanisms of oxidation and how they are coupled to energy conservation are still not well understood in these -proteobacteria, relative to the advances made with facultatively chemolithotrophic ␣-proteobacterial genera, such as Paracoccus and Starkeya (28,39,45,50). The availability of the complete genome sequence should enable elucidation of the sulfur-oxidation pathway(s) and lead to specifically focused biochemical investigations to resolve these knowledge gaps.Rec...
SUMMARYSaccharomyces cerevisiae accumulated Co2+ and Cdz+ by two processes : the first, which was metabolism-independent, was presumably cation binding to the cell surface; this was followed by metabolism-dependent, progressive uptake of relatively large amounts of the cations. Two K+ ions were released for each Co2+ ion taken up in freshly prepared cell suspensions whereas extensive loss of cellK+ followed the uptake of Cd2+. Co2+ and Cda+ appeared to be accumulated via a general cation uptake system, with limited specificity related to the ionic radii of the cations.
A re-evaluation of the taxonomy of Paracoccus denitrificans and a proposal for the combination Paracoccus pantotrophus comb. nov.Frederick A. Rainey,' Donovan P. Kelly Comparison of both 16s rRNA coding sequences and DNA-DNA hybridization of ten strains of a-subclass of Proteobacteria currently classified as strains of Paracoccus denitrificans has shown that they fall into two groups which are distinct from each other a t the species level. Comparison with published data on the cytochrome c profiles and other 16s rRNA coding sequences in the literature has confirmed these observations and enabled several other strains also to be assigned to these two groups. Group A comprises strains ATCC 1774IT (the type strain of P. denitrificans), LMD 22.2IT, DSM 413T, ATCC 19367, ATCC 13543, DSM 1404, DSM 1405, Pd 1222 (a genetic modification of DSM 4133 and NCIMB 8944. Group B comprises ATCC 35512T (the original type strain of Thiosphaera pantotropha), LMD 82.5T, LMD 92.63, DSM 65, LMG 4218, IAM 12479, JCM 6892, DSM 11072, DSM I1073 and DSM 11104. In light of these findings, it is proposed that: (1) strains of group A are retained as P. denitrificans, with ATCC 1774IT as the type strain of the type species; and (2) all strains of group B are assigned to the new species combination Paracoccus pantotrophus comb. nov., with strain ATCC 35512T as the type strain. Comparative 16s rRNA sequence analysis and DNA-DNA hybridization of strains of Paracoccus versutus confirm that this species is distinct from both P. denitrificans and P. pantotrophus, but that its nearest phylogenetic neighbour is P. pantotrophus.
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