Summary auto-generated
This study analyzed the phylogeny of mixotrophic thiobacilli, bacteria capable of both chemolithotrophic (sulfur-oxidizing) and heterotrophic growth. Researchers sequenced the complete 5S and 16S ribosomal DNA of Thiobacillus cuprinus and compared these sequences with other proteobacteria. The analysis revealed that T. cuprinus, T. intermedius, T. perometabolis, and T. thermosulfatus form a distinct phylogenetic cluster within the β1 subgroup of Proteobacteria, related to genera like Pseudomonas and Alcaligenes. Genome size analysis using pulsed-field gel electrophoresis showed considerable genetic diversity among these organisms, ranging from 3.6 to 5.7 megabase pairs. While restriction fragment analysis produced different groupings than rDNA sequencing, the authors concluded that rDNA sequence analysis more accurately reflects true phylogenetic relationships and physiological characteristics. Based on their distinctive metabolic capabilities, phylogenetic relatedness, and physiological differences from other thiobacilli and proteobacteria, the researchers proposed transferring these four mixotrophic species to a new genus, Thiomonas.
Key findings
- T. cuprinus, T. intermedius, T. perometabolis, and T. thermosulfatus form a phylogenetic cluster within the β1 subgroup of Proteobacteria, distinct from strictly chemolithoautotrophic thiobacilli
- These mixotrophic thiobacilli are most closely related to heterotrophic genera including Leptothrix, Sphaerotilus, and certain Burkholderia and Alcaligenes species
- Genome sizes of mixotrophic thiobacilli range from 3.6 to 5.2 megabase pairs, showing high genomic diversity within the group
- The authors propose establishing a new genus, Thiomonas, to accommodate these four mixotrophic thiobacillus species based on their unique characteristics and evolutionary relationships
- rDNA sequence analysis proved more reliable than restriction fragment analysis for determining true phylogenetic relationships among these distantly related organisms
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Abstract
The complete 5S and 16S ribosomal DNA (rDNA) sequences of the facultatively chemolithotrophic bacterium Thiobacillus cuprinus and results of a comparison of these sequences with homologous sequences from several proteobacterial species supported affiliation of T. cuprinus with the beta 1 subgroup of the Proteobacteria. T. cuprinus, Thiobacillus intermedius, Thiobacillus perometabolis, and Thiobacillus thermosulfatus form a phylogenetic cluster that comprises some of the thiobacilli capable of mixotrophic growth. This cluster is related to some pseudomonads and Alcaligenes species belonging to the beta subclass. In addition, a low-frequency restriction fragment analysis (LFRFA) of some mixotrophic thiobacilli and some related species was carried out by using pulsed-field gel electrophoresis (PFGE) to determine the SpeI and XbaI macrorestriction patterns and genome sizes of these organisms. The correlation of the LFRFA results and the 16S rDNA analysis results and the usefulness of the two analyses are discussed. The PFGE fingerprints suggested that Thiobacillus sp. strain ATCC 27793 is related to T. intermedius rather than to T. perometabolis, as described previously. The distinctive characteristics of the mixotrophic species analyzed in this work, their phylogenetic relatedness, and their physiological differences from other groups belonging to the Proteobacteria, including other thiobacilli, suggest that these organisms should be transferred to a new genus, the genus Thiomonas gen. nov.