Summary auto-generated
This study describes the reclassification of a sulfate-reducing bacterium isolated from Baltic Sea sediment. Strain SaxT, originally designated as a Desulfoarculus species, is formally described as a new genus and species, Desulfotignum balticum. The bacterium is a mesophilic, rod-shaped, gram-negative anaerobe capable of utilizing diverse substrates including aromatic compounds, fatty acids, and simple organic molecules. It can grow autotrophically on H2, CO2, and formate, and uses sulfate, thiosulfate, and sulfite as electron acceptors. Notably, strain SaxT employs the CO dehydrogenase pathway for complete oxidation of acetyl-CoA. Analysis of 16S rRNA gene sequences showed less than 94.1% identity with other sulfate-reducing bacteria, supporting its designation as a new genus. Additionally, phylogenetic analyses revealed that Desulfobacterium phenolicum belongs to the genus Desulfobacula and was reclassified as Desulfobacula phenolica. Fatty acid methyl ester (FAME) analysis demonstrated that both Desulfobacula species and strain SaxT share the biomarker fatty acid 10-Me 16:0, previously thought to be specific to Desulfobacter species, indicating its reliability as a taxonomic marker should be reconsidered.
Key findings
- Strain SaxT from Baltic Sea sediment represents a new genus and species, Desulfotignum balticum, based on 16S rRNA phylogenetics and morphological/physiological characteristics
- Desulfobacterium phenolicum is reclassified as Desulfobacula phenolica based on phylogenetic analyses showing closer relationship to Desulfobacula toluolica
- Desulfotignum balticum utilizes the CO dehydrogenase pathway for complete oxidation of acetyl-CoA to CO2 and can grow autotrophically
- The fatty acid 10-Me 16:0, previously considered a specific biomarker for Desulfobacter, is also present in high amounts in Desulfobacula and Desulfotignum species
- Strain SaxT grows on diverse substrates including aromatic compounds, fatty acids, and simple organic compounds with complete substrate oxidation under sulfate-reducing conditions
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Abstract
A mesophilic, sulfate-reducing bacterium (strain Sax(T)) was isolated from marine coastal sediment in the Baltic Sea and originally described as a 'Desulfoarculus' sp. It used a large variety of substrates, ranging from simple organic compounds and fatty acids to aromatic compounds as electron donors. Autotrophic growth was possible with H(2), CO(2) and formate in the presence of sulfate. Sulfate, thiosulfate and sulfite were used as electron acceptors. Sulfur and nitrate were not reduced. Fermentative growth was obtained with pyruvate, but not with fumarate or malate. Substrate oxidation was usually complete leading to CO(2), but at high substrate concentrations acetate accumulated. CO dehydrogenase activity was observed, indicating the operation of the CO dehydrogenase pathway (reverse Wood pathway) for CO(2) fixation and complete oxidation of acetyl-CoA. The rod-shaped cells were 0.8--1.0 microm wide and 1.5--2.5 microm long. Spores were not produced and cells stained Gram-negative. The temperature limits for growth were between 10 and 42 degrees C (optimum growth at 28--32 degrees degrees C). Growth was observed at salinities ranging from 5 to 110 g NaCl l(-1), with an optimum at 10--25 g NaCl l(-1). The G+C content of the DNA was 62.4 mol%. Vitamins were required for growth. Based on the 16S rRNA gene sequence, strain Sax(T) represents a new genus within the delta-subclass of the Proteobacteria. The name Desulfotignum balticum gen. nov., sp. nov. is proposed. After the 16S rDNA sequences of all members of the genus Desulfobacterium were published (GenBank accession nos. AJ237601--AJ237604, AJ237606, AJ237607), the need to reclassify most members of the genus Desulfobacterium became obvious due to their strong phylogenetic affiliation to other genera. Here, we propose to reclassify Desulfobacterium phenolicum as Desulfobacula phenolica comb. nov. Desulfotignum balticum, Desulfobacterium phenolicum and Desulfobacula toluolica contain cellular fatty acids which have so far only been found in members of the genus Desulfobacter.