Desulfotomaculum carboxydivorans sp. nov., a novel sulfate-reducing bacterium capable of growth at 100 % CO

Abstract

A moderately thermophilic, anaerobic, chemolithoheterotrophic, sulfate-reducing bacterium, strain CO-1-SRB^T, was isolated from sludge from an anaerobic bioreactor treating paper mill wastewater. Cells were Gram-positive, motile, spore-forming rods. The temperature range for growth was 30–68 °C, with an optimum at 55 °C. The NaCl concentration range for growth was 0–17 g l⁻¹; there was no change in growth rate until the NaCl concentration reached 8 g l⁻¹. The pH range for growth was 6·0–8·0, with an optimum of 6·8–7·2. The bacterium could grow with 100 % CO in the gas phase. With sulfate, CO was converted to H₂and CO₂and part of the H₂was used for sulfate reduction; without sulfate, CO was completely converted to H₂and CO₂. With sulfate, strain CO-1-SRB^Tutilized H₂/CO₂, pyruvate, glucose, fructose, maltose, lactate, serine, alanine, ethanol and glycerol. The strain fermented pyruvate, lactate, glucose and fructose. Yeast extract was necessary for growth. Sulfate, thiosulfate and sulfite were used as electron acceptors, whereas elemental sulfur and nitrate were not. A phylogenetic analysis of 16S rRNA gene sequences placed strain CO-1-SRB^Tin the genusDesulfotomaculum, closely resemblingDesulfotomaculum nigrificansDSM 574^TandDesulfotomaculumsp. RHT-3 (99 and 100 % similarity, respectively). However, the latter strains were completely inhibited above 20 and 50 % CO in the gas phase, respectively, and were unable to ferment CO, lactate or glucose in the absence of sulfate. DNA–DNA hybridization of strain CO-1-SRB^TwithD. nigrificansandDesulfotomaculumsp. RHT-3 showed 53 and 60 % relatedness, respectively. On the basis of phylogenetic and physiological features, it is suggested that strain CO-1-SRB^Trepresents a novel species within the genusDesulfotomaculum, for which the nameDesulfotomaculum carboxydivoransis proposed. This is the first description of a sulfate-reducing micro-organism that is capable of growth under an atmosphere of pure CO with and without sulfate. The type strain is CO-1-SRB^T(=DSM 14880^T=VKM B-2319^T).