Geobacter sulfurreducens subsp. ethanolicus, subsp. nov., an ethanol-utilizing dissimilatory Fe(III)-reducing bacterium from a lotus field

Abstract

An ethanol-utilizing Fe(III)-reducing bacterial strain, OSK2A^T, was isolated from a lotus field in Aichi, Japan. Phylogenetic analysis of the 16S rRNA gene sequences of OSK2A^T and related strains placed it within Geobacter sulfurreducens PCA^T. Strain OSK2A^T was shown to be a Gram-negative, motile, rod-shaped bacterium, strictly anaerobic, 0.76−1.65 µm long and 0.28−0.45 μm wide. Its growth occurred at 20−40℃, pH 6.0−8.1, and it tolerated up to 1% NaCl. The G+C content of the genomic DNA was 61.2 mol% and DNA-DNA hybridization value with Geobacter sulfurreducens PCA^T was 60.7%. The major respiratory quinone was MK-8. The major fatty acids were 16：1 ω7c, 16：0, 14：0, 15：0 iso, 16：1 ω5c, and 18：1 ω7c. Strain OSK2A^T could utilize H₂, ethanol, acetate, lactate, pyruvate, and formate as substrates with Fe(III)-citrate as electron acceptor. Amorphous Fe(III) hydroxide, Fe(III)-NTA, fumarate, malate, and elemental sulfur were utilized as electron acceptors with either acetate or ethanol as substrates. Results obtained from physiological, DNA-DNA hybridization, and chemotaxonomic tests support genotypic and phenotypic differentiation of strain OSK2A^T from its closest relative. The isolate is assigned as a novel subspecies with the name Geobacter sulfurreducens subsp. ethanolicus, subsp. nov. (type strain OSK2A^T=DSMZ 26126^T=JCM 18752^T).