Altererythrobacter terrae sp. nov., isolated from mountain soil

A Gram-negative, non-motile, non-spore-forming, ovoid-shaped bacterium designated as SWU3(T) was isolated from mountain soil collected at Seoul Women's University, South Korea. Based on 16S rRNA sequence analysis, strain SWU3(T) was found to belong to the genus Altererythrobacter. It shares high sequence similarities with A. dongtanensis JM27(T) (96.6 %), A. epoxidivorans JCS350(T) (96.6 %), and A. troitsensis KMM 6042(T) (96.5 %). Growth was observed between 15 and 37 °C (optimum, 30 °C) with pH of 6-9 (optimum, pH 7.0). It could tolerate 0-2 % (w/v) NaCl. Its predominant quinone was found to be ubiquinone (Q-10). Its major cellular fatty acids were determined to be C17:1 ω6c, C18:1 ω7c, and summed featured 3 (C16:1 ω7c/C16:1 ω6c), all of which are similar characteristics to those of species within the genus Altererythrobacter. Its G + C molar content was found to be 58.4 mol%. Phylogenetic evidence, together with phenotypic characteristics showed that strain SWU3(T) represents a new species of the genus Altererythrobacter. The name Altererythrobacter terrae sp. nov. is proposed and the type strain is SWU3(T) (=KEMB 9004-128(T) = JCM 19177(T)).

Accelerated methanogenesis from effluents of hydrogen-producing stage in anaerobic digestion by mixed cultures enriched with acetate and nano-sized magnetite particles

Potential for paddy soil enrichments obtained in the presence of nano-sized magnetite particles (named as PSEM) to promote methane production from effluents of hydrogen-producing stage in two-stage anaerobic digestion was investigated. The results showed that the addition of magnetite significantly accelerated methane production from acetate in a dose-independent manner. The results from high-throughput sequencing analysis revealed that Rhodocyclaceae-related species were selectively enriched, which were likely the key players for conversion of acetate to methane in PSEM. Compared to the paddy soil enrichments obtained in the absence of magnetite (named as PSEC), the maximum methane production rate in PSEM was significantly higher (1.5-5.5times higher for the artificial medium and 0.2-1.7times higher for the effluents). The accelerated methane production from the effluents indicated remarkably application potential of PSEM for improving performance of anaerobic digestion.

Asymmetric reduction of ketones and β-keto esters by (S)-1-phenylethanol dehydrogenase from denitrifying bacterium Aromatoleum aromaticum

Enzyme-catalyzed enantioselective reductions of ketones and keto esters have become popular for the production of homochiral building blocks which are valuable synthons for the preparation of biologically active compounds at industrial scale. Among many kinds of biocatalysts, dehydrogenases/reductases from various microorganisms have been used to prepare optically pure enantiomers from carbonyl compounds. (S)-1-phenylethanol dehydrogenase (PEDH) was found in the denitrifying bacterium Aromatoleum aromaticum (strain EbN1) and belongs to the short-chain dehydrogenase/reductase family. It catalyzes the stereospecific oxidation of (S)-1-phenylethanol to acetophenone during anaerobic ethylbenzene mineralization, but also the reverse reaction, i.e., NADH-dependent enantioselective reduction of acetophenone to (S)-1-phenylethanol. In this work, we present the application of PEDH for asymmetric reduction of 42 prochiral ketones and 11 β-keto esters to enantiopure secondary alcohols. The high enantioselectivity of the reaction is explained by docking experiments and analysis of the interaction and binding energies of the theoretical enzyme-substrate complexes leading to the respective (S)- or (R)-alcohols. The conversions were carried out in a batch reactor using Escherichia coli cells with heterologously produced PEDH as whole-cell catalysts and isopropanol as reaction solvent and cosubstrate for NADH recovery. Ketones were converted to the respective secondary alcohols with excellent enantiomeric excesses and high productivities. Moreover, the progress of product formation was studied for nine para-substituted acetophenone derivatives and described by neural network models, which allow to predict reactor behavior and provides insight on enzyme reactivity. Finally, equilibrium constants for conversion of these substrates were derived from the progress curves of the reactions. The obtained values matched very well with theoretical predictions.

Description of Azospira restricta sp. nov., a nitrogen-fixing bacterium isolated from groundwater

A novel, Gram-negative bacterial strain, SUA2T, isolated from groundwater, was characterized using a polyphasic approach. Cells are Gram-negative, non-spore-forming, straight to curved rods with a single polar flagellum. Strain SUA2T is oxidase- and catalase-positive and is able to fix nitrogen. Poly-β-hydroxybutyrate storage granules are produced. Dominant fatty acids when grown in R2A and VM ethanol media for 72 h at 37 °C are C16 : 0, C16 : 1 ω7c, C17 : 0 cyclo, C10 : 0 3-OH, C18 : 1 ω7c, C12 : 0 and C15 : 0. DNA G+C content is 67.9 mol%. Phenotypic and phylogenetic data indicate that strain SUA2T is related to, but clearly differentiated from Azospira oryzae. Strain SUA2T is thus proposed as a novel species of the genus Azospira with the name Azospira restricta sp. nov. The description of the genus Azospira is emended to include the characteristics of this novel species. The type strain of Azospira restricta is SUA2T (=NRRL B-41660T=DSM 18626T=LMG 23819T).