Structural analysis and reaction mechanism oaf malate dehydrogenase from Geobacillus stearothermophilus

Malate dehydrogenase (MDH) catalyzes the reversible reduction of oxaloacetate (OAA) to L-malate using nicotinamide adenine dinucleotide hydrogen. MDH has two characteristic loops, the mobile loop and the catalytic loop, in the active site. On binding to the substrate, the enzyme undergoes a structural change from the open-form, with an open conformation of the mobile loop, to the closed-form, with the loop in a closed conformation. In this study, three crystals of MDH from a moderate thermophile, Geobacillus stearothermophilus (gs-MDH) were used to determine four different enzyme structures (resolutions, 1.95–2.20 Å), each of which was correspondingly assigned to its four catalytic states. Two OAA-unbound structures exhibited the open-form, while the other two OAA-bound structures exhibited both the open- and closed-form. The structural analysis suggested that the binding of OAA to the open-form gs-MDH promotes conformational change in the mobile loop and simultaneously activates the catalytic loop. The mutations on the key amino acid residues involving the proposed catalytic mechanism significantly affected the gs-MDH activity, supporting our hypothesis. These findings contribute to the elucidation of the detailed molecular mechanism underlying the substrate recognition and structural switching during the MDH catalytic cycle.

First Insight into the Genome Sequence of Clostridium thermobutyricum DSM 4928, a Butyrate-Producing Moderate Thermophile

ABSTRACT The moderately thermophilic and Gram-positive bacterium Clostridium thermobutyricum is strictly anaerobic and forms subterminally located endospores. It was isolated from horse manure compost. C. thermobutyricum produces butyrate as the main fermentation product. The draft genome consists of one circular chromosome (3.425 Mb) and contains 3,201 predicted protein-coding genes.

Kinetics of Fe2+ Oxidization at Different Initial Fe2+ and Fe3+ Concentration in the Presence of Moderate Thermophilic Bacteria

In the bacterial leaching, the oxidation of Fe2+ is very important process. According to the results of this paper, Fe2+ and Fe3+ concentration effect on the growth of moderate thermophile. The optimum conditions for growth of moderate thermophile are the initial concentration of Fe2+ at 0.16mol/l. It indicates the existence of the optimum conditions including initial concentrations of Fe2+ and Fe3+ for the bio-oxidation Fe2+. To increase the initial concentration of Fe3+ can enhance the oxidation rate of Fe2+. The dynamic model of the moderate thermophile oxidation Fe2+ has been established by analyzing and calculating test data with the Matlab software.

Treatment of a Nickel-Copper Sulphide Concentrate Using Bioleaching

This paper describes bioleach test work performed in continuously operated bench-scale reactor systems on a nickel-copper containing sulphide concentrate at 45 and 70°C, respectively. Optimisation of the process focused on determining the effects of process parameters such as residence time, grind size and feed solids concentration on the leach kinetics, metal extractions and performance of both the moderate thermophile and thermophile cultures. The results showed that nickel recoveries in excess of 96% could be achieved using a moderate grind size and leach temperatures, whereas ultrafine grinding and higher operating temperatures were required to achieve Cu extractions in excess of 93%.

Pleomorphobacterium xiamenense gen. nov., sp. nov., a moderate thermophile isolated from a terrestrial hot spring

An aerobic, motile, moderately thermophilic rod, designated strain CLWT, was isolated from a terrestrial hot spring in an exposition garden in Xiamen City, Fujian Province, the People’s Republic of China. Strain CLWT formed beige, dry colonies on solid 2216E medium and flocks in liquid medium. Cells were Gram-stain-negative, short rods (1.0–3.0 µm long and 0.4–0.6 µm wide) with six or more polar flagella. The temperature and pH for growth of strain CLWT were 28–65 °C (optimum, 50–58 °C) and pH 5.5–9.5 (optimum, pH 6.0–8.0). Growth occurred in the presence of 0.3–6.0 % NaCl (optimum 2.5–4.5 %). Phylogenetic analysis based on 16S rRNA gene sequences showed that the closest relative of the isolate was Amaricoccus kaplicensis Ben 101T (94.3 % sequence similarity). The DNA G+C content of strain CLWT was 72.2 mol%. The respiratory quinone was ubiquinone 10. The predominant polar lipids consisted of phosphatidylglycerol and phosphatidylethanolamine. The major fatty acids (>10 %) were summed feature 8 (consisting of C18 : 1ω7c and/or C18 : 1ω6c), C18 : 1ω7c 11-methyl and C18 : 0. Based on phylogenetic, physiological and biochemical data and DNA G+C content, strain CLWT is considered to represent a novel species of a new genus in the family Rhodobacteraceae , for which the name Pleomorphobacterium xiamenense gen. nov., sp. nov. is proposed. The type strain of the type species is CLWT ( = LMG 26245T = CGMCC 1.10808T = MCCC 1A06272T).