| We have isolated two novel thermophilic bacteria, strain E13Tand PGDY12.They were screened by organic solvents from water-sediment samples collected at springs in Yunnan province of China.The strain E13 exhibits a unique and remarkable ability to preferably grow in the presence of ethanol and is able to tolerate 13%(v/v) ethanol at 60℃. Phylogenetic analysis based on 16S rRNA gene similarity showed the strain to be a member of species Anoxybacillus flavithermus (99.2% sequence similarity). DNA-DNA hybridization comparisons demonstrated a 64.8% DNA-DNA relatedness between strain E13T and A. flavithermus DSM 2641. On the basis of phenotypic characteristics, phylogenetic data and DNA-DNA hybridization data, it was concluded that the isolate merited classification as a novel subspecies of A. flavithermus, for which the name Anoxybacillus flavithermus subsp. yunnanensis subsp. nov. proposed. The type strain of this subspecies is E13T (=CCTCC AB2010187T=KCTC 13759T).The strain PGDY12 was characterized as a Gram-positive bacterium, and exhibited a unique and remarkable ability to tolerate solvents at 55℃.It was able to tolerate 100 % solvents, such as toluene, benzene and p-xylene on plate overlay and high concentrations of these solvents in liquid cultures. A comparison of growth showed that 0.2%(v/v) benzene and 0.15%(v/v) p-xylene were capable of enhancing the final cell yields. Transmission electron micrographs showed the incrassation of electron-transparent intracellular material and the distorted cytoplasm in case of the cells grown in toluene. We hypothesize that the unusual solvent tolerance in the strain PGDY12 is at least partially derived from the intracellular material that repels organic solvents. A phylogenetic analysis based on 16S rRNA sequence data indicated that the strain PGDY12 was member of the genus Anoxybacillus. The solvent tolerance properties are less known in thermophilic bacteria. The Anoxybacillus sp. PGDY12 is the first strictly thermophilic bacterium able to tolerate a broad range of solvents. This strain is a promising candidate for use as a high temperature biocatalyst in the biotechnological applications. The strain PGDY12 was deposited in the Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ) with the collection number DSM 23293T.At present, the reports about the tolerance of organic solvents are focus on the mesophiles. Besides the strain Anoxybacillus sp. PGDY12 which isolated previously, there are only two other thermophilic bacterium tolerated the organic solvents. There is litter knowledge about the effect of the temperature on the solvent tolerance. In this work, the mechanism of cell grow under the stress of toluene in different temperature was studied with Monod model and based on the theory of biochemical reaction kinetics. The biodynamic formula was formed to describe the relationship between the specific growth rate (μ) and the additional concentration of toluene. The results showed that this mathematical model can quantify describe the characteristic between the temperature and the toluene tolerance. That is why there is few wild type mesophiles with the character of the organic solvent tolerance。... |
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