Sphingobium jiangsuense sp. nov., a 3-phenoxybenzoic acid-degrading bacterium isolated from a wastewater treatment system.

A non-sporulating, non-motile, catalase- and oxidase-positive, Gram-negative, rod-shaped bacterial strain, designated BA-3T, was isolated from activated sludge of a wastewater treatment facility. The strain was able to degrade about 95 % of 100 mg 3-phenoxybenzoic acid l(-1) within 2 days of incubation. Growth occurred in the presence of 0-2 % (w/v) NaCl [optimum, 0.5 % (w/v) NaCl], at pH 5.5-9.0 (optimum, pH 7.0) and at 10-37 °C (optimum, 28 °C). Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that strain BA-3T was a member of the genus Sphingobium; it showed highest gene sequence similarity to Sphingobium qiguonii X23T (98.2 %), and similarities of <97.0 % with strains of other Sphingobium species. The polar lipid pattern, the presence of spermidine and ubiquinone Q-10, the predominance of summed feature 8 (C18:1ω6c and/or C18:1ω7c) in the cellular fatty acid profile and the DNA G+C content also supported affiliation of the isolate to the genus Sphingobium. Strain BA-3T showed low DNA-DNA relatedness values (21.3±0.8 %) with Sphingobium qiguonii X23(T). Based on phenotypic, genotypic and phylogenetic data, strain BA-3T represents a novel species of the genus Sphingobium, for which the name Sphingobium jiangsuense sp. nov. is proposed; the type strain is BA-3T (=CCTCC AB 2010217T= KCTC 23196T=KACC 16433T).

Expression, characterization, and site-directed mutation of a multiple herbicide-resistant acetohydroxyacid synthase (rAHAS) from Pseudomonas sp. Lm10.

A multiple herbicide-resistant acetohydroxyacid synthase (rAHAS) gene was cloned from Pseudomonas sp. Lm10. Sequence analysis showed that the rAHAS regulatory subunit was identical to that of Pseudomonas putida KT2440 (sensitive AHAS, sAHAS), whereas six different sites [H134→N (rAHAS→sAHAS), A135→P, S136→T, I210→V, F264→Y, and S486→W] were found in the catalytic subunit. The rAHAS and sAHAS were over expressed, purified and characterized. rAHAS showed higher resistance to four kinds of AHAS-inhibitor herbicides than sAHAS. The resistance factor of rAHAS was 56.0-fold, 12.6-fold, 6.5-fold, and 9.2-fold as compared with sAHAS when metsulfuron-methyl, imazethapyr, flumetsulam, and pyriminobac-methyl used as inhibitor, respectively. The specific activity of rAHAS was lower than that of sAHAS and the K (m) value of rAHAS for pyruvate was approximately onefold higher than the corresponding value for sAHAS. Data from site-directed mutagenesis demonstrated that alteration at A135, F264, and S486 resulted in resistance reduction, while the mutation at H134, S136, and I210 has little effect on the resistance. A135 was mainly responsible for resistance to imidazolinone; F264 conferred resistance to sulfonylurea and triazolopyrimidine sulfonamide; and S486 showed multiple herbicides resistance to the four herbicides.