SummaryDehalogenation is the key step in the degradation of halogenated aromatics, while reductive dehalogenation is originally thought to rarely occur in aerobes. In this study, an aerobic strain of Comamonas sp. 7D-2 was shown to degrade the brominated aromatic herbicide bromoxynil completely and release two equivalents of bromides under aerobic conditions. The enzymes involved in the degradation of bromoxynil to 4-carboxy-2-hydroxymuconate-6-semialdehyde, including nitrilase, reductive dehalogenase (BhbA), 4-hydroxybenzoate 3-monooxygenase and protocatechuate 4,5-dioxygenase, were molecularly characterized. The novel dehalogenase BhbA was shown to be a complex of a respiration-linked reductive dehalogenase (RdhA) domain and a NAD(P)H-dependent oxidoreductase domain and to have key features of anaerobic respiratory RdhAs, including two predicted binding motifs for [4Fe-4S] clusters and a close association with a hydrophobic membrane protein (BhbB). BhbB was confirmed to anchor BhbA to the membrane. BhbA was partially purified and found to use NAD(P)H as electron donors. Full-length bhbA homologues were found almost exclusively in marine aerobic proteobacteria, suggesting that reductive dehalogenation occurs extensively in aerobes and that bhbA is horizontally transferred from marine microorganisms. The discovery of a functional reductive dehalogenase and ring-cleavage oxygenases in an aerobe opens up possibilities for basic research as well as the potential application for bioremediation.
The aim of this study was to examine the origin of Cryphonectria hypovirus 1 (CHV1) which infects chestnut blight fungus, Cryphonectria parasitica. The genetic diversity of 39 CHV1 isolates from China, Japan and Italy was assessed by combining sequencing and restriction fragment length polymorphic (RFLP) experiments. Based on their partial sequences, 26 CHV1 isolates within 26 haplotypes were grouped into three subtypes. The 17 viruses from China were distributed between subtypes I and III, while all four of the isolates from Japan were subtype II. Of the five isolates from Italy, four were subtype I, and one (IT 192) was subtype III. Our analysis of the geographic distribution of the isolates indicated that all but one of the Chinese subtype III CHV1s are present in northern China; meanwhile all but three of the Chinese subtype I CHV1s are present in South China. Unlike in Europe where there is one predominant CHV1 subtype, our distribution analysis indicates that there has been gene flow between the populations in Asia. Cluster analysis based on the RFLP banding patterns showed that the viral isolates could be separated into four clusters. Most of the viral isolates (29 of 39, 74.4%) were grouped into one large cluster. Greater genetic diversity was observed among the CHV1s from China than among those from Japan and Italy. The Italian isolates were genetically more similar to the Japanese and South Chinese isolates than to the North Chinese isolates, indicating that CHV1 in Italy may have originated from Japan and/or South China.www.blackwell-synergy.com
An aerobic, Gram-stain negative, short rod-shaped, asporogenous, non-motile bacterium designated strain NK8 was isolated from a chlorobenzoate contaminated soil in China. Strain NK8 was observed to grow optimally at pH 7.0, 30 °C and in the absence of NaCl in LB medium. The G + C content of the total DNA of strain NK8 was found to be 65.5 mol%. The 16S rRNA gene sequence of strain NK8 showed high similarity to that of Aquamicrobium aerolatum Sa14 (97.3%), followed by Aquamicrobium lusatiense S1 (96.7%) and Mesorhizobium sangali SCAU7 (96.6%). The DNA-DNA relatedness between strain NK8 and A. aerolatum Sa14 was 35.5 ± 0.9%. The major fatty acids of strain NK8 were determined to be C cyclo ω8c (45.6%), C ω7c (33.4%) and C (8.4%). The respiratory quinone was found to be ubiquinone Q-10. The major polyamine was found to be spermidine. The polar lipid profile include the major compounds phosphatidylcholine and diphosphatidylglycerol, and moderate amounts of phosphatidylethanolamine, phosphatidylmonomethylethanolamine, aminolipid and phospholipid. Based on the differential biochemical and physiological characteristics, the geno-, chemo- and phenotypic characteristics, strain NK8 is proposed to represent a novel species of the genus Aquamicrobium, Aquamicrobium soli sp. nov. The type strain is NK8 (=KCTC 52165=CCTCC AB2016045).
Microbial dehalogenation plays key roles in the biodegradation and detoxification of halogenated aromatics. Although the hydrolytic dehalogenation of halogenated aliphatic hydrocarbons and carboxylic acids has been extensively studied, there are few reports on the hydrolytic dehalogenation of halogenated aromatics. In this study, the aerobic strain BSQ-1, isolated from soils contaminated with halogenated aromatics in Jiangsu, China, was able to completely degrade 0.12 mM o-tetrachlorophthalonitrile in 84 hours in the presence of 2 mM sodium acetate trihydrate and released one equivalent of chlorine ions. MS-MS and NMR analysis revealed that o-tetrachlorophthalonitrile was dehalogenated to 4-hydroxyl-o-trichlorophthalonitrile. The dehalogenation of o-tetrachlorophthalonitrile could occur under both aerobic and anaerobic conditions, showing that the observed dehalogenation was a hydrolytic process. The optimal temperature and pH for o-tetrachlorophthalonitrile dehalogenation by strain BSQ-1 were 30°C and 8, respectively. It was found that 0.2 mM Zn 2+ , Mg 2+ or Co 2+ enhanced dehalogenation activity, whereas 0.2 mM Fe 3+ , Ni 2+ , Cu 2+ , Ca 2+ , or Pb 2+ inhibited dehalogenation activity. Strain BSQ-1 was able to dehalogenate not only
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