Phenylurea herbicides (PHs) are frequently detected as major water contaminants in areas where there is extensive use. In this study, Diaphorobacter sp. strain LR2014-1, which initially hydrolyzes linuron to 3,4-dichloroanaline, and Achromobacter sp. strain ANB-1, which further mineralizes the produced aniline derivatives, were isolated from a linuronmineralizing consortium despite being present at low abundance in the community. The synergistic catabolism of linuron by the consortium containing these two strains resulted in more efficient catabolism of linuron and growth of both strains. Strain LR2014-1 harbors two evolutionary divergent hydrolases from the amidohydrolase superfamily Phh and the amidase superfamily TccA2, which functioned complementarily in the hydrolysis of various types of PHs, including linuron (N-methoxy-N-methyl-substituted), diuron, chlorotoluron, fluomethuron (N,N-dimethyl-substituted), and siduron. These findings show that a bacterial consortium can contain catabolically synergistic species for PH mineralization, and one strain could harbor functionally complementary hydrolases for a broadened substrate range.
The phenylurea herbicide linuron is globally used and has caused considerable concern because it leads to environmental pollution. In this study, a highly efficient linuron-transforming strain Sphingobium sp. SMB was isolated, and a gene (lahB) responsible for the hydrolysis of linuron to 3,4-dichloroaniline and N,O-dimethylhydroxylamine was cloned from the genome of strain SMB. The lahB gene encodes an amidohydrolase, which shares 20−53% identity with other biochemically characterized amidohydrolases, except for the newly reported linuron hydrolase Phh (75%). The optimal conditions for the hydrolysis of linuron by LahB were determined to be pH 7.0 and 30 °C, and the K m value of LahB for linuron was 37.3 ± 1.2 μM. Although LahB and Phh shared relatively high identity, LahB exhibited a narrow substrate spectrum (specific for linuron) compared to Phh (active for linuron, diuron, chlortoluron, etc.). Sequence analysis and site-directed mutagenesis revealed that Ala261 of Phh was the key amino acid residue affecting the substrate specificity. Our study provides a new amidohydrolase for the specific hydrolysis of linuron.
Background: Swep is an excellent carbamate herbicide that kills weeds by interfering with metabolic processes and inhibiting cell division at the growth point. Due to the large amount of use, swep residues in soil and water not only cause environmental pollution but also accumulate through the food chain, ultimately pose a threat to human health. This herbicide is degraded in soil mainly by microbial activity, but no studies on the biotransformation of swep have been reported. Results:In this study, a consortium consisting of two bacterial strains, Comamonas sp. SWP-3 and Alicycliphilus sp. PH-34, was enriched from a contaminated soil sample and shown to be capable of mineralizing swep. Swep was first transformed by Comamonas sp. SWP-3 to the intermediate 3,4-dichloroaniline (3,4-DCA), after which 3,4-DCA was mineralized by Alicycliphilus sp. PH-34. An amidase gene, designated as ppa, responsible for the transformation of swep into 3,4-DCA was cloned from strain SWP-3. The expressed Ppa protein efficiently hydrolyzed swep and a number of other structural analogues, such as propanil, chlorpropham and propham. Ppa shared less than 50% identity with previously reported arylamidases and displayed maximal activity at 30 °C and pH 8.6. Gly449 and Val266 were confirmed by sequential error prone PCR to be the key catalytic sites for Ppa in the conversion of swep. Conclusions:These results provide additional microbial resources for the potential remediation of swep-contaminated sites and add new insights into the catalytic mechanism of amidase in the hydrolysis of swep.
Dichlorprop [(RS)-2-(2,4-dichlorophenoxy)propanoic acid; DCPP], an important phenoxyalkanoic acid herbicide (PAAH), is extensively used in the form of racemic mixtures (Rac-DCPP), and the environmental fates of both DCPP enantiomers [(R)-DCPP and (S)-DCPP] mediated by microorganisms are of great concern. In this study, a bacterial strain Sphingopyxis sp. DBS4 was isolated from contaminated soil and was capable of utilizing both (R)-DCPP and (S)-DCPP as the sole carbon source for growth. Strain DBS4 preferentially catabolized (S)-DCPP as compared to (R)-DCPP. The optimal conditions for Rac-DCPP degradation by strain DBS4 were 30 °C and pH 7.0. In addition to Rac-DCPP, other PAAHs such as (RS)-2-(4-chloro-2-methylphenoxy)propanoic acid, 2,4-dichlorophenoxyacetic acid, 4-chloro-2-methylphenoxyacetic acid, and 2,4-dichlorophenoxyacetic acid butyl ester could also be catabolized by strain DBS4. Bioremediation of Rac-DCPP-contaminated soil by inoculation of strain DBS4 exhibited an effective removal of both (R)-DCPP and (S)-DCPP from the soil. Due to its broad substrate spectrum, strain DBS4 showed great potential in the bioremediation of PAAH-contaminated sites.
A Gram-stain-negative, non-spore-forming and rod-shaped bacterium, designated strain NS-102T, was isolated from herbicide-contaminated soil sampled in Nanjing, PR China, and its taxonomic status was investigated by a polyphasic approach. Cell growth of strain NS-102T occurred at 16–42 °C (optimum, 30 °C), at pH 5.0–8.0 (optimum, pH 6.0) and in the presence of 0–3.5 % (w/v) NaCl (optimum, without addition of NaCl). The 16S rRNA gene sequence of strain NS-102T shows high similarity to that of Agriterribacter humi YJ03T (96.9 % similarity), followed by Terrimonas terrae T16R-129T (93.8 %) and Terrimonas pekingensis QHT (93.6 %). Average nucleotide identity, average amino acid identity and digital DNA–DNA hybridization values between the draft genomes of strain NS-102T and A. humi YJ03T were 72.5, 69.4 and 18.6%, respectively. The only respiratory quinone was MK-7, and phosphatidylethanolamine and unidentified lipids were the major polar lipids. The major cellular fatty acids of strain NS-102T contained high amounts of iso-C15 : 0 (24.6 %), iso-C17 : 03-OH (24.1 %), iso-C15 : 0 G (16.6 %) and summed feature 3 (C16 : 1 ω6c and/or C16 : 1 ω7c) (15.6 %). The G+C content of the total DNA was determined to be 40.0 mol%. The morphological, physiological, chemotaxonomic and phylogenetic analyses clearly distinguished this strain from its closest phylogenetic neighbours. Thus, strain NS-102T represents a novel species of the genus Agriterribacter , for which the name Agriterribacter soli sp. nov. is proposed. The type strain is NS-102T (=CCTCC AB 2017249T=KCTC 62322T).
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