| Phthalates have been widely used as plasticizers in various kinds of chemical products such as polyvinylchloride (PVC) and polyethylene. Due to the widespread use of PAEs, they have considered as a ubiquitous environmental pollutant. Some PAEs and their degradation intermediates are considered as endocrine disrupting chemicals which can interfere with the reproductive system of animals and humans, and have been potentially harmful for human. It has been shown that hydrolysis, photolysis and volatilization of PAEs occurred very slowly, and because of its low energy consumption, high efficiency and environmental friendliness, biodegradation plays an important role in the decomposition of PAEs and has been regarded as one of important way to eliminate PAEs pollution in the environment.Several bacteria capable of utilizing PAEs as the sole carbon sourse and energy were isolated from greenhouse soil samples, and were named as LMB-1,LMB-2, LMB-3 and LMB-4 respectively. Based on the analysis of their 16S rRNA gene sequence, LMB-1 was identified as Rhizobium sp., LMB-2 and LMB-4 were identified as Pseudomonas sp., LMB-3 was identified as Streptomyces sp.. Their degradation rate to DEHP were 90.319%(LMB-1), 81.053%(LMB-2),78.788%(LMB-3) and 29.744%(LMB-4) separately..It showed Rhizobium sp. had a higher efficiency than other three strains. Therefore, degradation characteristics, metabolic pathway and genome of Rhizobium sp. LMB-1 were investigated in this paper. The strain LMB-1 was rod-shaped and Gram-negative aerobic bacterium with a size of 0.5-0.7 μmx 1.4-2.0 μm in the exponential growth phase in TSB medium and 0.6-0.7 μmx 1.2-1.4 μm in the MSM medium with DBP (100 mg/L). The substrate range tests showed that Rhizobium sp. LMB-1 degraded not only DMP, DEP and DBP but also long-chain DEHP with a MW of 390.56 g/mol, and the biodegradability decreased with an increase in the length of the phthalate alkyl chains. The optimal temperature and pH for the strain LMB-1 to degrade DBP were 37℃ and 6.0. The kinetics of DBP degradation by Rhizobium sp. LMB-1 indicated that the DBP degradation by strain LMB-1 could fit well with the first-order kinetic equations when the initial DBP concentration was not more than 200 mg/L. The results of degrading efficiency and cell growth revealed that a high initial DBP concentration in the medium likely caused the inhibition of the microbial merabolism and growth through substrate inhibition.The proposed biodegradation pathway of DBP in the strain LMB-1 showed that DBP was initially hydrolysed by β-oxidation to produce DEP, and the intermediate product DEP was subsequentely metabolized to PA by hydrolysis of ester group and demethylayion. Subsequent PA underwent aromatic ring cleavage and further metabolism.The genome of Rhizobium sp. LMB-1 was sequenced by using Illmina Miseq 2000 platform (GenBank accession number was JZUD00000000.1). Based on the assemble results of the sample LMB-1, the total lenghth of coding sequences (CDs) was 4,518,228 bp, the genome G+C content was 59.18%, and it contained 4959 coding sequences (CDs), a total of 2648 protein-coding genes were assigned with predicted function and had been categorized into 23 COG groups. Based on the kegg database analysis,195 metabolic maps had got. Three monooxygenase genes related with β-oxidation, four esterase genes catalyzing hydrolysis of ester group and one gene cluster involved in protocatechuic acid metabolic pathways were predicted. |
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