A bacterium that degrades 3-chloropropionic acid (3CP) was isolated from local paddy (rice) agricultural soil by enrichment culture. Taxonomic analysis identified the strain as Pseudomonas sp. Strain-mediated degradation of 3CP released chloride ions into the growth medium, and the degradation of ~100% of 20 mM 3CP was monitored by high performance liquid chromatography (HPLC). The putative Pseudomonas sp. dehalogenase that released the chloride ions from 3CP was induced by growth of the bacterium in the presence of 3CP as the sole carbon source. The dehalogenase showed activity against a specific type of halogenated aliphatic acids, and the highest activity was obtained with 3CP. However, the enzyme could only remove halogen atoms from 3-carbon alkanoic acids if the halogen was at the β-but not the -position. In crude bacterial extracts, the dehalogenase activity with 3CP was maximum at 30 °C, over a broad pH range (pH 7.5 optimum) and had an apparent K ms of 0.25 ± 0.04 mM and 0.67 ± 0.17 mM for 3CP and 2,3-dichloropropionic acid, respectively.
Aims: Trichoderma asperellum strain SD1 grows on 3-chloropropionic acid (3CP), a β-haloalkanoic acid, and produces a putative extracellular dehalogenase that can degrade this acid. Here we further characterized the fungal enzyme system responsible for biodegradation of 3CP. Methodology and results: The primary qualification of the ligninolytic potential in T. asperellum strain SD1 was performed using guaiacol oxidation. When strain SD1 was grown in liquid minimal medium with the presence of 3CP as the sole carbon source, no lignin peroxidase, manganese peroxidase, or laccase activity was detected. The ligninolytic condition was achieved only in the presence of glucose or when guaiacol was present as an inducer. Under nonligninolytic conditions, 3CP was utilized by strain SD1. Therefore, 3CP was utilized under ligninolytic conditions as well as under non-ligninolytic conditions, suggesting that extracellular peroxidases and laccase are not involved in the degradation of 3CP by T. asperellum strain SD1. Conclusion, significance, and Impact of study: Very few studies have explained the degradation of β-chlorosubstituted haloalkanoic acids such as 3CP by dehalogenases. This is the first report to identify a novel putative βhaloacid dehalogenase that degrades 3CP under ligninolytic and non-ligninolytic conditions. T. asperellum strain SD1, thus has the potential in the development of dehalogenating enzymes for industrial biocatalytic processes, in future.
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