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In this study, two newly isolated 2,4-dichlorophenol(2,4-DCP)-degrading strains, Pseudomonas sp. KZNSA (PKZNSA) and Klebsiella pneumoniae KZNSA (KpKZNSA), were enriched from an activated sludge sample with a known history of contamination with chlorinated organic compounds collected from a wastewater treatment plant located in Durban, South Africa. The strains could use 2,4-DCP as sole carbon and energy source. PKZNSA and KpKZNSA degraded 64 and 49% of 2,4-DCP, with the degradation rate constant of 0.14 and 0.03 mg/L d, respectively. Both PKZNSA and KpKZNSA were found to harbor the catabolic genes that encode the enzymes involved in 2,4-DCP degradation via the ortho-pathway which is further confirmed by the specific enzyme activity assays. The strains did not possess genes that encode the enzyme maleylacetate reductase, which is involved in funneling the last intermediate (maleylacetate) in the pathway into the Krebs cycle. Findings from this study will be helpful in the exploitation of these microorganisms and/or their enzymes in developing bioremediation strategies for the chlorophenol-polluted environment.

A 61.3 kDa Phenol hydroxylase (PheA) was purified and characterized from Pseudomonas sp. KZNSA (PKZNSA). Cell free extract of the isolate grown in mineral salt medium supplemented with 600 ppm phenol showed 21.58 U/mL of PheA activity with a specific activity of 7.67 U/mg of protein. The enzyme was purified to 1.6-fold with a total yield of 33.6%. The purified PheA was optimally active at pH 8 and temperature 30 °C, with ≈95% stability at pH 7.5 and temperature 30 °C after 2 h. The Lineweaver-Burk plot showed the vmax and Km values of 4.04 µM/min and 4.03 µM, respectively, for the substrate phenol. The ES-MS data generated from the tryptic digested fragments of pure protein and PCR amplification of a ≈600 bp gene from genomic DNA of PKZNSA lead to the determination of complete amino acid and nucleotide sequence of PheA. Bioinformatics tools and homology modelling studies indicated that PheA from PKZNSA is likely a probable protein kinase UbiB (2-octaprenylphenol hydroxylase) involving Lys and Asp at positions 153 and 288 for binding and active site, respectively. Characterization and optimization of PheA activity may be useful for a better understanding of 2,4-dichlorophenol degradation by this organism and for potential industrial application of the enzyme.

Catechol dioxygenases in microorganisms cleave catechol into cis-cis-muconic acid or 2-hydroxymuconic semialdehyde via the ortho- or meta-pathway, respectively. The aim of the study was to purify, characterize and predict template-based three-dimensional structure of catechol 1,2-dioxygenase (C12O) from indigenous Pseudomonas chlororaphis strain UFB2 (PcUFB2). Preliminary studies showed that PcUFB2 could degrade 40 ppm of 2,4-dichlorophenol (2,4-DCP). The crude cell extract showed 10.34 U/mL of C12O activity with a specific activity of 2.23 U/mg of protein. A 35 kDa protein was purified to 1.5-fold with total yield of 13.02 % by applying anion exchange and gel filtration chromatography. The enzyme was optimally active at pH 7.5 and temperature 30 °C. The Lineweaver-Burk plot showed the vmax and Km values of 16.67 µM/min and 35.76 µM, respectively. ES-MS spectra of tryptic digested SDS-PAGE band and bioinformatics studies revealed that C12O share 81% homology to homogentisate 1,2-dioxygenase reported in other Pseudomonas chlororaphis strains. Characterization and optimization of C12O activity can assist in understanding the 2,4-DCP metabolic pathway in PcUFB2 and its possible application in bioremediation strategies.