A considerable progress has been made to understand the mechanisms of biodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D). 2,4-D biodegradation pathway has been elucidated in many microorganisms including Cupriavidus necator JMP134 (previously known as Wautersia eutropha, Ralstonia eutropha and Alcaligenes eutrophus) and Pseudomonas strains. It generally involves the side chain removal of 2,4-D by α-ketoglutarate-dependent 2,4-D dioxygenase (tfdA) to form 2,4-dichlorophenol (2,4-DCP); hydroxylation of 2,4-DCP by 2,4-DCP hydroxylase (tfdB) to form dichlorocatechol; ortho or meta cleavage of dichlorocatechol by chlorocatechol 1,2-dioxygenase (tfdC) to form 2,4-dichloro-cis,cis-muconate; conversion of 2,4-dichloro-cis,cis-muconate to 2-chlorodienelactone by chloromuconate cycloisomerase (tfdD); conversion of 2-chlorodienelactone to 2-chloromaleylacetate by chlorodienelactone hydrolase (tfdE) and, finally, conversion of 2-chloromaleylacetate to 3-oxoadepate via maleylacetate by chloromaleylacetate reductase and maleylacetate reductase (tfdF), respectively, which is funnelled to the tricarboxylic acid cycle. The latest review on microbial breakdown of 2,4-D, other halogenated aromatic pesticides, and related compounds was compiled by Haggblom, however, a considerable progress has been made in this area of research since then. Thus, this review focuses on the recent advancement on 2,4-D biodegradation, the enzymes, and genes involved and their biotechlogical implications.

Catechol dioxygenases in microorganisms cleave catechol into cis-cis-muconic acid or 2-hydroxymuconic semialdehyde via the ortho- or meta-pathways, respectively. The aim of this study was to purify, characterize, and predict the 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 a temperature of 30 °C. The Lineweaver–Burk plot showed the v_max and K_m 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 shared 81% homology with homogentisate 1,2-dioxygenase reported in other Pseudomonas chlororaphis strains. The 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.

Three indigenous pseudomonads, Pseudomonas putida DLL-E4, Pseudomonas reactans and Pseudomonas fluorescens, were isolated from chlorophenol-contaminated soil samples collected from a sawmill located...

Two indigenous ascomycetes fungi, Trichoderma lixii strain FLU1 (TlFLU1) and Talaromyces pinophilus strain FLU12 (TpFLU12), were isolated from benzo(b)fluoranthene-enriched activated sludge and tested for bio-catalytically degrade fluoranthene as a sole carbon source. TlFLU1 and TpFLU12 degraded 98 and 99% of 400 mg/L of fluoranthene after 16 and 12 d incubation period, respectively. Degradation correlated with the upregulation of expression of ligninolytic enzymes. The GC-MS and FTIR analysis of the degradation products suggest that the degradation is initiated at the C1-C2 position of the compound ring via oxygenation and ring cleavage to form 9-oxo-9H-fluorene-1-carboxylic acid before undergoing ring cleavage to yield fluorenone, which then proceeds through the ß-Ketoadipate pathway via benzene-1,2,3-tricarboxylic acid. The degradation rate is better fitted in the first-order and zero-order kinetic model for TlFLU1 and TpFLU12, respectively. The metabolites from the TlFLU1 degradation media are shown to be toxic in Vibryo parahaemolyticus after 6 h of exposure with effective concentration (EC₅₀) and toxicity unit (TU) values of 14.25 mg/L and 7.018%, respectively, while also being observed as non-toxic from TpFLU12 degradation media with an EC₅₀ and TU values of 197.1 mg/L and 0.507%, respectively. Results from this study show efficient metabolism of fluoranthene into an innocuous state by TlFLU1 and TpFLU12.