Microbial degradation of 2,4-dichlorophenoxyacetic acid: Insight into the enzymes and catabolic genes involved, their regulation and biotechnological implications

Abstract

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.

Targeted metagenomics demonstrates the ecological role of IS1071in bacterial community adaptation to pesticide degradation

“…Downstream pathway enzymes included aromatic ring cleavage enzymes and enzymes that are involved in the further conversion of the (substituted) aromatic cleavage products to Krebs cycle intermediates. Similar to the upstream catabolic functions, several of these proteins could be directly linked to pesticide biodegradation like proteins encoding chloroanaline dioxygenase (contig 250 in BPS Kortrijk and contig 23 in L SM A) involved in the degradation of several pesticide groups including phenylurea herbicides such as linuron (Bers et al, 2013a) and enzymes of the modified ortho-cleavage pathway for chlorocatechol degradation (contigs 70, 117, 293 and 309 in BPS Kortrijk and contigs 21 and 33 in L SM A) for instance involved in degradation of chlorinated aromatic pesticides (Kumar et al, 2016).…”

Halophiles: biology, adaptation, and their role in decontamination of hypersaline environments

“…Over the past decade, a variety of thermophilic (Rye et al 2009), psychrophilic (Drienovska et al 2012;Novak et al 2013), and non-extremophilic microbes capable of degrading 2,4-D (Fulthorpe et al 1995;González et al 2012;Kumar et al 2014;Samir et al 2015) have been isolated from contaminated marine environments (Chiba et al 2009;Fulthorpe et al 1995;González et al 2012;Kumar et al 2014;Novak et al 2014;Samir et al 2015). However, studies on bioremediation of chlorinated compounds under hypersaline environments are sparse.…”

Potential roles for microbial endophytes in herbicide tolerance in plants

“…The ability of microbes to degrade herbicides and other pesticides appears to derive from the ability to detoxify natural products that in some way resemble xenobiotics. For example, the diversity of rhizobacterial tfdA ‐like genes linked to 2,4‐D metabolism appears to have evolved to detoxify natural analogues of the herbicide long before the first use of the compound in the early 1940s . In several cases, multiple degradation pathways have evolved to compete effectively to metabolise the agrochemical.…”

“…While removal of chemical residues from the environment has many positive features, the microbial degradation of pre‐emergence herbicides in the soil can ultimately regulate their activity in weed control applications. For example, when applied to the soil, 2,4‐D is known to have a short half‐life on account of complete microbial degradation . Rates of degradation are dependent on agronomic practice and environmental conditions, being accelerated by the presence of organic matter and by increases in temperature .…”

“…The POPHV6 strain was found within both the root and aerial tissues, suggesting that it was contributing to the metabolism of the herbicide throughout the plants. Other known rhizobacteria isolated from 2,4‐D‐treated soils and capable of degrading the herbicide in plant inoculation experiments included Burkholderia cepacia , Cupriavidus pinatubonensis JMP134 and Ralstonia eutropha JMP134 . Similarly, rhizobacteria and endophytic bacteria are also known to detoxify glyphosate and the s ‐triazine atrazine with soil application, favouring the enrichment with herbicide degrading species …”