The effect of structure and a secondary carbon source on the microbial degradation of chlorophenoxy acids

Abstract

a b s t r a c tPseudomonas putida, Aspergillus niger, Bacillus subtilis, Pseudomonas flourescens, Sphingomonas herbicidovorans and Rhodococcus rhodochrous growing on glucose in a medium containing one of three chlorophenoxy acids at a concentration of 0.1 g L À1 (clofibric acid, (R)-2-(4-chloro-2-methylphenoxy)propionic acid (mecoprop or MCPP) and 4-chloro-2-methylphenoxyacetic acid (MCPA)) degraded these compounds to varying degrees; from nonmeasurable to almost complete removal. These results with the addition of glucose (2.5 g L À1) as an easy to use carbon source indicated the formation of metabolites different from results reported in the literature for growth studies in which the chlorophenoxy acid was the sole carbon source. The metabolite, 4-chloro-2-methylphenol, which had been reported previously, was only observed in trace amounts for MCPP and MCPA in the presence of S. herbicidovorans and glucose. In addition, three other compounds (M1, M3 and M4) were observed. It is suggested that these unidentified metabolites resulted from ring opening of the metabolite 4-choloro-2-methylphenol (M2).The rate of biodegradation of the chlorophenoxy acids was influenced by the degree of steric hindrance adjacent to the internal oxygen bond common to all three compounds. The most hindered compound, clofibric acid, was converted to ethyl clofibrate by R. rhodochrous but was not degraded by any microorganisms studied. The more accessible internal oxygen bonds of the other two chlorophenoxy acids, MCPP and MCPA, were readily broken by S. herbicidovorans.

Biodegradation of clofibric acid and identification of its metabolites

“…However, CLF removal was still not observed after another 2 months of SBR operation (data not shown). These results show that not all activated sludge communities have the capacity to degrade CLF, which explains the contradictory biodegradation efficiencies observed in different WWTPs [9,11,12]. This motivated the use of a microbial community already adapted to chlorinated ring-based compounds.…”

“…While Evangelista et al [12] found that >90% of a 100 mg L −1 CLF solution was transformed by Rhodococcus rhodochrous in 20 days after acclimatisation, it was mainly transformed into its parent compound ethyl clofibrate, which accumulated in the solution. Winkler et al [2] found that CLF was not removed at an initial concentration of 90 g L −1 (over ∼400 h) and only 27% removal was obtained at 11 g L −1 (over ∼95 h) in a biofilm reactor fed with river water.…”

“…Clofibric acid is one of the most widely and routinely reported drug metabolites found in open waters [3,4]. The presence of pharmaceutically active compounds (PhACs) and their metabolites in aquatic systems has become a concern in the past including WWTP biomass [10][11][12]. This apparent contradiction motivated the study of the conditions necessary for CLF biodegradation and its metabolic pathway.…”

An assessment of biodegradability of quaternary carbon–containing fragrance compounds: Comparison of experimental OECD screening test results and in silico prediction data

“…The biodegradation result is thus derived exclusively from oxidation of the propionate part of the side chain. The combination of an ether function with a tetra‐substituted carbon containing a geminal dimethyl attached to it was previously concluded as difficult to degrade in the case of chlorophenoxy acids .…”

Successful Biodegradation of a Refractory Pharmaceutical Compound by an Indigenous Phenol-Tolerant Pseudomonas aeruginosa Strain

“…The maximum removal yield achieved was 51% for an initial CLA concentration of 2 mgL -1 . Furthermore, Evangelista et al (2010) studied the biodegradation of three chlorophenoxy acids using axenic cultures of bacteria under cometabolic conditions. Nevertheless, none of the tested microorganisms was able to degrade clofibric acid suggesting that the recalcitrance of clofibric acid is due to the additional methyl group adjacent to the ether bond (2010).…”