Biodegradation Of P-cresol Research Articles

Contribution of quinone-reducing microorganisms to the anaerobic biodegradation of organic compounds under different redox conditions

The capacity of two anaerobic consortia to oxidize different organic compounds, including acetate, propionate, lactate, phenol and p-cresol, in the presence of nitrate, sulfate and the humic model compound, anthraquinone-2,6-disulfonate (AQDS) as terminal electron acceptors, was evaluated. Denitrification showed the highest respiratory rates in both consortia studied and occurred exclusively during the first hours of incubation for most organic substrates degraded. Reduction of AQDS and sulfate generally started after complete denitrification, or even occurred at the same time during the biodegradation of p-cresol, in anaerobic sludge incubations; whereas methanogenesis did not significantly occur during the reduction of nitrate, sulfate, and AQDS. AQDS reduction was the preferred respiratory pathway over sulfate reduction and methanogenesis during the anaerobic oxidation of most organic substrates by the anaerobic sludge studied. In contrast, sulfate reduction out-competed AQDS reduction during incubations performed with anaerobic wetland sediment, which did not achieve any methanogenic activity. Propionate was a poor electron donor to achieve AQDS reduction; however, denitrifying and sulfate-reducing activities carried out by both consortia promoted the reduction of AQDS via acetate accumulated from propionate oxidation. Our results suggest that microbial reduction of humic substances (HS) may play an important role during the anaerobic oxidation of organic pollutants in anaerobic environments despite the presence of alternative electron acceptors, such as sulfate and nitrate. Methane inhibition, imposed by the inclusion of AQDS as terminal electron acceptor, suggests that microbial reduction of HS may also have important implications on the global climate preservation, considering the green-house effects of methane.

Biodegradation of p-Cresol by Bacillus sp. Strain PHN 1

A bacterium capable of utilizing p-cresol as sole source of carbon and energy was isolated from soil and identified as a Bacillus species. The organism also utilized phenol, o-cresol, m-cresol, 4-hydroxybenzoic acid, and gentisic acid as growth substrates. The organism degraded p-cresol to 4-hydroxybenzoic acid, which was further metabolized by a gentisate pathway, as evidenced by isolation and identification of metabolites and enzyme activities in the cell-free extract. Such a bacterial strain can be used for bioremediation of environments contaminated with phenolic compounds.

Simultaneous biodegradation ofp-cresol and phenol by the basidiomycetePhanerochaete chrysosporium

The fungus Phanerochaete chrysosporium BKM-F-1767 was able to degrade high concentrations of p-cresol (up to 150 mg L-1) provided that glucose was added as a carbon and energy source and conditions favourable to ligninolytic enzyme activities were used, i.e. a nitrogen-limited medium. The fungus also simultaneously degraded p-cresol (50 mg L-1) and phenol (50 mg L-1) in a mixture at similar rates. Kinetics of p-cresol biodegradation were almost identical whether the compound was tested individually or in a mixture with phenol.

Biodegradation of phenolic compounds by sulfate-reducing bacteria from contaminated sediments

The biodegradation of phenolic compounds under sulfate-reducing conditions was studied in sediments from northern Indiana. Phenol, p-cresol and 4-chlorophenol were selected as test substrates and added to sediment suspensions from four sites at an initial concentration of 10 mg/liter. Degradative abilities of the sediment microorganisms from the four sites could be related to previous exposure to phenolic pollution. Time to onset of biodegradation of p-cresol and phenol in sediment suspensions from a nonindustrialized site was approximately 70 and 100 days, respectively, in unacclimated cultures. In sediment slurries from three sites with a history of wastewater discharges containing phenolics, time to onset of biodegradation was 50-70 days for p-cresol and 50-70 days for phenol in unacclimated cultures. In acclimated cultures from all four sites, the length of the lag phase was reduced to 14-35 days for p-cresol and 25-60 days for phenol. Length of the biodegradative phase varied from 25 to 40 days for phenol and 10 to 50 days for p-cresol and was not markedly affected by acclimation. Substrate mineralization by sulfate-reducing bacteria was confirmed with radiotracer techniques using an acclimated sediment culture from one site. Addition of molybdate, a specific inhibitor of sulfate reduction, and bacterial cell inactivation inhibited sulfate reduction and substrate utilization. None of the sites exhibited the ability to degrade 4-chlorophenol, nor were acclimated phenol and p-cresol degrading cultures from a particular site able to cometabolize 4-chlorophenol.

Alternative nonlinear model for estimating second-order rate coefficients for biodegradation.

A modification of the second-order model for biodegradation was derived, applied to an example data set, and shown to be superior for describing the anaerobic biodegradation of p-cresol by an enriched bacterial consortium. The modified model circumvents the no-growth assumption implicit in the use of the second-order rate equation, but still requires the assumption of first-order kinetics over the course of substrate depletion. Violation of the no-growth assumption is particularly important since overestimates of the pseudo-first-order rate coefficient lead to underestimates of the time required for the removal of a xenobiotic chemical from a contaminated environment. Our calculations show that the errors introduced into the pseudo-first-order rate coefficient (and the resulting estimates of the second-order rate coefficient) approach 100% if one doubling occurs in activity over the course of substrate depletion. For an exemplary data set, use of a first-order model resulted in a 100% overestimate of the first-order decay coefficient, which would in turn lead to a corresponding overestimate of the second-order rate coefficient. The modified model we describe is a potential alternative to the pseudo-first-order model for the routine estimation of second-order rate coefficients.

An HPLC system for the automatic sampling and analysis of time-series kinetic studies

Robotics were used to automate a high performance liquid chromatography (HPLC) system which was designed for the unattended sampling and analysis of time-series kinetic studies. The system allowed for the direct injection of samples containing whole cells and particulates witout plugging the analytical column. Coarse debris was removed from the injected sample by a 0.5 μm inline filter. Finer particulates were removed by a guard column that was layered with three different size packing resins. To demonstrate the system's capabilities, data are presented from an 8 day progress curve showing the anaerobic biodegradation of p-cresol by a sulfate-reducing enrichment. On fitting the data to the Michaelis-Menten equation by nonlinear regression, the apparent kinetic constants K m and V max were calculated to be 126 μM and 4.0 μM/h, respectively, for p-cresol metabolism by the enrichment.

P-Cresol biodegradation under denitrifying conditions: isolation of a bacterial coculture

From polluted river sediment, two bacterial species were isolated which utilized p-cresol as the sole source of carbon when grown in coculture under nitrate-reducing conditions. One species, PC-07, metabolized p-cresol (pCr) anaerobically to p-hydroxybenzoate (pOHB), which in turn was further metabolized by the second isolate, PB-04. The PC-07 isolate was unable to degrade and utilize pOHB, and PB-04 was unable to utilize pCr, thereby demonstrating a syntrophic relationship for pCr utilization under anaerobic conditions. Nitrate served as external electron acceptor for both microorganisms under anaerobic conditions and was reduced via NO2− and N2O to N2. pCr, therefore, appears to be metabolized to ring fission products via the formation of pOHB under nitrate reducing conditions, with the metabolism being mediated by a 2-member microbiol food chain.