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Pathways for 3-chloro- and 4-chlorobenzoate degradation in Pseudomonas aeruginosa 3mT.

Ajith Kumar, P. V. and Kunhi, A. A. M. (2000) Pathways for 3-chloro- and 4-chlorobenzoate degradation in Pseudomonas aeruginosa 3mT. Biodegradation, 11 (4). pp. 247-61. ISSN 0923-9820

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A bacterial isolate, Pseudomonas aeruginosa 3mT exhibited the ability to degrade high concentrations of 3-chlorobenzoate (3-CBA, 8 g l(-1)) and 4-chlorobenzoate (4-CBA 12 g l(-1)) (Ajithkumar 1998). In this study, by delineating the initial biochemical steps involved in the degradation of these compounds, we investigated how this strain can do so well. Resting cells, permeabilised cells as well as cell-free extracts failed to dechlorinate both 3-CBA and 4-CBA under anaerobic conditions, whereas the former two readily degraded both compounds under aerobic conditions. Accumulation of any intermediary metabolite was not observed during growth as well as reaction with resting cells under highly aerated conditions. However, on modification of reaction conditions, 3-chlorocatechol (3-CC) and 4-chlorocatechol (4-CC) accumulated in 3-CBA and 4-CBA flasks, respectively. Fairly high titres of pyrocatechase II (chlorocatechol 1,2-dioxygenase) activity were obtained in extracts of cells grown on 3-CBA and 4-CBA. Meta-pyrocatechase (catechol 2,3-dioxygenase) activity against 4-CC and catechol, but not against 3-CC, was also detected in low titres. Accumulation of small amounts of 2-chloro-5-hydroxy muconic semialdehyde, the meta-cleavage product of 4-CC, was detected in the medium, when 4-CBA concentration was 4 mM or greater, indicating the presence of a minor meta-pathway in strain 3mT. However, 3-CBA exclusively, and more than 99% of 4-CBA were degraded through the formation of the respective chlorocatechol, via a modified ortho-pathway. This defies the traditional view that the microbes that follow chlorocatechol pathways are not very good degraders of chlorobenzoates. 4-Hydroxybenzoate was readily (and 3-hydroxybenzoate to a lesser extent) degraded by the strain, through the formation of protocatechuate and gentisate, respectively, as intermediary dihydroxy metabolites.

Item Type: Article
Uncontrolled Keywords: 3-chlorobenzoate, 4-chlorobenzoate, chlorocatechols, modified ortho-pathway, Pseudomonas aeruginosa
Subjects: 500 Natural Sciences and Mathematics > 05 Earth Sciences > 03 Environmental Sciences
500 Natural Sciences and Mathematics > 07 Life Sciences > 04 Microbiology > 02 Bacteriology
Divisions: Food Microbiology
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 22 Mar 2018 06:31
Last Modified: 29 Aug 2018 06:47
URI: http://ir.cftri.res.in/id/eprint/2130

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