Environmental significance of O‐demethylation of chloroanisoles by soil bacterial isolates as a mechanism that improves the overall biodegradation of chlorophenols
Summary
The biodegradation rate of chlorophenols in the environment seems to be limited by a competitive mechanism of O‐methylation which produces chloroanisoles with a high potential of being bioconcentrated in living organisms. In this work we report for the first time the isolation of three soil bacterial strains able to efficiently degrade 2,4,6‐trichloroanisole (2,4,6‐TCA). These strains were identified as
Xanthomonas retroflexus
INBB4,
Pseudomonas putida
INBP1 and
Acinetobacter radioresistens
INBS1. In these isolates 2,4,6‐TCA was efficiently metabolized in a minimal medium containing methanol and 2,4,6‐TCA as the only carbon sources, with a concomitant release of 3 mol of chloride ion from 1 mol of 2,4,6‐TCA, indicating complete dehalogenation of 2,4,6‐TCA. 2,4,6‐trichlorophenol (2,4,6‐TCP) was identified as a degradative intermediate, indicating that 2,4,6‐TCA underwent O‐demethylation as the first step in the biodegradation process. 2,4,6‐TCP was further transformed into 2,6‐dichloro‐
para
‐hydroquinone (2,6‐DCHQ) and subsequently mineralized. The degradation of chloroanisoles could improve the overall biodegradation of chlorophenols in the environment, because those chlorophenols previously biomethylated might also be later biodegraded.
Xanthomonas retroflexus
INBB4 has two O‐demethylation systems: one is an oxygenase‐type demethylase, and the other is a tetrahydrofolate (THF)‐dependent
O
‐demethylase. On the contrary O‐demethylation of 2,4,6‐TCA in
P. putida
INBP1 is just catalysed by an oxygenase‐type NADH/NADPH‐dependent
O
‐demethylase, whereas in
A. radioresistens
INBS1 a THF‐dependent
O
‐demethylase activity was detected.