Degradation of mono-chlorophenols by a mixed microbial community via a meta-cleavage pathway

A mixed microbial community, specially designed to degrade a wide range of substituted aromatic compounds, was examined for its ability to degrade mono-chlorophenols as sole carbon source in aerobic batch cultures. The mixed culture degraded 2-, 3-, and 4 -chlorophenol (1.56 mM) via a meta-cleavage pathway. During the degradation of 2- and 3-chlorophenol by the mixed culture, 3-chlorocatechol production was observed. Further metabolism was toxic to cells as it led to inactivation of the catechol 2,3-dioxygenase enzyme upon meta-cleavage of 3-chlorocatechol resulting in incomplete degradation. Inactivation of the meta-cleavage enzyme led to an accumulation of brown coloured polymers, which interfered with the measurement of cell growth using optical denstiy. Degradation of 4-chlorophenol by the mixed culture led to an accumulation of 5-chloro-2-hydroxymuconic semialdehyde, the meta-cleavage product of 4-chlorocatechol. The accumulation of this compound did not interfere with the measurement of cell growth using optical density. 5-chloro-2-hydroxymuconic semialdehyde was further metabolized by the mixed culture with a stoichiometric release of chloride, indicating complete degradation of 4-chlorophenol by the mixed culture via a meta-cleavage pathway.