Microbial degradation of chlorobenzoates (CBAs): Biochemical aspects and ecological implications

Abstract

The behavior of chlorobenzoates (CBAs) in soils and waters has been carefully considered, as these compounds are used themselves as herbicides. The Chlorobenzoic acids from mono- to tri-substituted compounds, were shown susceptible to microbial attack, even if more chlorinated isomers and/or having chlorine atoms in ortho position were demonstrated more refractory to biodegradation. CBAs can be totally mineralized with stoichiometric release of the chlorine atoms, both in aerobic and anaerobic conditions, or can undergo only co-metabolic transformations giving dead-end products, which the other microorganisms could utilize for their growth. The bacterial strategies for CBA degradation, elucidated with pure cultures or in microbial consortia, turn around the detachment of chlorine atoms that may occur through: (i) oxygenolytic elimination in an early stage mediated by more or less specific 1,2- or 1,6-dioxygenases leading to the formation of catechol or chlorocatechols; (ii) spontaneous C1-release at a later stage, by lactonization of the ortho-ring fission product; (iii) initial dehalogenation through hydrolytic or oxidative reactions with the formation of corresponding hydroxy derivatives; and (iv) reductive dechlorinations, mostly occurring in anaerobic conditions, and on polychlorinated compounds, with the formation of the corresponding derivatives carrying n-1 chlorine substituents.