Abstract

Hydroxybenzoic acids are the most important intermediates in the degradative pathways of various aromatic compounds. Microorganisms catabolize aromatic compounds by converting them to hydroxylated intermediates and then cleave the benzene nucleus with ring dioxygenases. Hydroxylation of the benzene nucleus of an aromatic compound is an essential step for the initiation and subsequent disintegration of the benzene ring. The incorporation of two hydroxyl groups is essential for the labilization of the benzene nucleus. Monohydroxybenzoic acids such as 2-hydroxybenzoic acid, 3-hydroxybenzoic acid, and 4-hydroxybenzoic acid through hydroxylation yield terminal aromatic intermediates like catechol, protocatechuic acid, gentisic acid, or pyrocatechuic acid that are susceptible for subsequent oxygenative cleavage of the benzene ring. These terminal aromatic intermediates are further degraded to cellular components through ortho-and /or meta-cleavage pathways and finally lead to the formation of constituents of the TCA cycle. Many groups of microorganisms have been isolated as degraders of hydroxybenzoic acids with diverse degradative routes and specific enzymes involved in their metabolic pathways. Various microorganisms carry out unusual non-oxidative decarboxylation of aromatic acids and convert them to respective phenols which have been documented. Further, Pseudomonas and Bacillus spp. are the most ubiquitous microorganisms, being the principal components of microflora of most soil and water environments.

• Keywords: Aromatic compounds; hydroxybenzoic acids; degradation; microorganisms; salicylic acid; 3-hydroxybenz