Utilization of aromatic compounds by bacteria. I. Aerobic and anaerobic destruction

Abstract

This review summarizes current information on the extent of environmental pollution by xenobiotics of aromatic nature, and their toxic effects on living organisms. Phenols, monocyclic (benzene, toluene, xylene etc) and polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, biphenуls, pyrene, benzpyrene, pyridine etc.) are the most dangerous pollutant aromatic compounds. A variety of microorganisms capable to destroy the aromatic compounds is described. The biodegradation of aromatic pollutants is carried out by denitrifying, sulfate-reducing, photosynthetic, fermentation, iron-reducing, acetogenic bacteria and methanogens. The paper analyzes and generalizes the ways of decomposition of compounds of aromatic nature under bacterial aerobic and anaerobic conditions, describes the peripheral ways of oxidation of aromatic compounds and their regulation, examines the ability of microorganisms to use substituents in the benzene ring as a source of carbon and nitrogen. The processes of aerobic and anaerobic biodegradation of aromatic compounds have common particularities, that are the key intermediates formation. These intermediates are involved into the central metabolism of the cell due to the activity of metabolic pathways of various groups of microorganisms. Under the aerobic conditions, the rupture of benzene ring can occur between two successively connected carbon atoms carrying hydroxyl groups (ortho-cleavage), or on other C-C bonds of the nucleus in meta-position (meta-clea­vage). The central metabolic pathways provide a formation of intermediate compounds of the Krebs cycle. Benzoyl-CoA is a central intermediate of decomposition of aromatic xenobiotics under anaerobic conditions. In this review, different variants of benzoyl-CoA pathway for the degradation of aromatic compounds by bacteria are considered. Due to the destruction of aromatic compounds by various microorganisms, a large number of intermediate metabolites are formed. They are further degraded by bacteria of various ecological trophic groups. At the result, complete decomposition of the aromatic compounds occurs. The ability of microorganisms to decompose xenobiotics enables sol­ving a number of environmental problems associated with both the use of chemical pesticides and the discharge of untreated industrial wastewater.

Keywords

• xenobiotics
• degradation
• aromatic compounds
• benzoyl-CoA pathway