Structure-biodegradation correlation of polyphenols for Thauera aromatica in anaerobic conditions

The anaerobic degradation of phenolic compounds depends greatly on their molecular structure. We have undertaken a systematic study on several phenol derivatives which are commonly found in industrial waters with the aim of investigating the structure-biodegradation relationship for bacteria in anaerobic conditions. The Thauera aromatica strain was used; this bacterium is able to use phenol as a sole carbon source in liquid cultures in the absence of molecular oxygen. Nitrate is the electron sink with complete reduction to N-2. A systematic study has demonstrated the ability of this bacterial strain to use 3,4-dihydroxybenzoic acid, 4-hydroxycinnamic acid (p-coumaric acid). 4-hydroxy-3-methoxycinnamic acid (ferulic acid), 3,4-dimethoxybenzoic acid (veratric acid), and 3,4,5-trihydroxybenzoic acid (gallic acid) as substrate. The matching of the depletion of the concentration of such compounds with the increment in bacterial growth in the cultures demonstrates that the substrates are used as the sole carbon source. Also, a correlation between the rate of growth of bacteria and nitrite concentration has been observed. The progressive reduction in nitrate into nitrite and N2 is monitored through analyses. The protein pattern extracted from bacteria grown on methylated substrates is now being compared with that of bacteria grown on non-methylated polyphenols that are structurally analogous in order to identify specific enzymes for demethylation processes.