CO2–H2-dependent anaerobic biotransformation of phthalic acid isomers in sediment slurries

This paper investigates the anaerobic biotransformation of three isomers of phthalic acid and benzoic acid in sediment slurries under four different atmospheres [N2, N2/H2 (19:1, v/v), CO2, and CO2/H2 (4:1, v/v)]. Significant differences were observed in lag periods and biotransformation rates among the phthalic acid isomers and under the different atmospheres. In most cases, the relative biotransformation rates of the three isomers of phthalic acid were ortho-phthalic acid > isophthalic acid > terephthalic acid. Benzoate was transformed faster than any isomer of phthalic acid. Since biotransformation of phthalic acid isomers in sediment slurries was enhanced by high initial levels of H2 and CO2 in the headspace, we propose a pathway for phthalic acid biodegradation in which the initial transformation to benzoate is CO2–H2 dependent. Acetogenic bacteria were investigated for their possible involvement in this transformation reaction, but when MPN counts were used to compare the growth dynamics of acetogenic bacteria with the time course of the terephthalic acid transformation under N2/H2 (19:1, v/v) and CO2/H2 (4:1, v/v) atmospheres, the results were inconclusive.