Enhanced anaerobic biotransformation of carbon tetrachloride with precursors of vitamin B12 biosynthesis

Abstract

Relatively low concentrations of Vitamin B(12) are known to accelerate the anaerobic biotransformation of carbon tetrachloride (CT) and chloroform (CF). However, the addition of vitamin B(12) for field-scale bioremediation is expected to be costly. The present study considered a strategy to generate vitamin B(12) by addition of biosynthetic precursors. One of the precursors, porphobilinogen (PB) involved in the formation of the corrin ring, significantly increased the CT biotransformation rates by 2.7-, 8.8- and 10.9-fold when supplemented at 160, 500 and 900 microM, respectively. A positive control with 10 microM of vitamin B(12) resulted in a 5.9-fold increase in the CT-bioconversion rate. PB additions provided high molar yields of inorganic chloride (57% of CT organochlorine), comparable to that obtained with vitamin B(12) supplemented cultures. The primary substrate, methanol, known to induce vitamin B(12) production in methanogens and acetogens, was required for PB to have a significant impact on CT conversion. The observation suggests that PB's role was due to stimulating vitamin B(12) biosynthesis. The present study therefore provides insights on how to achieve vitamin B(12) enhanced rates of CT bioremediation through the use of less complex compounds that are precursors of vitamin B(12). Although PB is a costly chemical, its large impact points to corrin ring formation as the rate-limiting step.