CHLOROFORM DEGRADATION IN METHANOGENIC METHANOL ENRICHMENT CULTURES AND BY METHANOSARCINA-BARKERI-227

The effects of methanol addition and consumption on chloroform degrada tion rate and product distribution in methanogenic methanol enrichment cultures and in cultures of Methanosarcina barkeri 227 were investiga ted. Degradation of chloroform with initial concentrations up to 27.3 mu M in enrichment cultures and 4.8 mu M in pure cultures was stimulat ed by the addition of methanol, However, methanol consumption was inhi bited by as little as 2.5 mu M chloroform in enrichment cultures and 0 .8 mu M chloroform in pure cultures, suggesting that the presence of m ethanol, not its exact concentration or consumption rate, was the most significant variable affecting chloroform degradation rate. Methanol addition also significantly increased the number of moles of dichlorom ethane produced per mole of chloroform consumed. In enrichment culture s, the number of moles of dichloromethane produced per mole of chlorof orm consumed ranged from 0.7 (methanol consumption essentially uninhib ited) to 0.35 (methanol consumption significantly inhibited) to less t han 0.2 (methanol not added to the culture), In pure cultures, the num ber of moles of dichloromethane produced per mole of chloroform consum ed was 0.47 when methanol was added and 0.24 when no methanol was adde d, Studies with [C-14]chloroform in both enrichment and pure cultures confirmed that methanol metabolism stimulated dichloromethane producti on compared with CO2 production. The results indicate that while the a ddition of methanol significantly stimulated chloroform degradation in both methanogenic methanol enrichment cultures and cultures of M. bar keri 227, the prospects for use of methanol as a growth substrate for anaerobic chloroform-degrading systems may be limited unless the incre ased production of undesirable chloroform degradation products and the inhibition of methanol consumption can be mitigated.