Corrinoid auxotrophy in the obligate organohalide respiring Dehalobacter restrictus

Corrinoids (derivatives of vitamin B12) are an essential cofactor of reductive dehalogenases, the key enzymes involved in the environmental-friendly process of organohalide respiration (OHR). However, genomic and physiological analyses of obligate OHR bacteria (such as Dehalobacter and Dehalococcoides) have delivered contrasting results on the ability of de novo corrinoid biosynthesis. This raised the question of the source of corrinoids for obligate OHR bacteria in the environment and their biosynthesis/scavenging mechanism of corrinoids. Dehalobacter is an important bacterial genus for the bioremediation of organohalides such as chloroethenes, chloroethanes and chloroform. Genomic analysis of D. restrictus revealed the presence of all the genes required for the production of corrinoids (1), however the strain is incapable of de novo biosynthesis. The general aim of the present study is to better understand the corrinoid metabolism of the genus Dehalobacter at the level of biosynthesis, regulation and transport. A detailed analysis revealed that the cbiH gene whose product is involved in the corrin ring contraction displays a frame-shift mutation which was confirmed experimentally, suggesting that it might represent a possible checkpoint behind the corrinoid auxotrophy. Moreover, in proteomic data of a D. restrictus culture growing in presence of vitamin B12 in the medium, several corrinoid biosynthesis proteins were not detected arguing for specific regulation mechanisms. The transport and scavenging metabolism of corrinoid by D. restrictus is now under scrutiny.