Biodegradation of vinyl chloride, cis-dichloroethene and 1,2-dichloroethane in the alkene/alkane-oxidising Mycobacterium strain NBB4

Abstract

Mycobacterium chubuense strain NBB4 can grow on both alkanes and alkenes as carbon sources, and was hypothesised to be an effective bioremediation agent for chlorinated aliphatic pollutants. In this study, the ability of NBB4 to biodegrade vinyl chloride (VC), cis-dichloroethene (cDCE) and 1,2-dichloroethane (DCA) was investigated under pure-culture conditions and in microcosms. Ethene-grown NBB4 cells were capable of biodegrading VC and cDCE, while ethane-grown cells could biodegrade cDCE and DCA. The stoichiometry of inorganic chloride release (1mol/mol in each case) indicated that VC was completely dechlorinated, while cDCE and DCA were only partially dechlorinated, yielding chloroacetate in the case of DCA, and unknown metabolites in the case of cDCE. The apparent maximum specific activities (k) of whole cells against ethene, cDCE, ethane and DCA were 93±4.6, 89±18, 39±5.5, and 4.8±0.9nmol/min/mg protein, respectively, while the substrate affinities (K(S)) of whole cells with the same substrates were 2.0±0.15, 46±11, 11±0.33 and 4.0±3.2μM, respectively. In microcosms containing contaminated aquifer sediments and groundwater, NBB4 cells removed 85-95% of the pollutants (cDCE or DCA at 2mM) within 24h, and the cells remained viable for >1month. Due to its favourable kinetic parameters, and robust survival and biodegradation activities, strain NBB4 is a promising candidate for bioremediation of chlorinated aliphatic pollutants.