Chloroform degradation by butane-grown cells of Rhodococcus aetherovorans BCP1

Abstract

The ability of a Rhodococcus aetherovorans strain, BCP1, to grow on butane and to degrade chloroform in the 0-633 microM range (0-75.5 mg l(-1)) via aerobic cometabolism was investigated by means of resting-cell assays. BCP1 degraded chloroform with a complete mineralization of the organic Cl. The resulting butane and chloroform maximum specific degradation rates were equal to 118 and 22 micromol mg(protein)(-1)day(-1), respectively. Butane inhibition on chloroform degradation was satisfactorily interpreted by means of a model of competitive inhibition, with an inhibition constant equal to 38 % of the estimated butane half-saturation constant, whereas chloroform (at 11 microM) did not inhibit butane utilization. Acetylene (1,720 microM) induced an almost complete inactivation of the degradation of both butane and chloroform, indicating that the studied cometabolic process is mediated by a monooxygenase enzyme. BCP1 proved capable of degrading vinyl chloride and 1,1,2-trichloroethane, but not 1,2-trans-dichloroethylene. BCP1 could grow on the intermediates of the most common butane metabolic pathways and on the aliphatic hydrocarbons from ethane to n-heptane. After growth on n-hexane, it was able to deplete chloroform (13 microM) with a degradation rate higher than that obtained, at the same chloroform concentration, after growth on butane.

Monooxygenases involved in the n-alkanes metabolism by Rhodococcus sp. BCP1: molecular characterization and expression of alkB gene

“…Similarly, chlorofom degradation ability was lost after the exposure of butane-grown biomass to acetylene, but not after the exposure to ATU. These results suggested that the chloroform transformation and the butane degradation were both dependent on a monooxygenase activity [304]. Moreover, since only a low inhibition of both butane utilization and chloroform degradation were observed in the presence of allylthiourea (ATU), the butane-monooxygenase of BCP1 was suggested not to contain copper as catalytic cofactor.…”

“…BCP1 had already been described to grow on most of the putative intermediates of butane and propane degradation pathway shown in Fig. 3.1, such as 1-and 2-propanol, 1-and 2-butanol, tert-butanol, propionic acid (propionate), butyric acid (butyrate), valeric acid (valerate), and propanone (acetone) [304].…”

“…BCP1 has been described by Frascari et al [304] for its ability to grow on n-alkanes ranging from C 2 to C 7 and for co-metabolizing lowchlorinated solvents under aerobic conditions. By contrast, Rh.…”

“…Namely, when both butane, as primary substrate, and chloroform, the cometabolic substrate, are added to the bioreactors at the same time, the degradation of the contaminant is retarded due to the physical competition of the two compounds for the active site of the enzymes involved in the degradation. The depletion of the cometabolic substrates starts when the primary substrates decreases to below determined threshold [304].…”

“…The chlorofom degradation data were interpreted by means of a model called 'cometabolism with competitive inhibition' [304], which was indicated by several authors as the most appropriate model for the aerobic cometabolism of chlorinated solvents [13,316,317]. The competitive inhibition model postulates the concurrent transformation of the two substrates n-butane and chloroform.…”