A three-component monooxygenase from Rhodococcus wratislaviensis may expand industrial applications of bacterial enzymes

The high-valent iron-oxo species formed in the non-heme diiron enzymes have high oxidative reactivity and catalyze difficult chemical reactions. Although the hydroxylation of inert methyl groups is an industrially promising reaction, utilizing non-heme diiron enzymes as such a biocatalyst has been difficult. Here we show a three-component monooxygenase system for the selective terminal hydroxylation of α-aminoisobutyric acid (Aib) into α-methyl-D-serine. It consists of the hydroxylase component, AibH1H2, and the electron transfer component. Aib hydroxylation is the initial step of Aib catabolism in Rhodococcus wratislaviensis C31-06, which has been fully elucidated through a proteome analysis. The crystal structure analysis revealed that AibH1H2 forms a heterotetramer of two amidohydrolase superfamily proteins, of which AibHm2 is a non-heme diiron protein and functions as a catalytic subunit. The Aib monooxygenase was demonstrated to be a promising biocatalyst that is suitable for bioprocesses in which the inert C–H bond in methyl groups need to be activated.

Bacterial degradation of a mixture of hydroxy- and metoxypolychlorinated biphenyls

In this work, the possibility of combining the methods of chemical functionalization of a mixture of polychlorinated biphenyls before the formation of a mixture of hydroxy- and methoxy-chlorinated biphenyls and the bacterial transformation of the compounds obtained with the aim of their utilization was investigated. As a result of a 100% conversion, a mixture of compounds identified as methoxy- (30 compounds), hydroxy- (44 compounds) and methoxy (hydroxy) derivatives (47 compounds) was obtained by reacting a mixture of Sovol with MeONa in MeOH and DMSO. PCB congeners. The total content of all hydroxy derivatives was 77.2%. It was established that the strain Rhodococcus wratislaviensis KT112-7 carries out the destruction of 73-93% of this mixture at the initial concentration of 0.25-1.50 g/l. The best result was obtained with a decomposition of 0.1 g/l of a mixture of methoxy- and hydroxy-polychlorobiphenyls (on the 10th day the total absence of the starting compounds). The specific rate of destruction was in direct correlation with the initial concentration of the mixture. It has been shown that during bacterial transformation there is no accumulation of toxic intermediate compounds.

Immobilization of Rhodococcus wratislaviensis Strain KT112-7 Сells in Order to Increase Efficiency of Biodegradation of Modified Polychlorinated Biphenyls

The degradation of a mixture of hydroxy- and methoxy-PCB obtained as a result of a chemical modification of a commercial mixture of PCB «Sovol» by the Rhodococcus wratislaviensis strain KT112-7 in plankton culture or immobilized on carbon carriers has been investigated. It was established that the KT112-7 strain in plankton culture degraded 73.2% of a mixture of modified PCBs for 96 h; the strain immobilized on BAU-A activated carbon and on Carbopon-B-active carbon fiber provided the 59.5% and 95.3% degradation for the same time, respectively (with the starting concentration of PBS of 0.5 g/L). The application of the R. wratislaviensis KT112-7 strain immobilized on the BAU-A carrier decreased the number of the PCB derivatives by 1.5 times at the end of the experiment; the corresponding result for the Carbopon-B-active-immobilized culture was 3 times; the set of PCBs after the treatment with the suspension culture remained unchanged. In practice, the immobilization of R. wratislaviensis КТ112-7 strain on carbon carriers can be used in the development of the techniques for the degradation of chemically modified PCB mixtures. polychlorinated biphenyls, immobilization, destruction, utilization, PCB, Rhodococcus. Funding-This work was supported by the Integrated Program of the Ural Branch of the Russian Academy of Sciences No. 18-3-8-19. The work was performed using the equipment of the Center for collective use «Spectroscopy and analysis of organic compounds».