Metabolism of 2-Mercaptobenzothiazole by Rhodococcus rhodochrous

Abstract

2-Mercaptobenzothiazole, which is mainly used in the rubber industry as a vulcanization accelerator, is very toxic and is considered to be recalcitrant. We show here for the first time that it can be biotransformed and partially mineralized by a pure-culture bacterial strain of Rhodococcus rhodochrous. Three metabolites, among four detected, were identified.2-Mercaptobenzothiazole (MBT) is the most important and most widely used member of the benzothiazole (BT) family. MBT is typically a rubber additive (16,17), but it has also other applications, such as inhibiting biocorrosion in cooling systems or in paper manufacturing (4). The annual MBT production in Western Europe is estimated to be excess of 40,000 tons.Direct discharges of MBT occur in effluents from factories producing and using MBT. Indirect sources of environmental contamination are mainly leachates from landfills where MBT is deposited and from rubber products (18). MBT can also be found in tannery wastewater (20). Finally, BTs have been found in urban runoff, in residential and highway road dust, and in urban particulate matter, most probably as a result of vehicle tire wear (18). The U.S. Environmental Protection Agency estimated that over 500 tons of MBT may be lost annually to the environment (22). Its toxicity towards microorganisms (3, 6, 7, 9), its allergenicity, resulting in serious dermatoses (11), and its potential mutagenic effects (12) make its presence in the environment of great concern.Information on the environmental fate of BT in the literature is scarce, and information on its biodegradative pathways is scarcer still. Several studies were first carried out in laboratories or in pilot-scale activated sludge systems in order to remove such a compound (5,20,21). These studies show that MBT is rather recalcitrant and is not completely mineralized when its concentration reaches a certain threshold. The metabolites observed under these conditions were benzothiazolylsulfonate and 2-methylthiobenzothiazole (MTBT) (10,20), the disulfide derivative of MBT (5).Only a few bacterial isolates have been shown to biotransform MBT. Drotar et al. (10) observed MBT-methylating activity in crude extracts of a variety of soil and water isolates, including a Corynebacterium sp., a Pseudomonas sp., and Escherichia coli, yielding the more stable methylated product MTBT, which accumulated in the medium.This paper reports studies of the biotransformation of MBT by Rhodococcus rhodochrous OBT18, isolated by De Wever et al. (8) from activated sludge from a wastewater treatment plant of an MBT-producing factory (Bayer, Antwerp, Belgium). This strain was previously shown to degrade BT, 2-hydroxybenzothiazole (OBT) (2, 8), and 2-aminobenzothiazole (ABT) (13). The main objective of this work was to identify the structure of the metabolites formed in order to establish the metabolic pathway of MBT for this strain. Because BT structures are difficult to analyze (due to the presence of N and S heteroatoms) and the metabolism of BT is almost unknown, various powerful...

Comparison of Microbial and Photochemical Processes and Their Combination for Degradation of 2-Aminobenzothiazole

“…The presence of a catechol 1,2-dioxygenase has already been evidenced in Rhodococcus pyridinovorans strain PA (18). It was also shown in Rhodococcus rhodochrous OBT18, as a diacid was observed during MBT biodegradation (19). This enzyme is known to transform catechol into diacid by the cleavage of a catechol ring.…”

“…The hypothesis of the formation of a complex between iron and a catechol, formed after a second step of hydroxylation of ABT, can be proposed. The formation of catechols has already been reported during the biodegradation by Rhodococcus rhodochrous OBT18 of two other benzothiazole derivatives (2-hydroxybenzothiazole [OBT] and MBT) (18,19). The noncomplexed catechol derivative of ABT could be the degradation product M2a, which was observed as traces only in the absence of FeNTA in the medium and which had a retention time very close to that of M2.…”

“…6OH-ABT was not further degraded even if it was used as the starting compound. The hydroxylation on position 6 on the aromatic ring is a common stage of benzothiazole biodegradation by Rhodococcus rhodochrous OBT18 (18,19). 4OH-ABT was not formed in the microbiological process.…”

“…The biodegradation of several benzothiazoles with various Rhodococcus strains isolated from wastewater treatment plants, including R. erythropolis BTS1, R. rhodochrous OBT18, and R. pyridinovorans PA, has been described in detail (4,11,15,(17)(18)(19). Several metabolites have been identified, and biodegradative pathways have been proposed for different benzothiazole derivatives.…”

Genome Sequence of Rhodococcus sp. Strain R04, a Polychlorinated-Biphenyl Biodegrader

“…Several strains belonging to the genus Rhodococcus have been isolated from various contaminated environments (1,3,10,11,12), which have proved to be ideal candidates for enhancing the bioremediation of contaminated sites and a wide range of biotransformations, such as steroid modifications, enantioselective synthesis, and the production of amides from nitriles (4, 14).…”