Microbial transformations of 2-substituted benzothiazoles

The occurrence of benzothiazoles in the environment seems to be restricted to aquatic compartments and is mainly associated with the manufacture and use of the rubber additive 2-mercaptobenzothiazole (MBT) and its derivatives. Although data on benzothiazole biotransformations in natural environments at ppb and ppt levels are scarce, the unsubstituted benzothiazole (BT) and 2-hydroxybenzothiazole (OBT) are generally considered to be biodegradable, whereas 2-methylthiobenzothiazole is recalcitrant. The fungicide 2-thiocyanomethylthiobenzothiazole is assumed to be hydrolysed to MBT, which is then further methylated. At higher concentration levels, similar conclusions can generally be drawn. In addition, BT, MBT, 2-aminobenzothiazole and benzothiazole-2-sulphonate can be biodegraded, although side- and end-products may form. For BT and MBT, threshold concentration were reported above which inhibitory effects on biological treatment processes occur. Due to the limited availability of axenic bacterial cultures capable of benzothiazole mineralization, only the initial steps of the degradation pathways have been elucidated so far.