Microbial transesterification of sugar‐corynomycolates

Growing cells of Arthrobacter sp. DSM 2567 and of the bacterium M9b were able to synthesize cell‐bound glycolipids. The carbon source determined the type of sugar moiety, whereas the α‐branched‐β‐hydroxy‐fatty acid remained constant. The incubation of resting cells of both bacteria in a simple buffer medium with various carbohydrates, including oligosaccharides and derivatives, led to the corresponding carbohydrate‐corynomycolates. Predominantly an enzymatic transesterification step seems to be responsible for the formation of new glycolipids; this was established by analytical data and 14C‐labeling studies. Concerning the substrate specifity, the transesterification reaction is characterized by a regioselective manner: (i) only the primary hydroxy‐groups at C‐6 (mono‐ and disaccharide) or C‐6′ (disaccharide) were acylated; (ii) 1‐β‐ or 4‐β‐substituents (including hydroxy groups) prevented the esterification; (iii) as for disaccharides with only one nonreducing moiety, the C‐6‐ and C‐6′‐positions were esterified one after another. In the presence of two nonreducing molecular ends with two possible C‐6‐esterification positions, both positions were substituted simultaneously. With regard to the studies on localization of the esterase after cell disruption, we found the enzymatic activity bound to the cell debris. In transesterification reactions comparable to resting whole cell experiments, the cell particles also were able to produce disaccharidecorynomycolates.