Spirochaeta aurantia has diacetyl chloramphenicol esterase activity

The free-living spirochaeta aurantia was nearly as susceptible to diacetyl chloramphenicol, the product of chloramphenicol acetyltransferase, as it was to chloramphenicol itself. This unexpected susceptibility to diacetyl chloramphenicol was wholly or partly the consequence of intrinsic carboxylesterase activity, as indicated by high-performance liquid chromatography, thin-layer chromotography, and microbiological esterase activity was cell associated, reduced by proteinase K, eliminated by boiling and independent of the presence of either chloramphenicol or diacetyl chloroamphenicol S. aurantia extracts also hydrolyzed other esterase substrates, and two of these, alpha-napthyl acetate and 4-methylumbelliferyl acetate identified an esterase of approximately 75 kDa in a nondenaturing gel. Carboxylesterases occur in Streptomyces species, but in this study their activity was weaker than that of S. aurantia. The S. aurantia esterase could reduce the effectiveness of cat as either a selectable marker or a reporter gene in this species.