Carbon source dependent biosynthesis of acarviose metabolites in Actinoplanes sp. SE50/110

•The acb gene cluster was expressed independently of the carbon source supplied.•Acarviose metabolites were present under all conditions tested.•The carbon source supplied determined the major acarviose metabolite.•A model for the biosynthesis of major & minor acarviose metabolites was developed.

In this work the biosynthesis of the type 2 diabetes mellitus therapeutic acarviosyl-maltose (acarbose) and related acarviose metabolites produced by Actinoplanes sp. SE50/110 was studied in liquid minimal medium supplemented with the defined carbon sources maltose, glucose, galactose or mixtures of maltose/glucose and maltose/galactose. Quantifying acarviosyl-maltose by HPLC and UV detection revealed that only cultures grown in maltose-containing minimal media produced acarviosyl-maltose in significant amounts. A qualitative analysis of the cytosolic and extracellular proteome for the presence of proteins from the acarbose biosynthesis gene cluster showed that these were not only synthesized in maltose-containing media, but also in media with glucose or galactose as the sole carbon source. A LC–MS-based detection method was applied to test the hypothesis that different acarviose metabolites are produced in media with maltose, glucose or galactose. The analysis revealed that a spectrum of acarviose metabolites (acarviose with 1–4 glucose equivalent units) was formed under all tested conditions. As expected, in maltose-containing minimal media acarviosyl-maltose was produced as the major component exceeding the remaining minor components by 2–3 orders of magnitude. In minimal medium supplemented with glucose acarviosyl-glucose was the major component, while in minimal medium with galactose no major component was present. Based on the results presented, a model for the intracellular biosynthesis of major and minor acarviose metabolites was developed.