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.