Chemical and biological modifications of glycopeptides have long been performed in order to obtain derivatives with improved antimicrobial activity or better pharmacokinetics. Deglycosilated derivatives of several different glycopeptides were produced and used either for biosynthetic or for antimicrobial activity studies, mainly obtained by chemical treatment or by biotransformation with yields of up to 80%, however, biotransformation requires a second fermentation step and a second downstream purification. Nonomuraea sp. ATCC 39727 is the producer of the lipoglycopeptide antibiotic complex A40926, which is the natural precursor of the semi-synthetic derivative dalbavancin (currently under clinical development with superior activity against Staphylococci and Enterococci, including some VanB isolates, and excellent pharmacokinetic characteristics). A40926 possesses the typical heptapeptide structure of the D-alanyl-D-alanine binding glycopeptides and is characterized by a Nacylaminoglucuronic acid and a mannose moiety bound to the aminoacids number 4 and 7 respectively. The A40926 demannosyl derivative showed improved activity against some classes of Staphylococci and was also used as the starting material for the synthesis of several semisynthetic A40926 derivatives, thus it is of primary importance the development of a rapid and convenient process for the production of demannosyl-A40926. In the course of a screening program for Nonomuraea sp. ATCC 39727 mutants with desirable characteristics (such as high productivity), we have isolated a clone showing a noteworthy activity in an overlay antimicrobial test. This mutant was able to directly produce demannosyl-A40926 with an abundance of ca 95% with respect to the other components of the antibiotic complex. The isolation of this strain allowed demannosyl-A40926 production by a single fermentation/purification process.