Ramoplanin is a lipoglycodepsipeptide produced by Actinoplanes sp. ATCC 33076 and active on bacterial cell wall biosynthesis by binding to Lipid II. A screening of an actinomycetes collection was performed to select enzymatic activities able to introduce specific modifications in the ramoplanin molecule. An extracellular mannosidase from Streptomyces GE 91081 was found to selectively remove one mannose unit from ramoplanin and tetrahydroramoplanin to give the corresponding mannosyl aglycones. These molecules show an improved microbiological activity versus some resistant staphylococci and streptococci, and are useful intermediates in the synthesis of novel ramoplanin-like antibiotics. The biotransformation of ramoplanin has been optimised to improve molar conversion and the transformation reaction rate. (C) 2007 Elsevier Inc. All rights reserved.