Journal
ANTIMICROBIAL AGENTS AND CHEMOTHERAPY
Volume 55, Issue 9, Pages 4283-4289Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/AAC.01372-10
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- The Deutsche Forschungsgemeinschaft (DFG) [SFB 766]
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The prevailing resistance mechanism against glycopeptides in Gram-positive pathogens involves reprogramming the biosynthesis of peptidoglycan precursors, resulting in D-alanyl-D-lactate depsipeptide termini. Amycolatopsis balhimycina produces the vancomycin-like glycopeptide balhimycin and therefore has to protect itself from the action of the glycopeptide. We studied the roles of the accessory resistance gene orthologs vanY(b), vnlR(b), and vnlS(b), which are part of the balhimycin biosynthetic gene cluster (represented by the subscript b). The VanY(b) carboxypeptidase cleaved the terminal D-Ala from peptidoglycan precursors, and its heterologous expression enhanced glycopeptide resistance in Streptomyces coelicolor. The VanRS-like two component system VnlRS(b) was not involved in glycopeptide resistance or in the expression of the vanHAX glycopeptide resistance genes. Mature A. balhimycina peptidoglycan contained mainly tri- and tetrapeptides, with only traces of the D-Ala-D-Ala-ending pentapeptides that are binding sites for the antibiotic produced. The structure of the peptidoglycan precursor is consistent with the presence of vanHAX genes, which were identified outside the balhimycin synthesis cluster. Both wild-type and non-antibiotic-producing mutant strains synthesized peptidoglycan precursors ending mainly with D-Lac, indicating constitutive synthesis of a resistant cell wall. A. balhimycina could provide a model for an ancestral glycopeptide producer with constitutively expressed resistance genes.
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