The Peptide Antibiotic Corramycin Adopts a ß-Hairpin-like Structure and Is Inactivated by the Kinase ComG.

The rapid development of antibiotic resistance, especially among difficult-to-treat Gram-negative bacteria, is recognized as a serious and urgent threat to public health. The detection and characterization of novel resistance mechanisms are essential to better predict the spread and evolution of antibiotic resistance. Corramycin is a novel and modified peptidic antibiotic with activity against several Gram-negative pathogens. We demonstrate that the kinase ComG, part of the corramycin biosynthetic gene cluster, phosphorylates and thereby inactivates corramycin, leading to the resistance of the host. Remarkably, we found that the closest structural homologues of ComG are aminoglycoside phosphotransferases; however, ComG shows no activity toward this class of antibiotics. The crystal structure of ComG in complex with corramycin reveals that corramycin adopts a ß-hairpin-like structure and allowed us to define the changes leading to a switch in substrate from sugar to peptide. Bioinformatic analyses suggest a limited occurrence of ComG-like proteins, which along with the absence of cross-resistance to clinically used drugs positions corramycin as an attractive antibiotic for further development.

Simple and reliable in situ CRISPR-Cas9 nuclease visualization tool is ensuring efficient editing in Streptomyces species.

CRISPR-Cas9 technology has emerged as a promising tool for genetic engineering of Streptomyces strains. However, in practice, numerous technical hurdles have yet to be overcome when developing robust editing procedures. Here, we developed an extension of the CRISPR-Cas toolbox, a simple and reliable cas9 monitoring tool with transcriptional fusion of cas9 nuclease to a beta glucuronidase (gusA) visual reporter gene. The Cas9-SD-GusA tool enables in situ identification of cells expressing Cas9 nuclease following the introduction of the plasmid carrying the CRISPR-Cas9 machinery. Remarkably, when the Cas9-SD-GusA system was applied under optimal conditions, 100% of the colonies displaying GusA activity carried the target genotype. In contrast, it was shown that the cas9 sequence had undergone major recombination events in the colonies that did not exhibit GusA activity, giving rise to "escaper colonies" carrying unedited genotype. Our approach allows a simple detection of "escaper" phenotype and serves as an efficient CRISPR-Cas9 optimisation tool.