A broad-spectrum antibacterial natural product from the cystic fibrosis isolate, Pantoea agglomerans Tx10.

The prevalence of antibiotic-resistant Gram-positive and Gram-negative pathogens has prompted considerable efforts to identify new antibacterials. Here we show that Pantoea agglomerans Tx10-an isolate from the sputum sample of a cystic fibrosis patient-is a strong competitor that inhibits the growth of a wide range of Gram-positive and Gram-negative bacteria through the production of a secreted compound. A genetic screen to identify the genes involved in the production of this compound resulted in the delineation of a 6-gene biosynthetic cluster. We called this compound Pantoea Natural Product 2 (PNP-2). Assays with mutants deficient in PNP-2 production revealed they were still able to inhibit Erwinia amylovora, suggesting the production of a second antibiotic, which we identified as Pantocin A. We generated Pantocin A knockouts, and a PNP-2/Pantocin A double knockout and used these to evaluate the spectrum of activity of both natural products. We show that strains of Enterobacter, E. coli, Klebsiella, Kosakonia, Pseudocitrobacter, Salmonella, Staphylococcus, and Streptococcus as well as the majority of Pantoea strains assayed are susceptible to PNP-2, indicating a broad spectrum of activity, and potential for therapeutic development.

Spontaneous and on point: Do spontaneous mutations used for laboratory experiments cause pleiotropic effects that might confound bacterial infection and evolution assays?

Many selectable phenotypes in microbial systems, including antibiotic resistance, can be conferred by single point mutations. This is frequently exploited in research, where the selection and use of microbial mutants that are spontaneously resistant to antibiotics like rifampicin and streptomycin facilitate the recovery and/or quantification of a target microbe. Such mutations are commonly employed as genetic markers for in vitro and in vivo experiments, often with little consideration as to the ultimate system-level impact of these single nucleotide mutations on the physiology of the microbe. There is substantial literature on the pleiotropic effects of point mutations conferring antibiotic resistance; yet, it is unclear whether this work is considered by the research communities outside of the discipline. This review examines some of the known pleiotropic effects of point mutations that provide selectable resistance markers, and how these mutations may impact general physiology and growth in host and non-host environments.