No abstract

Bacteria communicate via small diffusible molecules and thereby mediate group-coordinated behavior, a process referred to as quorum sensing. The prototypical quorum sensing system found in Gram-negative bacteria consists of a LuxI-type autoinducer synthase that produces N-acyl homoserine lactones (AHLs) as signals and a LuxR-type receptor that detects the AHLs to control expression of specific genes. However, many proteobacteria have proteins with homology to LuxR receptors yet lack any cognate LuxI-like AHL synthase. Here we show that in the insect pathogen Photorhabdus luminescens the orphan LuxR-type receptor PluR detects endogenously produced α-pyrones that serve as signaling molecules at low nanomolar concentrations. Additionally, the ketosynthase PpyS was identified as pyrone synthase. Reconstitution of the entire system containing PluR, the PluR-target operon we termed pcf and PpyS in Escherichia coli demonstrated that the cell-cell communication circuit is portable. Our research thus deorphanizes a signaling system and suggests that additional modes of bacterial communication may await discovery.

Commuting between kingdoms: The biosynthesis of the only nonplant stilbene 1 from Photorhabdus bacteria has been solved by identification of all the genes involved in its biosynthesis and by feeding experiments. Stilbene 1 is derived from the condensation of two β‐ketoacyl thioesters and is required for the normal development of Heterorhabditis nematodes, the natural host of Photorhabdus.

Members of the genus Xenorhabdus are entomopathogenic bacteria that associate with nematodes. The nematode-bacteria pair infects and kills insects, with both partners contributing to insect pathogenesis and the bacteria providing nutrition to the nematode from available insect-derived nutrients. The nematode provides the bacteria with protection from predators, access to nutrients, and a mechanism of dispersal. Members of the bacterial genus Photorhabdus also associate with nematodes to kill insects, and both genera of bacteria provide similar services to their different nematode hosts through unique physiological and metabolic mechanisms. We posited that these differences would be reflected in their respective genomes. To test this, we sequenced to completion the genomes of Xenorhabdus nematophila ATCC 19061 and Xenorhabdus bovienii SS-2004. As expected, both Xenorhabdus genomes encode many anti-insecticidal compounds, commensurate with their entomopathogenic lifestyle. Despite the similarities in lifestyle between Xenorhabdus and Photorhabdus bacteria, a comparative analysis of the Xenorhabdus, Photorhabdus luminescens, and P. asymbiotica genomes suggests genomic divergence. These findings indicate that evolutionary changes shaped by symbiotic interactions can follow different routes to achieve similar end points.

Structure elucidation of natural products including the absolute configuration is a complex task that involves different analytical methods like mass spectrometry, NMR spectroscopy, and chemical derivation, which are usually performed after the isolation of the compound of interest. Here, a combination of stable isotope labeling of Photorhabdus and Xenorhabdus strains and their transaminase mutants followed by detailed MS analysis enabled the structure elucidation of novel cyclopeptides named GameXPeptides including their absolute configuration in crude extracts without their actual isolation.

Type II polyketide synthases are involved in the biosynthesis of numerous clinically relevant secondary metabolites with potent antibiotic or anticancer activity. Until recently the only known producers of type II PKSs were members of the Gram-positive actimomycetes, well-known producers of secondary metabolites in general. Here we present the second example of a type II PKS from Gram-negative bacteria. We have identified the biosynthesis gene cluster responsible for the production of anthraquinones (AQs) from the entomopathogenic bacterium Photorhabdus luminescens. This is the first example of AQ production in Gram-negative bacteria, and their heptaketide origin was confirmed by feeding experiments. Deletion of a cyclase/aromatase involved in AQ biosynthesis resulted in accumulation of mutactin and dehydromutactin, which have been described as shunt products of typical octaketide compounds from streptomycetes, and a pathway for AQ formation from octaketide intermediates is discussed.

The microbiota confers colonization resistance, which blocks Salmonella gut colonization 1. As diet affects microbiota composition, we studied whether food-composition shifts enhance susceptibility to infection. Shifting mice to diets with reduced fiber or elevated fat contents for 24h boosted S. Typhimurium or E. coli gut colonization and plasmid transfer. Here, we studied the effect of dietary fat. Colonization resistance was restored within 48h of return to maintenance diet. Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Overlooked, but widespread! A new class of ketosynthases (DarB) involved in the biosynthesis of 1,3‐cyclohexanediones and dialkylresorcinols has been identified and characterized in detail. The presence of homologues in 89 different bacteria, including several pathogens, reveals that DarB as well as the corresponding natural products might be widespread, thus presenting a new but so far overlooked pathway to natural products.