The Global Regulators Lrp, LeuO, and HexA Control Secondary Metabolism in Entomopathogenic Bacteria

Abstract

Photorhabdus luminescens TTO1 and Xenorhabdus nematophila HGB081 are insect pathogenic bacteria and producers of various structurally diverse bioactive natural products. In these entomopathogenic bacteria we investigated the role of the global regulators Lrp, LeuO, and HexA in the production of natural products. Lrp is a general activator of natural product biosynthesis in X. nematophila and for most compounds in TTO1. Microarray analysis confirmed these results in X. nematophila and enabled the identification of additional biosynthesis gene clusters (BGC) regulated by Lrp. Moreover, when promoters of two X. nematophila BGC were analyzed, transcriptional activation by Lrp was observed. In contrast, LeuO in X. nematophila and P. luminescens has both repressing and activating features, depending on the natural product examined. Furthermore, heterologous overexpression of leuO from X. nematophila in the closely related Xenorhabdus szentirmaii resulted in overproduction of several natural products including novel compounds. The presented findings could be of importance for establishing a tool for overproduction of secondary metabolites and subsequent identification of novel compounds.

High Levels of the Xenorhabdus nematophila Transcription Factor Lrp Promote Mutualism with the Steinernema carpocapsae Nematode Host

“…As such, characterizing these profiles will facilitate the assignment of specific gene products and pathways to their functional roles in one symbiotic association or the other. The X. nematophila Lrp regulon has been characterized by using microarray analysis to compare gene expression in an lrp mutant to that in wild-type X. nematophila that was heterogeneous with respect to Lrp (23,38,39). Recent attempts in our laboratory to compare gene expression profiles of plasmid-encoded fixed-highand low-Lrp strains were inconclusive, likely due to variability in plasmid maintenance (data not shown).…”

“…Lrp may play a role in this behavior by regulating either the sensing or the production of small-molecule signals derived from insect tissues (such as ammonia), nematodes (such as pheromones), or bacteria (such as secondary metabolites) (40,41). X. nematophila Lrp controls the production of numerous small molecules, many of which have an unknown biological function (23,27,39). An intriguing possibility that awaits further investigation is that one or more X. nematophila Lrp-dependent small molecules either trigger or enhance the dispersal behavior of the S. carpocapsae nematode host, thereby increasing its own fitness by ensuring transmission to the next insect host.…”

1st Gießen Symposium of Insect Biotechnology, October 9-10, 2017 (published online)

“…We have analysed the deletion of known global regulators from Gram-negative bacteria on the natural product biosynthesis in Xenorhabdus and Photorhabdus (Engel 2017) and did identify the RNA chaperon Hfq playing a major role in natural product biosynthesis. In hfq mutants of several strains analysed so far, all natural products were reduced 10 to 100-fold, most of them below the limit of detection (Tobias 2017).…”

“…While several natural products have been identified and isolated from these bacteria during the last ten years due to efforts from several labs (Bode 2009, Challinor and Bode 2016, Vizcaino 2013, the majority of these compounds are still unknown. Therefore, these natural products are not accessible for a detailed analysis of their function in the natural ecosystem or as drugs in a more applied way (antibiotics, anticancer compounds, biotechnology etc) and methods for faster access to these natural products is desirable.We have analysed the deletion of known global regulators from Gram-negative bacteria on the natural product biosynthesis in Xenorhabdus and Photorhabdus (Engel 2017) and did identify the RNA chaperon Hfq playing a major role in natural product biosynthesis. In hfq mutants of several strains analysed so far, all natural products were reduced 10 to 100-fold, most of them below the limit of detection (Tobias 2017).…”

CpxR negatively regulates the production of xenocoumacin 1, a dihydroisocoumarin derivative produced by Xenorhabdus nematophila

“…The mutation of lrp could significantly reduce the production of antibiotics, including xenortides, xenematides, and Xcn1. Correspondingly, its mutant exhibited no antimicrobial activities against Micrococcus luteus and Bacillus subtilis (Cowles et al., ; Engel, Windhorst, Lu, Goodrichblair, & Bode, ; Goodrich‐Blair, ). Both two‐component systems, CpxRA and EnvZ/OmpR, are involved in responding to the nematode and other insect environments, which regulate the mutualistic and pathogenic interactions of X. nematophila with its host (Herbert & Goodrich‐Blair, ; Herbert et al., ; Park & Forst, ).…”