Who's the boss here? The post-transcriptional global regulator Hfq takes over control of secondary metabolite production in the nematode symbiont Photorhabdus luminiscens

Abstract

A Trojan? Dr. Jekyll and Mr. Hyde? This is Photorhabdus luminiscens: an enterobacterial symbiont of nematodes of the Heterorhabditis genus, and, at the same time, an insect killer. It colonizes the nematode gut; the worm gets into a host insect, where it regurgitates the bacteria; P. luminiscens then spreads throughout the insect hemolymph and secrete toxins that kill the host (Clarke, 2014). At this stage, the capacity of P. luminiscens to produce a wide set of secondary metabolites (SM) is turned on to serve a dual task: to keep the decaying insect tissue free of other competitor bacteria, and to serve as food and source of developmental factors for the nematode transition from infective juveniles into hermaphrodites with reproductive ability (Joyce et al., 2011) (Fig. 1). It is therefore a journey with changing environments for P. luminiscens, which has attracted interest not only in terms of the regulatory processes modulating its adaptation to the varying ecological niches to which it is exposed, but also because of the biological properties and diversity of the SM that it can produce. Such prolific secondary metabolism is mainly determined by a number of non-ribosomal peptide synthetase and polyketide synthase gene clusters, whose expression regulatory details have been poorly explored