LuxS-dependent AI-2 production is not involved in global regulation of natural product biosynthesis inPhotorhabdusandXenorhabdus

Abstract

The Gram-negative bacteriaPhotorhabdusandXenorhabdusare known to produce a variety of different natural products (NP). These compounds play different roles since the bacteria live in symbiosis with nematodes and are pathogenic to insect larvae in the soil. Thus, a fine tuned regulatory system controlling NP biosynthesis is indispensable. Global regulators such as Hfq, Lrp, LeuO and HexA have been shown to influence NP production ofPhotorhabdusandXenorhabdus. Additionally, photopyrones as quorum sensing (QS) signals were demonstrated to be involved in the regulation of NP production inPhotorhabdus.In this study, we investigated the role of another possible QS signal, autoinducer-2 (AI-2), in regulation of NP production. The AI-2 synthase (LuxS) is widely distributed within the bacterial kingdom and has a dual role as a part of the activated methyl cycle pathway, as well as being responsible for AI-2 precursor production. We deletedluxSin three different entomopathogenic bacteria and compared NP levels in the mutant strains to the wild type (WT) but observed no difference to the WT strains. Furthermore, the absence of the small regulatory RNAmicA, which is encoded directly upstream ofluxS, did not influence NP levels. Phenotypic differences between theP. luminescens luxSdeletion mutant and an earlier describedluxSdeficient strain ofP. luminescenssuggested that two phenotypically different strains have evolved in different laboratories.