Comparative analysis of the Photorhabdus luminescens and the Yersinia enterocolitica genomes: uncovering candidate genes involved in insect pathogenicity

Background: Photorhabdus luminescens and Yersinia enterocolitica
are both enteric bacteria which are associated with insects. P.
luminescens lives in symbiosis with soil nematodes and is highly
pathogenic towards insects but not to humans. In contrast, Y.
enterocolitica is widely found in the environment and mainly known
to cause gastroenteritis in men, but has only recently been shown
to be also toxic for insects. It is expected that both pathogens
share an overlap of genetic determinants that play a role within
the insect host. Results: A selective genome comparison was
applied. Proteins belonging to the class of two-component
regulatory systems, quorum sensing, universal stress proteins, and
c-di-GMP signalling have been analysed. The interorganismic
synopsis of selected regulatory systems uncovered common and
distinct signalling mechanisms of both pathogens used for
perception of signals within the insect host. Particularly, a new
class of LuxR-like regulators was identified, which might be
involved in detecting insect-specific molecules. In addition, the
genetic overlap unravelled a two-component system that is unique
for the genera Photorhabdus and Yersinia and is therefore suggested
to play a major role in the pathogen-insect relationship. Our
analysis also highlights factors of both pathogens that are
expressed at low temperatures as encountered in insects in contrast
to higher (body) temperature, providing evidence that temperature
is a yet under-investigated environmental signal for bacterial
adaptation to various hosts. Common degradative metabolic pathways
are described that might be used to explore nutrients within the
insect gut or hemolymph, thus enabling the proliferation of P.
luminescens and Y. enterocolitica in their invertebrate hosts. A
strikingly higher number of genes encoding insecticidal toxins and
other virulence factors in P. luminescens compared to Y.
enterocolitica correlates with the higher virulence of P.
luminescens towards insects, and suggests a putative broader insect
host spectrum of this pathogen. Conclusion: A set of factors shared
by the two pathogens was identified including those that are
involved in the host infection process, in persistence within the
insect, or in host exploitation. Some of them might have been
selected during the association with insects and then adapted to
pathogenesis in mammalian hosts.