In Vivo Expression of the Mannose-Resistant Fimbriae of Photorhabdus temperata K122 during Insect Infection

Abstract

Photorhabdus temperata K122 is an entomopathogenic bacterium symbiotically associated with nematodes of the family Heterorhabditidae. Surface fimbriae are important for the colonization of many pathogenic bacteria, and here we report the nucleotide sequence and analysis of the expression of a 12-kbp fragment encoding the mannose-resistant fimbriae of P. temperata (mrf). The mrf gene cluster contains 11 genes with an organization similar to that of the mrp locus from Proteus mirabilis. mrfI (encoding a putative recombinase) and mrfA (encoding pilin), the first gene in an apparent operon of nine other genes, are expressed from divergent promoters. The mrfI-mrfA intergenic region contains inverted repeats flanking the mrfA promoter. This region was shown to be capable of inversion, consistent with an ON/OFF regulation of the operon. In in vitro liquid cultures, both orientations were detected. Nevertheless, when we analyzed the expression of all of the genes in the mrf locus by semiquantitative reverse transcription-PCR during infection of Galleria mellonella (greater wax moth) larvae, expression of mrfA was not detected until 25 h postinfection, preceding the death of the larvae at 32 h. In contrast, mrfJ (a putative inhibitor of flagellar synthesis) was expressed throughout infection. Expression of mrfI was also detected only late in infection (25 to 30 h), indicating a possible increase in inversion frequency at this stage. In both in vitro liquid cultures and in vivo larval infections, the distal genes of the operon were expressed at substantially lower levels than mrfA. These results indicate the complex regulation of the mrf cluster during infection.Photorhabdus luminescens K122 is a gram-negative insect pathogen belonging to the gamma subdivision of the Enterobacteriaceae (10,16,38,39). In a recent reclassification, P. luminescens K122 was renamed Photorhabdus temperata (19). Despite the fact that it is a pathogen to insects, P. temperata also forms a natural symbiotic association in the intestines of nematodes of the family Heterorhabditidae (20). P. temperata presents numerous advantages as a model system for the study of both symbiosis and virulence in the same organism, since the bacteria and the nematode together constitute a highly efficient pathogenic interaction with a broad host range of insects.For initiation of the pathogenic process, the nematode transports the bacteria into the interior of insect larvae, where they are released into the hemolymph. By releasing several toxins (6, 12, 18), the bacteria rapidly kill the larvae and multiply to large numbers (14). This virulence phase is followed, as the bacteria reach stationary phase, by the secretion of many hydrolytic enzymes (proteases [13,15,40], lipase [42], phospholipase, and DNase) and other enzymes, which degrade the macromolecular structures of the larva. This phase, which can be called the bioconversion phase, is essential for the development and reproduction of the hermaphrodite nematode (11,15). In addition, during the bioconversion pha...

Pleiotropic Role of Quorum-Sensing Autoinducer 2 inPhotorhabdus luminescens

“…This latter observation could be related to alteration of virulence, as it has been recently suggested that MrfA plays an important role in the pathogenic process of Photorhabdus temperata (39). In P. luminescens, the luxS-deficient strain exhibited an attenuated and delayed pathogenicity, consistent with the reduced virulence observed in luxS-deficient strains of Neisseria meningitidis, Streptococcus pneumoniae, and Vibrio vulnificus (32,64,77).…”

Unique organization and regulation of the mrx fimbrial operon in Xenorhabdus nematophila

“…The mrx operon consists of five structural genes (mrxACDGH) and one putative regulatory gene, mrxJ. BLAST analysis revealed that the mrx genes were most closely similar to the mrp and mrf orthologous genes of Proteus mirabilis (Zhao et al, 1997) and Photorhabdus temperata (Meslet-Cladiere et al, 2004), respectively (Fig. 1).…”

Pathogenesis of Proteus mirabilis Infection

“…Notably, MrpJ paralogs are not restricted to P. mirabilis as they have been detected in fimbrial operons from related genera (264–266). Because fimbriae allow bacteria to adhere or form biofilms in specific environments, and thus respond to niche-specific signals, MrpJ paralogs have been proposed to orchestrate genetic programs that are beneficial to those environments (132, 267).…”