Xenorhabdus bovienii T228 phase variation and virulence are independent of RecA function

Abstract

5005Colony pleomorphism, or phase variation, expressed by entomopathogenic bacteria belonging to the genus Xenorhabdus, is an important factor which determines the association of the bacteria with their nematode symbiont and the outcome of infection of susceptible insect larvae by the bacteriumnematode parasitic complex. The mechanism underlying phase variation is unknown. To determine whether RecA-mediated processes are linked to phase variation, the recA gene of Xenorhabdus bovienii was cloned and sequenced. When expressed in a recA-deleted strain of Escherichia coli, the X. bovienii recA clone was able to complement the loss of RecA function. X. bovienii chromosomal recA insertion mutants showed increased sensitivity to UV. Phase 1 forms did not show altered ability to convert to phase 2 and no significant differences in expression of other phase-dependent characteristics, including phospholipase C, haemolysin, protease, antibiotic activity and Congo Red binding, were noted. Furthermore, the LD 50 of the X. bovienii recA insertion mutant for Galleria mellonella larvae was not significantly different from that of wild-type strains. From these data the authors conclude that recA is unlikely to be involved in phase variation, the expression of phasedependent characteristics, or virulence factors involved in killing of susceptible larvae.

Identification and phylogenetic analysis of Arsenophonus- and Photorhabdus-type bacteria from adult Hippoboscidae and Streblidae (Hippoboscoidea)

“…Much like in previous studies the genera Xenorhabdus, Photorhabdus, Morganella, Providencia, Proteus, and Arsenophonus formed a monophyletic group (Forst et al, 1997;Gherna et al, 1991;O'Hara et al, 2000;Pinyon et al, 2002;Suzuki et al, 1996). An average sequence similarity of 94% between this group and the other included Enterobacteriacea is lower than the average within the group (96.1%), thus clearly separating them from other Enterobacteriacea.…”

Phenotypic variation and host interactions of Xenorhabdus bovienii SS‐2004, the entomopathogenic symbiont of Steinernema jollieti nematodes

“…data). Studies to date indicate the mechanism underlying phenotypic variation does not involve DNA rearrangements (Akhurst et al, 1992) changes in plasmid content (Leclerc and Boemare, 1991), or recombination-dependent mechanisms (Pinyon et al, 2000). In X. nematophila the transcription factor Lrp is a positive regulator of primary form traits; lrp mutants are phenotypically secondary form , suggesting phenotypic variation may be an epigenetic phenomenon.…”

Construction of a recA mutant of Azospirillum lipoferum and involvement of recA in phase variation⋆

“…At the 3′ end of the recA gene and overlapping the stop codon, lies a 29 nucleotides GC‐rich hairpin‐forming sequence with a folding energy of −147.5 kcal mol −1 followed by six thymines, which could function as a transcriptional terminator. Such stem‐loop structures have been found downstream of Xenorhabdus bovienii and X. nematophilus recA gene [32].…”

“…The recA insertion mutant had significantly reduced ability to repair DNA lesions caused by exposure to UV radiation or an alkylating agent, as previously reported for A. brasilense Sp7 [37] and other bacteria. As in X. bovienii [32], resistance to UV‐induced damage was only partially restored to wild type level when complementing with a plasmid‐borne functional copy of recA . Since it could be that the recA:: Km mutant 4B recA expresses the N‐terminal half of the protein (which would lack the C‐terminus), abnormal multimers containing truncated and wild type peptides might form and hinder the coprotease and recombination activities of RecA in the complemented strain [38].…”