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Photorhabdus phase variants express a novel fimbrial locus, mad , essential for symbiosis
Author(s) -
Somvanshi Vishal S.,
KaufmannDaszczuk Bettina,
Kim Kwisuk,
Mallon Shane,
Ciche Todd A.
Publication year - 2010
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2010.07270.x
Subject(s) - biology , photorhabdus , fimbria , microbiology and biotechnology , mutant , pilus , photorhabdus luminescens , genetics , phase variation , locus (genetics) , gene , virulence
Summary Fimbriae are adhesive organelles known to enable pathogens to colonize animal tissue, but little is known of their function in mutualistic symbioses. Photorhabdus colonization of Heterorhabditis bacteriophora nematodes is essential for the pair's insect pathogenic lifestyle. Maternal nematodes acquire Photorhabdus symbionts as a persistent intestinal biofilm prior to transmission to infective juvenile (IJ) stage offspring developing inside the maternal body. Screening 8000 Photorhabdus mutants for defects in IJ colonization revealed that a single fimbrial locus, named mad for m aternal a dhesion d efective, is essential. The mad genes encode a novel usher/chaperone assembled fimbria regulated by an ON/OFF invertible promoter switch. Adherent Photorhabdus cells in maternal nematode intestines had the switch ON opposite to the OFF orientation of most other cells. A Δ madA mutant failed to adhere to maternal intestines and be transmitted to the IJs. Mad fimbriae were detected on TT01 phase ON cells but not on Δ madA phase ON cells. Also required for transmission is madJ , predicted to encode a transcriptional activator related to GrlA. Expression of madA–K or madIJK restored the ability of madJ mutant to adhere. The Mad fimbriae were not required for insect pathogenesis, indicating the specialized function of Mad fimbriae for symbiosis.