The alternative σ factor HrpL negatively modulates the flagellar system in the phytopathogenic bacterium Erwinia amylovora under hrp-inducing conditions

• Published in: FEMS microbiology letters 2006-04, Vol.257 (2), p.221-227
• Main Authors: Cesbron, Sophie, Paulin, Jean-Pierre, Tharaud, Michel, Barny, Marie-Anne, Brisset, Marie-Noëlle
• Format: Article
• Language: English
• Subjects: Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Down-Regulation; Erwinia amylovora; Erwinia amylovora - genetics; Erwinia amylovora - pathogenicity; fire blight; Flagella; Flagellin; Flagellin - genetics; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Genetics; inverse regulation; Life Sciences; Maloideae; Microbiology; Microbiology and Parasitology; Motility; Pathogens; Plant Diseases - microbiology; Plant Leaves - microbiology; Rosaceae - microbiology; Secretion; Seedlings; Seedlings - microbiology; Sigma Factor - genetics; type III secretion system; Virulence; σ factor
• ISSN: 0378-1097; 1574-6968
• DOI: 10.1111/j.1574-6968.2006.00172.x

abstract In this work we present evidence of an opposite regulation in the phytopathogenic bacteria Erwinia amylovora between the virulence-associated Type III secretion system (TTSS) and the flagellar system. Using loss-of-function mutants we show that motility enhanced the virulence of wild-type bacteria relative to a nonmotile mutant when sprayed on apple seedlings with unwounded leaves. Then we demonstrated through analyses of motility, flagellin export and visualization of flagellar filament that HrpL, the positive key regulator of the TTSS, also down-regulates the flagellar system. Such a dual regulation mediated by an alternative σ factor of the TTSS appears to be a level of regulation between virulence and motility not yet described among Proteobacteria.