Open AccessBigR, a Transcriptional Repressor from Plant-Associated Bacteria, Regulates an Operon Implicated in Biofilm Growth
Author(s) -
Rosicler L. Barbosa,
Celso Eduardo Benedetti
Publication year - 2007
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.00331-07
Subject(s) - operon , biology , xylella fastidiosa , agrobacterium tumefaciens , repressor , biofilm , transcription (linguistics) , agrobacterium , regulator gene , promoter , gene , genetics , microbiology and biotechnology , regulation of gene expression , transcription factor , bacteria , gene expression , mutant , transformation (genetics) , linguistics , philosophy
Xylella fastidiosa is a plant pathogen that colonizes the xylem vessels, causing vascular occlusion due to bacterial biofilm growth. However, little is known about the molecular mechanisms driving biofilm formation inXylella -plant interactions. Here we show that BigR (for “biofilm growth-associated repressor”) is a novel helix-turn-helix repressor that controls the transcription of an operon implicated in biofilm growth. This operon, which encodes BigR, membrane proteins, and an unusual beta-lactamase-like hydrolase (BLH), is restricted to a few plant-associated bacteria, and thus, we sought to understand its regulation and function inX. fastidiosa andAgrobacterium tumefaciens . BigR binds to a palindromic AT-rich element (the BigR box) in theXylella andAgrobacterium blh promoters and strongly represses the transcription of the operon in these cells. The BigR box overlaps with two alternative −10 regions identified in theblh promoters, and mutations in this box significantly affected transcription, indicating that BigR competes with the RNA polymerase for the same promoter site. Although BigR is similar to members of the ArsR/SmtB family of regulators, our data suggest that, in contrast to the initial prediction, it does not act as a metal sensor. Increased activity of the BigR operon was observed in bothXylella andAgrobacterium biofilms. In addition, anA. tumefaciens bigR mutant showed constitutive expression of operon genes and increased biofilm formation on glass surfaces and tobacco roots, indicating that the operon may play a role in cell adherence or biofilm development.