Open AccessInactivation of the Agrobacterium tumefaciens ActSR system affects resistance to multiple stresses with increased H2O2 sensitivity due to reduced expression of hemH
Author(s) -
Chitrasak Kullapanich,
James M. Dubbs,
Skorn Mongkolsuk
Publication year - 2019
Publication title -
microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.352
H-Index - 35
eISSN - 1465-2080
pISSN - 1350-0872
DOI - 10.1099/mic.0.000838
Subject(s) - catalase , agrobacterium tumefaciens , mutant , chemistry , cumene hydroperoxide , complementation , hydrogen peroxide , operon , oxidative stress , biochemistry , microbiology and biotechnology , biology , gene , transformation (genetics) , catalysis
The Agrobacterium tumefaciens ActSR two-component regulatory system is a member of a homologous group of global redox-responsive regulatory systems that adjust the expression of energy-consuming and energy-supplying metabolic pathways in order to maintain cellular redox balance. In this study, the transcriptional organization of the hrpB-actSR locus was determined and the effect of actSR system inactivation on stress resistance was investigated. It was found that hrpB is transcribed as a monocistronic mRNA and actS is transcribed along with actR as a bicistronic mRNA, while actR is also transcribed as a monocistronic message. Each message is initiated from a separate promoter. Inactivation of actR resulted in decreased resistance to membrane stress (sodium dodecyl sulfate), acid stress (pH 5.5), iron starvation (bipyridyl) and iron excess (FeCl 3 ), and antibiotic stress (tetracycline and ciprofloxacin). Resistance to oxidative stress in the form of organic peroxide (cumene hydroperoxide) increased, while resistance to inorganic peroxide (H 2 O 2 ) decreased. An actR insertion mutant displayed reduced catalase activity, even though transcription of katA and catE remained unchanged. Complementation of the actR inactivation mutant with plasmid-encoded actR or overexpression of hemH , encoding ferrochelatase, restored wild-type catalase activity and H 2 O 2 resistance levels. Gel mobility shift and hemH promoter -lacZ fusion results indicated that ActR is a positive regulator of hemH that binds directly to the hemH promoter region. Thus, inactivation of the A. tumefaciens ActSR system affects resistance to multiple stresses, including reduced resistance to H 2 O 2 resulting from a reduction in catalase activity due to reduced expression of hemH .