The chromosomal response regulatory gene chvI of Agrobacterium tumefaciens complements an Escherichia coli phoB mutation and is required for virulence

Abstract

In an effort to identify the Agrobacterium tumefaciens phosphate regulatory gene(s), we isolated a clone from an A. tumefaciens cosmid library that restored regulated alkaline phosphatase activity to an Escherichia coli phoB mutant. The gene that complemented phoB was localized by subcloning and deletion analysis, and the DNA sequence was determined. An open reading frame, denoted chvI, was identified that encoded a predicted protein with amino acid similarity to the family of bacterial response regulators and 35% identify to PhoB. Surprisingly, an A. tumefaciens chvI mutant showed normal induction of phosphatase activity and normal virG expression when grown in phosphate-limiting media. However, this mutant was unable to grow in media containing tryptone, peptone, or Casamino Acids and was also more sensitive than the wild type to acidic extracellular pH. This mutant was avirulent on Kalanchoeë diagremontiana and was severely attenuated in vir gene expression. The pH-inducible expression of virG was also abolished. Growth of the chvI mutant was inhibited by K. diagremontiana wound sap, suggesting that avirulence may be due, in part, to the inability of this mutant to survive the plant wound environment.

A two‐component regulatory system playing a critical role in plant pathogens and endosymbionts is present in Brucella abortus and controls cell invasion and virulence

“…Also, insertion mutations in either chvG (the sensor histidine protein kinase) and chvI (the response regulator) render A. tumefaciens unable to elicit tumour formation in susceptible plants (Charles and Nester, 1993). Furthermore, although the genes regulated by ChvIChvG are unknown, it is significant that the chvI and chvG mutants show the increased sensitivity to surfactants (Charles and Nester, 1993;Mantis and Winans, 1993) reported here for the B. abortus bvrR and bvrS mutants. Thus, as hypothesized by Charles and Nester (1993) for A. tumefaciens, it is likely that these regulatory elements control the synthesis and/or assembly of OM components essential in the interaction with eukaryotic cells.…”

“…The GþC content of the whole sequence was similar to that observed for B. abortus chromosomal DNA (58%) (Hoyer and McCullough, 1968). A database search of the deduced amino acid sequence for the BvrR and BvrS proteins revealed a high level of identity with a two-component regulatory system of Rhizobium (Sinorhizobium) meliloti (ChvI-ExoS;Osteras et al, 1995;Cheng and Walker, 1998) and A. tumefaciens (ChvI-ChvG;Charles and Nester, 1993;Mantis and Winans, 1993). BvrR had 85% identity (89% similarity) and 83% identity (87% similarity) to the R. meliloti and A. tumefaciens ChvI respectively.…”

Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria

“…This system was found in a search for chromosomally located virulence genes (71). Mutations in either chvG or chvI abolished tumorigenesis and caused sensitivity to acidic pH (71,305). Among the genes whose acid-inducible expression is controlled by ChvG-ChvI is virG, whose product activates the vir regulon (see below) (305); the aopA gene, which encodes a surface-exposed outer membrane protein; and the katA gene, which encodes a catalase that is important for detoxification of H 2 O 2 released during plant infection (Table 1) (287).…”

“…However, the same promoter is also activated rather strongly by phosphate starvation, and sequence analysis suggests that this regulation might occur via orthologs of the PhoR-PhoB proteins of enteric bacteria (530). The downstream virG promoter is activated by acidic pH, acting via the ChvG-ChvI two-component system (305). These latter stimuli are thought to "prime the pump," that is, to increase the pool size of VirG sufficiently that positive autoregulation can occur.…”

The two-component system BvrR/BvrS essential for Brucella abortus virulence regulates the expression of outer membrane proteins with counterparts in members of the Rhizobiaceae

“…It has been demonstrated that the ChvI͞ExoS system of S. meliloti controls the succinoglycan production necessary for endosymbiosis (8). Also, A. tumefaciens ChvI͞ ChvG mutants are not tumorigenic in plants, are comparatively sensitive to detergents, antibiotics, and acid pH, and have altered cell envelope permeability (9,10). However, little is known on the molecular determinants controlled by these regulatory systems.…”