Response of the bvg regulon of Bordetella pertussis to different temperatures and short-term temperature shifts

Abstract

Bordetella pertussis produces a number of virulence factors whose expression is coordinately regulated by the bvgA3 locus. Transcription of virulence genes is repressed by environmental factors such as low temperature (25 "C) and chemical stimuli. Temperature shift of bacterial cultures from 25 "C to 37 "C activates two classes of bvg-regulated virulence genes: the early genes, which are activated within 10 min, and late genes, which require 2 4 h for activation. During the interval between the activation of the early and late genes, the intracellular concentration of BvgA increases 50-fold. It has been proposed that this increased concentration may be required for the activation of the late genes. Here we have analysed the response of the bvg locus to intermediate temperatures and to repeated temperature shifts. Temperature shifts of B.pertussis cultures from 22 "C to 28 "C, 32 "C or 35 "C resulted in the synthesis of low, intermediate, and high amounts of BvgA. This implied that the intracellular concentration of BvgA is temperature-dependent. We have also observed that the amount of virulence factors produced correlates with the BvgA concentration. When bacteria grown at 37 "C were shifted to 22 "C, transcription from the adenylate cyclase toxin haemolysis promoter (PAC) was repressed after 30 min, while transcription from the bvg (P,) and filamentous haemagglutinin (PFHA) promoters was repressed after 2 h. During this time, the amount of BvgA did not decrease. A subsequent temperature shift from 22 "C to 37 "C induced transcription from the P, and P, , promoters after 10 min and transcription from the PAC promoter after 20 min. This result shows that in the presence of a high concentration of BvgA, the time lag between temperature shift and late promoter transcription is reduced from 2 4 h to 20 min. The above data support the proposal that the concentration of BvgA plays a role in activating expression of the late genes.

Growth Phase- and Nutrient Limitation-Associated Transcript Abundance Regulation inBordetella pertussis

“…Since B. pertussis appears to survive only in the human airway, it may have evolved to link growth phase and virulence with changing conditions in different locations of this restricted environment or during different stages of infection. Prior studies have suggested that Bvg-regulated expression of virulence factors may occur in a temporally or spatially defined sequence (10,30). A possible model for the B. pertussis infectious cycle consists of elaboration of adhesins, toxins, and other virulence factors during early stages of infection, thus permitting colonization, evasion of host immunity, and acquisition of nutrients, followed by declining virulence factor production when bacteria reach high densities and have depleted locally available nutrients.…”

Assembly of Fimbrial Structures inPseudomonas aeruginosa: Functionality and Specificity of Chaperone-Usher Machineries

“…The cup gene clusters of genes were described as poorly expressed under laboratory conditions (37) and are regulated by a complex regulatory network involving the HNS-like protein MvaT, acting in a phase-variable manner (38) as a transcriptional repressor for cupA (37) and, to a lesser extent, for cupB and cupC (37). A two-component regulatory system, namely, the RocS1 (the sensor of the Roc1 [regulation of cup 1] system)-RocRRocA1 system, homologous to the BvgS-BvgR-BvgA system of Bordetella pertussis (26,39), which controls a number of virulence factors in this bacterium (13), has recently been identified as controlling cupB and cupC gene cluster expression (20). The overproduction of the regulator RocA1 or the sensor RocS1 is sufficient to observe the overexpression of cupB-lacZ and cupC-lacZ transcriptional fusions.…”

Bordetella pertussis Autoregulates Pertussis Toxin Production through the Metabolism of Cysteine

“…Studies have shown that virulence factor expression is influenced by temperature, pH, glutamate levels, free fatty acids, and environmental compounds like nicotinic acid and SO 4 2Ϫ (15,16,23,25,26,35,37,56). Addition of heptakis-(2,6-Odimethyl)-␣-cyclodextrin to the medium increases Ptx yields significantly (15,16,58).…”

“…Expression of the vir regulon in B. pertussis is affected by diverse environmental signals (31,32,35). The presence of sulfate anion (SO 4 2Ϫ ) or nicotinic acid (31,32) or growth at low temperature (37) results in decreased expression of ptx and other virulence genes. Naturally occurring BvgS mutants (49), site-directed mutants (34), and serum-resistant mutants (12) have been shown to be less sensitive to these environmental signals.…”