RESPONSE OF THE BVG REGULON OF BORDETELLA-PERTUSSIS TO DIFFERENT TEMPERATURES AND SHORT-TERM TEMPERATURE SHIFTS

Bordetella pertussis produces a number of virulence factors whose expr ession is coordinately regulated by the bvgAS locus. Transcription of virulence genes is repressed by environmental factors such as low temp erature (25 degrees C) and chemical stimuli. Temperature shift of bact erial cultures from 25 degrees C to 37 degrees C activates two classes of bvg-regulated virulence genes: the early genes, which are activate d within 10 min, and late genes, which require 2-4 h for activation. D uring the interval between the activation of the early and late genes, the intracellular concentration of BvgA increases 50-fold. It has bee n proposed that this increased concentration may be required for the a ctivation of the late genes. Here we have analysed the response of the bvg locus to intermediate temperatures and to repeated temperature sh ifts. Temperature shifts of B. pertussis cultures from 22 degrees C to 28 degrees C, 32 degrees C or 35 degrees 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 degrees C were shifted to 22 degrees C, transcription from the adenylate cyclase tox in haemolysis promoter (P-AC) was repressed after 30 min, while transc ription from the bvg (P-1) and filamentous haemagglutinin (P-FHA) prom oters was repressed after 2 h. During this time, the amount of BvgA di d not decrease. A subsequent temperature shift from 22 degrees C to 37 degrees C induced transcription from the P-1 and P-FHA promoters afte r 10 min and transcription from the P-AC promoter after 20 min. This r esult skews 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 th e late genes.