GLUCOSE-1-PHOSPHATE UTILIZATION BY LISTERIA-MONOCYTOGENES IS PRFA DEPENDENT AND COORDINATELY EXPRESSED WITH VIRULENCE FACTORS

Virulence genes of the facultative intracellular pathogen Listeria mon ocytogenes are coordinately regulated by the activator protein PrfA, e ncoded by prfA, a member of the cyclic AMP receptor protein family of bacterial transcription factors. We found that prfA mutants that cons titutively overexpress the virulence regulon due to a Gly145Ser substi tution in PrfA (M.-T. Ripio, G. Dominguez-Bernal, M. Lara, M. Suarez, and J.-A. Vazquez-Boland, J. Bacteriol. 179:1533-1540, 1997) rapidly u tilized glucose-1-phosphate (G-1-P) as a carbon source for growth, in contrast to wild-type strains, which characteristically do not. Wild-t ype strains acquired the capacity for readily metabolizing G-1-P upon exposure to environmental conditions that activate the expression of p rfA and PrfA-dependent virulence genes (i.e., culture at 37 degrees C in charcoal-treated medium). In these strains, G-1-P utilization follo wed an expressional pattern identical to that of virulence genes contr olled by PrfA, with repression at 20 degrees C. Tn917 insertions in L. monocytogenes mutants selected for G-1-P utilization deficiency mappe d to the plcA-prfA operon, a Delta prfA strain was totally unable to u tilize G-1-P, and trans complementation with prfA constructs restored the ability to efficiently metabolize and grow on G-1-P to these mutan ts. Thus, G-1-P utilization by L. monocytogenes is under the tight pos itive control of the central virulence regulator, PrfA, and is coexpre ssed with PrfA-dependent pathogenicity determinants. It was recently r eported that readily utilized carbohydrates, such as glucose or cellob iose, repress virulence genes in L. monocytogenes. We confirmed this b ut, interestingly, found that G-1-P does not inhibit expression of the PrfA regulon, indicating that this sugar follows a catabolic pathway that bypasses the repressor mechanism triggered by other readily metab olized carbon sources. PrfA dependence and coexpression with virulence genes suggest that utilization of exogenous G-1-P may be relevant to Listeria pathogenesis. G-1-P is the precursor metabolite and primary d egradation product of glycogen and is therefore available within the m ammalian cell. Based on our results, we hypothesize that G-1-P could p lay an important role as a growth substrate for intracellular Listeria .