Autoregulation of expression of secreted proteins in Listeria monocytogenes

The spectrum of proteins secreted by L. monocytogenes greatly depends on the composition of the cultivation medium. The introduction of activated charcoal (AC) into brain heart infusion (BHI) leads to the secretion of a number of additional proteins with mol.wt. ranging between 20 and 100 kD, whose production is not observed in pure BHI. The effect depends on the absorption capacity of AC: when adsorption capacity is reduced due to a decrease in the concentration of AC or its preliminary saturation with the components of the cultivation medium a drop in the level of the production of additional proteins is observed. The preliminary treatment of the medium with AC with its subsequent elimination prior to inoculation doses not change the spectrum of secreted proteins, though greatly inhibits the growth of L. monocytogenes. The data obtained in this investigation indicate that the effect produced by AC is based on the elimination of some product of L. monocytogenes vital activity from the cultivation medium; this product acts as the autoregulator of the synthesis of a number of secreted proteins.