[Effect of gramicidin D on the exoprotease activity of Bacillus thuringiensis]

A treatment of Bacillus thuringiensis cells with gramicidine D in the medium containing the yeast and polysaccharides increases the lag-phase up to 12 h without a change of the rate during the logarithmic phase of the culture growth. The exoprotease activity of cells treated with gramicidine reaches a maximum value 4 h earlier in comparison with the control culture, and the activity level is increased 2-fold. At a concentration increasing the exoprotease activity, gramicidine was found to induce the permeability of Bac. thuringiensis membranes for potassium ions. An additional introduction of 250 mM KCl or NaCl into the medium inhibits only the exoprotease activity of cells treated with gramicidine. It is assumed that the ability of gramicidine to increase the exoprotease activity of Bac. thuringiensis may be due to a change in the intrabacterial ionic composition.