Suppression of toxin production in Clostridium difficile VPI 10463 by amino acids

The impact of various growth conditions on the expression of toxins and oth er proteins by Clostridium difficile VPI 10463 was studied. During non-star ved conditions, the rate of toxin synthesis paralleled that of total protei n during both exponential growth and stationary phase, and in both defined and complex media. Biotin limitation reduced growth rate and bulk protein s ynthesis, whereas toxin expression continued, leading to a 50- to 200-fold increase in intracellular toxin levels. Concomitantly, several 22 kDa prote ins were up-regulated as revealed by two-dimensional PACE analysis. The tox in yield was 30-fold higher in peptone yeast extract (PY) than in PY contai ning glucose (PYG). By contrast, glucose limitation reduced toxin yields by 20- to 100-fold in defined media. By elevating the buffering capacity and bicarbonate concentration, toxin yields were Increased by 10-fold in PY and PYC. The high toxin production by C. difficile during growth in PY was low ered 100-fold by adding a blend of nine amino acids and several 60-100 kDa proteins were concomitantly down-regulated. It was concluded that toxin exp ression in C. difficile VPI 10463 was not affected by growth rate, growth p hase, catabolite repression or the stringent response. Instead the Eo-expre ssion of toxins and a few specific additional proteins appeared to be influ enced by metabolic pathways involving CO2 assimilation, carboxylation react ions end metabolism of certain amino acids.