Effect of reducing agents on the acidification capacity and the proton motive force of Lactococcus lactis ssp. cremoris resting cells

Reducing agents are potential inhibitors of the microbial growth. We have shown recently that dithiothreitol (DTT), NaBH4 and H2 can modify the proton motive force of resting cells of Escherichia coli by increasing the membrane protons permeability [Eur. J. Biochem. 262 (1999) 595]. In the present work, the effect of reducing agents on the resting cells of Lactococcus lactis ssp. cremoris, a species widely employed in dairy processes was investigated. DTT did not affect the acidification nor the ΔpH, in contrast to the effect previously reported on E. coli. The ΔΨ was slightly increased (30 mV) at low pH (pH 4) in the presence of 31 mM DTT or 2.6 mM NaBH4. In the case of Na2S2O4, small amounts (0.9 mM) drastically decreased the acidification range and this product was shown to abolish the ΔpH. These results are discussed in terms of the diversity of action of the chemical reagents and strain sensitivity.