PROTON-ATPASE ACTIVITY IN CELLS OF LACTOBACILLI GROWN IN THE PRESENCEOF PROPIONATE

Lactobacillus helveticus ATCC 15009 and CRL 581, and Lact. casei LC3 w ere grown in a complex medium with and without 15 mmol l(-1) of neutra lized propionic acid and assayed for proton-translocating ATPase activ ity. The enzyme activity was higher when the medium contained fatty ac id than in its absence for all strains studied. Characteristics of thi s increased ATPase were identical to those of the enzyme located on th e membrane of normal cells. The substrate consumption rate of resting cells was increased by propionate. This effect was reverted by the spe cific H+-ATPase inhibitor N,N'-dicyclohexylcarbodiimide indicating tha t the increment of fermentative activity was related to the H+-ATPase activity. These results suggest that the amplification of H+-ATPase ac tivity could be involved in the inhibition of lactobacilli growth in c ultures where propionic acid is unavoidably present, such as some mixe d cultures with propionibacteria.