Short-chain fatty acids like propionic (PPA) and valproic acids (VP) can alter gut microbiota, which is suggested to play a role in development of autism spectrum disorders (ASD). In this study we investigated the role of various concentrations of PPA and VP in gut enteric gram-negative Escherichia coli K12 and gram-positive Enterococcus hirae ATCC 9790 bacteria growth properties, ATPase activity and proton flux. The specific growth rate (µ) was 0.24 h -1 and 0.82 h -1 in E. coli and E. hirae, respectively. Different concentrations of PPA reduced the value of µ similarly in both strains. PPA affects membrane permeability only in E. hirae. PPA decreased DCCD-sensitive ATPase activity in the presence of K + ions by 20% in E. coli and 40% in E. hirae suggesting the importance of the F O F 1 -K + transport system in the regulation of PPA-disrupted homeostasis. Moreover, the H + flux during PPA consumption could be the protective mechanism for enteric bacteria. VP has a selective effect on the µ depending on bacteria. The overwhelming effect of VP was detected on the K + -promoted ATPase activity in E. hirae. Taken together it can be suggested that PPA and VP have a disruptive effect on E. coli and E. hirae growth, viability, bioenergetic and biochemical properties, which are connected with the alteration of F O F 1 -ATPase activity and H + flux rate or direction.