The ability of acidic pH, growth inhibitors, and glucose to increase the proton motive force and energy spilling of amino acid-fermenting Clostridium sporogenes MD1 cultures

Clostridium sporogenes MD1 grew rapidly with peptides and amino acids as an energy source at pH 6.7. However, the proton motive force (Delta p) was only -25 mV, and protonophores did not inhibit growth. When extracellular pH was decreased with HCl, the chemical gradient of protons (Z Delta pH) and the electrical membrane potential (Delta Psi) increased. The Delta p was -125 mV at pH 4.7, even though growth was not observed. At pH 6.7, glucose addition did not cause an increase in growth rate, but Delta Psi increased to -70 mV. Protein synthesis inhibitors also significantly increased Delta Psi. Non-growing, arginine-energized cells had a Delta Psi of -80 mV at pH 6.7 or pH 4.7, but Delta Psi was not detected if the F1F0 ATPase was inhibited. Arginine-energized cells initiated growth if other amino acids were added at pH 6.7, and Delta Psi and ATP declined. At pH 4.7, ATP production remained high. However, growth could not be initiated, and neither Delta Psi nor the intracellular ATP concentration declined. Based on these results, it appears that C. sporogenes MD1 does not need a large Delta p to grow, and Delta p appears to serve as a mechanism of ATP dissipation or energy spilling.