The effect of acidic pH on the ability of Clostridium sporogenes MD1 to take up and retain intracellular potassium

Authors: Flythe, Michael; Russell, James

Submitted to: Federation of European Microbiological Societies Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2006
Publication Date: 11/20/2006
Citation: Flythe, M.D., Russell, J.B. 2006. The effect of acidic pH on the ability of Clostridium sporogenes MD1 to take up and retain intracellular potassium. Federation of European Microbiological Societies Microbiology Letters. 12:245-252.

Interpretive Summary: American cattle consume over 150 million tons of fermented plant materials (silage) each year. However, silages are frequently contaminated with clostridia. Clostridia ferment amino acids, produce ammonia and increase silage pH. If the silage pH increases, molds and other toxic microorganisms proliferate. Clostridium sporogenes isolated from silage could be inhibited by a bacteriocin from Streptococcus bovis HC5,and this inhibition could be explained by a loss of intracellular potassium. However, C. sporogenes has a very unusual physiology. When C. sporogenes is growing it does not have a protonmotive force across its cell membrane. The question then arose, how could this bacterium take up potassium in the first place? Our latest work showed that it has two systems of uptake. The protonmotive force driven one is only functional after growth is already inhibited, but it has an ATP-driven one when it is growing. Research on silage microbiology has the potential to decrease the cost of American cattle production and protect cattle and consumers from potentially toxic bacteria.

Technical Abstract: At pH values less 5.5, Clostridium sporogenes MD1 accumulated potassium even though it had little protonmotive force, and an ATPase inhibitor (N, N'- dicyclohexylcarbodiimide) prevented this uptake. These results suggested that potassium transport was ATP-driven, and a protonophore (3, 3', 4', 5 - tetrachlorosalicylanilide) did not eliminate uptake. However, potassium uptake could also be driven by an artificial pH gradient, and in this case the protonophore acted as an inhibitor. These latter results indicated that the cells also had a protonmotive force driven transporter. When the pH less than 5.1, the cells could not retain potassium, rapid efflux was observed, and intracellular volume collapsed.