Inorganic cation transport and energy transduction in Enterococcus hirae and other Streptococci

Energy metabolism by bacteria is well understood from the chemiosmotic view point. We know that bacteria extrude protons across the plasma membrane, es tablishing an electrochemical potential that provides the driving force for various kinds of physiological work. Among these are the uptake of sugars, amino acids, and other nutrients with the aid of secondary porters and the regulation of the cytoplasmic pH and of the cytoplasmic concentration of p otassium and other ions. Bacteria live in diverse habitats a,ld ale often e xposed to severe conditions. In some circumstances, a proton circulation ca nnot satisfy, their requirements and must be supplemented with a complement of primary transport systems. This review is concerned with cation transpo rt in the fermentative streptococci, particularly, Enterococcus hirae. Stre ptococci lack respiratory chains, relying on glycolysis ol arginine ferment ation for the production of ATP. One of the major findings with E. hirae an d other streptococci is that ATP plays a much more important role in transm embrane transport than it does in nonfermentative organisms, probably due t o the inability of this organism to generate a large proton potential. The movements of cations in streptococci illustrate the interplay between a var iety of primary and secondary modes of transport.