Changes in electrical conductivity during bacterial growth

Abstract

PARALLEL measurements of the electrical conductivity and bacterial count in a solution containing glucose and peptone, in which a small amount of inoculum of Bact. subtilis has been introduced, show the typical lag, logarithmic and stationary phases, and have brought out the striking result that, even before the multiplication of bacteria takes place, there is an appreciable increase in conductivity. This result is to be attributed to the initial activity of bacteria through their multi-enzyme systems in splitting up the peptone in the medium into aminoacids, which are absorbed by the bacteria from the surrounding medium and provide the nutrient material for their growth. Chemical estimation of the amino-acids formed in the medium revealed a close parallelism between their concentration and the electrical conductivity of the suspension at various stages of bacterial growth. This investigation has thus clearly shown that amino-acid formation takes place through bacterial action in the medium before the bacteria begin to multiply. © 1951 Nature Publishing Group.