Utilization of electron acceptors by lactobacilli isolated from sourdough

Abstract

Lactobacillus sanfrancisco is frequently a prevalent organism in wheat and rye sourdoughs. Its growth and metabolism are strongly affected by agitation and the availability of maltose and electron acceptors such as oxygen and fructose. Upon agitation of a culture the length of the lag phase was reduced. The growth rate and final cell yield increased in the presence of oxygen and electron acceptors. Growing cells formed lactate and ethanol from maltose under anaerobic conditions. Intermediately excreted glucose did not repress maltose utilization. Upon aeration or addition of fructose to cultures growing on maltose, acetate was formed instead of ethanol. Fructose was reduced to mannitol. Added fumarate and malate were converted to lactate and did not serve as electron acceptors. The following observations are suggested to contribute to the competitiveness ofL. sanfrancisco in sourdough. Glucose is excreted in abundance of maltose and represses the maltose metabolism of competitors, maltose is split by maltose phosphorylase without the expenditure of adenosine 5′-triphosphate (ATP), and additional metabolic energy is generated by the activity of acetate kinase in the presence of fructose which is abundant in the polyfructosanes of flour. The metabolic features ofL. pontis, L. reuteri, L. amylovorus andL. fermentum are to be described in a following communication.