UTILIZATION OF ELECTRON ACCEPTORS BY LACTOBACILLI ISOLATED FROM SOURDOUGH .2. LACTOBACILLUS-PONTIS, L-REUTERI, L-AMYLOVORUS, AND L-FERMENTUM

The metabolism of maltose and the use of electron accepters has been i nvestigated in strains of lactobacilli which are known to be stable el ements in sourdoughs, which, traditionally, have been used for a long time. The metabolic features of Lactobacillus sanfrancisco have been d escribed by us in a previous communication. Similar principles have be en detected for the competitiveness of L. pontis, L. reuteri, L. ferme ntum and L. amylovorus, as well as species-specific characteristics. B ased on these findings the metabolic key reactions have been identifie d and the use of electron accepters present in sourdough are presented in a schematic overview. In contrast to L. sanfrancisco, these specie s can not use oxygen as an electron acceptor, and the length of their lag phase was not affected by agitation. Malate and fumarate were redu ced to succinate, and fructose was used, depending on the species, as an electron acceptor, carbon source or both. All heterofermentative so urdough lactobacilli efficiently split maltose using maltose phosphory lase. Glucose was excreted, which induced glucose repression in compet ing indigenous micro-organisms, without affecting the maltose metaboli sm of sourdough lactobacilli. Lactobacilli generate additional adenosi ne 5'-triphosphate (ATP) from acetyl phosphate in the presence of elec tron accepters. These special features are suggested to represent a ge neral principle which accounts for the prevalence of specific heterofe rmentative lactobacilli which are propagated over long periods present in sourdough fermentations.