Metabolic pathway of α-ketoglutarate in Lactobacillus sanfranciscensis and Lactobacillus reuteri during sourdough fermentation

Abstract

To identify metabolites of α-ketoglutarate (α-KG) in Lactobacillus sanfranciscensis and Lactobacillus reuteri in modified MRS and sourdough. Lactobacillus sanfranciscensis and L. reuteri were grown with additional α-KG in mMRS and in wheat sourdough. In mMRS, α-KG was used as an electron acceptor and converted to 2-hydroxyglutarate (2-OHG) by both organisms. Production of 2-OHG was identified by high performance liquid chromatography (HPLC) and confirmed by gas chromatography (GC). Crude cell extracts of L. sanfranciscensis and L. reuteri grown with or without α-KG exhibited OHG dehydrogenase activity of 6.3 ± 0.3, 2.3 ± 0.9, 1.2 ± 0.2, and 1.1 ± 0.1 mmol l(-1) NADH (min x mg protein)(-1), respectively. The presence of phenylalanine and citrate in addition to α-KG partially redirected the use of α-KG from electron acceptor to amino group acceptor. In wheat sourdoughs, α-KG was predominantly used as electron acceptor and converted to 2-OHG. Lactobacillus sanfranciscensis and L. reuteri utilize α-KG as electron acceptor. Alternative use of α-KG as amino group acceptor occurs in the presence of abundant amino donors and citrate. The use of α-KG as electron acceptor in heterofermentative lactobacilli impacts the formation of flavour volatiles through the transamination pathway.