In a medium containing glucose, lactate carbon is incorporated by gonococci predominantly into fatty acids and glucose carbon incorporation is increased: implications regarding lactate stimulation of metabolism

The reason for stimulation by lactate of metabolism of gonococci growing in a medium containing glucose, which enhances pathogenicity by increasing gr owth rate, lipopolysaccharide (LPS) synthesis and protein formation, has be en investigated. Tricine dodecylpolyacrylamide gel electrophore sis (SDS-PA GE) and thin layer chromatography (TLC) on homogenates of gonococci grown i n this medium with [C-14]lactate showed that lactate carbon was preferentia lly incorporated into lipid and LPS. Nuclear magnetic resonance (NMR) spect roscopy on lipid extracted from gonococci grown in the glucose containing m edium with [C-13]lactate showed that lactate carbon was incorporated into f atty acid moieties and not into ethanolamine or glycerol moieties. In contr ast, NMR on lipid from gonococci grown with [C-13]glucose indicated glucose carbon in both moieties. When unlabelled lactate was added, lipid synthesi s from [C-13]glucose was stimulated and small amounts of different fatty ac ids were formed. The NMR data shows that gluconeogenesis from lactate carbo n does not occur in the presence of glucose, suggesting that lactate is use d solely for rapid production, via py ruvate, of acetyl CoA, the precursor not only for fatty acid synthesis but also for the constituents and product s of the citric acid cycle, including ATP. The rapid formation of a high le vel of acetyl CoA is the probable reason for the stimulation of metabolism and oxygen uptake by lactate. C-14 label on LPS was detected in its fatty a cids. Most proteins that stained with silver in tricine SDS-PAGE were not s ignificantly labelled by [C-14]lactate in the glucose-containing medium. Tw o of three appreciably labelled proteins were identified by N-terminal sequ encing as GroEL and porin 1B, and one of the two less labelled proteins was similar to peroxiredoxin type proteins. There were no signs of specific in duction of these proteins by lactate and their labelling was consistent wit h fatty acids in attached lipid.