Analysis of glutamine synthetase activity from Lactobacillus hilgardii LMG 7934

Abstract

Lactic acid bacteria (LAB) are Gram-positive, non-spore forming, facultative anaerobic or microaerophilic bacteria living in various nutrients-rich ecological niches and are widely used for dairy food and silage production as well as probiotics for the Human and animals. While bacteria can assimilate various nitrogen-containing compounds, the glutamine and ammonium are the most preferred nitrogen sources since they could be directly involved into the nitrogen metabolism of the cell. In bacterial cells, the glutamine can be synthetized from glutamate and ammonium ions by the metalloenzyme glutamine synthetase (GS). In contrast to other bacteria which generally have one gene encoding for the glutamine synthetase, two genes encoding proteins with 53% mutual identity and predicted glutamine synthetase activity were found in the genome of Lactobacillus hilgardii LMG 7934. One gene (glnA_2) is located in the glnRA operon with the transcriptional factor GlnR gene (glnR) similarly to GS genes from other bacteria. The second GS gene (glnA_1) is monocistronic. While the biosynthetic activity glutamine synthetases could be detected in L. hilgardii cells, which protein plays the major role is still unclear.

Targeted and Nontargeted Metabolomics of Amino Acids and Bioactive Metabolites in Probiotic-Fermented Unhopped Beers Using Liquid Chromatography High-Resolution Mass Spectrometry

“…This shows that LAB (L. paracasei Lpc-37) was the key contributor to the utilization of glutamine (via glutaminase), which has been shown to be the preferred source of nitrogen by LAB . The majority of other amino acids were not utilized by LAB due to the lack of both isocitrate dehydrogenase and nicotinamide adenine dinucleotide-dependent glutamate dehydrogenase (NAD–GDH) .…”

“…This shows that LAB (L. paracasei Lpc-37) was the key contributor to the utilization of glutamine (via glutaminase), which has been shown to be the preferred source of nitrogen by LAB. 38 The majority of other amino acids were not utilized by LAB due to the lack of both isocitrate dehydrogenase and nicotinamide adenine dinucleotide-dependent glutamate dehydrogenase (NAD−GDH). 39 Several studies have demonstrated different pathways for the increase in the glutamate content during LAB metabolism, including the action of glutamate synthase (GS−GOGAT) or glutaminase, 40,41 production from glucose via Krebs cycle intermediates in LAB, 42 and elevated NADP-GDH and glutamic acid exporter gene activity, resulting in the conversion of α-ketoglutarate to glutamate along with the excretion of glutamate into beer.…”