Analysis of glutamine synthetase activity from Lactobacillus hilgardii LMG 7934

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.