Glutaminase activity and glutamine-dependent acid resistance in enteric bacteria

Many neutralophilic bacteria have developed several strategies to overcome the life-threatening effect of the exposure to a mild-to-harsh acid stress [1]. Among these strategies, the amino acid-dependent systems were shown to be quite widespread amongst gram-positive and –negative bacteria, and their activities overlap so to cover a rather large pH range, from 6 to <2 [1]. Recently an acid resistance (AR) system relying on the amino acid glutamine, the most readily available amino acid in the free form, was shown to be operative in E. coli, L. reuteri and some Brucella species [2-4]. This system imports L-glutamine via the antiporter GadC, also a structural component of the glutamate-dependent AR system, and exports via GadC either glutamate or GABA, depending on whether only the deamination of glutamine into glutamate occurs, or glutamate is also decarboxylated to yield GABA by the enzyme GadB. We have undertaken a bioinformatic analysis to study the distribution of the glutaminase-dependent AR system in enteric bacteria and developed two assays. The first assay was developed for a rapid screening of the glutaminase activity and the growth conditions that support its maximum expression. The second assay was developed to measure the amount of glutamate/GABA exported. Our results indicate that the glutamine-dependent AR is likely to be of prominent importance in enteric bacteria. [1] Lund et al. (2014) FEMS MIcrobiol Rev 38:1091-125. [2] Lu et al. (2013) Cell Res 23:635–644. [3] Teixeira et al. (2014) Food Microbiol 42:172-180. [4] Freddi et al. (2017) Front Microbiol 8:2236.