# Protection Elicited by Glutamine Auxotroph of Yersinia pestis

## TL;DR

A modified version of Yersinia pestis, the plague-causing bacterium, that cannot make glutamine is harmless and protects animals from plague, suggesting a new vaccine strategy.

## Contribution

A new live attenuated vaccine candidate for plague was developed by targeting the glnALG operon in Yersinia pestis.

## Key findings

- Deleting the glnALG operon in Y. pestis completely attenuated its virulence in mice and guinea pigs.
- The ΔglnALG strain provided 100% protection against a lethal wild-type Y. pestis challenge.
- The glnALG operon is a promising molecular target for antivirulence therapy and vaccine development.

## Abstract

Background/Objectives: Yersinia pestis is an important zoonotic pathogen responsible for the rare but deadly disease of people with bubonic, septic, or pneumonic forms of plague. The emergence of multidrug-resistant Y. pestis strains has attracted more and more researchers’ attention to the search for molecular targets for antivirulence therapy, including anti-nutritional-virulence therapy. The glnALG operon plays a crucial role in regulating the nitrogen content within a bacterial cell. This operon codes for three genes: the structural gene glnA and the two regulatory genes glnL and glnG. In this study, we tested the effect of the deletion of glnA and glnALG on the pathogenic properties of Y. pestis. Methods: To assess the contribution of nitrogen metabolism to Y. pestis virulence, knockout mutants ΔglnA and ΔglnALG were constructed. The former was unable to synthesize glutamine, while the latter was not only defective in glutamine synthesis but also lacked the two-component sensor–transcriptional activator pair GlnL and GlnG, which could partially compensate for the decrease in intracellular glutamine concentrations by transporting it from the host or by catabolic reactions. For vaccine studies, immunized mice and guinea pigs were injected s.c. with 200 LD100 of the wild-type Y. pestis strain. Results: A single knockout mutation in the glnA gene did not affect the virulence of Y. pestis in mice and guinea pigs. Knockout of the entire glnALG gene cluster was required for attenuation in these animals. The ΔglnALG strain of Y. pestis did not cause death in mice (LD50 > 105 CFU) and guinea pigs (LD50 > 107 CFU) when administered subcutaneously and provided 100% protection of animals when subsequently infected with 200 LD100 of the Y. pestis virulent wild-type strain 231. Conclusions: Y. pestis, defective in both the glutamine synthetase GlnA and the two-component sensor–transcriptional activator pair GlnL-GlnG, completely lost virulence and provided potent protective immunity to mice and guinea pigs subsequently challenged with a wild-type Y. pestis strain, demonstrating the potential use of the glnALG operon as a new molecular target for developing a safe and efficient live plague vaccine.