Nadya Rakovitsky, Michal Bar Oz, Karin Goldberg, Simon Gibbons, Oren Zimhony, Daniel Barkan
Nitrogen metabolism plays a central role in the physiology of microorganisms, and Glutamine Synthetase (GS) genes are present in virtually all bacteria. In , four GS genes are present, but only is essential, whereas was shown to be non-essential for as well as growth and pathogenesis, and is postulated to be involved in D-glutamine and iso-glutamine synthesis. Whilst investigating the activity of an antimicrobial compound in , we found a spontaneous temperature-sensitive mutant in (I133F), and used it to investigate the role of in . We deleted the native and replaced it with a mutated allele. This re-created the temperature sensitivity-as after 3-4 seemingly normal division cycles, became essential for growth. This essentiality could not be salvaged by neither L, D- nor iso-glutamine, suggesting an additional role of in over its role in . We also found that overexpression of the global Nitrogen regulator enabled bypassing the essentiality of , allowing the creation of a complete deletion mutant. The discrepancy between the importance of in Mtb and stresses the caution in which results in one are extrapolated to the other.
