In Escherichia coli, intracellular ppGpp content in response to nutritional deficiency is controlled by the balanced action of RelA (synthetase I) and the dual-function (synthetase/hydrolase) SpoT. Generally ascribed to the detrimental effects of high (p)ppGpp levels, the co-existence of spoT null (DspoT) with relA proficient alleles has been considered synthetically lethal. However, in a recent work we have reported the construction of DspoT mutants in a relA+background accumulating nearly wild type (WT) ppGpp levels when cells were cultured on a rich complex medium. Sequencing of the genomes from various selected DspoT clones identified in all of them suppressor mutations located in relA. In two of them, additional inactivating mutations were found in glnB and yejB, two genes that have not been characterized as genetically linked to relA. To know whether mutations resulting in the total abolishment of the glnB and yejB genes could compensate the detrimental effects of spoT deletions in E. coli in this work we obtained multiple independent DspoTDglnB and DspoTDyejB clones. Importantly, these clones expressed WT RelA, displayed a nearly WT growth phenotype, and accumulated nearly WT ppGpp and glycogen contents when cultured in a rich complex medium. None of these mutants, however, could grow on glucose minimal medium. The overall data (a) show that different mutations other than in relA can be selected in E. coli cells compensating the detrimental effects of spoT deletion, and (b) point to the occurrence in E. coli of mechanism(s), other than SpoT-mediated ppGpp hydrolytic breakdown, that prevent ppGpp over-accumulation. To our knowledge this is the first report describing the production of spoT null mutants of E. coli expressing WT RelA.

Trabajo presentado en el XXXVII Congreso de la Sociedad Española de Bioquímica y Biología Molecular (SEBBM), celbrado en Granada del 9 al 12 de septiembre de 2014.

Peer Reviewed