. Isolation and characterization of an S. meliloti acid sensitive Tn5 mutant.

CASTELLANOS L, DRAGHI WO, PISTORIO M, GIUSTI MA, LOZANO M, TORRES TEJERIZO G, LAGARES A Y DEL PAPA MF.

Mar del Plata, Buenos Aires

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular- SAIB; 2007

SAIB

Soils acidity may significantly reduce the productivity of some leguminous plants because the acid sensitivity of their prokaryotic symbiont Sinorhizobium meliloti, in particular, is sensitive to low pH, growing either very slowly or not at all, at pH 5.5 or below. The identification of genetic determinants of tolerance to acidity in S. meliloti has been considered as an important point. However, the molecular mechanisms of acid tolerance has shown a complex view that at present needs much more basic information to make progress in the understanding of genetic systems that bacteria use to protect themselves from the medium acidity and allows cells to survive or grow under acidic conditions. To advance on the genetics of acid tolerance in S. meliloti, we generated a collection of Tn5B20 mutants and we screen the collection for acid sensitive phenotypes. One mutant out of 2,000 clones failed to grow on minimal medium at pH 5.5 but not at neutral pH. Genetic analysis showed that mutant namely LPU630 carries a transposon insertion within an ORF with sequence similarity to a putative ATP-binding component of an ABC transporter with an unusual central domain located immediately upstream of a putative transcriptional regulator protein. The acid-sensitive mutant was exposed to various stress conditions, including oxidative, heat, salt as well as the presence of bivalent metals. Additionally LPU630 was tested in its ability to nodulate alfalfa in order to analyze the relevance of the affected locus in symbiosis at both acidic and neutral pH