Functional characterization of the YiiP transporter of Shinorizobium melliloti.

RAIMUNDA D.; ELSO- BERBERIAN, GRACIELA

Córdoba

Congreso; XLII Reunión Anual de la Sociedad Argentina de Biofísica; 2013

Saociedad Argentina de Biofísica

Transition metals (copper, nickel, cobalt, manganese, etc.) are essential micronutrients. In bacteria they participate as co-factors in various fundamental enzymes required during infection to overcome initial oxidative burst imposed by the host. However, intracellular transition metal accumulation leads to toxicity and cell death. Therefore bacterial cells strive to keep null the free transition metal concentration while assuring their quota for metalloprotein synthesis in different compartments. Thus, a direct role of membrane transporters in periplasmic metalloprotein synthesis can be postulated. The legume symbiont bacterium S. meliloti, is responsible of the biological N(2) fixation occurred in the nodules of alfalfa. S. meliloti Rm1021 possesses two homologous genes codifying for Cation Difussion Facilitator (CDF) transporters of unknown transport specificity and unknown functional roles during plant infection. In this line, we first generated the deletion mutant strain of the SmYiiP (delta_smyiip) and compared its resistance to transition metal to that of the wild type (WT) strain. The growth fitness in vitro of the mutant strain was reduced only in presence of Mn2+. Supporting the role of SmYiiP as Mn2+ exporter the incubation of Äsmyiip and WT cells with sub-lethal Mn2+ concentrations resulted in 2-fold increase of the metal in the first strain. Normal levels of resistance to Mn2+ were attained by complementation with the gene under regulation of its promoter, discarding polar effects. Nodulation assays in alfalfa plants showed that the strain delta_smyiip induces less number of nodules (nod-) compared to plants infected with the WT strain. This correlates with the lower weight of plants inoculated with the mutant strain. The results indicate that SmYiiP is a Mn2+ exporter and that this metal homeostasis is relevant in S. meliloti for infection and nodulation.Acknowledgements: CONICET (G111220090100063)