Truncated hemoglobin from Azospirillum brasilense protects against salt stress?.

MELINA AMENTA; FLORENCIA SALCEDO; LORENZO LAMATTINA; CECILIA CREUS

Rosario

Congreso; IX Congresode Microbiología General de la Sociedad Argentina de Microbiología General; 2013

SAMIGE

Bacteria living in the rhizosphere have to cope with a variety of stressful conditions including high Na+ content as those found in alkaline soils. Azospirillum brasilense is a beneficial plant growth promoting rhizobacteria, highly used in agronomic practices due to its beneficial effects on crops. We previously showed that a gene coding for putative truncated hemoglobin in A. brasilense Sp245 (AztrHb) is related to O2 depletion and high nitric oxide (NO) levels produced when bacteria arrive to late exponential growing phase. The aims of this work were: (i) to assess the role of the AztrHb in protecting from salt stress using a heterologous expression system in Escherichia coli, and (ii) to study the expression in A. brasilense growing under high NaCl conditions. The ability to tolerate high NaCl of E. coli cultures expressing AztrHb was analyzed in LB-Agar plates with 2.5 or 5 % NaCl. AztrHb-transformed cells were more tolerant to 2.5 and 5% NaCl compared to those transformed with the empty vector. A. brasilense Sp245 susceptibility to 100, 200, or 300 mM NaCl were tested in liquid Nfb-NO3- media, or RC media in plate. Both assays indicated that A. brasilense Sp245 growth were 40 % lower in 300 mM NaCl than in control or less saline conditions. To explore AztrHb gene induction in response to salt, A.brasilense Sp245 were grown in liquid Nfb-NO3- media to exponential phase and treated with 100, 200, or 350 mM NaCl for 1 h. After that, RNA samples were taken. Semi quantitative RT-PCR analysis indicated that AztrHb expression was induced by NaCl treatment and this induction was higher in 350 mM NaCl treated cells. The high AztrHb expression in A. brasilense growing in NaCl together with the protection against NaCl stress observed in AztrHb-transformed E. coli, let us to hypothesize a role of AztrHb to preserve the homeostasis of A. brasilense in soils with high salt concentrations.