Dynamic response of the Sinorhizobium meliloti membrane during cyclic temperature changes

PAULUCCI NS; DARDANELLI MS; CESARI AB; PERILLO MA; REGUERA YB

Cuidad Autónoma de Buenos Aires

Congreso; Reunión Conjunta de las Sociedades de BioCiencias; 2017

SAIC, SAIB, SAI, SAA, SAB, SAFE, SAFIS, SAH, SAP

Sinorhizobium meliloti establish simbiosis with Medicago sativa. The production and storage of inoculants involve suboptimal conditions. Adaptation and survival in many harmful environmental conditions implies changes in the dynamics and plasticity of the bacterial membrane but may affect the symbiotic capacity. In this work, we evaluate how cyclic changes in temperature affect the viability and phospholipids (PL) composition of Sinorhizobium meliloti and how these modifications affect the adhesion to alfalfa roots. Culture was grown at 28°C until late exponential phase (control), then it was exposed to: (a) 3 h at 10°C, (b) 3 h at 40°C and (c) 3 h at 10°C. At each stage, an aliquot was taken to assess: the viability (CFU / ml), PL composition, the phase transition temperature (Tm) of the membrane lipid extract (by differential scanning calorimetry) and bacterial adhesion to alfalfa roots (CFU/ml). The viability decreases after stage-(a), increases after stage-(b) and remain constant after stage-(c). The main PLs were phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and cardiolipin (CL). Exposure (a) resulted in a decrease in PC (34%) and PG (51%) while PE and CL increased (140% and 238%). The same cells submitted to (b) exhibited an inverse response (increase of PC and PG and decrease of PE and CL) and after stage-(c), the PL composition was slightly modified. The vesicles prepared with lipids extracted from control and from cells at the different stages of the T cycle differed in their Tm (14.8ºC; 9.8ºC;14.2ºC;11.8ºC). At the end of stage-(a) a reduction in bacterial adhesion (80%) with respect to the control (100%) was observed. After stage-(b) the adhesion increased 150%, remaining constant after returning to 3h at 10°C (stage-(c)). The successive thermal changes on the same bacterial population modifies the PL composition of the cellular envelope and affect its capacity of early interaction with alfalfa.