CHANGE IN LIPID COMPOSITION OF Bradyrhizobium CELL ENVELOPED REVEAL A RAPID RESPONSE TO WATER DEFICIT INVOLVING LYSOPHOSPHATIDYLETHANOLAMINE SYNTHESIS IN OUTER MEMBRANE

A. B. CESARI; N.S. PAULUCCI; BIASUTTI. M.A; DARDANELLI M.S.

Buenos Aires

Congreso; Reunion SAIB 2017; 2017

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

The membrane lipid bilayer is one of the primary cellular targets affected by variations in medium osmolarity, which cause changes in fluidity that may exert negative effects. We evaluate the behavior of the membrane of Bradyrhizobium sp. SEMIA6144 during adaptation to water deficit induced by polyethylene glycol (PEG). B. sp. SEMIA6144 was exposed to PEG shock (1 h, 5 h and 24 h). We used AFM to investigate if PEG caused changes in cell morphology. Fractions of internal and external cell membrane were obtained and lipids were extracted. The fatty acids (FA) were analyzed by GC. Identification of phospholipids (PL) was performed using TLC. For its quantification, [1-14C] sodium acetate was added to culture. Membrane and multilamellar vesicles prepared from lipids cell fluidity was determined by measuring fluorescence polarization of DPH. To determine the PLA activity during PEG shock, outer membrane was used as enzyme source. One-way ANOVA was used to analyze the results.Although cell viability was reduced and surface morphology was affected in PEG presence, cells tolerated these conditions. A dehydrating effect was observed on the morphology of the cell surface, as well as a fluidizing effect on the membrane was observed 10 min after PEG shock; however, the bacteria were able to restore optimal membrane fluidity. The total lipids analysis indicated that a rapid response (1 h) was mediated by an increase in lysophosphatidylethanolamine (205 %) at the expense of phosphatidylethanolamine (76 %) and an increase in saturated fatty acids (17 %). When the cells were exposed to PEG shock for 5 h and 24 h, the amount of lysophosphatidylethanolamine decreased (75 %) while phosphatidylethanolamine increased (287 %). The detailed analysis of the phospholipid composition of each membrane indicated that 1 h of shock caused an increase of LPE (165 %) in the outer membrane at the expense of PC and PE, through an increase in PLA activity (70 %). The amount of LPE did not remain constant during PEG shock, but after 24 h the outer membrane was composed of large amounts of PC and less amount of LPE similar to the control. The inner membrane composition was also modified after 1 h of shock, observing an increase of PC (9 %) at the expense of PE (30 %), the proportions of these phospholipids were then modified to reach 24 h of shock values similar to the control. MVLs prepared with the lipids of cells exposed to 1 h shock presented higher rigidity compared to the control (from 0.14 to 0.21), indicating that changes in the composition of phospholipids after 1 h of shock allow restoring fluidity after the PEG effect and would allow cells to maintain surface morphology.