Reorganization of Azospirillum brasilense cell membrane is mediated by lipid composition adjustment to maintain optimal fluidity during water deficit.

AIMS: We study the Azospirillum brasilense tolerance to water deficit and the dynamics of adaptive process at the level of the membrane. METHODS AND RESULTS: Azospirillum brasilense was exposed to polyethylene glycol (PEG) growth and PEG shock. Tolerance, phospholipids and fatty acid (FA) composition and membrane fluidity were determined. Azospirillum brasilense was able to grow in the presence of PEG; however, its viability was reduced. Cells grown with PEG showed membrane fluidity similar to those grown without, the lipid composition was modified, increasing phosphatidylcholine and decreasing phosphatidylethanolamine amounts. The unsaturation FAs degree was reduced. The dynamics of the adaptive response revealed a decrease in fluidity 20 min after the addition of PEG, indicating that the PEG has a fluidizing effect on the hydrophobic region of the cell membrane. Fluidity returned to initial values after 60 min of PEG exposure. CONCLUSION: Azospirillum brasilense is able to perceive osmotic changes by changing the membrane fluidity. This effect is offset by changes in the composition of membrane phospholipid and FA, contributing to the homeostasis of membrane fluidity under water deficit. SIGNIFICANCE AND IMPACT OF THE STUDY: This knowledge can be used to develop new Azospirillum brasilense formulations showing an adapted membrane to water deficit.

Monounsaturated fatty acid aerobic synthesis in Bradyrhizobium TAL1000 peanut-nodulating is affected by temperature.

AIMS: The aim of this work was to clarify the mechanism of monounsaturated fatty acid (MUFA) synthesis in Bradyrhizobium TAL1000 and the effect of high temperature on this process. METHODS AND RESULTS: Bradyrhizobium TAL1000 was exposed to a high growth temperature and heat shock, and fatty acid composition and synthesis were tested. To determine the presence of a possible desaturase, a gene was identify and overexpressed in Escherichia coli. The desaturase expression was detected by RT-PCR and Western blotting. In B. TAL1000, an aerobic mechanism for MUFA synthesis was detected. Desaturation was decreased by high growth temperature and by heat shock. Two hours of exposure to 37°C were required for the change in MUFA levels. A potential ∆9 desaturase gene was identified and successfully expressed in E. coli. A high growth temperature and not heat shock reduced transcript and protein desaturase levels in rhizobial strain. CONCLUSIONS: In B. TAL1000, the anaerobic MUFA biosynthetic pathway is supplemented by an aerobic mechanism mediated by desaturase and is down-regulated by temperature to maintain membrane fluidity under stressful conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: This knowledge will be useful for developing strategies to improve a sustainable practice of this bacterium under stress and to enhance the bioprocess for the inoculants' manufacture.