Changes in the lipid composition of Bradyrhizobium cell envelope reveal a rapid response to water deficit involving lysophosphatidylethanolamine synthesis from phosphatidylethanolamine in outer membrane

Abstract

We evaluate the behavior of the membrane of Bradyrhizobium sp. SEMIA6144 during adaptation to polyethylene glycol (PEG). A dehydrating effect 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. Shock for 1 h caused an increase of lysophosphatidylethanolamine in the outer membrane at the expense of phosphatidylcholine and phosphatidylethanolamine (PE), through an increase in phospholipase activity. The amount of lysophosphatidylethanolamine did not remain constant during PEG shock, but after 24 h the outer membrane was composed of large amounts of phosphatidylcholine and less amount of lysophosphatidylethanolamine similar to the control. The inner membrane composition was also modified after 1 h of shock, observing an increase of phosphatidylcholine at the expense of PE, the proportions of these phospholipids were then modified to reach 24 h of shock values similar to the control. Vesicles prepared with the lipids of cells exposed to 1 h shock presented higher rigidity compared to the control, indicating that changes in the composition of phospholipids after 1 h of shock restoring fluidity after the PEG effect and would allow cells to maintain surface morphology.

Membrane Rigidity and Phosphatidic Acid (PtdOH) Signal: Two Important Events in Acinetobacter guillouiae SFC 500‐1A Exposed to Chromium(VI) and Phenol

“…Model systems such as MLV are useful to predict how the lipid components of cell membranes will behave (Cesari et al, ). The fluorescent polarization assay using MLV synthesized from lipids of cells exposed to Cr(VI) and Cr(VI) + phenol for 16 h seems to confirm the rigidity effect produced on the membrane mainly by changes in PL, such as the decrease in PtdEtn and the increase in Ptd2Gro.…”

“…Firstly, PLA 2 activity was determined after 1 h of exposure to both contaminants, while PL composition was determined after 16 h, so lysoPtdEtn may not be constant over time, as was also observed by Cesari et al (2018) in Bradyrhizobium SEMIA6144 cells exposed to polyethylene glycol (PEG). Another possibility is that lysoPtdEtn was diluted due to the use of a total membrane fraction to determine the PL profile, because it is well known that this enzyme is the main component in the outer membrane, as was described for Yersinia pseudotuberculosis after shifting the growth temperature from 8 to 37 C or after exposure of the cells to heat shock, and in Bradyrhizobium SEMIA6144 cells after PEG shock (Cesari et al, 2018;Davydova et al, 2016). Moreover, Gcrard (1979) reported that lysoPtdEtn accumulation is often accompanied by an increase in Ptd2Gro, as was found in A. guillouiae SFC 500-1A cells.…”

“…Fluorescence polarization measurements were performed using a FluoroMax®‐4 (HORIBA Scientific, Japan) Horiba spectrofluorometer with a polarizer, following the parameters described by Cesari et al ().…”

“…The fluidity and order parameters of biological membranes may be modulated by alterations in the polar head groups or acyl chains of phospholipids (PL) (Cesari et al, 2018;Rowlett et al, 2017;Smułek et al, 2015). These changes may be accomplished by varying the total PL amount and/or their class distribution, regulating the fatty acid (FA) unsaturation degree or changing the type of FA incorporated into PL by synthesis or turnover, via phospholipase activity (Cesari et al, 2016;Markowicz et al, 2010;Smułek et al, 2015).…”

“…In fact, phospholipases are an ubiquitous and heterogeneous group of enzymes that play a critical role in multiple physiological processes and regulate many critical cellular events including membrane homeostasis, nutrient acquisition, signal transduction, and interaction with host cells (Dennis, ). As intermediaries in PL metabolism and turnover, lysophospholipids such as lysophosphatidylethanolamine (lysoPtdEtn) are produced via phospholipase A (PLA)‐mediated hydrolysis of the acyl group of a PL to lysophospholipids and FA (Cesari et al, ; Song and Rhee, ). In microorganisms like bacteria, PLA 2 is activated under diverse stress conditions (Belosludtsev et al, ; Istivan and Coloe, ; Zheng et al, ).…”