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Abstract:
Membranes of six spiroplasma strains belonging to different Spiroplasma species and subgroups were isolated by a combination of osmotic lysis and sonication in the presence of EDTA to block endogenous phospholipase activity. Analysis of membrane lipids showed that in addition to free and esterified cholesterol the spiroplasmas incorporated exogenous phospholipids from the growth medium. Sphingomyelin was preferentially incorporated from phosphatidylcholine-sphingomyelin vesicles or from the serum used to supplement the growth medium. Palmitate was incorporated better than oleate into membrane lipids synthesized by the organisms during growth. The major phospholipid synthesized by the spiroplasmas was phosphatidylglycerol. The positional distribution of the fatty acids in phosphatidylglycerol of Spiroplasma floricola resembled that found in Mycoplasma species, in which the saturated fatty acids prefer position 2 in the glycerol backbone and not position 1 as found in Acholeplasma species and elsewhere in nature. Electron paramagnetic resonance analysis of spin-labeled fatty acids incorporated into S. floricola membranes exhibited homogeneous single-component spectra without immobilized regions. The S. floricola membranes were more rigid than those of Acholeplasma laidlawii and less rigid than those of Mycoplasma gallisepticum.
Insights
Spiroplasma membranes incorporate external phospholipids, with sphingomyelin preferred. Fatty acid composition and membrane fluidity studies reveal unique characteristics in Spiroplasma floricola, differing from other related bacteria.
Area of Science:
- Microbiology
- Lipid Biochemistry
- Membrane Biophysics
Background:
- Spiroplasmas are helical, wall-less bacteria with unique membrane compositions.
- Understanding spiroplasma membrane lipid incorporation and structure is crucial for their biology and potential interactions.
Purpose of the Study:
- To investigate the lipid composition and membrane properties of various spiroplasma strains.
- To determine the incorporation of exogenous phospholipids and fatty acids into spiroplasma membranes.
- To analyze the membrane fluidity and fatty acid distribution in Spiroplasma floricola.
Main Methods:
- Isolation of spiroplasma membranes using osmotic lysis and sonication with EDTA.
- Analysis of membrane lipid composition, including cholesterol and phospholipids.
- Incorporation studies using radiolabeled fatty acids and exogenous phospholipid sources.
- Electron paramagnetic resonance (EPR) spectroscopy for membrane fluidity assessment.
Main Results:
- Spiroplasmas incorporated exogenous phospholipids, particularly sphingomyelin, from growth media.
- Palmitate was preferentially incorporated over oleate into synthesized membrane lipids.
- Phosphatidylglycerol was the major synthesized phospholipid, with unique fatty acid positional distribution in S. floricola.
- S. floricola membranes exhibited homogeneous fluidity and intermediate rigidity compared to Mycoplasma and Acholeplasma species.
Conclusions:
- Spiroplasmas actively modulate their membrane lipid composition by incorporating exogenous lipids.
- The specific fatty acid composition and positional distribution in S. floricola contribute to its distinct membrane biophysical properties.
- Spiroplasma membrane structure and fluidity are influenced by both endogenous synthesis and exogenous lipid uptake.