Osmotic response in Lactobacillus casei ATCC 393: biochemical and biophysical characteristics of membrane.

The biochemical and biophysical properties of the membrane and some general characteristics of the response of Lactobacillus casei ATCC 393 (reclassified Lactobacillus zeae) to hyperosmotic conditions were studied. Under hypertonic conditions, the hydrophobicity and the bile salt sensitivity of the cultures were increased. The glycolipid AcylH3DG is only present in membranes of NaCl containing medium, whereas, H4DG undergoes a significant increment and H2DG a significant decrease. The fluidity of both the purified membranes and the total lipid vesicles, as determined with the fluorescent probe DPH, did not change in conditions of high salinity. This was coincident with changes in the fatty acid (FA) composition where an increase in the saturated/unsaturated FA ratio was compensated by a rise in the fluidifying 11,12-methyleneoctadecanoic FA (cyc 19:0). Under osmotic stress conditions, Laurdan and acridine orange in total lipid vesicles showed increased lateral lipid packing and proton permeability, respectively.