Roles of membrane structure and phase transition on the hyperosmotic stress survival of Geobacter sulfurreducens

Abstract

Geobacter sulfurreducens is a delta-proteobacterium bacteria that has biotechnological applications in bioremediation and as biofuel cells. Development of these applications requires stabilization and preservation of the bacteria in thin porous coatings on electrode surfaces and in flow-through bioreactors. During the manufacturing of these coatings the bacteria are exposed to hyperosmotic stresses due to dehydration and the presence of carbohydrates in the medium. In this study we focused on quantifying the response of G. sulfurreducens to hyperosmotic shock and slow dehydration to understand the hyperosmotic damage mechanisms and to develop the methodology to maximize the survival of the bacteria. We employed FTIR spectroscopy to determine the changes in the structure and the phase transition behavior of the cell membrane. Hyperosmotic shock resulted in greatly decreased membrane lipid order in the gel phase and a less cooperative membrane phase transition. On the other hand, slow dehydration resulted in increased membrane phase transition temperature, less cooperative membrane phase transition and a small decrease in the gel phase lipid order. Both hyperosmotic shock and slow dehydration were accompanied by a decrease in viability. However, we identified that in each case the membrane damage mechanism was different. We have also shown that the post-rehydration viability could be maximized if the lyotropic phase change of the cell membrane was eliminated during dehydration. On the other hand, lyotropic phase change during re-hydration did not affect the viability of G. sulfurreducens. This study conclusively shows that the cell membrane is the primary site of injury during hyperosmotic stress, and by detailed analysis of the membrane structure as well as its thermodynamic transitions it is indeed possible to develop methods in a rational fashion to maximize the survival of the bacteria during hyperosmotic stress.

Lateral reorganization of plasma membrane is involved in the yeast resistance to severe dehydration

“…Several studies have shown that decreasing the rate of perturbation improves cell survival after extreme dehydration. This kinetic effect was observed during dehydrations performed according to drying [22] or hyperosmotic treatments [13,23]. These results suggest that the structural evolution of the membrane depends on the kinetics of applying a strongly dehydrating medium to the cells.…”

“…This event increases the cell surface-to-volume ratio (s/v), causing plasma membrane deformations such as ruffles, wrinkles, and surface roughness [9,10]. The fluidity and structural arrangement of membrane lipids also change; for example, their mobility decreases and the transition from the liquid lamellar to gel or hexagonal phases can occur under conditions of low water content [11][12][13].…”

Gel Domains in the Plasma Membrane of Saccharomyces cerevisiae

“…a solid ordered phase. This gel lipid phase is not commonly found in living cells, especially eukaryotic cells, under physiological conditions (27)(28)(29)(30). Although the amplitude of this lifetime component was small (Fig.…”

Crystallization around solid-like nanosized docks can explain the specificity, diversity, and stability of membrane microdomains

“…Another study based on FTIR (Fourier-transform infrared spectroscopy), also using live A. laidlawii bacteria, showed that, at 30°C (i.e., the growth temperature), a significant percentage of lipids was in the gel phase, and that below 20°C, the membranes were entirely in gel phase, whilst very high viability was still preserved (98–99%; Cameron et al, 1983). A recent study also based on FTIR has shown that, in Geobacter sulfurreducens, gel phases are caused by osmotic stress or desiccation (Ragoonanan et al, 2008). Although the above studies, which are mostly based on “forced-feeding” saturated fatty acids are not entirely physiological, they do show that bacterial cells can survive and even grow containing high amounts of gel phase in their PM.…”