A DYNAMICALLY REGULATED TRANSFORMATION OF A BACTERIAL BILAYER-MEMBRANE TO A CROSS-LINKED 2-DIMENSIONAL SHEET DURING ADAPTATION TO UNFAVORABLE ENVIRONMENTAL PRESSURES

To maintain an optimum dynamic range, membranes of living systems must have the ability to regulate their translational and vibrational moti on in the face of environmental changes that might offset them. This i s done through structural modifications of the lipids. Sarcina ventric uli was used as a case study to explore membrane structural reorganiza tions which allow some organisms to adapt to extreme environmental cha nges. It is capable of a variety of unusual and dramatic chemical proc esses including lipid alkyl chain tail-to-tail and lipid head-to-head coupling. There is also interlipid headgroup transfer or shuffling. Th e tail-to-tail coupling activity is capable of joining foreign (exogen ously added) hydrocarbon chains to the native chains. The adaptative p rocesses occur dynamically and instantaneously and render this organis m tolerant to low and high pH, moderately high temperatures, the prese nce of organic solvents, and a wide spectrum of antibiotics at concent rations as high as 200 mu g/mL. Chemical analyses indicate that the me mbrane of Sarcina ventriculi exists in a dynamic equilibrium somewhere between a bilayer and cross-linked bipolar monolayer. Based on the de gree of cross-linking of both the alkyl chains and the headgroups, und er more extreme conditions, the membranes should approach highly cross -linked, two-dimensional molecular sheets. These structural reorganiza tions parallel the same strategies used by organic chemists in their e ffort to synthesize stabilized monolayers and vesicles. Catalytic acti vities present in the membranes of this and similar organisms hold muc h potential for use in stabilizing supramolecular arrays and nano stru ctures.