RESUMEN
The fatty acid composition of the membrane of the conditional auxotroph fabB2 can be altered by allowing the cells to grow at non-permissive temperature (37°C) in the presence of a cis-unsaturated fatty acid. The phage 9NA, a virulent phage of Salmonella typhimurium, can not multiply in fabB2. Synthesis and maturation of the phage DNA are differentially affected by variation in the fatty acid composition of the cell membrane. The replicating DNA associates with the membrane complex, the site of DNA synthesis. The association is comparatively weak in oleic, claidic, palmitoleic, palmitelaidic and linolelaidic acid enriched cells. When the cells are grown in the presence of palmitoleic acid, a large pool of concatemeric phage DNA accumulates in the cytoplasm within 10 min of infection. The conversion of concatemeric DNA to monomeric one i.e., mature phage length DNA, is inhibited in such cells. The presence of concatemeric DNA can be visualized by electron microscope. Such a situation is not observed when the cells are grown in media supplemented with other types of unsaturated fatty acids. The mechanism by which the host cell membrane lipid controls phage development is yet to be worked out.
RESUMEN
The transport of α-methyl-D-glucoside and two aminoacids, L-phenylalanine and L-leucine by a temperature sensitive fatty acid requiring mutant of Salmonella typhimurium was studied under conditions of supplementation with cis or trans-unsaturated fatty acids. The results of such experiments definitely establish a relationship between the fatty acids composition of the membrane and the transport property of the cells. Cells grown in the presence of trans–unsaturated fatty acids cannot transport so efficiently as compared to the cis-unsaturated fatty acid-grown cells except linolelaidic acid, a trans-transunsaturated fatty acid. Protein: phospholipid ratio of the membrane also varies significantly under such conditions. The affinity of L-phenylalanine transport carrier for the substrate changes remarkably in cells grown in the presence of different cis or trans-unsaturated fatty acids and indicate the possible role of membrane lipids in membrane assembly as well as regulation of the activity of L-phenylalanine transport system.
RESUMEN
The effects of changes in fatty acid composition of the cell membrane on different biological functions of Salmonella typhimurium have been studied with the help of a temperature sensitive fatty acid auxotroph which cannot synthesise unsaturated fatty acids at high temperature. On being shifted to nonpermissive temperature the cells continue growing for another one and half to two generations. The rates of protein and DNA syntheses run parallel to the growth rate but the rate of RNA synthesis is reduced. Further, there is a gradual reduction in the rate of transport of exogenous uridine and thymidine into the soluble pool. The transport process can be restored by supplementing the growth medium with cis-unsaturated fatty acids but not trans-unsaturated ones although the growth of the cells is resumed by supplementation with either cis or trans-unsaturated fatty acids. However, supplementation with trans, trans-unsaturated fatty acids leads to only partial recovery of the transport process. The rate of oxygen uptake is also affected in cells grown in the presence of the trans-unsaturated fatty acids, elaidic acid and palmitelaidic acid. Analysis of cells grown under different fatty acid supplementation indicate that fatty acid composition of the cell membrane, especially the ratio of unsaturated to saturated fatty acids varies with temperature shift and supplementation of the growth media with fatty acids.