Influence of altered plasma membrane fatty acid composition on cesium transport characteristics and toxicity in Saccharomyces cerevisiae

Impact of effective microorganisms on the transfer of radioactive cesium into lettuce and barley biomass

Soil microorganisms play an important role in determining the physical and chemical properties of soils. Soil microorganisms have both direct and indirect effects on the physical and chemical states of radionuclides and their availability for uptake by plant roots. Controlling the soil microorganisms to immobilize radionuclides is a promising strategy to reduce the content of radionuclides in the food chain. In this study, we evaluated the impact of effective microorganisms (EM) comprising lactic-acid bacteria, photosynthetic bacteria, and yeast on the transfer of 137Cs into the aboveground biomass of barley and lettuce. The application of EM or fermented organic fertilizer (bokashi) alone to sod-podzolic sandy-loam soil significantly reduced the aggregated transfer factor of 137Cs in barley by 37% and 44%, respectively. The combination of EM with bokashi or potassium fertilizer produced the largest reductions in 137Cs transfer into barley biomass (50% and 63%, respectively). EM had a stronger effect on 137Cs transfer into barley compared to lettuce. Laboratory experiments suggested that the effect of microorganisms on 137Cs uptake can be attributed to a reduction in the proportion of bioavailable physicochemical forms of 137Cs in the soils treated with EM and bokashi. This study, to the best of our knowledge, is the first to report the mechanism by which microbial fertilizers reduce the transfer of 137Cs into plants.

Stimulation of strontium accumulation in linoleate-enriched Saccharomyces cerevisiae is a result of reduced Sr2+ efflux

The influence of modified plasma membrane fatty acid composition on cellular strontium accumulation in Saccharomyces cerevisiae was investigated. Growth of S. cerevisiae in the presence of 1 mM linoleate (18:2) (which results in 18:2 incorporation to approximately 70% of total cellular and plasma membrane fatty acids, with no effect on growth rate) yielded cells that accumulated Sr2+ intracellularly at approximately twice the rate of S. cerevisiae grown without a fatty acid supplement. This effect was evident over a wide range of external Sr2+ concentrations (25 microM to 5 mM) and increased with the extent of cellular 18:2 incorporation. Stimulation of Sr2+ accumulation was not evident following enrichment of S. cerevisiae with either palmitoleate (16:1), linolenate (18:3) (n-3 and n-6 isomers), or eicosadienoate (20:2) (n-6 and n-9 isomers). Competition experiments revealed that Ca2+- and Mg2+-induced inhibition of Sr2+ accumulation did not differ between unsupplemented and 18:2-supplemented cells. Treatment with trifluoperazine (TFP) (which can act as a calmodulin antagonist and Ca2+-ATPase inhibitor), at a low concentration that precluded nonspecific K+ efflux, increased intracellular Sr2+ accumulation by approximately 3.6- and 1.4-fold in unsupplemented and 18:2-supplemented cells, respectively. Thus, TFP abolished the enhanced Sr2+ accumulation ability of 18:2-supplemented cells. Moreover, the rate of Sr2+ release from Sr2+-loaded fatty acid-unsupplemented cells was found to be at least twice as great as that from Sr2+-loaded 18:2-enriched cells. The influence of enrichment with other fatty acids on Sr2+ efflux was variable. The results reveal an enhanced Sr2+ accumulation ability of S. cerevisiae following 18:2-enrichment, which is attributed to diminished Sr2+ efflux activity in these cells.

Enrichment with a polyunsaturated fatty acid enhances the survival of Saccharomyces cerevisiae in the presence of tributyltin

The toxicity of inorganic metal species towards Saccharomyces cerevisiae has been shown to be markedly dependent on cellular fatty acid composition. In this investigation, the influence of fatty acid supplementation on the toxicity of the lipophilic organometal, tributyltin was investigated. Growth of S. cerevisiae was increasingly inhibited when the tributyltin concentration was increased from 0 to 10 microM. However, the inhibitory effect was partly alleviated by supplementation of the medium with 1 mM linoleate (18:2), a treatment that leads to large-scale incorporation of this polyunsaturated fatty acid (to > 60% of total fatty acids) in yeast membrane lipids. Cells that were previously enriched with 18:2 also showed reduced loss of vitality compared to cells grown in the absence of a fatty acid supplement, when exposed to tributyltin. For example, addition of tributyltin to a concentration of 0.1 microM was associated with an approximate 10% reduction in the H+ efflux activity of 18:2-enriched cells, but a 70% reduction in that of fatty acid-unsupplemented cells. Despite the increased tributyltin resistance of 18:2-enriched S. cerevisiae, the level of cell-associated tributyltin was found to be approximately two-fold higher in these organisms than in fatty acid-unsupplemented cells. These results demonstrate an increased resistance of 18:2-enriched membranes to the direct toxic action(s) of tributyltin. This is in contrast to the previously reported effect of 18:2 enrichment on sensitivity of S. cerevisiae to inorganic metal cations.