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Exogenous fatty acids are directly incorporated into bacterial membranes, heavily influencing cell envelope properties, antibiotic susceptibility, and bacterial ecology. Here, we quantify fatty acid biosynthesis metabolites and enzymes of the fatty acid synthesis pathway to determine how exogenous fatty acids inhibit fatty acid synthesis in Escherichia coli. We find that acyl‐CoA synthesized from exogenous fatty acids rapidly increases concentrations of long‐chain acyl‐acyl carrier protein (acyl‐ACP), which inhibits fatty acid synthesis initiation. Accumulation of long‐chain acyl‐ACP is caused by competition with acyl‐CoA for phospholipid synthesis enzymes. Furthermore, we find that transcriptional regulation rebalances saturated and unsaturated acyl‐ACP while maintaining overall expression levels of fatty acid synthesis enzymes. Rapid feedback inhibition of fatty acid synthesis by exogenous fatty acids thus allows E. coli to benefit from exogenous fatty acids while maintaining fatty acid synthesis capacity. We hypothesize that this indirect feedback mechanism is ubiquitous across bacterial species. [ABSTRACT FROM AUTHOR]

Yeast is a poikilothermic organism and adapts its lipid composition to the environmental temperature to maintain membrane physical properties. Studies addressing temperature‐dependent adaptation of the lipidome have described changes in the phospholipid composition at the level of sum composition (e.g. PC 32:1) and molecular composition (e.g. PC 16:0_16:1). However, there is little information at the level of positional isomers (e.g. PC 16:0/16:1 versus PC 16:1/16:0). Here, we used collision‐ and ozone‐induced dissociation (CID/OzID) mass spectrometry to investigate homeoviscous adaptation of PC, PE and PS to determine the phospholipid acyl chains at the sn‐1 and sn‐2 position. Our data establish the sn‐molecular species composition of PC, PE and PS in the lipidome of yeast cultured at different temperatures. [ABSTRACT FROM AUTHOR]

The Arctic is exposed to unprecedented warming, at least three times higher than the global average, which induces significant melting of the cryosphere. Freshwater inputs from melting glaciers will subsequently affect coastal primary production and organic matter quality. However, due to a lack of basic knowledge on the physiology of Arctic organisms, it remains difficult to understand how these future trophic changes will threaten the long‐term survival of benthic species in coastal habitats. This study aimed to gain new insights into the seasonal lipid dynamics of four dominant benthic bivalves (Astarte moerchi, Hiatella arctica, Musculus discors, and Mya truncata) collected before and after sea ice break‐up in a high‐Arctic fjord (Young Sound, NE Greenland). Total lipid content and fatty acid composition of digestive gland neutral lipids were analyzed to assess bivalve energy reserves while the fatty acid composition of gill polar lipids was determined as a biochemical indicator of interspecies variations in metabolic activity and temperature acclimation. Results showed a decrease in lipid reserves between May and August, suggesting that bivalves have only limited access to fresh organic matter until sea ice break‐up. The lack of seasonal variation in the fatty acid composition of neutral lipids, especially essential ω3 fatty acids, indicates that no fatty acid transfer from the digestive glands to the gonads occurs between May and August, and therefore, no reproductive investment takes place during this period. Large interspecies differences in gill fatty acid composition were observed, which appear to be related to differences in species life span and metabolic strategies. Such differences in gill fatty acid composition of polar lipids, which generally influence metabolic rates and energy needs, may imply that not all benthic species will be equally sensitive to future changes in primary production and organic matter quality in Arctic coastal habitats. [ABSTRACT FROM AUTHOR]

Recently published work showed that members of the PAQR protein family are activated by cell membrane rigidity and contribute to our ability to eat a wide variety of diets. Cell membranes are primarily composed of phospholipids containing dietarily obtained fatty acids, which poses a challenge to membrane properties because diets can vary greatly in their fatty acid composition and could impart opposite properties to the cellular membranes. In particular, saturated fatty acids (SFAs) can pack tightly and form rigid membranes (like butter at room temperature) while unsaturated fatty acids (UFAs) form more fluid membranes (like vegetable oils). Proteins of the PAQR protein family, characterized by the presence of seven transmembrane domains and a cytosolic N‐terminus, contribute to membrane homeostasis in bacteria, yeasts, and animals. These proteins respond to membrane rigidity by stimulating fatty acid desaturation and incorporation of UFAs into phospholipids and explain the ability of animals to thrive on diets with widely varied fat composition. Also see the video abstract here: https://youtu.be/6ckcvaDdbQg [ABSTRACT FROM AUTHOR]

All living organisms adapt their membrane lipid composition in response to changes in their environment or diet. These conserved membrane‐adaptive processes have been studied extensively. However, key concepts of membrane biology linked to regulation of lipid composition including homeoviscous adaptation maintaining stable levels of membrane fluidity, and gel‐fluid phase separation resulting in domain formation, heavily rely upon in vitro studies with model membranes or lipid extracts. Using the bacterial model organisms Escherichia coli and Bacillus subtilis, we now show that inadequate in vivo membrane fluidity interferes with essential complex cellular processes including cytokinesis, envelope expansion, chromosome replication/segregation and maintenance of membrane potential. Furthermore, we demonstrate that very low membrane fluidity is indeed capable of triggering large‐scale lipid phase separation and protein segregation in intact, protein‐crowded membranes of living cells; a process that coincides with the minimal level of fluidity capable of supporting growth. Importantly, the in vivo lipid phase separation is not associated with a breakdown of the membrane diffusion barrier function, thus explaining why the phase separation process induced by low fluidity is biologically reversible. SYNOPSIS: Key concepts of membrane biology linked to regulation of lipid composition have been predominantly assessed in vitro via model membranes or lipid extracts. Here, living bacteria are found to be surprisingly tolerant towards changes in membrane fluidity, thus questioning the dogma that careful regulation of membrane fluidity is critical for supporting general activities of membrane‐associated processes. Low membrane fluidity triggers reversible, large‐scale lipid phase separation and protein segregation in intact, protein‐crowded membranes of living bacteria.In vivo gel‐fluid phase separation determines the minimal level of fluidity capable of supporting growth, but is not associated with a breakdown of the membrane diffusion barrier function.Lipid phase separation drives segregation of membrane proteins into the fluid phase and severely limits and confines lateral diffusion of membrane proteins.Very low levels of membrane fluidity interfere with essential cellular processes including cytokinesis, envelope expansion, chromosome replication/segregation and maintenance of membrane potential. [ABSTRACT FROM AUTHOR]

Changes in temperature disrupt the fluidity of cellular membranes, which can negatively impact membrane integrity and cellular processes. Many ectotherms, including Drosophila melanogaster (Meigen), adjust the glycerophospholipid composition of their membranes to restore optimal fluidity when temperatures change, a type of trait plasticity termed homeoviscous adaptation., Existing data suggest that plasticity in the relative abundances of the glycerophospholipids phosphatidylethanolamine ( PE) and phosphatidylcholine ( PC) underlies cellular adaptation to temporal variability in the thermal environment. For example, laboratory populations of D. melanogaster evolved in the presence of temporally variable temperatures have greater developmental plasticity of the ratio of PE to PC ( PE/ PC) and greater fecundity than do populations evolved at constant temperatures., Here, we extend this work to natural populations of D. melanogaster by evaluating thermal plasticity of glycerophospholipid composition at different life stages, in genotypes isolated from Vermont, Indiana and North Carolina, USA. We also quantify the covariance between developmental and adult (reversible) plasticity, and between adult responses of the membrane to cool and warm thermal shifts., As predicted by physiological models of homeoviscous adaptation, flies from all populations decrease PE/ PC and the degree of lipid unsaturation in response to warm temperatures. Furthermore, these populations have diverged in their degree of membrane plasticity. Flies from the most variable thermal environment (Vermont, USA) decrease PE/ PC to a greater extent than do other populations when developed at a warm temperature, a pattern that matches our previous observation in laboratory-evolved populations. We also find that developmental plasticity and adult plasticity of PE/ PC covary across genotypes, but that adult responses to cool and warm thermal shifts do not., When combined with our previous observations of laboratory-evolved populations, our findings implicate developmental plasticity of PE/ PC as a mechanism of thermal adaptation in temporally variable environments. While little is known about the genetic bases of plastic responses to temperature, our observations suggest that both environmentally sensitive and environmentally specific alleles contribute to thermal adaptation of membranes and that costs of plasticity may arise when the adult environment differs from that experienced during development. [ABSTRACT FROM AUTHOR]

Phospholipids of the cell membrane have been studied from the viewpoint of how overwintering insects inhabiting temperate zones adapt to low temperature. The transition of cell membrane phospholipids from a liquid crystalline phase to a gel phase is a crucial cause of cold or freezing injuries. We determined the qualitative and quantitative changes of phospholipids in the last instar larvae of the rice stem borer in summer and winter. We found that the total amount of their phospholipids did not change significantly between summer and winter and that the sum of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) comprised about 85% of their total phospholipids. In summer, the ratio of their PE to PC was almost one, while from autumn to mid-winter it increased and reached three in February. The fatty acid compositions of PC hardly changed, and the percentage of unsaturated fatty acids did not exceed 50%. In contrast, the percentage of unsaturated fatty acids of PE in overwintering larvae increased up to 80% as ambient temperatures fell and oleic acid mainly contributed to the high percentage of unsaturation. In the present study, the relationship between the quantitative and qualitative changes of phospholipids and adaptation of the rice stem borer to cold winter climate are discussed. [ABSTRACT FROM AUTHOR]