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1. Thermal behaviour of lipids in short-lived seeds of Australian rainforest species

   https://doi.org/10.1093/aob/mcaf181  

   Sommerville, Karen D; Hill, Lisa; Offord, Catherine A; Walters, Christina (August 2025, Annals of Botany)

   Abstract Background and AimsRecent studies on desiccation-tolerant Australian rainforest seeds demonstrated that some were short-lived in storage. We sought to understand structural changes of storage lipids that might occur during storage at −20 °C that could contribute to a short lifespan. MethodsWe used differential scanning calorimetry (DSC) to examine exothermic and endothermic transitions during freezing and thawing in dry seed samples of 23 species. Seed samples and extracted triacylglycerols (TAGs) were cooled to −150 °C and rewarmed to 50 °C at 10 °C min−1; slower and faster rates of cooling/warming were used for a subset of species to examine lipid crystallization and melting kinetics. Thermograms were analysed for temperature and enthalpy of observed peaks, and these were compared with expected values to detect anomalies. Extracted lipids were further analysed using gas chromatography to characterize fatty acid composition. The thermal profiles of six species were used to design experiments comparing the impact of storage at −20 °C with storage at temperatures outside the range of thermal transitions. Key ResultsThermal activity was detected in 22 species within the narrow temperature range of −30 and −10 °C; activity at broader temperature ranges was also detected depending on species, cooling protocol and fatty acid composition. A profound interaction between DSC parameters and time at low temperature, as well as fatty acid composition, suggested that TAG crystallization rates contribute to low-temperature sensitivity. We confirmed that damage from TAG crystallization could be avoided by storing seeds at temperatures above TAG crystallization and melting events; storage at cryogenic temperatures improved survival over storage at −20 °C but requires further optimization to maintain pre-storage germination potential. ConclusionsWe conclude that the crystallization and melting of TAGs during storage may negatively impact seed longevity. Seed thermal profiles and rate of TAG crystallization may serve as predictive tools for sensitivity to storage at −20 °C. 

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2. Influence of very-long-chain polyunsaturated fatty acids on membrane structure and dynamics

   https://doi.org/j.bpj.2022.06.015  

   Victoria Cheng, Rameshu Rallabandi (June 2022, Biophysical journal)

   The unique attributes of very-long-chain polyunsaturated fatty acids (VLC-PUFAs), their long carbon chains (n > 24) and high degree of unsaturation, impart unique chemical and physical properties to this class of fatty acids. The changes imparted by VLC-PUFA 32:6 n-3 on lipid packing and the compression moduli of model membranes were evaluated from π-A isotherms of VLC-PUFA in 1,2-distearoyl-sn-3-glycero-phosphocholine (DSPC) lipid monolayers. To compare the attractive or repulsive forces between VLC-PUFA and DSPC lipid monolayers, the measured mean molecular areas (MMAs) were compared with the calculated MMAs of an ideal mixture of VLC-PUFA and DSPC. The presence of 0.1, 1, and 10 mol % VLC-PUFA shifted the π-A isotherm to higher MMAs of the lipids comprising the membrane and the observed positive deviations from ideal behavior of the mixed VLC-PUFA:DSPC monolayers correspond to repulsive forces between VLC-PUFAs and DSPC. The MMA of the VLC-PUFA component was estimated using the measured MMAs of DSPC of 47.1 ± 0.7 Å2/molecule, to be 15,000, 1100, and 91 Å2/molecule at 0.1, 1, and 10 mol % VLC-PUFA:DSPC mixtures, respectively. The large MMAs of VLC-PUFA suggest that the docosahexaenoic acid tail reinserts into the membrane and adopts a nonlinear structure in the membrane, which is most pronounced at 0.1 mol % VLC-PUFA. The presence of 0.1 mol % VLC-PUFA:DSPC also significantly increased the compression modulus of the membrane by 28 mN/m compared with a pure DSPC membrane. The influence of VLC-PUFA on lipid “flip-flop” was investigated by sum-frequency vibrational spectroscopy. The incorporation of 0.1 mol % VLC-PUFA increased the DSPC flip-flop rate fourfold. The fact that VLC-PUFA promotes lipid translocation is noteworthy as retinal membranes require a high influx of retinoids which may be facilitated by lipid flip-flop. 

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3. Nitrogen Deprivation in Fremyella diplosiphon Augments Lipid Production without Affecting Growth

   https://doi.org/10.3390/en13215769  

   Tabatabai, B. (November 2020, Energies)

   Metabolic products such as lipids and proteins produced in cyanobacteria represent an excellent source of biomass and do not compete with agricultural land use unlike soybean and corn. Given their potential use as novel materials for biodiesel production, we aimed to explore the eect of cultivation period and nitrogen concentration on the growth rate and lipid content of Fremyella diplosiphon, a model cyanobacterium. In this study, F. diplosiphon grown in BG11/HEPES medium supplemented with 1.5 g L􀀀1 sodium nitrate (NaNO3) for 7, 10, 15, and 20 days were compared to the untreated control in media amended with 0.25, 0.5, and 1.0 g L􀀀1 NaNO3. Cultures were inoculated in liquid media and grown under continuous fluorescent light in an orbital incubator shaker, and extracted lipids subjected to gravimetric analysis and gas chromatography-mass spectroscopy to determine the best culture conditions for lipid production. Our results demonstrated that a reduction in nitrogen concentration had no significant effect on the growth rate across all cultivation periods; however, the accumulation of total lipid content was significantly influenced by nitrogen concentration. A maximum lipid production (40%) with no reduction in growth was observed in 10-day old cultures in a BG11/HEPES medium supplemented with 1.0 g L􀀀1 NaNO3. Fatty acid methyl ester composition of transesterified lipids demonstrated high amounts of methyl palmitate (50–70%) followed by methyl octadecenoate (17–30%) in the accumulated lipids at all treatments. Trace quantities of methyl dodecanoate, methyl hexadecanoate, methyl octadecanoate, and methyl octadecadienoate (1–8%) were also observed in all tested samples, indicating that nitrogen deprivation in culture media increases lipid production without affecting growth. 

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4. Exogenous Fatty Acids Remodel Staphylococcus aureus Lipid Composition through Fatty Acid Kinase

   https://doi.org/10.1128/JB.00128-20  

   DeMars, Zachary; Singh, Vineet K.; Bose, Jeffrey L. (June 2020, Journal of Bacteriology)

   Stock, Ann M. (Ed.)

   ABSTRACT Staphylococcus aureus can utilize exogenous fatty acids for phospholipid synthesis. The fatty acid kinase FakA is essential for this utilization by phosphorylating exogenous fatty acids for incorporation into lipids. How FakA impacts the lipid membrane composition is unknown. In this study, we used mass spectrometry to determine the membrane lipid composition and properties of S. aureus in the absence of fakA . We found the fakA mutant to have increased abundance of lipids containing longer acyl chains. Since S. aureus does not synthesize unsaturated fatty acids, we utilized oleic acid (18:1) to track exogenous fatty acid incorporation into lipids. We observed a concentration-dependent incorporation of exogenous fatty acids into the membrane that required FakA. We also tested how FakA and exogenous fatty acids impact membrane-related physiology and identified changes in membrane potential, cellular respiration, and membrane fluidity. To mimic the host environment, we characterized the lipid composition of wild-type and fakA mutant bacteria grown in mouse skin homogenate. We show that wild-type S. aureus can incorporate exogenous unsaturated fatty acids from host tissue, highlighting the importance of FakA in the presence of host skin tissue. In conclusion, FakA is important for maintaining the composition and properties of the phospholipid membrane in the presence of exogenous fatty acids, impacting overall cell physiology. IMPORTANCE Environmental fatty acids can be harvested to supplement endogenous fatty acid synthesis to produce membranes and circumvent fatty acid biosynthesis inhibitors. However, how the inability to use these fatty acids impacts lipids is unclear. Our results reveal lipid composition changes in response to fatty acid addition and when S. aureus is unable to activate fatty acids through FakA. We identify concentration-dependent utilization of oleic acid that, when combined with previous work, provides evidence that fatty acids can serve as a signal to S. aureus . Furthermore, using mouse skin homogenates as a surrogate for in vivo conditions, we showed that S. aureus can incorporate host fatty acids. This study highlights how exogenous fatty acids impact bacterial membrane composition and function. 

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5. Dietary polyunsaturated fatty acids effect on cecal microbiome profile of maturing broiler chicken

   https://doi.org/10.1016/j.psj.2025.105167  

   Jadhav, Vidya V; Fasina, Yewande O; Harrison, Scott H (July 2025, Poultry Science)

   Diet has been reported to impact the diversity and function of gut microbiota. Our study investigated the effect of dietary fat types on cecal microbial composition and predicted function in broiler chickens at days 41 and 55 of age. Four dietary fat sources were evaluated and compared to a control dietary fat source of poultry fat. These were for two diets rich in omega-3 polyunsaturated fatty acids (PUFA) - fish oil and flaxseed oil, a diet rich in long-chain saturated fatty acid (SFA) - lard, and a diet rich in medium-chain saturated fatty acid - coconut oil. At day 55, broiler chickens fed a PUFA-rich diet maintained cecal microbial diversity while broiler chickens fed a SFA-rich diet exhibited a significant reduction in diversity compared to the control diet-fed chickens. More specifically, PUFA intake was associated with elevated levels of microbial carbohydrate metabolizing capability, contributing to efficient energy utilization and enhanced short-chain fatty acid production capability. In contrast, SFA-rich diets lowered abundances for key microbial families like Lachnospiraceae and Bifidobacteriaceae hampering nutrient digestibility and pathogen resistance. The microbiomes for chickens fed lard and coconut oil diets showed a significant reduction in SCFA-producing microbial taxa abundance while the microbial functional profile indicated reduced carbohydrate metabolism. Our findings underscore the contrasting effects of SFA-rich fat and PUFA-rich fat on the cecal microbiota of broiler chickens. The results suggest that incorporating PUFArich dietary fats into broiler feed may offer potential benefits by modulating the cecal gut microbiota toward outcomes associated with elevated carbohydrate utilization without hampering nutrient digestibility and pathogen resistance. 

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