Free Lipids Research Articles

Alternative lipid synthesis in response to phosphate limitation promotes antibiotic tolerance in Gram-negative ESKAPE pathogens.

Gram-negative ESKAPE pathogens, including A cinetobacter baumannii , are responsible for a dramatic increase in the morbidity and mortality of patients in healthcare settings over the past two decades. Infections are difficult to treat due to antibiotic resistance and tolerance; however, broadly conserved mechanisms that promote antibiotic treatment failure have not been extensively studied. Herein, we identify an alternative lipid biosynthesis pathway that is induced in phosphate starvation that enables Gram-negative ESKAPE pathogens, including A. baumannii , Klebsiella pneumoniae , and Enterobacter cloacae to build lipid bilayers in the absence of glycerophospholipids, which are the canonical bilayers lipid. Replacement of the anionic phosphate in the lipid headgroup with zwitterionic ornithine and lysine promote survival against colistin, a last resort antimicrobial used against Gram-negative infections. These studies suggest that ESKAPE pathogens can remodel their bilayers with phosphate free lipids to overcome colistin treatment and that aminolipid biosynthesis could be targeted to improve antimicrobial treatment.

Metabolic changes associated with PFAS exposure in firefighters: A pilot study

This pilot study investigated the association between occupational exposure to per- and polyfluoroalkyl substances (PFASs) and metabolic profiles among two groups of aviation firefighters (n = 37), with an average of 6 and 31 years of working experience (here referred as junior and senior firefighters) at airports across Australia, with samples collected in 2013. PFAS levels in serum were determined in a previous study to be >17 times higher in the senior firefighter group, reflecting the difference in their occupational exposure to fluorosurfactants among the groups. The aim was to examine metabolic patterns across a broad range of PFAS exposure by comparing metabolic differences and their associations with PFAS levels. In this cross-sectional study, the length of firefighting experience and PFAS levels in serum were both further associated with changes in several classes of metabolites, including free fatty acids, bile acids, amino acids, lipids and metabolites related to gut microbial metabolism. The metabolites associated with the length of firefighting experience showed similarities with the metabolites associated with PFAS levels. A non-monotonic response to PFAS concentrations, particularly in saturated fatty acids, was also observed. In the junior firefighter group, the PFAS concentrations were positively associated with saturated fatty acids, i.e., the saturated fatty acid levels increased with increased PFAS levels. In the senior firefighter group, the trend was opposite, with saturated fatty acids decreasing with increasing levels of PFAS. Accounting for potential confounding factors such as BMI and age could not explain the results. While the study population was small, our results plausibly indicate that PFAS exposure can lead to a metabolic compensation strategy that is disrupted at high, long-term exposures. Our study also suggests that serum metabolites serve as better effect-based markers of the impact of exposure than the traditional clinical measurements alone, such as total triglycerides or total cholesterol.

Multi-omics analyses reveal mechanism for high resistant starch formation in an indica rice SSIIIa mutant

Soluble starch synthase IIIa (SSIIIa) is a key enzyme involved in amylopectin biosynthesis in rice, and deficiency of SSIIIa results in high content of resistant starch, which is benefit to human health. However, little is known about metabolic differences and carbon re-allocation in the seeds of the indica rice ss3a mutant. We found that SSIIIa deficiency impaired the storage of starch, but increased the soluble sugars, free amino acids and lipids. By multi-omic analyses, we found inactivation of SSIIIa triggered carbon repartitioning by downregulating sucrose synthase, grain incomplete filling 1, fructokinase and hexokinase (HK), and promoted the accumulation of soluble sugars. Meanwhile, the downregulation of HK and upregulation of plastidic phosphoglucomutase reduced the carbon flow through glycolysis and promoted glycogenesis. The downregulation of OsbZIP58 and the deleterious effect on ribosome formation might result in the reduction of storage protein synthesis and increased free amino acids content in ss3a. The higher levels of amylose and lipids could form more amylose-lipid complexes (starch phospholipids), resulting in a higher resistant starch content. Taken together, our study unraveled a functional cross talk between starch, protein and lipids in rice endosperm during seed development of ss3a, providing new insights for formation of high resistant starch in rice.

Lipid composition and algaenan structure of Botryococcus braunii race L revealed by sequential stepwise pyrolysis

The dried biomass and isolated algaenan of Botryococcus braunii (B. braunii) race L were analyzed using sequential stepwise pyrolysis at 50 °C intervals from 310 °C to 610 °C to investigate algaenan structure. Initial pyrolysis at 310 °C primarily produced free lipids mirroring the extracted products. At 360 °C, distinct isomers of lycopadiene and C40 isoprenoid ketone (i-C40 ketone), derived from the isolated algaenan, indicated the onset of biopolymer degradation. Intermediate pyrolysis (410–510 °C) yielded various isomers of lycopadiene and i-C40 ketone, along with minor short-chain isoprenoids. The consistent formation of C40 isoprenoid isomers up to 460 °C, followed by a decrease at 510 °C, suggested their presence in the algaenan. At 560 °C, high-temperature pyrolysis showed a bimodal distribution of C8 – C32n-alkane/n-alkene doublets, with a reduction in isoprenoids. This shift from isoprenoids to alkyl groups during pyrolysis reflects the diverse thermal stabilities of algaenan moieties. The consistent distributions of lycopadienes and i-C40 ketones during intermediate pyrolysis stages suggested they both present as side chain. The sustaining 9:1 ratio of lycopadienes to i-C40 ketones during intermediate pyrolysis suggests these components are linked to the main chain via ester groups, with a constant ratio of 9:1 in side chains. Aliphatic polyaldehyde, more resistant to be fractured, with a long linear chain serves as the main chain, capable of fragmentation to produce n-alkanes/n-alkenes. Functional group and alkyl moiety identifications were confirmed by FT-IR and NMR spectra. The results demonstrate that sequential stepwise pyrolysis provides detailed chromatographic profiles and transformation data, proving invaluable for understanding algaenan structures in modern microalgae and offers enhanced insights into functional groups and algaenan composition.

Rapid sulfurization obscures carotenoid distributions in modern euxinic environments

Anoxygenic phototrophic bacteria (green and purple sulfur bacteria) thrive in anoxic environments where light penetrates a sulfide-containing (euxinic) water column. Genomic data and photosynthetic bacterial carotenoid pigments should provide complementary information on the spatio-temporal dynamics of anoxygenic phototrophs in modern euxinic environments. In turn, these contemporary depositional settings often serve as analogues for ancient counterparts. However, in some modern environments, DNA-informed patterns of phototrophic sulfur bacteria occurrence do not match distributions of their carotenoid inventories. One possible explanation for these seemingly incompatible observations is that the rapid sulfurization of carotenoids and incorporation into macromolecules via multiple carbon–sulfur bonds prevents or confounds their detection by conventional means. Here, to evaluate this conundrum, we revisit some representative contemporary euxinic environments where anoxygenic phototrophic bacteria have mostly been detected based on genomic analyses. Although free intact carotenoids are sporadically detected in surface sediments, their distributions do not reveal a complete picture. Exogenously sourced fossil carotenoids (e.g., paleorenieratane) is an additional complication. Carotenoid inventories obtained by desulfurization with Raney nickel, on the other hand, stand in stark contrast to those present as free lipids. In particular, sulfur-linked carotenoids present in euxinic lake sediments provide a more complete picture of compositions of anoxygenic sulfur bacterial communities and account for discrepancies reported in previous studies. We observe a closer alignment between genomic data and patterns of sulfurized carotenoids and, importantly, our results highlight how sulfurization serves as a pathway for the rapid modification of highly functionalised lipids and their sequestration into the macromolecular component of sediment extracts.

Preferential extraction of degraded organic matter and mineral protection of aromatic structures based on molecular marker analysis

The humic fractions were sequentially extracted from soils to study the heterogenous properties of soil organic matter (SOM). However, the bulk characteristics of these samples, such as elemental compositions and functional groups, could not fully reveal their diverse compositions. We sequentially extracted humic acids (HAs) from a sediment, and analyzed its molecular markers (benzene polycarboxylic acids (BPCAs), lignin-derived phenols, free lipids and bound lipids) to illustrate the diverse compositions of SOM. Our results suggested that the investigated HAs were derived from terrestrial C3 plants as reflected by the range of their δ13C values (−27.08 ‰ in HA1 to −27.85 ‰ in HA6), more specifically, non-woody tissue of angiosperm and belowground part as suggested by lignin and lipid markers. With the increasing times of extraction, the relative abundances of lignin-derived phenols, free lipids, and bound lipids increased, while those of the condensed aromatics (as indicated by BPCAs) decreased. We also observed that with the increasing times of extraction, the carbon preference index (CPI) increased, the ratios of acids to aldehydes of vanilly units (Ad/Al)v and δ13C of HAs decreased, suggesting that the extensively degraded organic compositions were selectively extracted because of their favored dissolution. Our results emphasize that the complete extraction of organic compositions is essential to ensure reliable analysis on SOM properties and turnover. The distribution of individual BPCAs suggested that the highly condensed aromatics were preferentially extracted. These might be attributed to the less condensed aromatics were more strongly associated with mineral particles, which is important for the protection of aromatic carbons in the environment.

Internal lipids and their fatty acids composition in a sheep wool fiber under biodestruction with fleece microorganisms

Microbiological destruction of fibers is a common damage to sheep’s wool. Considering the defining role of internal lipids in the formation of wool fibers surface the aim of the work was to study the structure and lipid composition of the normal and damaged wool. The research was carried out on ewes of the Askanian fine-wool breed. The content of microorganisms was estimated after sowing on dense nutrient environments. Wool fibers surface was studied by scanning electron microscopy, the content of internal lipids by thin layer chromatography after preliminary alkaline hydrolysis of the fiber, and fatty acids composition by gas-liquid chromatography. Biodestructed wool was shown to contain almost three times more bacteria, as well as higher levels of actinomycetes and mushrooms compared to intact wool. The violation of the cuticular layer was detected as the result of the fleece microflora activity. In a defective wool the content of the free internal lipids and non-esterified fatty acids was increased while the content of protein-bound lipids and esterified cholesterol as well as of ceramides was decreased as compared to normal wool. The level of 18-methyleicosanoic acid in the protein-bound lipids of damaged wool was decreased, indicating the destruction of the thioester bonds by which structural lipids are covalently linked to proteins through 18-methyleicosanoic acid. Keywords: 18-methyleicosanoic acid, biodestruction, fatty acids, internal lipids, microorganisms, protein-bound lipids, sheep’s wool fiber

Role of trace minerals in bull reproductive physiology and semen quality

Testicular dysfunction is often associated with an imbalance in antioxidant/oxidant homeostasis, leading to negative effects of oxidative stress on germ cell proliferation, steroidogenesis, and sperm function. Trace minerals (TM) are involved in basic homeostatic and enzymatic processes like free radical detoxification, cellular respiration, carbohydrates, lipids, nucleic acids, synthesis and metabolism of proteins, and stabilization of membranes and DNA. Dietary source of TM is necessary to support these processes. Supplementing cattle with TM is nowadays a common practice to help support growth, reproduction, and immunity. This review provides information on roles of TM in bulls testicular and sperm functions, and effects of TM mineral supplementation on bull reproductive parameters.

Data-dependent and -independent acquisition lipidomics analysis reveals the tissue-dependent effect of metformin on lipid metabolism.

Despite the well-recognized health benefits, the mechanisms and site of action of metformin remains elusive. Metformin-induced global lipidomic changes in plasma of animal models and human subjects have been reported. However, there is a lack of systemic evaluation of metformin-induced lipidomic changes in different tissues. Metformin uptake requires active transporters such as organic cation transporters (OCTs), and hence, it is anticipated that metformin actions are tissue-dependent. In this study, we aim to characterize metformin effects in non-diabetic male mice with a special focus on lipidomics analysis. The findings from this study will help us to better understand the cell-autonomous (direct actions in target cells) or non-cell-autonomous (indirect actions in target cells) mechanisms of metformin and provide insights into the development of more potent yet safe drugs targeting a particular organ instead of systemic metabolism for metabolic regulations without major side effects. To characterize metformin-induced lipidomic alterations in different tissues of non-diabetic male mice and further identify lipids affected by metformin through cell-autonomous or systemic mechanisms based on the correlation between lipid alterations in tissues and the corresponding in-tissue metformin concentrations. A dual extraction method involving 80% methanol followed by MTBE (methyl tert-butyl ether) extraction enables the analysis of free fatty acids, polar metabolites, and lipids. Extracts from tissues and plasma of male mice treated with or without metformin in drinking water for 12days were analyzed using HILIC chromatography coupled to Q Exactive Plus mass spectrometer or reversed-phase liquid chromatography coupled to MS/MS scan workflow (hybrid mode) on LC-Orbitrap Exploris 480 mass spectrometer using biologically relevant lipids-containing inclusion list for data-independent acquisition (DIA), named as BRI-DIA workflow followed by data-dependent acquisition (DDA), to maximum the coverage of lipids and minimize the negative effect of stochasticity of precursor selection on experimental consistency and reproducibility. Lipidomics analysis of 6 mouse tissues and plasma allowed a systemic evaluation of lipidomic changes induced by metformin in different tissues. We observed that (1) the degrees of lipidomic changes induced by metformin treatment overly correlated with tissue concentrations of metformin; (2) the impact on lysophosphatidylcholine (lysoPC) and cardiolipins was positively correlated with tissue concentrations of metformin, while neutral lipids such as triglycerides did not correlate with the corresponding tissue metformin concentrations; (3) increase of intestinal tricarboxylic acid (TCA) cycle intermediates after metformin treatment. The data collected in this study from non-diabetic mice with 12-day metformin treatment suggest that the overall metabolic effect of metformin is positively correlated with tissue concentrations and the effect on individual lipid subclass is via both cell-autonomous mechanisms (cardiolipins and lysoPC) and non-cell-autonomous mechanisms (triglycerides).

Conversion of Natural Soil to Paddy Promotes Soil Organic Matter Degradation in Small-Particle Fractions: δ13C and Lipid Biomarker Evidence

The stabilization mechanism of soil organic matter (SOM) has received considerable attention. It is widely accepted that mineral sorption/protection is important for SOM stabilization. However, it remains unclear which organic carbon component is beneficial for mineral protection. We collected soil samples from a paddy field (TP) to compare with natural soil (NS). To illustrate the behavior of different SOM pools and their protection by particles, we separated the soils into different particle-size fractions and then removed the active minerals using an acid mixture (1 M HCl/10% HF). The different carbon pools were analyzed using stable carbon isotopes and lipid biomarkers. Our study showed that acid treatment evidently increased the extractability of free lipids, usually over 60%, which confirmed the predominant role of minerals in SOM protection. For NS, the δ13C values increased with decreasing soil particle sizes and soil depths, indicating that 13C-enriched SOM was selectively preserved. However, this trend disappeared after cultivation, which was mainly attributed to the combined effects of the input of 13C-depleted fresh SOM and decomposition of the preserved 13C-enriched SOM. Meanwhile, based on the degradation parameters of the overall lipid biomarkers, SOM showed higher degradation states in clay and silt fractions than in the sand fraction before cultivation. It is possible that the small particle-size fractions could selectively absorb highly degraded SOM. The clay-associated SOM showed a low degradation state, but its carbon content was low after cultivation. We propose that the previously protected SOM was degraded after cultivation and was replaced by relatively fresh SOM, which should be carefully monitored during SOM management.

No-tillage farming for two decades increases plant- and microbial-biomolecules in the topsoil rather than soil profile in temperate agroecosystem

The impact of conservation tillage on the composition, stability, and origin (plant- or microbial-derived) of soil organic matter (SOM) within soil profiles remains unclear. In this study, we characterized the impact of different tillage practices on the molecular composition and status of SOM. These tillage practices included conventional tillage (CT) and conservation tillage such as rotary tillage (RT) and no-tillage (NT). Our investigation spanned a two-decade period within a temperate agroecosystem. Soil samples were collected down to a 30 cm profile, and four biomarkers, namely free lipids, lignin phenols, neutral sugars, and amino sugars, in conjunction with 13C NMR techniques were used to quantify SOM characteristics. The results revealed that conservation tillage (especially NT) led to improvements in both the quantity and composition of SOM when compared to CT in the topsoil (0–5 cm), but not in deeper layers (5–30 cm). More precisely, the NT topsoil, as opposed to CT, exhibited enhancements in two categories: (1) an increase in plant-derived compounds such as long-chain lipids (≥ C20) and steroids by 51%, lignin phenols by 106%, and plant-derived neutral sugars by 61%, and (2) an augmentation in microbial-derived biomolecules, which includes microbial-derived neutral sugars by 49% and microbial necromass carbon (MNC) by 94%. Furthermore, NT, relative to CT, increased the contribution of MNC to soil organic carbon in topsoil (up to 64%, mainly fungal necromass). This highlighted the predominant role of microbial-derived biomolecules in SOM formation. Similarly, RT treatments enhanced the microbial-derived neutral sugars by 18%, plant-derived neutral sugars by 14%, and lignin phenols by 43% relative to CT in the topsoil. Collectively, our study suggests that NT practice could be considered an effective strategy for enhancing SOM accumulation and persistence by fostering the accrual of plant- and microbial-derived biomolecules in the topsoil.

The effects of corona discharge from a cold plasma source on the physicochemical properties and shelf-life of milk

Milk is a nutrient-rich food and a risk source of foodborne pathogens, yet traditional thermal processing/pasteurization can affect its nutritional value. However, recently, consumer demand for healthy, fresh, and safe “green process” foods has increased, so emerging non-thermal food cold plasma (CP) technology has largely addressed consumer demands for safe and healthy foods by effectively eliminating pathogens from milk. In this study, we examined CP treatment duration (0, 1, 5, and 10 min) and membrane filtration (MF) effects on whole and skim milk with respect to milk characteristics, microbial growth, and xanthine oxidase activity over a 0– 15-day storage period. This study revealed that the shelf life of whole milk and MF skimmed milk with CP10 min amounted to 15 days and that the TPC was <6 log colony forming units (CFU/mL), while titratable acidity was <0.18% in compliance with regulatory standards, with insignificant color changes. Additionally, pH and lipid oxidation values in CP and MF groups were positively correlated with storage time (p < 0.05). Thus, CP treatment released free lipids into milk, with minor oxidative reactions. Critically, no significant effects were observed in terms of nutritional value and xanthine oxidase activity. Hence, we provide valuable processing insights for dairy manufacturers and show that CP10 min treatment positively impacted total plate count (TPC) and thermo-resistant bacteria. Our goal is to reduce the heat load on milk without compromising nutritional quality while maintaining food safety.

Carboxylic acid accumulation and secretion contribute to the alkali-stress tolerance of halophyte Leymus chinensis.

Leymus chinensis is a dominant halophytic grass in alkalized grasslands of Northeast China. To explore the alkali-tolerance mechanism of L. chinensis, we applied a widely targeted metabolomic approach to analyze metabolic responses of its root exudates, root tissues and leaves under alkali-stress conditions. L. chinensis extensively secreted organic acids, phenolic acids, free fatty acids and other substances having -COOH or phosphate groups when grown under alkali-stress conditions. The buffering capacity of these secreted substances promoted pH regulation in the rhizosphere during responses to alkali stress. L. chinensis leaves exhibited enhanced accumulations of free fatty acids, lipids, amino acids, organic acids, phenolic acids and alkaloids, which play important roles in maintaining cell membrane stability, regulating osmotic pressure and providing substrates for the alkali-stress responses of roots. The accumulations of numerous flavonoids, saccharides and alcohols were extensively enhanced in the roots of L. chinensis, but rarely enhanced in the leaves, under alkali-stress conditions. Enhanced accumulations of flavonoids, saccharides and alcohols increased the removal of reactive oxygen species and alleviated oxygen damage caused by alkali stress. In this study, we revealed the metabolic response mechanisms of L. chinensis under alkali-stress conditions, emphasizing important roles for the accumulation and secretion of organic acids, amino acids, fatty acids and other substances in alkali tolerance.

Different responses of lipids and lignin phenols to nitrogen addition in meadow grassland soil

PurposeNitrogen (N) enrichment can affect the composition and stability of soil organic carbon (SOC) pools by altering vegetation and soil properties. However, the response of plant-derived carbon components in soil to different N addition levels is unclear. We investigated the changes and potential driving processes of plant-derived carbon components (especially lignins and lipids) in meadow grassland soils under long-term N addition in eastern Inner Mongolia, China.Materials and methodsBiomarker technology was utilised to analyse changes in plant-derived carbon components (C>20 free lipids, bound lipids, and lignin phenols) in soil under different N addition levels, including changes in soil chemical properties, enzyme activity, plant biomass, and diversity under N addition, as well as the specific pathways involved.Results and discussionWe found that high levels of N addition significantly reduced the concentration of soil lignin phenols whereas increased the accumulation of lipids (free and bound lipids). Compared with changes in plant biomass and diversity, soil chemical properties and enzyme activity play a more significant role in regulating the accumulation and degradation of plant-derived carbon. Structural equation modelling (SEM) showed that decreases in lignin phenol concentration were related to specific biochemical decomposition processes (increased polyphenol oxidase activity and decreased C/N). The increase in lipids associated with the protective effects of minerals mediated by pH.ConclusionsIn general, plant-derived carbon components showed inconsistent responses to N addition, lignin phenol concentration decreased and lipid concentration increased, which was mainly related to the change of soil biochemical properties. Plant-derived carbon components only showed significant changes under high N addition levels. Furthermore, our research indicates that SOC sequestration and functioning are highly dependent on soil biochemical properties, which weakens the influence of changes in plant carbon input on soil carbon storage.

Lipid Monolayer on Cell Surface Protein Templates Functional Extracellular Lipid Assembly.

When the ancestors of men moved from aquatic habitats to the drylands, their evolutionary strategy to restrict water loss is to seal the skin surface with lipids. It is unknown how these rigid ceramide-dominated lipids with densely packed chains squeeze through narrow extracellular spaces and how they assemble into their complex multilamellar architecture. Here it is shown that the human corneocyte lipid envelope, a monolayer of ultralong covalently bound lipids on the cell surface protein, templates the functional barrier assembly by partly fluidizing and rearranging the free extracellular lipids in its vicinity during the sculpting of a functional skin lipid barrier. The lipid envelope also maintains the fluidity of the extracellular lipids during mechanical stress. This local lipid fluidization does not compromise the permeability barrier. The results provide new testable hypotheses about epidermal homeostasis and the pathophysiology underlying diseases with impaired lipid binding to corneocytes, such as congenital ichthyosis. In a broader sense, this lipoprotein-mediated fluidization of rigid (sphingo)lipid patches may also be relevant to lipid rafts and cellular signaling events and inspire new functional materials.

Critical micellar concentration determination of pure phospholipids and lipid-raft and their mixtures with cholesterol.

Phospholipids in biological membranes establish a chemical equilibrium between free phospholipids in the aqueous phase (CMC) and self-assembled phospholipids in vesicles, keeping the CMC constant. The CMC is different for each phospholipid, depends on the amount of cholesterol, and, according to the lipid-chaperone hypothesis, controls the interaction between free phospholipids and amyloidogenic proteins (such as amylin, amyloid-β, and α-synuclein, all of which are, respectively, associated with a different proteinopathy), which governs the formation of a toxic complex between free lipids and proteins that leads to membrane destruction. Here, we provide quantitative measurements of CMCs and bilayer stability of pure phospholipids, lipid rafts, and their mixture with cholesterol by fluorescence methods (using pyrene as a probe) and light scattering techniques (resonance Rayleigh scattering and fixed-angle light scattering) performed on LUVs, as well as AFM to measure LUV dimensions. Also, we test the lipid-chaperone hypothesis on human IAPP interacting with different mixture of POPC cholesterol. Stated the importance of CMC in membrane stability and protein aggregation processes, these results could be a starting point for the development of a quantitative kinetic model for the lipid chaperone hypothesis.

Immune Control of Gut Microbiota Prevents Obesity and the Effect of Antibiotic on Microbial Population

Gut microbiota have gained increasing recognition for their vital role in human health, particularly in their interactions with the immune system, including their involvement in obesity prevention through the production of IgA antibodies. These microbiotas are instrumental in lipid breakdown, utilizing lipases to break down phospholipids and triglycerides into polar head groups and free lipids. The loss of these beneficial microbes has been suggested as a potential cause for disruptions in various homeostatic mechanisms within our bodies. Factors contributing to this loss may encompass antibiotic usage, heightened sanitation practices, and low-fiber diets. Obesity, more prevalent in developed nations, is linked to the diminished regulatory immune responses associated with specific beneficial microbial species. This review article aims to provide a comprehensive exploration of how gut microbiota influence lipid metabolism, considering T-cell-mediated regulation, and examines the effects of antibiotics on the gut microbial population.

Organic sulfur from source to sink in low‐sulfate Lake Superior

AbstractOrganic sulfur plays a crucial role in the biogeochemistry of aquatic sediments, especially in low sulfate (&lt; 500 μM) environments like freshwater lakes and the Earth's early oceans. To better understand organic sulfur cycling in these systems, we followed organic sulfur in the sulfate‐poor (&lt; 40 μM) iron‐rich (30–80 μM) sediments of Lake Superior from source to sink. We identified microbial populations with shotgun metagenomic sequencing and characterized geochemical species in porewater and solid phases. In anoxic sediments, we found an active sulfur cycle fueled primarily by oxidized organic sulfur. Sediment incubations indicated a microbial capacity to hydrolyze sulfonates, sulfate esters, and sulfonic acids to sulfate. Gene abundances for dissimilatory sulfate reduction (dsrAB) increased with depth and coincided with sulfide maxima. Despite these indicators of sulfide formation, sulfide concentrations remain low (&lt; 40 nM) due to both pyritization and organic matter sulfurization. Immediately below the oxycline, pyrite accounted for 13% of total sedimentary sulfur. Both free and intact lipids in this same interval accumulated disulfides, indicating rapid sulfurization even at low concentrations of sulfide. Our investigation revealed a new model of sulfur cycling in a low‐sulfate environment that likely extends to other modern lakes and possibly the ancient ocean, with organic sulfur both fueling sulfate reduction and consuming the resultant sulfide.

Lipidomics Reveals the Effects of Detergents on Skin Surface Lipids in Young Adults

Background: Detergent is a chemical product commonly used in people’s daily life. Contact with detergent solutions can damage the human skin barrier and cause skin diseases. Skin surface lipids (SSLs) play a decisive role in skin barrier function. This study aimed to observe the changes of SSLs in young adults after exposure to detergent solutions to explore the underlying mechanism of skin barrier function damage. Methods: A self-controlled study on youth adults was conducted in Zhengzhou, China, in November 2020. The study lasted for a total of 1 week, and skin barrier function was assessed by trans-epidermal water loss (TEWL) values. The changes of SSLs before and after exposure to the detergent with subjects were measured using ultra-performance liquid chromatography quadrupole time of flight mass spectrometry. Results: The skin barrier function of subjects’ hands was impaired after exposure to detergent (TEWL value increased, p < 0.001). A total of 520 SSLs were detected, divided into 6 main categories. The average relative abundance of these 6 major lipids decreased after exposure. Sphingolipids (mainly ceramides), free fatty acids (mainly long-chain fatty acids), cholesterol lipids, and glycerophospholipids are the most severely damaged lipids. Conclusion: Detergent solutions can damage the skin barrier function and SSLs of young hands; interventions targeting SSLs to eliminate detergent damage to human skin may be of value.

Generation of key aroma compounds in fat and lean portions of non-smoked bacon induced via lipid pyrolysis reaction

This study explored the evolution of key aroma compounds and their lipid precursors in the lean (LN) and fat (FT) portions of non-smoked bacon during hot air drying. The results showed that the LN portion contained most of the aroma compounds in the bacon (>88%). The volatile content of the FT portion increased as the drying time increased, whereas that of the LN portion reached a maximum within 24 h and then decreased. Based on the highest volatile contents (4889.48 ± 202.06 µg/kg) and sensory scores, 24 h was considered the optimal drying time. For key aroma compounds, hexanal and 2,3-octanedione were derived from free fatty acids and polar lipids. Notably, 1-octen-3-ol was generated only from polar lipids in the FT and LN portions. The 2-undecenal and (E, E)-2,4-decadienal were produced by the oxidation of neutral lipids in the FT portion. Dihydro-5-pentyl-2(3H)-furanone was derived from polar lipids in the LN portion. Altogether, these findings provide theoretical insights into improving the aroma of bacon by optimizing raw material selection and processing methods.