Monounsaturated C18 Research Articles

Fatty acid elongation by ELOVL6 hampers remyelination by promoting inflammatory foam cell formation during demyelination

A hallmark of multiple sclerosis (MS) is the formation of multiple focal demyelinating lesions within the central nervous system (CNS). These lesions mainly consist of phagocytes that play a key role in lesion progression and remyelination, and therefore represent a promising therapeutic target in MS. We recently showed that unsaturated fatty acids produced by stearoyl-CoA desaturase-1 induce inflammatory foam cell formation during demyelination. These fatty acids are elongated by the "elongation of very long chain fatty acids" proteins (ELOVLs), generating a series of functionally distinct lipids. Here, we show that the expression and activity of ELOVLs are altered in myelin-induced foam cells. Especially ELOVL6, an enzyme responsible for converting saturated and monounsaturated C16 fatty acids into C18 species, was found to be up-regulated in myelin phagocytosing phagocytes in vitro and in MS lesions. Depletion of Elovl6 induced a repair-promoting phagocyte phenotype through activation of the S1P/PPARγ pathway. Elovl6-deficient foamy macrophages showed enhanced ABCA1-mediated lipid efflux, increased production of neurotrophic factors, and reduced expression of inflammatory mediators. Moreover, our data show that ELOVL6 hampers CNS repair, as Elovl6 deficiency prevented demyelination and boosted remyelination in organotypic brain slice cultures and the mouse cuprizone model. These findings indicate that targeting ELOVL6 activity may be an effective strategy to stimulate CNS repair in MS and other neurodegenerative diseases.

Enhancement of carbon bio-fixation and lipid accumulation in Coccomyxa subellipsoidea with triethanolamine CO2 absorbent manipulation

The scenario probed carbon bio-fixation and lipid accumulation in Coccomyxa subellipsoidea with triethanolamine (TEA) CO2 absorbent manipulation. The results stated that CO2 bio-fixation (691.9 mg/L/d), CO2 utilization efficiency (57.84%), CO2 bio-fixation amount (3.86 g), biomass (2.58 g/L), and lipid accumulation (232.30 mg/L/d) in C. subellipsoidea with 100 mg/L TEA batch manipulation were separately 1.28-, 1.28-, 1.26-, 1.26-, and 1.72-fold more than that without TEA management. TEA fed-batch manipulation further augmented carbon fixation and the fixed carbon conversion into lipid with the maximum instantaneous CO2 fixation rate (1065.9 mg/L/d) and lipid productivity (538.7 mg/L/d) that were 1.97- and 3.98-fold more than that without TEA manipulation case. TEA manipulation also heightened the proportions of C16-C18 fatty acids (over 89%) and mono-unsaturated C18:1 (approximate 40.85%) which were commendable for high-quality biofuels-making. Such virtues were attributed to that TEA balanced pH fluctuation, converted CO2 into purposive HCO3- species, modulated glycolysis and TCA cycle to discharge appreciable energy, alleviated oxidative stress to block oxidative attack on lipids, and functioned as precursors to collectively boost CO2 sequestration and lipid accumulation in C. subellipsoidea. The outcomes were expected to provide exemplifications in developing win-win strategy for CO2 sequestration and lipid production by microalgae.

Effect of Pd particle size on activity and cis-trans selectivity in partial hydrogenation of soybean oil-derived FAMEs over Pd/SiO2 catalysts

Partial hydrogenation of soybean oil-derived fatty acid methyl esters (FAMEs) was performed to improve oxidative stability of biodiesel. The reaction was tested in a semi-batch reactor at 100 °C, 0.4 MPa. The effect of Pd particle size on activity and cis-trans selectivity was investigated over SiO2- and MCM-41-supported Pd catalysts, with different Pd loadings (0.5 and 1 wt.%). For Pd/SiO2 catalysts with relatively large Pd particle sizes (6.1–7.8 nm), the adsorption of polyunsaturated C18:2 and C18:3 FAMEs was promoted on the flat metal surface, providing 2- to 3-fold higher turnover frequency (TOF) compared with Pd/MCM-41 catalysts. In contrast, the Pd/MCM-41 catalysts with relatively small Pd particle sizes (2.7–4.0 nm), showed higher selectivity towards the desired monounsaturated C18:1 FAMEs due to lower affinity of isolated double bond (presented in C18:1) on the Pd surface. In addition, selectivity towards the desired cis-C18:1 FAMEs was found to be highly sensitive to Pd particle size. The 0.5Pd/MCM-41 catalyst with small Pd particle size (2.7 nm), provided high cis-C18:1 selectivity, resulting in a biodiesel with better cold flow property compared with the trans-isomers. With partial hydrogenation over the prepared Pd catalysts, biodiesel with significantly improved oxidative stability (>10 h) could be obtained.

196 Steroid concentrations in bovine follicular fluid are affected by metabolic stress

The negative energy balance (NEB) in dairy cows, early postpartum, is related to reduced fertility. A metabolic characteristic of NEB is elevated levels of free fatty acids (NEFA) in blood and follicular fluid with an effect on the cumulus-oocyte complex (COC; Leroy et al. 2005 Reproduction 130, 485-495, https://doi.org/10.1530/rep.1.00735; Aardema et al. 2011 Biol. Reprod. 85, 62-69, https://doi.org/10.1095/biolreprod.110.088815; Aardema et al. 2013 Biol. Reprod. 88, 164, https://doi.org/10.1095/biolreprod.112.106062). In this study, we investigated the effect of elevated NEFA levels on granulosa cells and consequently steroid production during NEB. Both 17β-oestradiol (E2) and progesterone (P4) levels in follicular fluid and oocyte competence were measured during NEB, as oocyte competence and steroid production are related (Aardema et al. 2013 Theriogenology 80, 576-583, https://doi.org/10.1016/j.theriogenology.2013.05.025). Heifers were directed towards a control (CTR; n=6) or NEB group (NEB; n=6; fasting heifer model; Jorritsma et al. 2003 Theriogenology). Cycle synchronization and superstimulation were performed as previously reported; invivo matured oocytes were, by ovariectomy at 22h after the induced LH peak, individually collected from follicles (≥8 to ≤20mm) and invitro fertilized and cultured until Day 8. Levels of nonesterified fatty acids (NEFAs) in follicular fluid were, in CTR, 80μM palmitic (C16:0), 70μM stearic (C18:0), and 100μM oleic acid (C18:1) and, in NEB, 150μM C16:0, 100μM C18:0, and 200μM C18:1 (Aardema et al. 2013 Biol. Reprod. Vol, page range). Follicular fluid of individual follicles was frozen and stored at −20°C until E2 and P4 radioimmunoassay analysis. At Day 5 and 8 of culture, embryos were scored for developmental competence, according to Aardema et al. (2013 Biol. Reprod. Vol, page range). Oocytes developing to a blastocyst all originated from follicles with, formerly in control animals defined, optimal follicular fluid levels of E2 ≤0.25 μM and P4 ≥0.26 μM (Aardema et al. 2013 Theriogenology 80, 576-583, https://doi.org/10.1016/j.theriogenology.2013.05.025). Overall E2 levels in follicular fluid in NEB appeared to be lower than those in CTR. There was a reduced positive value of 0.33 (vs. 0.49 in CTR) for predicting the competence of oocytes to develop into a blastocyst, and reduced specificity of 0.26 (vs. 0.75 in CTR) for oocytes originating from follicles with optimal steroid levels in NEB. The sensitivity and negative predictive value were 1.0 in both NEB and CTR. Levels of P4 in follicular fluid were unaffected by NEB. The lower level of E2 indicates an effect of NEB on steroid synthesis in granulosa cells. Recently, it was demonstrated that invitro exposure to monounsaturated C18:1, in contrast to saturated C16:0 or C18:0, resulted in reduced E2 production and expression of CYP19A1 in granulosa cells (Sharma 2018 Endocrine Connections 8, 493-505, https://doi.org/10.1530/EC-19-0011). These data suggest that elevated levels of NEFAs, C18:1 in particular, affect the function of granulosa cells and the follicular steroid environment of the COC, in contrast to the effect of C18:1 on the COC, which appears to protect the oocyte against lipotoxic events by saturated NEFAs by massive lipid accumulation in cumulus cells (Aardema et al. 2011 Biol. Reprod. 85, 62-69, https://doi.org/10.1095/biolreprod.110.088815; Aardema et al. 2013 Biol. Reprod. 88, 164, https://doi.org/10.1095/biolreprod.112.106062). Elevated levels of C18:1 may also result in increased lipid storage in granulosa cells and could affect the steroid synthesis of cholesterol that is also stored in lipid droplets. How elevated NEFA levels during the NEB affect granulosa cells is under investigation.

Lipidomics of Brain Tissues in Rats Fed Human Milk from Chinese Mothers or Commercial Infant Formula.

Holistic benefits of human milk to infants, particularly brain development and cognitive behavior, have stipulated that infant formula be tailored in composition like human milk. However, the composition of human milk, especially lipids, and their effects on brain development is complex and not fully elucidated. We evaluated brain lipidome profiles in weanling rats fed human milk or infant formula using non-targeted UHPLC-MS techniques. We also compared the lipid composition of human milk and infant formula using conventional GC-FID and HPLC-ELSD techniques. The sphingomyelin class of lipids was significantly higher in brains of rats fed human milk. Lipid species mainly comprising saturated or mono-unsaturated C18 fatty acids contributed significantly higher percentages to their respective classes in human milk compared to infant formula fed samples. In contrast, PUFAs contributed significantly higher percentages in brains of formula fed samples. Differences between human milk and formula lipids included minor fatty acids such as C8:0 and C12:0, which were higher in formula, and C16:1 and C18:1 n11, which were higher in human milk. Formula also contained higher levels of low- to medium-carbon triacylglycerols, whereas human milk had higher levels of high-carbon triacylglycerols. All phospholipid classes, and ceramides, were higher in formula. We show that brain lipid composition differs in weanling rats fed human milk or infant formula, but dietary lipid compositions do not necessarily manifest in the brain lipidome.

Cultivation, characterization, and properties of Chlorella vulgaris microalgae with different lipid contents and effect on fast pyrolysis oil composition.

A systematic study of the effect of nitrogen levels in the cultivation medium of Chlorella vulgaris microalgae grown in photobioreactor (PBR) on biomass productivity, biochemical and elemental composition, fatty acid profile, heating value (HHV), and composition of the algae-derived fast pyrolysis (bio-oil) is presented in this work. A relatively high biomass productivity and cell concentration (1.5g of dry biomass per liter of cultivation medium and 120 × 106 cells/ml, respectively) were achieved after 30h of cultivation under N-rich medium. On the other hand, the highest lipid content (ca. 36wt.% on dry biomass) was obtained under N-depletion cultivation conditions. The medium and low N levels favored also the increased concentration of the saturated and mono-unsaturated C16:0 and C18:1(n-9) fatty acids (FA) in the lipid/oil fraction, thus providing a raw lipid feedstock that can be more efficiently converted to high-quality biodiesel or green diesel (via hydrotreatment). In terms of overall lipid productivity, taking in consideration both the biomass concentration in the medium and the content of lipids on dry biomass, the most effective system was the N-rich one. The thermal (non-catalytic) pyrolysis of Chlorella vulgaris microalgae produced a highly complex bio-oil composition, including fatty acids, phenolics, ethers, ketones, etc., as well as aromatics, alkanes, and nitrogen compounds (pyrroles and amides), originating from the lipid, protein, and carbohydrate fractions of the microalgae. However, the catalytic fast pyrolysis using a highly acidic ZSM-5 zeolite, afforded a bio-oil enriched in mono-aromatics (BTX), reducing at the same time significantly oxygenated compounds such as phenolics, acids, ethers, and ketones. These effects were even more pronounced in the catalytic fast pyrolysis of Chlorella vulgaris residual biomass (after extraction of lipids), thus showing for the first time the potential of transforming this low value by-product towards high added value platform chemicals.

The enhanced biomass and lipid accumulation in Coccomyxa subellipsoidea with an integrated treatment strategy initiated by brewery effluent and phytohormones.

Brewery effluent (BE) as an appreciable and sustainable resource presented new possibilities in low-cost algal biomass production, whereas the relatively low essential macronutrients hindered extensive applications as growth medium for microalgae cultivation. The objective of this study was to investigate the feasibility of an integrated treatment strategy initiated by BE coupling phytohormones in augmenting biomass and lipid accumulation in Coccomyxa subellipsoidea. Results revealed that BE coupling synthetic 1-naphthaleneacetic acid (NAA) accomplished the favorable lipid productivity of 481.76mg/L/days, representing 6.80- to 9.71-fold more than that of single BE as well as standard Basal media. BE coupling NAA feeding also heightened the proportions of C16-C18 fatty acids (over 96%) and mono-unsaturated C18:1 (approximate 45%) which were prone to high-quality biofuels-making. Such profound lipids accumulation might be attributable to that BE coupling NAA treatment drove most of metabolic flux (i.e. acetyl-CoA) derived from TCA cycle and glycolysis flowing into lipid accumulation pathway. Concurrently, the complete removal of total nitrogen and total phosphorus by C. subellipsoidea with assistance of NAA were easily complied with the permissible dischargeable limits for BE. These present results strongly demonstrated that BE coupling NAA was a potential feeding strategy in boosting algal lipid productivity and further provided great possibilities in linking affordable algal biomass production with high-efficient biological contaminants removal.

PH-Driven Self-Assembly of Acidic Microbial Glycolipids.

Microbial glycolipids are a class of well-known compounds, but their self-assembly behavior is still not well understood. While the free carboxylic acid end group makes some of them interesting stimuli-responsive compounds, the sugar hydrophilic group and the nature of the fatty acid chain make the understanding of their self-assembly behavior in water not easy and highly unpredictable. Using cryo-transmission electron microscopy (cryo-TEM) and both pH-dependent in situ and ex situ small angle X-ray scattering (SAXS), we demonstrate that the aqueous self-assembly at room temperature (RT) of a family of β-d-glucose microbial glycolipids bearing a saturated and monounsaturated C18 fatty acid chain cannot be explained on the simple basis of the well-known packing parameter. Using the "pH-jump" process, we find that the molecules bearing a monosaturated fatty acid forms vesicles below pH 6.2, as expected, but the derivative with a saturated fatty acid forms infinite bilayer sheets below pH 7.8, instead of vesicles. We show that this behavior can be explained on the different bilayer membrane elasticity as a function of temperature. Membranes are either flexible or stiff for experiments performed at a temperature respectively above or below the typical melting point, TM, of the lipidic part of each compound. Finally, we also show that the disaccharide-containing acidic cellobioselipid forms a majority of chiral fibers, instead of the expected micelles.

Effect of environmental conditions on various enzyme activities and triacylglycerol contents in cultures of the freshwater diatom, Asterionella formosa (Bacillariophyceae)

A detailed analysis of triacylglycerols (TAGs) contents, fatty acid patterns and key enzyme activities in the freshwater diatom Asterionella formosa was performed under various conditions, including nitrate, iron and silicon limitation (stress conditions), or bicarbonate and phytohormones supplementation (stimulation conditions). Of all the conditions tested, the addition of bicarbonate produced the greatest increase (5-fold) in TAGs contents compared to the control while the biomass increased. The addition of phytohormones also allowed a significant increase in TAGs of about 3-fold while the biomass increased. Silicon, unlike iron and nitrate limitation, also triggered a significant increase in TAGs contents of 3.5-fold but negatively affected the biomass. Analysis of fatty acid profiles showed that the mono-unsaturated C16:1 fatty acid was the most abundant in A. formosa, followed by C16:0, C14:0 and eicosapentaenoic acid (EPA; C20:5 n-3). EPA levels were found to increase under nitrate and iron limitation. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoribulokinase (PRK), phosphofructokinase (PFK), glucose-6-phosphate dehydrogenase (G6PDH) and malate dehydrogenase (MDH) activities differed with growth conditions. Most enzymes were up-regulated in stimulated cells while in the case of stressed cells, the pattern of activities was more variable. Detailed analysis of all enzyme activities showed that the most important enzyme among those tested was GAPDH which could be a good candidate for genetic engineering of high lipid-producing algae. This study provides a better understanding of key enzymes and biochemical pathways involved in lipid accumulation processes in diatoms.

Peculiarities of <I>Alteromonas macleodii</I> strains reflects their deep/surface habitation rather than geographical distribution

The phenotypic, chemotaxonomic and genetic peculiarities of 5 deep strains of Alteromonas macleodii (isolated from Adriatic and Ionian Sea water from a depth of 1,000-3,500 m) and 5 strains of the same species isolated from the surface layer of Aegean, Andaman, Black Sea and Atlantic Ocean water near the British shore have been studied. Electron microscopy has shown that the deep strains' cells were, on average, two times longer (2.1±0.2×0.7±0.1 µm) than the surface strains' (1.1±0.1×0.6±0.1 µm). Using fatty acid analysis (particularly the mono-unsaturated C16:1 and C18:1 fatty acids contents) the deep and surface isolates were clearly separated into two clusters. Distinctions between them were also found in different lectin binding capacity, which is probably determined by the structure of their extracellular polysaccharide matrix. Analysis of the results of PCR with primers to repeated nucleotide sequences revealed a higher level of genetic polymorphism in surface strains in comparison with the deep isolates. This division was confirmed by the cluster analysis method though it was not as clear as in the fatty acids analysis. The described peculiarities are probably reflective of specific conditions in which A. macleodii strains live on the surface or in the depth of the world's oceans.

Litoricola marina sp. nov.

A Gram-negative, non-pigmented, non-motile, chemoheterotrophic marine bacterium, designated strain IMCC2782(T), was isolated from a surface seawater sample of the Yellow Sea, Korea. On the basis of 16S rRNA gene sequence analysis and phenotypic and genotypic characterization, strain IMCC2782(T) is shown to represent a novel species of the genus Litoricola. Strain IMCC2782(T) grew at 15-37 degrees C and tolerated 7.5% NaCl. Based on 16S rRNA gene sequences, strain IMCC2782(T) was related most closely to the type strain of Litoricola lipolytica (97.1% similarity) but showed less than 90 % similarity to the type strains of other bacterial species. The predominant fatty acids were mono-unsaturated C(18 : 1) and C(16 : 1). The G+C content of the DNA of strain IMCC2782(T) was 59.6 mol%. A low level of DNA-DNA relatedness (28.1%) together with several phenotypic characteristics, including enzyme activities, served to differentiate strain IMCC2782(T) from the type strain of L. lipolytica. Therefore, strain IMCC2782(T) is considered to represent a novel species of the genus Litoricola, for which the name Litoricola marina sp. nov. is proposed. The type strain is IMCC2782(T) (=KCTC 22683(T) =NBRC 105824(T)).

Structure–effect relation of C18 long-chain fatty acids in the reduction of body weight in rats

To investigate the relationship between chemical structure and physiological effect, the efficacy and the molecular mechanisms involved in the reduction of body weight by C18 fatty acids (stearic, elaidic, oleic, linoleic and 2-hydroxyoleic acids (2-OHOA)). Ad libitum fed, lean Wistar Kyoto rats treated orally with up to 600 mg kg(-1) of the fatty acids or vehicle every 12 h for 7 days. Besides, starved rats and rats pairfed to the 2-OHOA-treated group served as additional controls under restricted feeding conditions. Body weight, food intake, weight of various fat depots, plasma leptin, hypothalamic neuropeptides, uncoupling proteins (UCP) in white (WAT) and brown adipose tissue (BAT) and phosphorylation level of cyclic AMP (cAMP) response element-binding protein (CREB) in WAT. Only treatment with oleic acid and 2-OHOA induced body weight loss (3.3 and 11.4%, respectively) through reduction of adipose fat mass. Food intake in these rats was lower, although hypothalamic neuropeptide and plasma leptin levels indicated a rise in orexigenic status. Rats pairfed to the 2-hydroxyoleic group only lost 6.3% body weight. UCP1 expression and phosphorylation of CREB was drastically increased in WAT, but not BAT of 2-OHOA-treated rats, whereas no UCP1 expression could be detected in WAT of rats treated with oleic acid. Both cis-configured monounsaturated C18 fatty acids (oleic acid and 2-OHOA) reduce body weight, but the introduction of a hydroxyl group in position 2 drastically increases loss of adipose tissue mass. The novel molecular mechanism unique to 2-hydroxyoleic, but not oleic acid, implies induction of UCP1 expression in WAT by the cAMP/PKA pathway-dependent transcription factor CREB, most probably as part of a transdifferentiation process accompanied by enhanced energy expenditure.

Substrate specificity of Arabidopsis 3-ketoacyl-CoA synthases

The very long chain fatty acids (VLCFA) incorporated into plant lipids are derived from the iterative addition of C2 units provided by malonyl-CoA to an acyl-CoA by the 3-ketoacyl-CoA synthase (KCS) component of a fatty acid elongase (FAE) complex. Mining of the Arabidopsis genome sequence database revealed 20 genes with homology to seed-specific FAE1 KCS. Eight of the 20 putative KCSs were cloned, expressed in yeast, and isolated as (His) 6 fusion proteins. Five of the eight (At1g71160, At1g19440, At1g07720, At5g04530, and At4g34250) had little or no activity with C16 to C20 substrates while three demonstrated activity with C16, C18, and C20 saturated acyl-CoA substrates. At1g01120 KCS (KCS1) and At2g26640 KCS had broad substrate specificities when assayed with saturated and mono-unsaturated C16 to C24 acyl-CoAs while At4g34510 KCS was specific for saturated fatty acyl-CoA substrates.

Lipid profile: a useful chemotaxonomic marker for classification of a new cyanobacterium in Spirulina genus

The morphological, physiological and genetic characteristics of an isolate cyanobacterium from hard sand of the lake Venere in the Pantelleria island (Italy) were described. The isolate with a small-size coiled helix shape, growing optimally at pH 9.2–9.5 at 30°C under continuous illumination and aeration, possessed a 61.5 mol% of Guanine + Cytosine content of DNA. The lipid profile showed the presence of mono-, di-glycosyl, sulphoquinovolosyl and phosphatidyl (MGDG, DGDG, SQDG and PG). The fatty acid profile was also studied, characterized by the absence of γ-linolenic acid and the presence of saturated and monounsaturated C16 and C18. The latter was also present as a dienoic component. The fatty acid composition was affected by growth temperature by increasing the degree of desaturation at a lower temperature and the biosynthesis of shorter acyl chains. The effects of growth conditions other than temperature, physical, nutritional and chemical on lipid composition were also studied. The overall features of the cyanobacterium isolated from Pantelleria clustered it into Spirulina genus.

Assignment of Vibrio sp. strain ABE-1 to Colwellia maris sp. nov., a new psychrophilic bacterium.

A psychrophilic bacterium, previously described as Vibrio sp. strain ABE-1T, has been reassigned by phenotypic characterization, chemotaxonomic analysis and 16S rRNA phylogenetic analysis. The organism was curved rods and it could reduce nitrate to nitrite and hydrolyse gelatin and DNA, but not chitin. NaCl was required for growth. This strain was susceptible to the vibriostatic compound O/129. The major isoprenoid quinone was ubiquinone-8 and the DNA G + C content was 39.4 mol%. The whole-cell fatty acids comprised saturated and monounsaturated fatty acids with 10-18 C atoms; saturated and monounsaturated C16 fatty acids were predominant. Strain ABE-1T contained the unique trans-unsaturated fatty acid, 9-trans-hexadecenoic acid. Although strain ABE-1T has been identified as a Vibrio species, the strain did not ferment glucose. Phylogenetic analysis based on 16S rRNA sequencing indicated that strain ABE-1T was more closely related to Colwellia species than to Vibrio species. However, strain ABE-1T differed from other reported Colwellia species in terms of phylogenetic position, some phenotypic characteristics, chemotaxonomic analysis and relatedness by DNA-DNA hybridization. Accordingly, the name Colwellia maris is proposed. The type strain is ABE-1T (= JCM 10085T).

Cerulenin-Induced Modifications in the Fatty Acid Composition Affect Excitation Energy Transfer in Thylakoids of Petunia hybrida Leaves

Cerulenin-induced modifications in the fatty acid composition have been used to investigate the influence of acyl lipids on excitation energy distribution in thylakoid membranes of Petunia hybrida by means of 77 K fluorescence spectroscopy. Although cerulenin has no effect on relative contents of chlorophyll and acyl lipids, changes in the fatty acid composition of all thylakoid acyl lipids have been observed. The main cerulenin effect seems to be an increase in linoleic acid at the expense of saturated and monounsaturated C16- and C18-fatty acids resulting most likely in an increase in acyl lipid species containing both linoleic and linolenic acid. Low temperature (77 K ) fluorescence kinetics reveal a remarkable decrease in the ratio of the variable divided by the maximal fluorescence of photosystem II (F2(v)/F2(M)), taken as indicator for cerulenin-induced changes in this photosystem. Calculations of the excitation energy distribution terms based on a grouped bipartite model of photosynthesis suggest that a decrease in this ratio is caused by changes in energy transfer probabilities responsible for both, photochemical trapping of photosystem II and energetic cooperativity (grouping) between different photosystem II-light harvesting complex-units. Moreover, changes in the conformation responsible for spillover energy transfer are most likely to occur. Correlations between cerulenin-induced modifications of fatty acid composition and energy distribution support the assumption that excitation energy transfer depends on the structural state of the lipid matrix.