Agressivité deConidiobolus obscurus vis-a-vis du puceron du pois,Acyrthosiphon pisum (Hem.: Aphididae] 1.-Comportement des conidies sur la cuticule avant la pénétration du tube germinatif dans l'insecte

Résumé Sept souches deConidiobolus obscurus (Hall & Dunn) Remaudière & Keller ont pu être classées en 2 groupes en fonction de leur pathogénicité vis-à-vis du puceron du pois. Les conidies primaires des souches agressives germent en pourcentage plus élevé que les conidies des souches non agressives (incapables d'infecter des pucerons). Elles ont aussi une meilleure propension à émettre des tubes germinatifs plut?t que des conidies secondaires.

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Summary Seven strains ofConidiobolus obscurus (Hall & Dunn) Remaudière & Keller were classified into 2 groups depending on their pathogenicity against the pea aphid. Variations in germination patterns on the aphid cuticle were related to differences in pathogenicity of the strains. Primary conidia of the virulent strains germinated in higher concentration than the avirulent ones; furthermore, the former have a greater tendandy to produce germ tubes than secondary conidia.

     

The effect of eight fungicides on germination of Conidiobolus obscurus resting spores

Conidiobolus obscurus resting spore germination was greater than 60% after 21 days incubation in 700 ppm concentrations of Rhodiasoufre, Pelt 44, Dithane M-45, Plantvax, and Saprol. No germ tubes were produced under the same treatment with Bavistine, Quin 20, or Benlate at the same dosage. Germination in distilled water was 85%. After only 24 hr contact with Quin 20 (700 ppm) followed by a distilled water wash, germination was not reduced. A higher ability to penetrate the spore wall may account for greater fungicide activity. Resting spores were found to be more resistant to certain fungicides than conidia; however, no general rule could be applied.     

First survey on ecological host range of aphid pathogenic fungi (Phylum Entomophthoromycota) in Tunisia

Summary. The natural occurrence of fungal pathogens of aphids and their ecological host range was investigated in Tunisia from 2009 to 2012. The survey focused on aphid infesting different crops and weeds and included 10 different aphid species. Samples were collected from eight agricultural crops sites belonging to three different bioclimatic zones. Four pathogens from the phylum Entomophthoromycota were found to occur naturally in Tunisian ecosystems: Pandora neoaphidis (Entomophthorales: Entomophthoraceae), Entomophthora planchoniana (Entomophthorales: Entomophthoraceae), Conidiobolus obscurus (Entomophthorales: Ancylistaceae) and Neozygites fresenii (Neozygitales: Neozygitaceae). The occurrence of entomophthoralean fungi depended on the sampling area, the bioclimatic zone, and aphid species. P. neoaphidis and E. planchoniana were the predominant pathogens infecting a wide range of aphid species whereas C. obscurus and N. fresenii were sporadically present on a limited number of aphid species. This study is the first survey on ecological host range of entomophthoralean fungi in Tunisia, and the first documentation of C. obscurus and N. fresenii to occur in Tunisia and Maghreb Region.     

Nucleolar organizing regions (NORs) of common vole chromosomes as nuclear markers of genome differentiation in data from a hybrid zone of two karyoforms, <Emphasis Type="Italic">arvalis</Emphasis> and <Emphasis Type="Italic">obscurus</Emphasis>

Contrasting chromosome location of nucleolar organizing regions (NORs), a poorly studied differentiating feature of two karyoforms of the 46-chromosome common voles, arvalis and obscurus, is demonstrated in the heterozygous karyotype of a natural hybrid from the arvalis/obscurus contact zone in European Russia. It was deduced from the karyotype analysis that the obscurus form was parental in this case and the arvalis form was defined as maternal via the markers of the mitochondrial genome. The similarities in the levels of chromosome polytypy and the lineage differentiation of the arvalis/obscurus and obscurus mitochondrial genomes according to the new and earlier published data is noticeable.     

Carotenoid and lipid production by the autotrophic microalga Chlorella protothecoides under nutritional, salinity, and luminosity stress conditions

Today microalgae represent a viable alternative source for high-value products. The specie Chlorella protothecoides (Cp), heterotrophically grown, has been widely studied and provides a high amount of lutein and fatty acids (FA) and has a good profile for biodiesel production. This work studies carotenoid and FA production by autotrophic grown Cp. Cp was grown until the medium’s nitrogen was depleted, then diluted in NaCl solution, resulting in nutritional, luminosity, and salinity stresses. Different NaCl concentrations were tested (10, 20, 30 g/L) at two different dilutions. After dilution, a color shifting from green to orange-red was noticed, showing carotenoid production. The best production of both carotenoids and FA was attained with a 20 g/L NaCl solution. The total carotenoid content was 0.8 % w/w (canthaxanthin (23.3 %), echinenone (14.7 %), free astaxanthin (7.1 %), and lutein/zeaxanthin (4.1 %)). Furthermore, the total lipid content reached 43.4 % w/w, with a FA composition of C18:1 (33.64 %), C16:0 (23.30 %), C18:2 (11.53 %), and less than 12 % of C18:3, which is needed to fulfill the biodiesel quality specifications (EN 14214).     

The effect of nitrogen limitation on acetyl-CoA carboxylase expression and fatty acid content in Chromera velia and Isochrysis aff. galbana (TISO)

Lipids from microalgae have become a valuable product with applications ranging from biofuels to human nutrition. While changes in fatty acid (FA) content and composition under nitrogen limitation are well documented, the involved molecular mechanisms are poorly understood. Acetyl-CoA carboxylase (ACCase) is a key enzyme in the FA synthesis and elongation pathway. Plastidial and cytosolic ACCases provide malonyl-CoA for de novo FA synthesis in the plastid and FA elongation in the endoplasmic reticulum, respectively. The present study aimed at investigating the expression of plastidial and cytosolic ACCase in Chromera velia and Isochrysis aff. galbana (TISO) and their impact on FA content and elongation level when grown under nitrogen-deplete conditions. In C. velia, plastidial ACCase was significantly upregulated during nitrogen starvation and with culture age, strongly correlating with increased FA content. Conversely, plastidial ACCase of I. aff. galbana was not differentially expressed in nitrogen-deplete cultures, but upregulated during the logarithmic phase of nitrogen-replete cultures. In contrast to plastidial ACCase, the cytosolic ACCase of C. velia was downregulated with culture age and nitrogen-starvation, strongly correlating with an increase in medium-chain FAs. In conclusion, the expression of plastidial and cytosolic ACCase changed with growth phase and nutrient status in a species-specific manner and nitrogen limitation did not always result in FA accumulation.     

Effect of selected plant species within biodiverse pasture on in vitro fatty acid biohydrogenation and tissue fatty acid composition of lamb

The effect of botanical diversity on supply of polyunsaturated fatty acids (PUFA) to ruminants in vitro, and the fatty acid (FA) composition of muscle in lambs was investigated. Six plant species, commonly grown as part of UK herbal ley mixtures (Trifolium pratense, Lotus corniculatus, Achillea millefolium, Centaurea nigra, Plantago lanceolata and Prunella vulgaris), were assessed for FA profile, and in vitro biohydrogenation of constituent PUFA, to estimate intestinal supply of PUFA available for absorption by ruminants. Modelling the in vitro data suggested that L. corniculatus and P. vulgaris had the greatest potential to increase 18:3n-3 supply to ruminants, having the highest amounts escaping in vitro biohydrogenation. Biodiverse pastures were established using the six selected species, under-sown in a perennial ryegrass-based sward. Lambs were grazed (~50 days) on biodiverse or control pastures and the effects on the FA composition of musculus longissimus thoracis (lean and subcutaneous fat) and musculus semimembranosus (lean) were determined. Biodiverse pasture increased 18:2n-6 and 18:3n-3 contents of m. semimembranosus (+14.8 and +7.2 mg/100 g tissue, respectively) and the subcutaneous fat of m. longissimus thoracis (+158 and +166 mg/100 g tissue, respectively) relative to feeding a perennial ryegrass pasture. However, there was no effect on total concentrations of saturated FA in the tissues studied. It was concluded that enhancing biodiversity had a positive impact on muscle FA profile reflected by increased levels of total PUFA.     

Mitochondrial activity,hemocyte parameters and lipid composition modulation by dietary conditioning in the Pacific oyster Crassostrea gigas

Several parameters can affect membrane lipid composition in bivalves, including diet. Although two fatty acids (FA) 22:6n-3 and 20:5n-3 are essential membrane components, they are sparingly synthesized by bivalves and must be obtained from their diet. Here, effects of dietary modifications of membrane lipid composition were studied at both cellular and subcellular levels in the oyster Crassostrea gigas. To this end, we compared oysters fed two monoalgal diets that differed markedly in their FA composition and a mix of both. As expected, algae impacted phospholipids, in particular 22:6n-3 and 20:5n-3, reflecting differences of dietary microalgae FA composition. Meantime, total saturated FA, total monounsaturated FA, total polyunsaturated FA and total non-methylene-interrupted FA varied little and phospholipid class composition was only slightly affected by diets. Measures made in hemocytes indicated that only mitochondrial membrane potential was affected by diets. Total ROS production as well as mitochondrial superoxide production did not differ with diet. There was no difference in phosphorylating (state 3) and non-phosphorylating (state 4) rates of oxygen consumption rates or in cytochrome c oxidase activity of mitochondria isolated from gills between the three diets. Similarly, neither cytochromes a, b, c or c ₁ content nor citrate synthase activities were changed, suggesting that number and morphology of mitochondria were not affected by dietary treatment. These results suggest that oysters could possess high homeostatic capabilities, at both cellular and subcellular levels, to minimize the effect of dietary FA and related membrane lipid FA modifications on mitochondrial functions. These capabilities could be a means to face variations in diet composition in their natural environment and to preserve important oyster physiological functions such as growth and reproduction.     

Altered Fecal Microbiota Composition Associated with Food Allergy in Infants

Increasing evidence suggests that perturbations in the intestinal microbiota composition of infants are implicated in the pathogenesis of food allergy (FA), while the actual structure and composition of the intestinal microbiota in human beings with FA remain unclear. Microbial diversity and composition were analyzed with parallel barcoded 454 pyrosequencing targeting the 16S rRNA gene hypervariable V1-V3 regions in the feces of 34 infants with FA (17 IgE mediated and 17 non-IgE mediated) and 45 healthy controls. Here, we showed that several key FA-associated bacterial phylotypes, but not the overall microbiota diversity, significantly changed in infancy fecal microbiota with FA and were associated with the development of FA. The proportion of abundant Bacteroidetes, Proteobacteria, and Actinobacteria phyla were significantly reduced, while the Firmicutes phylum was highly enriched in the FA group (P < 0.05). Abundant Clostridiaceae 1 organisms were prevalent in infants with FA at the family level (P = 0.016). FA-enriched phylotypes negatively correlated with interleukin-10, for example, the genera Enterococcus and Staphylococcus. Despite profound interindividual variability, levels of 20 predominant genera were significantly different between the FA and healthy control groups (P < 0.05). Infants with IgE-mediated FA had increased levels of Clostridium sensu stricto and Anaerobacter and decreased levels of Bacteroides and Clostridium XVIII (P < 0.05). A positive correlation was observed between Clostridium sensu stricto and serum-specific IgE (R = 0.655, P < 0.001). The specific microbiota signature could distinguish infants with IgE-mediated FA from non-IgE-mediated ones. Detailed microbiota analysis of a well-characterized cohort of infants with FA showed that dysbiosis of fecal microbiota with several FA-associated key phylotypes may play a pathogenic role in FA.     

Patterns of Occurrence of Sharks in Sydney Harbour,a Large Urbanised Estuary

Information about spatial and temporal variability in the distribution and abundance of shark-populations are required for their conservation, management and to update measures designed to mitigate human-shark interactions. However, because some species of sharks are mobile, migratory and occur in relatively small numbers, estimating their patterns of distribution and abundance can be very difficult. In this study, we used a hierarchical sampling design to examine differences in the composition of species, size- and sex-structures of sharks sampled with bottom-set longlines in three different areas with increasing distance from the entrance of Sydney Harbour, a large urbanised estuary. During two years of sampling, we obtained data for four species of sharks (Port Jackson, Heterodontus portusjacksoni; wobbegong, Orectolobus maculatus; dusky whaler, Carcharhinus obscurus and bull shark, Carcharhinus leucas). Only a few O. maculatus and C. obscurus were caught, all in the area closest to the entrance of the Harbour. O. maculatus were caught in all seasons, except summer, while C. obscurus was only caught in summer. Heterodontus portusjacksoni were the most abundant species, caught in the entrance location mostly between July to November, when water temperature was below 21.5°C. This pattern was consistent across both years. C. leucas, the second most abundant species, were captured in all areas of Sydney Harbour but only in summer and autumn when water temperatures were above 23°C. This study quantified, for this first time, how different species utilise different areas of Sydney Harbour, at different times of the year. This information has implications for the management of human-shark interactions, by enabling creation of education programs to modify human behaviour in times of increased risk of potentially dangerous sharks.     

Fatty Acid Composition of Muscle,Adipose Tissue and Liver from Muskoxen (Ovibos moschatus) Living in West Greenland

Information about lipid content and fatty acid (FA) composition of muskoxen (Ovibos moschatos) edible tissues is very limited in comparison to other meat sources. Thus, this work aims to present the first in-depth characterization of the FA profile of meat, subcutaneous adipose tissue and liver of muskoxen living in West Greenland. Furthermore, we aim to evaluate the effect of sex in the FA composition of these edible tissues. Samples from muscle (Longissimus dorsi), subcutaneous adipose tissue and liver were collected from female and male muskoxen, which were delivered at the butchery in Kangerlussuaq (West Greenland) during the winter hunting season. The lipid content of muscle, adipose tissue and liver averaged 284, 846 and 173 mg/g of dry tissue, respectively. This large lipid contents confirms that in late winter, when forage availability is scarce, muskoxen from West Greenland still have high fat reserves, demonstrating that they are well adapted to seasonal feed restriction. A detailed characterization of FA and dimethylacetal composition of muskoxen muscle, subcutaneous adipose tissue and liver showed that there are little differences on FA composition between sexes. Nevertheless, the 18:1cis-9 was the most abundant FA in muscle and adipose tissue, reaching 43% of total FA in muscle. The high content of 18:1cis-9 suggests that it can be selectively stored in muskoxen tissues. Regarding the nutritional composition of muskoxen edible tissues, they are not a good source of polyunsaturated FA; however, they may contribute to a higher fat intake. Information about the FA composition of muskoxen meat and liver is scarce, so this work can contribute to the characterization of the nutritional fat properties of muskoxen edible tissues and can be also useful to update food composition databases.     

Lipid productivity and fatty acid composition in Chlorella and Scenepdesmus strains grown in nitrogen-stressed conditions

Thirty Chlorella and 30 Scenedesmus strains grown in nitrogen-stressed conditions (70 mg L^?1 N) were analyzed for biomass accumulation, lipid productivity, protein, and fatty acid (FA) composition. Scenedesmus strains produced more biomass (4.02?±?0.73 g L^?1) after 14 days in culture compared to Chlorella strains (2.57?±?0.12 g L^?1). Protein content decreased and lipid content increased from days 8 to 14 with an increase in triacylglycerol (TAG) accumulation in most strains. By day 14, Scenedesmus strains generally had higher lipid productivity (53.5?±?3.7 mg lipid L^?1 day^?1) than Chlorella strains (35.1?±?2.8 mg lipid L^?1 day^?1) with the lipids consisting mainly of C16–18 TAGs. Scenedesmus strains generally had a more suitable FA profile with higher amounts of saturated fatty acids and monounsaturated fatty acids (MUFAs) and a smaller polyunsaturated fatty acid (PUFA) component. Chlorella strains had a larger PUFA component and smaller MUFA component. The general trend in the FA composition of Chlorella strains was oleic > palmitic > α-linolenic = linoleic > eicosenoic > heptadecenoic > stearic acid. For Scenedesmus strains, the general trend was oleic > palmitic > linoleic > α-linolenic > stearic > eicosenoic > palmitoleic > heptadecenoic acid. The most promising strains with the highest lipid productivity and most suitable FA profiles were Scenedesmus sp. MACC 401, Scenedesmus soli MACC 721, and Scenedesmus ecornis MACC 714. Although Chlorella sp. MACC 519 had lower lipid productivity, the FA profile was good with a lower PUFA component compared to the other Chlorella strains analyzed and a low linolenic acid concentration.     

Fulvic acid affects proliferation and maturation phases in Abies cephalonica embryogenic cells

Embryogenic cell masses (ECM) of Abies cephalonica were grown on proliferation media in the presence and absence of fulvic acid (FA), whose molecular composition and conformational rigidity were evaluated by CPMAS-¹³C NMR spectroscopy. To assess the physiological effects of this humic material during proliferation and maturation stages of somatic embryogenesis (SE), proliferation rate, proportion of consecutive developmental stages of pro-embryogenic masses (PEM), cellular ATP and glucose-6-phosphate were evaluated at regular intervals. FA increased the proliferation rate, especially during the early sampling days, and the percentage of PEM in their advanced developmental stage. Cellular ATP and glucose-6-phospahte were increased by FA pre-treatment during the maturation phase. Furthermore, the effects of the anti-auxin p-chlorophenoxyisobutyric acid (PCIB), such as a decrease of growth and the enhancement of PEM III induction, were inverted by FA. Proton pumping ATPase and PPase activities were decreased in microsomes from PCIB-treated ECM, while they increased in the presence of FA. This fulvic matter also induced a delay in somatic embryo formation during the maturation phase. Both the improvement of the PEM proliferation and the reduction of the subsequent maturation process of A. cephalonica are explained by a release from the complex humic structure of low molecular-weight molecules, which may interact with the plant hormonal signaling pathway. These effects appear to be related to the hydrophilic and conformationally labile nature of FA. The structure-activity relationship observed here suggests that the influence of FA on ECM may be attributed to specific bioactive molecules that are preferentially released from the FA loose superstructure.     

Dietary lipid quality and mitochondrial membrane composition in trout: responses of membrane enzymes and oxidative capacities

To examine whether membrane fatty acid (FA) composition has a greater impact upon specific components of oxidative phosphorylation or on overall properties of muscle mitochondria, rainbow trout (Oncorhynchus mykiss) were fed two diets differing only in FA composition. Diet 1 was enriched in 18:1n-9 and 18:2n-6 while Diet 2 was enriched in 22:6n-3. The FA composition of mitochondrial phospholipids was strongly affected by diet. 22:6n-3 levels were twice as high (49 %) in mitochondrial phospholipids of fish fed Diet 2 than in those fed Diet 1. 18:2n-6 content of the phospholipids also followed the diets, whereas 18:1n-9 changed little. All n-6 FA, most notably 22:5n-6, were significantly higher in fish fed Diet 1. Nonetheless, total saturated FA, total monounsaturated FA and total polyunsaturated FA in mitochondrial phospholipids varied little. Despite a marked impact of diet on specific FA levels in mitochondrial phospholipids, only non-phosphorylating (state 4) rates were higher in fish fed Diet 2. Phosphorylating rates (state 3), oxygen consumption due to flux through the electron transport chain complexes as well as the corresponding spectrophotometric activities did not differ with diet. Body mass affected state 4 rates and cytochrome c oxidase and F ₀ F ₁ ATPase activities while complex I showed a diet-specific effect of body mass. Only the minor FA that were affected by body mass were correlated with functional properties. The regulated incorporation of dietary FA into phospholipids seems to allow fish to maintain critical membrane functions even when the lipid quality of their diets varies considerably, as is likely in their natural environment.     

Biologie des pucerons des céréales dans l'ouest de la France II. Répartition spatio-temporelle et action limitative de trois espèces d'Entomophthoraceae

Résumé L'étude comparée de l'action limitative de 3 espèces d'Entomophthoraceae sur les pucerons des céréales a été effectuée dans l'Ouest de la France (Bassin de Rennes essentiellement) de 1975 à 1978. La quasi-totalité des cas de mycose sont dus àErynia neoaphidis Remaud. & Henn.,Conidiobolus obscurus (Hall & Dunn) Remaud. & Keller etEntomophthora planchoniana Cornu. L'analyse de la répartition des différentesEntomophthoraceae au cours de l'année montre queE. neoaphidis est l'espèce qui a la plus grande période d'activité (elle se manifeste pendant pratiquement toute l'année sur les populations anholocycliques) et qui infecte, à un moment donné, le plus de pucerons.C. obscurus dispara?t en général en hiver après la formation abondante de spores durables et ne réappara?t qu'au cours du printemps. D'une année sur l'autre, à un instant donné,C. obscurus est rarement déterminé sur plus de 25% du total des pucerons mycosés récoltés. Enfin,E. planchoniana a une période d'activité essentiellement estivale qui peut se prolonger en automne sur les pucerons pullulant sur ma?s. C'est sur ces derniers qu'elle semble la plus efficace. Sur blé d'hiver, l'action apparente deE. neoaphidis et deC. obscurus n'est pas la même selon l'espèce de pucerons et la position de ceux-ci sur la plante:E. neoaphidis est encore plus pathogène pourM. dirhodum que pourS. avenae etC. obscurus semble davantage parasiter les pucerons situés sur le feuillage que ceux situés sur les épis. Enfin, l'étude de l'action deE. neoaphidis, C. obscurus etE. planchoniana en fonction de la taille de la colonie (ou du ?groupe? de pucerons) montre que l'action deE. neoaphidis semble indépendante de la densité de pucerons alors que le développement deC. obscurus dans les colonies est moins rapide que l'augmentation de taille de celles-ci. D'une manière générale, l'action deE. planchoniana est moins bien connue du fait du manque de matériel. La prédominance deE. neoaphidis s'explique par l'excellente adaptation de cette espèce à l'anholocyclie des pucerons, par sa faible spécificité à l'intérieur du groupe des aphides et par le nombre important de conidies qu'elle projette en atmosphère saturante. Cette espèce semble avoir les meilleures potentialités entomopathogènes en tant qu'agent de lutte biologique en cultures céréalières, mais son emploi futur sera subordonné à sa production de masse sous forme stable et pathogène.

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Summary The role of 3 species ofEntomophthoraceae on cereal aphids in the West of France from 1975 to 1978 was compared. Almost all the infected aphids were killed byErynia neoaphidis Remaud. & Henn.,Conidiobolus obscurus (Hall & Dunn), Remaud. & Keller andEntomophthora planchoniana Cornu. A study of the distribution of the different species ofEntomophthoraceae during the year shows thatE. neoaphidis has the longest period of activity and infects most aphids. C. obscurus generally disappears in winter after an abundant formation of resting spores and reappears during the spring. On each sampling date,C. obscurus infects generally no more than 25% of the diseased aphids.E planchoniana occurs essentially during the summer and autumn on aphids living on ma?ze on which it seems to spread efficiently. On winter wheat the action ofE. neoaphidis andC. obscurus is different, depending on the species of aphid and on the position occupied by the aphids on the plant:E. neoaphidis is more pathogenic forM. dirhodum than forS. avenae andC. obscurus seems more pathogenic for the aphids (whatever the species) on leaves than for the aphids on ears. Finally the efficiency ofE. neoaphidis, C. obscurus andE. planchoniana relative to the size of the populations of the different samples was studied: the pathogenicity ofE. neoaphidis seems to be density independant, whereas the development ofC. obscurus in the colonies is slower than the rate at which they increase in size. Little is known about the pathogenicity ofE. planchoniana because of the lack of material. The prevalence ofE. neoaphidis is explained by its adaptation to the anholocycly of the aphids, by the broad spectrum of species it infects and by the numerous conidia it produces in a moist atmosphere. This species seems to have the best potential as an agent of biological control in cereal but currently its mass production poses problems.

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Avec la collaboration technique d'Augustine Gellé etSylvie Tanguy     

Genome-wide association study identifies quantitative trait loci regions involved in muscle acidic profile in Large White heavy pigs

The widespread use of genome-wide association studies resulted in the discovery of genomic regions associated with fatty acid (FA) composition in different porcine tissues, but little information exists about the genes involved in FA composition of meat obtained from heavy pigs selected for the production of Italian dry-cured hams. To this objective, we genotyped with a single nucleotide polymorphism (SNP) panel 795 Italian Large White heavy pigs to identify the markers and genomic regions associated with Semimembranosus muscle FA profile. Heritability estimates for intramuscular fat FA profile were of low-to-moderate magnitude, suggesting that these traits may be improved with genomic selection. On the whole, 45 SNPs were significantly associated with 14 FAs, and 4 of them (ALGA008109, ALGA0081097, CASI0010164 and SIRI0000267) were associated with more than 1 FA. The palmitoleic : palmitic and oleic : stearic ratios displayed the highest number of significant markers and the most significant associations (Bonferroni adjusted P < 5.00E−07). Of particular interest, the palmitoleic : palmitic ratio was strongly associated with markers located at 111 to 114 Mb on chromosome 14, in the same chromosomal region where Stearoyl-CoA desaturase Δ9 (SCD) gene is located. Several significant chromosomal regions were found; some of them harbour key genes playing pivotal roles in FA desaturation and elongation, such as SCD and some members of the Elongation of Very Long-Chain FA (ELOVL) gene family. The results suggest that the identification of causal mutations in these regions may provide a set of markers useful for selection schemes aimed at improving FA composition in pork products.     

Effects of growth phase and nitrogen starvation on expression of fatty acid desaturases and fatty acid composition of Isochrysis aff. galbana (TISO)

Very long-chain polyunsaturated fatty acids (VLC-PUFAs) are important dietary requirements for maintaining human health. Many marine microalgae are naturally high in ω − 3 VLC-PUFAs, however, the molecular mechanisms underpinning fatty acid (FA) desaturation and elongation in algae are poorly understood. An advanced molecular understanding would facilitate improvements of this nascent industry. We aimed to investigate expression responses of four front-end fatty acid desaturase genes and downstream effects on FA profiles to nitrogen limitation and cultivation growth stage in Isochrysis aff. galbana (TISO). Cultures were grown in nitrogen-replete and -deplete medium; samples were harvested during logarithmic, late logarithmic and stationary growth phases to analyse FA content/composition and gene expression of ?⁶-, ?⁸-, ?⁵- and ?⁴-desaturases (d6FAD (putative), d8FAD, d5FAD and d4FAD, respectively). d6FAD (putative) exhibited no differential expression, while d8FAD, d5FAD and d4FAD were significantly upregulated during logarithmic growth of nutrient-replete cultures, coinciding with rapid cell division. In conclusion, it is demonstrated that expression of some FADs in I. aff. galbana varies with culture age and nitrogen status which has downstream consequences on FA desaturation levels. This has implications for the commercial production of VLC-PUFAs where a trade-off between total lipid yield and VLC-PUFAs has to be made.