title: Effect of environmental conditions on various enzyme activities and triacylglycerol contents in cultures of the freshwater diatom, Asterionella formosa (Bacillariophyceae).
abstract: 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.
authors.affiliation: Aix Marseille Université, CNRS, UMR 7281 Laboratoire de Bioénergétique et Ingénierie des Protéines, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20 France.
authors.forename: Malika
authors.initials: M
authors.lastname: Mekhalfi
authors.affiliation: UMR 7282 Enzymology at Interfaces and Physiology of Lipolysis, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20 France.
authors.forename: Sawsan
authors.initials: S
authors.lastname: Amara
authors.affiliation: UMR 7282 Enzymology at Interfaces and Physiology of Lipolysis, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20 France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Robert
authors.affiliation: UMR 7282 Enzymology at Interfaces and Physiology of Lipolysis, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20 France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Carrière
authors.affiliation: Aix Marseille Université, CNRS, UMR 7281 Laboratoire de Bioénergétique et Ingénierie des Protéines, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20 France. Electronic address: bmeunier@imm.cnrs.fr.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Gontero
mesh_terms: D003470:Culture Media; D017377:Diatoms / Q000201:enzymology* / Q000254:growth & development; D005227:Fatty Acids / Q000378:metabolism; D005618:Fresh Water; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D050356:Lipid Metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D013312:Stress, Physiological; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D003470:Culture Media; D005227:Fatty Acids; D014280:Triglycerides; D008291:Malate Dehydrogenase; D005954:Glucosephosphate Dehydrogenase; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D017853:Phosphotransferases (Alcohol Group Acceptor); C022390:phosphoribulokinase
keywords: Bicarbonate; Iron; Nitrogen; Phytohormone; Silicon limitation