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Microbial Nutrition Cell metabolism Nutritional Categories of Microorganisms • Microorganisms are often grouped according to the sources of energy they use: – Phototrophs use light as an energy source • Photosynthesis – Chemotrophs use chemicals as energy sources • Chemoorganotroph • Chemolithotroph Biochemical Components of Cells • Water: 80 % of wet weight • Dry weight – – – – Protein 40-70 % Nucleic acid 13-34% Lipid 10-15 % Also monomers, intermediates and inorganic ions Macronutrients • Cells make proteins, nucleic acids and lipids • Macronutrients – macromolecules, metabolism – C, H, O, N, S, P, K, Mg, Fe – Sources • Organic compounds • Inorganic salts Micronutrients • Elements needed in trace quantities – Co, Cu, Mn, Zn, V – Enzymes – tap water • Growth factors – Organic compounds – Vitamins Defined / Complex Media • Defined – Prepared with precise amounts of chemicals – Known composition • Complex – Exact composition unknown – Digests of beef, soybean, yeast Other Culturing Considerations • • • • pH Oxygen concentration Temperature Light / carbon dioxide (phototrophic organisms) Role of Oxygen in Nutrition • Obligate aerobes – require O2 • Obligate anaerobes – O2 is toxic • Facultative anaerobes • Microaerophilic organisms Transport of Nutrients into the Cell • Nutrients are obtained from the environment • Many of the nutrients are polar • Cannot diffuse across the cell membrane • Proteins embedded in the membrane • Transport against a concentration gradient active transport Bioenergetics • Living cells require energy for growth, biosynthesis, reproduction and transport • Energy needed to drive the biochemical reactions of cells is stored and transferred via adenosine triphosphate (ATP) Fermentation and Respiration • Chemoorganotrophs obtain their energy from oxidation of organic compounds – loss of electrons/removal of hydrogen • Fermentation – No terminal electron acceptor • Respiration – Terminal electron acceptor (e.g. O2) Glycolysis C6H12O6 glucose NAD+ ADP NADH + H+ ATP C3H4O3 pyruvic acid Substrate-level phosphorylation CH2 ADP ATP CH3 COPO3H2 C COOH COOH phosphoenol pyruvic acid O pyruvic acid Fermentation products • Need to regenerate NAD+ • Reduce pyruvic acid NADH + H+ C3H4O3 pyruvic acid NAD+ C3H5O3 lactic acid Oxidative phosphorylation • Occurs in respiration (aerobic and anaerobic) • Proton motive force – Electrons from NADH are passed along an electron transport chain – Protons are pumped across membrane – Electrochemical gradient – Drives ATP synthesis from ADP and Pi Summary • Nutrients – Macronutrients/micronutrients – Defined/complex media – Cell membranes • Energy production – Different modes Further reading Madigan MT, JM Martinko, J Parker, 2000. Brock Biology of Microorganisms, 9th Edition. Chapters 3 and 4.