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 macromolecules, metabolism C, H, O, N, S, P, K, Mg, Fe Sources Organic compounds Inorganic salts

Micronutrients Elements needed in trace quantities Growth factors Co, Cu, Mn, Zn, V Enzymes tap water Growth factors Organic compounds Vitamins

Defined / Complex Media 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

Substrate-level phosphorylation

Fermentation products Need to regenerate NAD+ Reduce pyruvic 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 Energy production 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.