Microbial Nutrition Cell metabolism Nutritional Categories of Microorganisms

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 • • p. H Oxygen concentration Temperature Light / carbon dioxide (phototrophic organisms)

Role of Oxygen in Nutrition • Obligate aerobes – require O 2 • Obligate anaerobes – O 2 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. O 2)

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 – Macronutrients/micronutrients – Defined/complex media – Cell membranes • Energy production – Different modes

Further reading Madigan MT, JM Martinko, J Parker, 2000. Brock Biology of Microorganisms, 9 th Edition. Chapters 3 and 4.