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Microbial Nutrition The Common Nutrient Requirements of Microbial Cells >95% of dry weight of bacterial cells is made up of 10 major components carbohydrates, nucleic acids proteins, lipids, – Carbon (C) – Oxygen (O) – Hydrogen (H) – Nitrogen (N) – Sulfur (S) – Phosphorous (P) mg/l –components – Potassim (K) – Calcium (Ca) – Magnesium (Mg) – Iron (fe) Minor components mcg/l (mg/l) –components – – – – – – – Manganese (Mn) Zinc (Zn) Cobalt (Co) Molybdenum (Mo) Nickel (Ni) Copper (Cu) Others (B, Se, …) Usually enough in water sources to satisfy requirements Major nutritional type Sources of energy, hydrogen/electrons, and carbon Representative microorganisms Photoautotroph (Photolithotroph) Light energy, inorganic Algae, Purple and hydrogen/electron(H/e-) donor, green bacteria, CO2 carbon source Cyanobacteria Photoheterotroph (Photoorganotroph) Light energy, inorganic H/edonor, Organic carbon source Purple nonsulfur bacteria, Green sulfur bacteria Chemical energy source (inorganic), Inorganic H/edonor, CO2 carbon source Sulfur-oxdizing bacteria, Hydrogen bacteria, Nitrifying bacteria Chemical energy source (organic), Organic H/e- donor, Organic carbon source Most bacteria, fungi, protozoa II. Requirements for Carbon, Hydrogen, and Chemoautotroph Oxygen-often satisfied (Chemolithotroph) together Chemoheterotroph (Chenoorganotroph) Terms and Definitions: Categorization based on nutritional requirements Carbon Source Autotroph CO2 = principle carbon source Includes photosynthetic bacteria and those capable of oxidizing inorganic material for energy generation Heterotroph Utilize more reduced and complex carbon sources derived from other organisms (“nourished by others”) Organic compounds used to provide carbon Prototroph Any microorganism that can synthesize its nutrients from inorganic material Auxotroph a mutant organism, especially a microorganism, that has a nutritional requirement not shared by the parent organism Energy Source Phototroph They use the energy from light to carry out various cellular metabolic processes. Chemotroph Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs) Hydrogen or Electron Source Lithotrophs Use reduced inorganic compounds as electron source (“Rock eaters”) Organotrophs Use organic compounds as H and electron donors Nitrogen Amino acids Nucleic acids (purines and pyrimidines) Some carbohydrates and lipids Enzyme co-factors Phosphorous ATP Co-factors Nucleic acids (phosphodiester bonds) Phospholipids (lipid bilayer) Some proteins Sulfur S-containing amino acids Some carbohydrates Thiamine Biotin Uptake – Specific Mechanimsms Utilizing Selective Permeability Nutrient Uptake of nutrition Nutrient molecules frequently cannot cross selectively permeable plasma membranes through passive diffusion and must be transported by one of three major mechanisms involving the use of membrane carrier proteins. • Passive transport / simple diffusion • Facilitated diffusion • Active transport • Group translocation Passive diffusion Passive diffusion is the process in which molecules move from a region of higher concentration to one of lower concentration as a result of random thermal agitation. A few substances, such as glycerol, can cross the plasma membrane by passive diffusion. Facilitated Diffusion Requires large concentration gradient for efficient transport Differs from passive diffusion which utilizes osmosis to achieve transfer of small substances (glycerol, H2O, O2, CO2) The rate of diffusion across selectively permeable membranes is greatly increased by the use of carrier proteins, sometimes called permeases, which are embedded in the plasma membrane. Since the diffusion process is aided by a carrier, it is called facilitated diffusion. The rate of facilitated diffusion increases with the concentratiotin gradient much more rapidly and at lower concentrations of the diffusing molecule than that of passive diffusion A model of facilitated diffusion The membrane carrier can change conformation after binding an external molecule and subsequently release the molecule on the cell interior. It then returns to the outward oriented position and is ready to bind another solute molecule. Because there is no energy input, molecules will continue to enter only as long as their concentration is greater on the outside. Probably involves a conformational change of carrier to deliver components across the lipid bilayer – Therefore material Not effective for lipid-insoluble utilized much by bacteria but it does occur (e.g glycerol uptake by E. coli) Active Diffusion – Active transport is the transport of solute molecules to higher concentrations, or against a concentration gradient, with the use of metabolic energy input – Transport of molecules AGAINST a concentration gradient Material is more concentrated inside the cell than the outside Ability to concentrate solutes in dilute environments – Metabolic energy required ATP hydrolysis or Proton motive forces (proton gradients generated by electron transport) Types of active transport – Symport is the linked transport of two substances in the same direction – Antiport is the linked transport of two substances in opposite directions Group Translocation Group Translocation – Transfer of solutes coupled with chemical modification – Example: Phosphoenolpyruvate (PEP): Sugar phosphotransferase system (PTS) – Sugars are transported ad phosphorylated using PEP as the phosphate donor – Glucose, fructose, mannitol, sucrose, N-acetyl glucosamine, cellobiose, and other solutesn – PTS proteins cann also serve as chemoreceptors in chemotaxis The best-known group translocation system is the phosphoenolpyruvate: sugar phosphotransferase system (PTS), which transports a variety of sugars into procaryotic cells while Simultaneously phosphorylating them using phosphoenolpyruvate (PEP) as the phosphate donor. Simple comparison of transport systems Items Passive diffusion Facilitated diffusion Active transport Group translocation carrier Non Yes Yes Yes transport speed Slow Rapid Rapid Rapid against gradient Non Non Yes Yes transport molecules No specificity Specificity Specificity Specificity metabolic energy No need Need Need Need Solutes molecules Not changed Changed Changed Changed proteins