Microbial Nutrition

1. Microbial Nutrition

2. I. The Common Nutrient Requirements of Microbial Cells

3. >95% of dry weight of bacterial cells is made up of 10 major components • g/l – used for carbohydrates, proteins, lipids, nucleic acids • Carbon (C) • Oxygen (O) • Hydrogen (H) • Nitrogen (N) • Sulfur (S) • Phosphorous (P)

4. mg/l – enzyme activity, heat-resistance of spores, co-factors, cytochrome components • Potassim (K) • Calcium (Ca) • Magnesium (Mg) • Iron (fe)

5. Minor components • mcg/l (mg/l) – enzyme activity, co-factors, nitrogen fixation, vitamin components • Manganese (Mn) • Zinc (Zn) • Cobalt (Co) • Molybdenum (Mo) • Nickel (Ni) • Copper (Cu) • Others (B, Se, …) • Usually enough in water sources to satisfy requirements

6. Specialized Requirements • Silica • Diatoms need silicic acid for silica walls (H4SiO4) • High sodium concentrations • Halophiles

7. II. Requirements for Carbon, Hydrogen, and Oxygen-often satisfied together

8. Terms and Definitions: Categorization based on nutritional requirements

9. Carbon Source

10. Autotroph • CO2 = principle carbon source • Includes photosynthetic bacteria and those capable of oxidizing inorganic material for energy generation

11. Heterotroph • Utilize more reduced and complex carbon sources derived from other organisms (“nourished by others”) • Organic compounds used to provide carbon

12. Prototroph • Utilizes same components as most members of the same species

13. Auxotroph • Mutated microbe that has lost the ability to synthesize critical precursors • Must have nutritional precursors supplied

14. Energy Source

15. Phototroph • Light energy harvested by photosynthetic processes • Carbon from CO2

16. Chemotroph • Organic or inorganic compounds provide energy by oxidative processes

17. Hydrogen or Electron Source

18. Lithotrophs • Use reduced inorganic compounds as electron source • “Rock eaters”

19. Organotrophs • Use organic compounds as H and electron donors

20. III. Major Nutritional Microorganism Types

21. Photolithhotrophic autotrophs (aka photautotrophs) • Carbon and energy source: • CO2 • Light energy • H/e- source = inorganic donor • e.g. H2O, hydrogen, H2S and elemental sulfur • Examples • Algae (eukaryotic) • Cyanobacteria • Purple and green sulfur bacteria

22. Photoorganotroic heterotrophs • Carbon and energy source • CO2 and organic compounds • Light energy • H/e- source • Organic donor • Examples • Purple non-sulfur bacteria • Green non-sulfur bacteria

23. Chemolithotrophic autotrophs (aka chemoautotrophs) • Carbon and energy source • CO2 • Inorganic compounds • (a few chemolithotrophs get carbon from organic sources = chemolithotrophic heterotrophs = mixotrophic – inorganic energy, organic carbon) • H/e- source • Oxidation of inorganic compounds • H2S, S, NO2, H2, Fe2+

24. Examples • Sulfur oxidizers (Thiobacillus) • Hydrogen bacteria • Nitrifying bacteria (nitrites, ammonia) (Nitrobacter, Nitrosomonas) • Iron bacteria (Siderocapsa) • Play major role in ecological transformation of compounds (ammonia to nitrate; sulfur to sulfate • NH3 NO3- • S•  SO42-

25. Chemoorganotrophic heterotroph (aka chemoheterotrophs) • Carbon and energy source • Organic • H/e- source • Organic donor • Examples • Protozoa • Fungi • Most non-photosynthetic bacteria • Most pathogens (medically important bacteria = chemoheterotrophs)

26. IV. Nitrogen, Phosphorous and Sulfur are needed for the basic building blocks of cells

27. Nitrogen • Amino acids • Nucleic acids (purines and pyrimidines) • Some carbohydrates and lipids • Enzyme co-factors

28. Phosphorous • ATP • Co-factors • Nucleic acids (phosphodiester bonds) • Phospholipids (lipid bilayer) • Some proteins

29. Sulfur • S-containing amino acids • Some carbohydrates • Thiamine • Biotin

30. Growth Factors

31. Organic compounds required by microorganisms for growth and NOT synthesized by that mircoorganism • Obtain compounds or their precursors from the external environment • Three major classes • Amino acids, purines/pyrimidines, vitamins • Minor classes • Heme (H. influenzae), cholesterol (some Mycoplasma)

32. VI. Nutrient Uptake – Specific Mechanimsms Utilizing Selective Permeability

33. 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)

34. Facilitative diffusion employs carrier proteins called permeases to transfer components selectively across the PM • No metabolic energy needed • Works effectively even in low concentration gradients • Requires concentration gradient to facilitate uptake • Equilibrium will be established • But substance is NOT accumulated against a gradient

35. Probably involves a conformational change of carrier to deliver components across the lipid bilayer • Therefore effective for lipid-insoluble material • Not utilized much by bacteria but it does occur (e.g glycerol uptake by E. coli)

36. Active Transport • Transport of molecules AGAINST a concentration gradient • Material is more concentrated on the inside of the cell than on the outside • Ability to concentrate solutes in dilute environments • Metabolic energy required • ATP hydrolysis or • Proton motive forces (proton gradients generated by electron transport)

37. Carrier proteins utilized  energy dependent in PM (ATP) • Membrane-bouond • Multi-subunit • Form a pore • AKA permeases • May associate with substrate binding proteins in the periplasmic space of Gram-negative bacteria where substrate is handed over for entry across PM (e.g. arabinose, lactose, maltose, galactose, robose, glutamate, histidine, leucine)

38. 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

39. 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

40. Iron uptake • Ferric iron (Fe3+) is insoluble uner aerobic conditions • Bacteria must transport iron across PM to use in cytochromes and many enzymes • the organism secretes siderophores that complex with the very insoluble ferric ion, which is then transported into the cell • Siderophores = iron chelators

41. Types of siderophores • Hydroxamates (e.g. ferrichrome used by fungi) • Catecholates (e.g. enterobactin used by E. coli)

42. Iron handed off to the cell after siderophore binds to siderophore receptor protein on the microorganism

43. VII. Types of Culture Media

44. When media component are known = Defined Media (synthetic media)

45. When exact composition of some components is not nown = Complex Media (enriched, artificial, crude) • Required by fastidious organisms • Fastidious organisms are difficult to culture on ordinary media because of its need for secial nutritional factors (stringent physiological requirements for growth and survival)

46. Complex media often contains blood or serum • Sometimes blood must be lysed (chocolate agar) to release hemin and NAD (e.g Haemohilus and Neisseria – which do not produce siderophores) • Other undefined components: • Peptones (hydrolyzed protein) • Meat extracts or infusions (lean meat) – amino acids, peptides, nucleotdes, vitamins, mnerals and organic acids • Yeast extract (Brewer’s yeast – B vitamins, nitrogen and carbon compounds)

47. Agar added if solid medium is required • Agar = complex polysaccharide from red algae • General purpose media favors the growth of a variety of microbe types • Example: Tryptic soy broth • Can be enriched with blood components

48. Enriched media are supplemented by blood or other special nutrients to encourage the growth of fastidious heterotrophs

49. Selective Media supports the growth of particular microorganisms while inhibiting the growth of others • Examples • Bile salts and dyes – suppress Gram-positive bacteria while favoring the growht of Gram-negative bacteria • Can select based on enzymes e.g. cellulose utilization requires cellulase • Antibiotic resistance (plasmid-encoded, R-plasmid)

50. Differential Media distinguished different bacterial groups • Examples: • Blood agar – hemolysis (alpha, beta or gamma hemolysis) • Eosin methylene blue agar (EMB) – used to identify lactose fermenters (colony turns dark purple)