Chapter 5: Microbial Metabolism

What is Metabolism? Metabolism = all chemical reactions that occur in a cell/organism; catabolism + anabolism. Catabolism = breakdown of food molecules to produce energy and molecular subunits (example: amino acids from proteins) Anabolism = building of macromolecules that the organism needs (proteins from amino acid subunits or DNA from nucleotides)

Metabolic (also called biochemical) pathways e 1 e 2 e 3 A B C D Feedback inhibition = shutting off of biochemical pathway; product in pathway binds to e1 which changes its shape and stops its work

Enzymes Type of molecule – usually proteins; a few RNA molecules called ribozymes too. Words ending with –ase are enzymes Shape determines function Active site E = enzyme, S = substrate, P = product E + S ES E + P

Enzyme catalyzed reactions

Enzyme-substrate complexes

What affects enzyme activity? Temperature pH Concentration of substrate Inhibitors Ex. Folic acid pathway Sulfanilamide competes with PABA; no folic acid made Ex. Fluoride in drinking water and toothpaste inhibit cavity-causing bacteria

Denaturation of proteins

How temperature, pH, and substrate concentration affect enzyme activity --

How inhibitors work --

Energy molecules in cells ATP  ADP + P i NADH  NAD + + H + + 2e - FADH 2  FAD + 2H + + 2e -

Catabolism of Glucose 1. Aerobic respiration – efficient energy production (1 glucose converted to 38 ATP) 2. Anaerobic respiration – less efficient (less than 38 ATP); no oxygen 3. Fermentation – least efficient (2 ATP produced); usually without oxygen

Process:Start moleculeEnd moleculeEnergy molecules produced Waste GlycolysisGlucosePyruvate2 NADH 2 ATP -- Oxidation of pyruvatePyruvateAcetyl-CoA2 NADH2 CO 2 Krebs cycle (citric acid cycle) Acetyl-CoA--6 NADH 2 ATP 2 FADH 2 4 CO 2 Electron transport chain/chemiosmosis NADH FADH 2 NAD+ FAD ATPWater Aerobic Respiration

Anaerobic respiration Uses parts of all of the aerobic processes (but not all) Final electron acceptor not oxygen Possible e- acceptors: Nitrogen compounds NO 3 -  NO 2, N 2 O, N 2 Sulfur compounds SO 4 -2  H 2 S Carbon compounds CO 3 -2  CH 4

Fermentation Only produces 2 ATP molecules from 1 glucose Occurs without oxygen (O 2 ) Detour from glycolysis to a short fermentation pathway Produces by-products as NAD + and FAD are regenerated By-products produced include acids, alcohols, gases, etc.

Practical example: Fact: Clostridium perfringens causes gas gangrene Problem: How to cure gas gangrene… Patients affected: Anyone with an anaerobic site of tissue damage; diabetics particularly prone to this disease (Diabetics have poor circulation, nerve damage, lessened pain sensations, lower ability to heal) Diagnosis: Odors, specimen collection and identification of bacteria, X-ray for pockets of gas in tissues Treatment: Essential -- Remove dead tissue (sometimes even amputation of affected limb); Possible -- expose tissues to oxygen through a hyperbaric chamber and/or antibiotic regimen

This photomicrograph reveals Clostridium perfringens grown in Schaedler’s broth using Gram-stain. (Photo by CDC/Don Stalons, 1974.)

Wagner Grade 5 - Unsalvagable Gangrene Gangrene or necrosis to the extent that the foot is beyond salvage and will require a major limb- or life-sparing amputation.

Why do microbes have the ability to switch back and forth between aerobic respiration and an anaerobic process? ProcessAdvantagesDisadvantages Aerobic respirationMakes many ATPs from 1 glucose Requires oxygen; produces oxygen free radicals Anaerobic processes (fermentation or anaerobic respiration) Survival without oxygenMakes less ATP from glucose; slower growth; d etrimental waste products

What about anabolic reactions? What about other food sources besides glucose?

The End