6. Microbial Metabolism

• Metabolism


  The series of biochemical reactions by which the cell breaks down or biosynthesizes various metabolites
• Nutrient requirements


  Differ due to the metabolic capacities of microbes
• Elements predominant in the cell

  • C
  • H
  • O
  • N
  • P
  • S
• Carbon


  • Needed in the largest amount, amounting to 50% of a cell's dry weight
• Oxygen and hydrogen


  • Cover 25% of a cell's dry weight when combined
• Nitrogen


  • Occupies 13% of the cell's dry weight
• Phosphorus, Sodium, Potassium, Magnesium, and Selenium


  • Make up 5% of a cell's dry weight when combined
• Microbial nutrients


  • Macronutrients
  • Micronutrients
• Macronutrients


  Required in large amounts
• Micronutrients


  Required in minute amounts
• Micronutrients


  • Trace elements as co-factor of certain enzymes
  • Vitamins as growth factors (organic micronutrient)
  • Iron (Fe) plays a major role in cellular respiration

  
• Active transport of nutrients into the cell

  An energy requiring process driven by ATP (or some other energy-rich compound) or by the proton motive force
• Classes of transport systems

  • Simple
  • Group translocation
  • ABC systems
• Simple transport


  Major transport systems comprising of reactions that are driven by the energy inherent in the proton motive force

  
• Simple transport systems


  • Symport reactions
  • Antiport reactions
• Group translocation


  The transported substance is chemically modified during the transport process, driven by an energy-rich organic compound
• ABC transport systems


  Transport systems that employ a periplasmic binding protein along with transmembrane and ATP-hydrolyzing components
• Energy classes of microorganisms

  • Chemotrophs
  • Phototrophic organisms

  
• Chemotrophs


  Organisms that conserve energy from chemicals
• Chemotrophs


  • Chemoorganotrophs
  • Chemolithotrophs
• Chemoorganotrophs


  Use organic chemicals as their electron donors
• Chemolithotrophs


  Use inorganic chemicals as their electron donors
• Phototrophic organisms


  Convert light energy into chemical energy (ATP)
• Phototrophic organisms


  • Oxygenic
  • Anoxygenic
• Heterotroph


  Its cell carbon is obtained from one or another organic compound
• Autotroph

  Uses carbon dioxide (CO2) as its carbon source
• Most chemolithotrophs and phototrophs are autotrophs
• Autotrophs


  Also called primary producers because they synthesize new organic matter from inorganic carbon (CO2)
• Calvin cycle


  The major biochemical pathway by which phototrophic organisms incorporate CO2 into cell material
• Enzymes


  Protein catalysts that increase the rate of biochemical reactions by activating the substrates that bind to their active site
• Enzymes


  • Highly specific in the reactions they catalyze, and this specificity resides in the three-dimensional structures of the polypeptide(s) that make up the protein(s)
• Redox reactions


  Chemical reactions in the cell accompanied by changes in energy, expressed in kilojoules
• ∆G0


  A measure of the energy released or consumed in a reaction under standard conditions, reveals which reactions can be used by an organism to conserve energy
• Reduction potential (E0')


  The tendency of a compound to accept or release electrons
• Redox reactions in a cell often employ redox coenzymes such as NAD+/NADH as electron shuttles
• ATP


  The prime energy carrier in the cell, consists of the ribonucleoside adenosine to which three phosphate molecules are bonded in series
• Categories of metabolism


  • Anabolism
  • Catabolism

  
• Anabolism

  Any process that results in synthesis of cell molecules and structures, consumes energy
• Catabolism


  Breaks the bonds of larger molecules into smaller molecules, releases energy

  
• Much of the energy released during catabolic reactions is used to drive anabolic reactions