Bacterial Metabolism

Bacterial Growth

Bacteria multiply by binary fission, with rate of growth limited by nutrients, temperature, and accumulation of toxic byproducts.

The generation time measures period of division, and for most organisms is measured in minutes.

Bacterial growth occurs in 4 phases:

Lag phase: adaptation to environment and synthesis of required enzymes

Log phase: rapid division; pahse of highest antibiotic activity

Stationary phase: nutrients become depleted and toxic metabolites accumulate; rate of reproduction equals rate of cell death

Death phase: death rate exceeds reproduction

Bacterial Metabolism

Bacteria require various factors for growth:

carbon source: simple carbohydrates, sugars, or proteins. some may fix carbon dioxide

nitrogen source: protein, amino acids, nitrates, ammonium salts. some may fix nitrogen gas

essential nutrients: vary among bacteria; fastidious organisms require complex molecules, blood, and vitamins to grow

temperature: mesophiles grow best between 20-40 C; others do better at low or high temperatures. Most human pathogens are mesophiles

oxygen: acts as a final electron accepter in aerobic organisms; anaerobic bacteria lack the means of detoxifying superoxide (O2-).

inorganic ions, iron: required for enzyme activity; bacteria produce sidophores that bind to insoluble Fe3+ and trabnsport it across the membrane.

pH: most organisms prefer neutral conditions and will die at a pH less than 6.

water: bacteria require soluble nutrients that enter the cell via diffusion. growth is inhibited in strong solutions of ie salt, sugar, and bacteria with weak cell walls burst in hypotonic solutions.

Catabolism

Lipids may be acted upon by lipase to produce glycerol and fatty acids, which can then be converted to glucose or oxidized, respectively.

Proteins may also be sued for energy by breakdown to amino acids.

Respiration vs Fermentation

Both aerobic and anaerobic bacteria use glycolysis to produce pyruvate friom glucose.

Aerobic bacteria use oxygen as the final electron acceptor in respiration, allowing the TCA cycle to function and produce a great deal of energy.

Anaerobic bacteria transfer electrons to organic acids and alcohols during fermention of pyruvate. End prodcuts include lactic acid, butric acid, butanediol, propionic acid, acetic acid, succinic acid, and ethanol.