BACTERIAL NUTRITION AND GROWTH

All bacteria require two things for growth:

                  1)      A source of energy

2)      A source of matter for building additional cells:

C, O, H, N, S, P, trace minerals.

Elemental Assay of E. coli (dry weight)

50% carbon

20% oxygen

14% nitrogen

8% hydrogen

3% phosphorus

2% sulfur

2% potassium

0.05% calcium, magnesium, chlorine

0.2% iron

0.3% trace elements

• Carbon, the backbone of functional biological molecules: cells vary in their ability to synthesize all of their carbon compounds. Range of carbon compounds utilized: CO, CH₄, to complex organic compounds.
• Hydrogen: structural molecule, participant in process of energy generation. Protons (H⁺) involved in ATP production, CO₂ reduction, anaerobic and aerobic respiration.
• Nitrogen in amino acids, nucleic acids. membranes, cell walls, and most macromolecules. Most free-living microbes assimilate ammonia from their environment or reduce nitrate. An array of microbial types can "fix" atmospheric nitrogen.
• Sulfur in certain amino acids, some B-vitamins (biotin and thiamine). Reduced inorganic sulfur (e.g. H₂S) used as energy source for thiobacilli. Sulfur serves as terminal electron acceptor in some Archaea.
• Phosphorus: a constituent of high energy compounds (ATP), phospholipids in membranes, nucleic acids.
• Oxygen: equal amounts in aerobes and anaerobes, but free oxygen toxic to anaerobes, so they obtain it in a combined form from the substrate.

Trace elements, though not required in large amounts, are essential for cellular growth:

Some Important Cofactors and Examples of Their Functions:

K+       Principle cellular counterion

Mg++   DNA polymerase

Ca++    Intracellular signalling, wall structure

Fe++    Cytochromes

Mn++   PsII, photosynthesis

Co++   Vitamin B12 constituent (methylations)

Cu++   Superoxide dimutase

Zn++   Some DNA binding proteins

Organic Growth Factors are essential organic compounds that an organism is unable TO synthesize. They must be obtained directly from the environment.

Examples: Vitamins, Amino acids, Purines, pyrimidines

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These elements are assembled into macromolecules:

The composition of prokaryotic cells

                                             % dry Weight

Protein                                           55

RNA                                               20.5

Ribosomal                      80% of total RNA

Transfer                         15% of total RNA

Messenger                     5% of total RNA

DNA                                               3.1

Lipid                                              9.1

Lipopolysaccharide                         3.4

Peptidoglycan                                 2.5

Glycogen                                        2.5

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Bacteria are often categorized according to their source of carbon, energy, and electrons (hydrogen

Carbon sources:

         Autotrophs                   CO₂ sole or principal source

         Heterotrophs                Reduced organic molecules

Energy sources:

         Phototrophs                          Light

         Chemotrophs                Oxidation of organic or inorganic compounds

Hydrogen sources:

Lithotrophs                           Reduced inorganic molecules

Organotrophs               Organic molecules