Microbial NutritionCell metabolism

Nutritional Categories of Microorganisms

• Microorganisms are often grouped according to the sources of energy they use:

– Phototrophs use light as an energy source• Photosynthesis

– Chemotrophs use chemicals as energy sources• Chemoorganotroph

• Chemolithotroph

Biochemical Components of Cells

• Water: 80 % of wet weight

• Dry weight– Protein 40-70 %– Nucleic acid 13-34%– Lipid 10-15 %– Also monomers, intermediates and inorganic

ions

Macronutrients

• Cells make proteins, nucleic acids and lipids

• Macronutrients– macromolecules, metabolism– C, H, O, N, S, P, K, Mg, Fe– Sources

• Organic compounds

• Inorganic salts

Micronutrients

• Elements needed in trace quantities – Co, Cu, Mn, Zn, V– Enzymes– tap water

• Growth factors– Organic compounds– Vitamins

Defined / Complex Media

• Defined– Prepared with precise amounts of chemicals– Known composition

• Complex– Exact composition unknown– Digests of beef, soybean, yeast

Other Culturing Considerations

• pH• Oxygen concentration• Temperature• Light / carbon dioxide (phototrophic organisms)

Role of Oxygen in Nutrition

• Obligate aerobes – require O2

• Obligate anaerobes – O2 is toxic

• Facultative anaerobes

• Microaerophilic organisms

Transport of Nutrients into the Cell

• Nutrients are obtained from the environment

• Many of the nutrients are polar

• Cannot diffuse across the cell membrane

• Proteins embedded in the membrane

• Transport against a concentration gradient - active transport

Bioenergetics

• Living cells require energy for growth, biosynthesis, reproduction and transport

• Energy needed to drive the biochemical reactions of cells is stored and transferred via adenosine triphosphate (ATP)

Fermentation and Respiration

• Chemoorganotrophs obtain their energy from oxidation of organic compounds– loss of electrons/removal of hydrogen

• Fermentation– No terminal electron acceptor

• Respiration– Terminal electron acceptor (e.g. O2)

Glycolysis

C6H12O6

C3H4O3

glucose

pyruvic acid

ADP

ATP

NAD+

NADH + H+

Substrate-level phosphorylation

CH2

COPO3H2

COOH

CH3

C

COOH

O

ADP ATP

phosphoenolpyruvic acid

pyruvic acid

Fermentation products

• Need to regenerate NAD+

• Reduce pyruvic acid

C3H4O3 C3H5O3

pyruvic acid lactic acid

NADH + H+ NAD+

Oxidative phosphorylation

• Occurs in respiration (aerobic and anaerobic)

• Proton motive force– Electrons from NADH are passed along an

electron transport chain– Protons are pumped across membrane– Electrochemical gradient– Drives ATP synthesis from ADP and Pi

Summary

• Nutrients– Macronutrients/micronutrients– Defined/complex media– Cell membranes

• Energy production– Different modes

Further reading

Madigan MT, JM Martinko, J Parker, 2000. Brock Biology of Microorganisms, 9th Edition. Chapters 3 and 4.