Cell Chemistry, Nutrition, and Microbial Culture Techniques

Nutrients

Supply of monomers (or precursors of) required by cells for growth

Macronutrients

Nutrients required in large amounts

Micronutrients

Nutrients required in trace amounts

Carbon

Required by ALL cells; typical bacterial cell is ~50% carbon (by dry weight); major element in ALL classes of macromolecules

Heterotrophs

Use organic carbon

Autotrophs

Use carbon dioxide (CO2)

Nitrogen

Typical bacterial cell is ~13% nitrogen (by dry weight); key element in proteins, nucleic acids, and many more cell constituents

Phosphorus (P)

Synthesis of nucleic acids and phospholipids

Sulfur (S)

Sulfur-containing amino acids (cysteine and methionine); vitamins (e.g., thiamine, biotin, lipoic acid) and coenzyme A

Potassium (K)

Required by enzymes for activity

Magnesium (Mg)

Stabilizes ribosomes, membranes, and nucleic acids; also required for many enzymes

Calcium (Ca)

Helps stabilize cell walls in microbes; plays key role in heat stability of endospores

Sodium (Na)

Required by some microbes (e.g., marine microbes)

Iron

Key component of cytochromes and FeS proteins involved in electron transport

Growth factors

Organic compounds required in small amounts by certain organisms; examples: vitamins, amino acids, purines, pyrimidines

Vitamins

Most commonly required growth factors; most function as coenzymes

Culture media

Nutrient solutions used to grow microbes in the laboratory

Defined media

Precise chemical composition is known

Minimal media

Nothing more than the essential compounds

Complex media

Composed of digests of chemically undefined substances (e.g., yeast and meat extracts)

Enriched media

Contain complex media plus additional nutrients

Selective media

Contain compounds that selectively inhibit growth of some microbes

Differential media

Contain an indicator (dye), detects particular chemical reactions

Pure culture

Culture containing only a single kind of microbe (species, strain even)

Contaminants

Unwanted (usually unknown) organisms in a culture

Solid media

Prepared by addition of a gelling agent (agar or gelatin)

Streak plate

Technique where isolated colonies are obtained at the end of the streak

Spread Plate

CFU = # colonies/dilution factor * plating factor

Metabolism

The sum total of all of the chemical reactions that occur in a cell

Catabolic reactions (catabolism)

Energy-releasing metabolic reactions

Chemorganotrophs

Microorganisms that obtain energy from organic compounds

Chemolithotrophs

Microorganisms that obtain energy from inorganic compounds

Phototrophs

Microorganisms that obtain energy from light

Heterotrophs

Microorganisms that obtain carbon from organic sources

Autotrophs

Microorganisms that obtain carbon from inorganic sources