MICROBIO 4.1

MICROBIAL GROWTH & CONTROL

Growth Requirements

Nutrients, temperature, pH

Nutrients

• Source of carbon

• Source of energy

• Oxygen

• Nitrogen

• Growth factors & Trace elements

Autotroph

Organism that uses inorganic carbon sources (CO2 or molecules w/o carbon)

Heterotroph

Organism that uses organic sources of carbon (molecules w/ carbon, usually bound by H bonds)

Phototroph

Organism that gains energy from light

Chemotroph

Organism that gains energy from chemicals

Obligate aerobes

Organisms that depend on oxygen for energy generation (oxidative phosphorylation)

Have antioxidants (vitamin C or E) that detoxify ROS

Obligate anaerobes

Oxygen is toxic to these organisms; metabolic pathways use an alternative electron acceptor

NOT all oxygen; toxic oxygen is FREE oxygen (ROS)

Reactive Oxygen Species (ROS)

FREE oxygen that can take electrons from other molecules & damage lipids, proteins, DNA

O₂ (singlet oxygen)

O₂^- (superoxide anion)

O₂^2- (peroxide ion)

OH^- (hydroxyl radical)

Facultative anaerobes

Grows better with oxygen, but can live w/o it

e.g. E. coli

Nitrogen for microbial growth

Bacterial cells are FOURTEEN percent Nitrogen (amino acid, protein, nucleic acid)

Growth limiting nutrient

Trace elements

Elements needed in miniscule amounts to support metabolism

Growth factors

Organic chemicals needed in small quantities to support metabolism

e.g. amino acids → used for making proteins; cholesterol → used for cell membrane

Thermophiles

Organisms that thrive at GREATER than 45 degrees C.

e.g. Hot springs, thermal vents, bottom of landfill

*This means some microbes CAN survive autoclaving

Mesophiles

Organisms that thrive at 10-50 degrees C.

These cause human disease (37 degrees C)

Psychrophiles

Organisms that thrive at LESS than 20 degrees C.

e.g. Fungi, algae, bacteria, archaea; polar regions, glaciers

CAN SURVIVE REFRIGERATION & cause spoilage of food

Acidophiles

Thrive in acidic environment (<7)

e.g. bacteria & fungi

Neutrophile

Thrive at pH 6.5-7.5

Many pathogens are neutrophilic; human tissue pH is ~7

Stomach (acidic) inhibit bacterial growth

Alkalinophiles

Up to pH 11.5

e.g. soil or alkaline water

Enoculum

Sample of microbe (we will mostly be talking about mesophiles)

Medium

Broth (liquid) or solid media; the environment grown

Culture

Refer to microbes grown in media

OR

Refer to the process of isolating & growing microorganism for:

• ID purpose;

• Can confirm infection diagnosis

• Research

• Use as macromolecule factories

Colonies

Cluster of cells arising from ONE parent cell; genetically identical

Incubation period

Time when microbe is being cultured @ optimal temperature for growth

Growth media

Nutrient rich broth for general purpose growth (e.g. LB)

TWO types: DEFINED & UNDEFINED

DEFINED growth media

Media with EXACT quantities of all ingredients (molecule-specific)

UNDEFINED growth media

Media with mixtures of unknown ratios added (e.g. yeast or beef extract)

Selective media

Grows specific bacteria; LIMITS others

• Add ingredients

  • Dyes → limit gram-positive (Eosin, Methylene blue, bile salts, Crystal violet)

  • Antibiotics, salts

• Eliminate nutrient

  • Sugar → TSA doesn’t contain glucose

  • Amino acids

Can inhibit foreign microbes

Ensure isolated growth of slow growing organisms

Differential media

Distinguishes two microbes by change in media OR colonies

• Because of different metabolic pathways

• Indicators like dyes OR pH detectors are added

Enriched media

Grows fastidious (picky) organisms; contain essential nutrients for particular microbes