A measure of viable cells in which a colony represents an aggregate of cells derived from a single progenitor cell
Types of bacteria by temperature
Psycrophilic – <20°C
Mesophilic – 16-40°C
Thermophilic – > 40°C
At low temps, bacteria become dormant
At high temperatures, bacteria can be killed
Nutrition types
Photoautotrophs
Photoheterotrophs
Chemoautotrophs or Lithotrophs
Chemoheterotrophs or heterotrophs
Photoautotrophs
Use light as energy source and CO2 as carbon source
Photoheterotrophs
Use light as energy source and organic compounds as carbon source
Chemoautotrophs or Lithotrophs
Use inorganic compounds (e.g. H2, NH3, NO2, H2S) as energy source and CO2 as carbon source
Chemoheterotrophs or heterotrophs
Use organic compounds as both energy and carbon source
Essential elements for bacterial growth
Carbon
Oxygen
Nitrogen
Hydrogen
Phosphorus
Sulphur
Potassium
Magnesium
Calcium
Iron
Growth factors
Required in small amounts to fulfil specific roles in biosynthesis
Types of growth factors
Purines and pyrimidines
Amino acids
Vitamins
Auxotrophs
Bacterial strains that need growth factors not needed by wild-type strains
Water activity (AW)
Denotes the water availability for microbial growth
AW of pure water is 1.0
Types of halophiles
Mild: 1-6%
Moderate: 6-15%
Extreme: 15-30%
Osmophiles
Organisms that survive in high sugar environments
Xerophiles
Organisms that live in dry environments
Types of organisms by oxygen requirement
Obligate aerobes
Obligate anaerobes
Facultative anaerobes (or facultative aerobes)
Aerotolerant anaerobes
All cells contain enzymes capable of reacting with O2, e.g. Oxidation of flavoproteins by O2 invariably result in the formation of H2 O2 and superoxide
In aerobes, the potential for lethal accumulation of superoxide is prevented by superoxide dismutase
Nearly all organisms contain catalase, which decomposes H2 O2
Anaerobes lack superoxide dismutase and catalase and therefore undergo lethal oxidations by various oxygen radicals
Types of bacteria by pH
Acidophiles
Neutrophiles
Alkaliphiles
Binary Fission
Growth of cells (usually lengthening), Duplication of chromosome, Septum synthesis and constriction, Cell divides into two identical daughter cells
FtsZ
Cell division protein that appears at the earliest moment of cell division and has a structural role in assembling at the site of septum
Sporulation
Process where vegetative cells form endospores when conditions for growth become harsh, involving activation of many genes. Endospores can remain dormant for years but can rapidly convert back to vegetative cells through germination.
Endospore structure
Exosporium – protein covering
Spore coat – layers of spore specific proteins
Cortex – composed of loosely linked peptidoglycan and contains dipicolinic acid (DPA)