Download Bacterial Growth Requirements

Bacterial Growth
Growth Requirements
Environmental Effects
Bacterial Growth Characteristics

Culture Media
– Chemicals
» Carbon
» Nitrogen
» Micronutrients (S, P, Fe, Mg, K, Na, etc.)
– Solid or Liquid
» Agar for solid support
– Sterilization usually using an autoclave
Bacterial Growth Characteristics

Agar
– Extract of seaweed (red algae) a
polysaccharide of galactose and galacturonic
acid
– In 1881, Fannie Hesse, who was working as a
technician for her husband in the laboratory of
Robert Koch, suggested agar
– Used as setting agent in jam making for some
time
– Replaced gelatin (poor temperature
characteristics and supports growth)
– Dissolves at 90°C and solidifies at 40°C
Bacterial Growth Characteristics

Culture Media
– Selective and Differential Media
– Complex vs. chemically defined
Bacterial Growth Characteristics

Selective and Differential Media
– Differential - differentiates between
organisms based upon colony morphology
(especially color) on media
– Selective - permits only certain organisms
to grow (e.g. high salt or other inhibitors)
Bacterial Growth Characteristics

Complex vs. chemically defined
– Chemically defined – each component has
a know chemical formula and/or structure,
e.g. minimal media (glucose, ammonium
nitrate, and a defined mixture of salts)
– Complex media (undefined) – components
come from non defined sources, e.g.
tryptone, peptone, yeast extract, oatmeal
Bacterial Growth/Environmental
Energy sources
 Carbon sources
 Physical influences on growth

Bacterial Growth/Environmental

Energy sources
– Organisms acquire energy as a result of
oxidation/reduction reactions
– Light energy - phototroph
– Chemical energy - chemotroph
» organic (reduced forms of carbon)
» inorganic (reduced metals)
Bacterial Growth/Environmental

Carbon sources
– autotrophs use carbon dioxide
– heterotrophs use reduced organic carbon
sources:
» sugars
» organic acids
» alcohols
Bacterial Growth/Environmental

Nitrogen sources
– Reduced (ammonia)
– Nitrates and Nitrites
– Nitrogen Fixation
Bacterial Growth/Environmental

Nutritional Classifications - based upon
energy & carbon source
– photoautotroph - uses light energy and
carbon dioxide as carbon source
– photoheterotroph - uses light energy and
an organic carbon source
– chemoautotroph - uses an inorganic
chemical as energy and carbon dioxide
– chemoheterotroph - uses an organic
chemical as energy and an organic carbon
source
Bacterial Growth - Physical

Physical Influences on Growth
–
–
–
–
–
Temperature
pH
Osmotic pressure
Oxygen availability
Oxygen toxicity
Bacterial Growth - Physical

Temperature
– psychrophillic - an organism that exhibits optimal
growth at about 15 deg. C and does not grow
above 20 deg. C
– mesophillic - an organism that exhibits optimal
growth at about 30-37 deg. C and does not grow
below 10 or above 50 deg. C
– thermophillic - an organism that exhibits optimal
growth between 50-60 deg. C and does not grow
below 40 deg. C or above 70 deg. C
– Hyperthermophillic – growth between 70 and 110
deg C
Bacterial Growth - Physical

pH
– most bacterial prefer pH 7 or slightly acidic
– can tolerate to pH 4 due to production of
organic acids during glucose metabolism
Bacterial Growth - Physical

Osmotic Pressure
– ideal seems to be about 0.5% to 1.0% NaCl
– some organisms tolerate much higher salt,
e.g. Staphylococcus will go to 10% NaCl
– halophiles - adapted to high salt
concentrations many belong to Archea
bacteria
Bacterial Growth - Physical

Toxic Oxygen - Forms
–
–
–
–
Singlet oxygen
Superoxide free radicals
Peroxides
Hydroxyl free radicals
Bacterial Growth - Physical

Toxic Oxygen - Neutralization
– Catalase:
» 2 H2O2  2 H2O + O2
– Superoxide dismutase:
» 2 O2 - + 2 H+  O2 + H2O2
– Peroxidases:
» H2O2  H+ + H2O
Bacterial Growth - Physical

Oxygen Classification
–
–
–
–
Aerobic - grows in presence of oxygen
Obligate aerobe - requires oxygen
Anaerobic - grows in absence of oxygen
Obligate anaerobe - will only grow in
absence of oxygen
– Facultative anaerobe - will grow both
anaerobically or aerobically
Bacterial Growth - Physical

Oxygen Classification
– Aerotolerant - only grow anaerobically but
will tolerate oxygen
– Microaerophillic - growth occurs only in
presence of low concentrations of oxygen
Bacterial Growth - Physical
Catalase
SOD
Obligate Aerobe
+
+
Faculatative Anaerobe
+
+
Obligate Anaerobe
-
-
Aerotolerant Anaerobe
-
+
Microaerophiles
-
-