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Bmic 3.4 - Coggle Diagram
Bmic 3.4
physical environmental factors that affect microbial growth
pH
Affects biochemical reactions(enzymatic activities, redox reactions etc.)
microbes usually have a narrow range round the neutral pH
neutrophiles:6.5 to 7.5
acidophiles:<4
alkalinophiles: up to 11.5
Many microbes produce acid by-products, lowering pH and inhibiting further microbial growth--lactobacilli produce lactic acid and other organic acids during growth
Temperature
minimum and maximum growth temperature, optimum growth temperature
Mesophiles-20C to 45C
Thermophiles-50C to 60C
Psychrophiles-10C to 20C
Hyperthermophiles-90C to 120C
Affects biochemical reactions
Low temp: slow growth, low RoR
High temp: denature cellular proteins, cell death
Gaseous atmosphere
Some microbes require O2 during respiration to generate energy, some do not require O2 at all(anaerobes). Some are even killed in the presence of O2
Toxicity of O2
Metabolic reactions often transform oxygen into highly reactive forms:
Superoxide radical (O2-)
Peroxide anion (O22-)
Hydroxyl radical (OH)
Some microbes cannot detoxify reactive oxygen radicals and so the radicals kill the macromolecules, killing the cells
Neutralisation
3 enzymes
Superoxide dismutase
neutralizes O2-
2O2- + 2H+ H2O2 + O2
Catalases
break down H2O2
to water and O2
2H2O2 2H2O + O2
Peroxidases
reduce H2O2 to water
using NADH
H2O2 + NADH + H+ 2H2O + NAD+
Hydroxyl radicals are generated from H2O2; since H2O2 is readily removed, these radicals rarely accumulate
Strict aerobes(must have oxygen to grow) and facultative anaerobes(do not require O2 to grow, but grow more in the presence of O2) possess these enzymes to neutralize reactive oxygen species
Grow at surface of the tube, grow throughout the tube9facultative anaerobe)
Aerotolerant anaerobes-anaerobic growth, can continue to grow in O2(tolerate)
Microaerophiles have limited ability to detoxify oxygen
Microaerophiles requires O2 at low levels (2% - 10%) but killed by atmospheric levels of O2
grow below surface of broth
Strict anaerobes(anaerobic growth), do not require O2 to grow, so do not possess these enzymes to neutralise toxic oxygen
grow at the bottom of tube
Capnophile – grows bests at increased CO2 and reduced O2 levels
Water availability
solvent
for nutrients and enzymes
important
reactant
in metabolic reactions
water is essential for the microbes survival
Some bacteria sporulate while algae and protozoa encyst (to enclose or become enclosed by a cyst, thick membrane, or shell.) during dry conditions
Water Activity(Aw)
A measure of “free water” that is available to the cell
when Aw decreases, solute concentration increases
Most bacteria require an Aw of >=0.96
Yeast and mould can grow at low Aw(<0.9)
Xerotolerant
microbes can live in an Aw as low as 0.6
Osmotic pressure-pressure exerted on ppm membrane by solution
Hypertonic – net loss of water; plasmolysis
Hypotonic – net gain of water; if no cell wall lysis
Halophiles require higher salt concentration to grow
Typically marine microbes (seawater: 2.8% – 3.5% NaCl)
Some can tolerate up to 20% - 30% salt, eg. Staphylococcus aureus (a skin commensal)