Bms1026 Microbial Growth

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Metabolism

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The sum of chemical reactions in an organism (those releasing energy - those consuming energy)

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Anabolic reactions

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The phase of the metabolism in which simple substrates are synthesised into complex materials that make up the cell.

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Catabolic reactions

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The phase of the metabolism in which complex materials are broken down into simpler molecules often with the release of energy.

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Aerobic respiration - Glycolysis

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Glucose (6c) -> 2 x pyruvate (3c)
with the overall release of 2ATP and 2NADH

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Aerobic respiration - Link reaction

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(3c) Pyruvate -> Acetyl coA (2c)
with the overall release of co2 and NADH

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Anaerobic respiration - fermentation

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Pyruvate -> Lactic acid (reduction)
with the release of NAD+

Pyruvate -> Acetaldehyde -> Alcohol (oxidation)
with the release of co2 and NAD+

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Chemotrophs

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Organisms that obtain energy from chemical means by oxidising electron donors in their environments.

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Phototrophs

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Organisms that obtain energy from light via proton capture.

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Chemoheterotrophs/photoheterotrophs

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Use organic carbon sources of macromolecules. (cant fix their own carbon from co2)

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Chemoautotrophs/photoautotrophs

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Produce complex macromolecules from smaller monomers/co2 fixing.

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Species richness

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Total number of species present in a habitat (increases as nutrients increases)

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Species abundance

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Proportion of each species in the ecosystem (decreases as nutrients increases)

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Affect of oxygen - Obligate Aerobes

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Need aerobic conditions to survive.

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Affect of oxygen - Facultative Aerobes

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Prefer anaerobic conditions, but can survive and respire using oxygen (have protection against oxidative damage)

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Affect of oxygen - Obligate Aerobes

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Need anaerobic conditions to survive (have no protection against oxidative damage and free radicals)

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Affect of oxygen - Facultative Anaerobes

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Prefer aerobic conditions but can respire anaerobically if needed.

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Affect of oxygen - Microaerophilic organisms

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Require oxygen but can only tolerate very small amounts (usually slightly below atmospheric o2)

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Affect of oxygen - Aerotolerant

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Do not require oxygen as respire anaerobically but are not affected by oxygen/oxidative damage.

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Affect of oxygen - Damage

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Formation of superoxide free radicals are formed and need neutralising (using SOD - superoxide dismutase)
o2- + o2- + 2h+ -> h2o2 +o2
h2o2 -> 2h2o + o2 (with catalase and peroxidase)

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Affect of temperature - Psychrophiles

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Can survive in temps between -10 and 20 degrees c.

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Affect of temperature - Psychrotrophs

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Can survive in temps between 0 and 30 degrees c.

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Affect of temperature - Mesophiles

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Can survive in temps between 10 - 50 degrees c (most bacteria).

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Affect of temperature - Thermophiles

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Can survive in temps between 40 - 72 degrees c.

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Affect of temperature - Hyperthermophiles

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Can survive in tempts between 68 and 110 degrees c (most archea)

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Affect of temperature - Protein denaturing

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Increase thermal stability by folding differently to create a very hydrophobic core which is less prone to unravelling or have heat shock proteins that refold denatured proteins.

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Affect of temperature - DNA damage

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Use of reverse DNA gyrase which keeps DNA coiled, Histone like proteins are found which act as DNA binding proteins and help prevent uncoiling. Cytoplasm can contain solute that prevents chemical damage.

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Affect of temperature - Membrane fluidity

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As temperature increases membranes tend to become more fluid to counteract this membranes contain more saturated fatty acids so the fatty acids can pack more closely together and increase stability (Archea tend to lack lipid bilayers so are more rigid and stronger at higher temps)

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Affect of temperature - Growth temperatures

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microbes have a minimum, maximum and optimum growth temperature. The maximum tends to drop quite fast after the optimum.

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Affect of PH - Acidophile

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Can survive at PH's between 1 and 4

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Affect of PH - Neutrophile

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Can survive at PH's between 5 and 9

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Affect of PH - Alkaliphile

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Can survive at PH's between 7.5 and 11

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Affect of PH - Maintaing PH homeostasis

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Have many mechanisms to help maintain a constant PH is acidic conditions (reverse for alkali):
- Increase H+ impermeability of membrane,
- Reduce size of membrane channels,
- Contain cytoplasmic buffering molecules,
- Contain repaire proteins to fix damaged DNA,
- Transport high no. of unreactive cations into cell,
- Have many active proton pumps.

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Affect of water activity - Definition

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Aw = Psolution/Pwater
= the water vapour pressure of a solution divided by that of pure water
(bacteria need 0.9, fungi 0.7)

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Affect of water activity - Xerophiles

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Can survive in very dry conditions with lo water activity.

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Affect of salinity - Non-halophile

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Can only survive in no or very low concs of salt (<1M).

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Affect of salinity - Halotolerant

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Can survive in salt concs up to 3M but survive best at lower concentrations.

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Affect of salinity - Halophile

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Can survive in a broad range of salt concs from 0.5-4M (cant survive in 0m)

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Affect of salinity - Extreme Halophile

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Can survive in very high concs of salt and needs at least 2m.

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Affect of salinity - Hypotonic

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Cell has a higher conc of solute (eg salt) than environment causes intake of water and possible bursting.

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Affect of salinity - Isotonic

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Equal concentrations of solute (eg salt) inside the cell and in the environment so no net movement of water occurs.

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Affect of salinity - Hypertonic

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Cell has a lower conc of solute (eg salt) than environment cause release of water and shrinking of cell.

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Affect of salinity - Osmoregulation

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Can accumulate K+ instead of Na+ which will protect proteins or exclude salt from the cytoplasm.

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Controlling growth - Temperature

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Heat preservation - Pasteurisation, boiling, flaming, autoclaving, incineration etc.
Cold preservations - freezing so that ice crystals can disrupt cell membranes or slow/inhibit growth.

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Controlling growth - PH

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Addition of acids (pickling) or insitu fermentation of non harmful microbes to decrease PH.

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Controlling growth - Water activity

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Decreasing water activity by drying, salting, freeze drying or adding sugar is often used in food preservation

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Controlling growth - Chemical mechanisms

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Can be -cidal (kill microbes) or -static (inhibit growth)
eg. Sterilants kill all forms of microbe life
Disinfectants only kill cells, not spores.