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Lecture 8


. Chemical Requirements for Growth

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A living microbes are made up C, N, P, O, S, H, K, Fe, Mg, and Ca. These elements must be obtained in quite large qualities In addition, microbes require some in smaller amounts (micronutrients) e.g. Mn, Zn, Co, Mo etc..
Modes of microbial nutrition.
Microbes can be classified based on how they obtain their carbon and energy.
Heterotrophs
Gain there Carbon from organic the compounds they utilize
Chemoheterotrophs use organic compounds for energy and carbon just like us.
Photoheterotrophs organisms that can use light for energy ("photo") and organic compounds ("hetero") for carbon
Autotrophs Can obtain Carbon from non-organic sources (i.e. fix carbon dioxide and turn it into organic molecules) Sometimes called self feeders.
Photoautotrophs get energy from light energy like plants, (e.g.. cyanobacteria and many other bacteria).
Chemoautotrophs use chemical energy and fix CO2 (e.g. sulfur oxidizing and nitrifiers) "Chemolithoautotrophs" is a term sometimes used for chemoautotrophs that use inorganic compounds for energy,
Fastidious Organisms
Require a range of vitamins performed peptides, nucleotides and other specific growth factors
Mildly fastidious organisms can be grown on Nutrient Agar or Broth
More fastidious organisms require more complex mixture and need Enriched media. Such as Blood Agar . milk or liver broth.
Very fastidious organisms may need living cell to grow on.

How do microbes feed?

Bacteria, Fungi feed by absorbing chemicals from their environment. Everything that gets into the cell must enter via diffusion (e.g. O2, H2O, CO2) or via some sort of transport protein or channel. In contrast, most protozoa can phagocytize chunks of material (including whole bacterial cells) and digest them in vacuoles that act like little stomachs.
Diffusion - small or uncharged molecules can diffuse across the plasma membrane.
Facilitated diffusion is just diffusion that utilizes a specific trans-membrane protein (a permease)
Active Transport utilizes transporter and use ATP to take up nutrients against the diffusion gradient

Microbial Digestion

Microbes consume polymers and insoluble substrates by breaking them down outside their cells using enzymes released into their surroundings:

Extracellular enzymes
The enzymes released by various bacteria can be used to identify the bacteria and will determine the type of food it can use
Bacillus produce extracellular amylase
Cytophaga produces extracellular cellulases
Pseudomonus produces many enzyme and can make a lot of changes to food ( food spoilage)
Siderophores
Compounds are used to capture metal irons
Emulsifying agents
"biosurfactants" are extracellular compounds produced by microbes that eat oils.
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The End

 

Prepared by Barry Brazier