Gr 11 Micro-organism Nutrition

Types of Microbes

Microorganisms may be differentiated according to their diverse morphological and metabolic characteristics:

• Microorganisms may differ in their cellular organisation – e.g. prokaryotes versus eukaryotes
• Microorganisms may exhibit different nutritional requirements – e.g. autotrophic versus heterotrophic
• Their method of respiration may vary according to type – e.g. aerobic versus anaerobic respiration
• They may have different structural characteristics – e.g. shape or cell wall composition

According to the three domain classification scheme, there are three distinct types of cellular organisms to which all living things may belong:

• Eukarya: Contain a membrane-bound nucleus (includes plants, animals, protists and fungi)
• Eubacteria: Lack a nucleus and consist of the traditional or 'true' bacteria (e.g. most pathogenic forms, E.coli, S. aureus, etc.)
• Archaea: Lack a nucleus and consist of the extremophiles or 'ancient' bacteria (e.g. methanogens, thermophiles, halophiles)

Archaea

Methanogens

• Obligate anaerobes (cannot survive in the presence of oxygen)
• Produce methane as a waste product and are found in marshes, the guts of animals and oxygen depleted soils (e.g. landfills)

Thermophiles

• Can survive abnormally high temperatures and live at temperatures close to boiling (60 – 100ºC)
• Are found in hot springs and near geothermal lava flows (e.g. deep sea vents and volcanic calderas)

Halophiles

• Live in saline habitats with very high salt concentrations
• Found in regions of the Great Salt Lake and the Dead Sea

Eubacteria

Nutrition

Microorganisms can be categorised according to their mode of nutrition:

• Photoautotrophs use light energy to synthesise organic molecules (e.g. cyanobacteria)
• Chemoautrophs use energy from chemical oxidation to synthesise organic molecules (e.g. nitrogen-fixating bacteria)
• Heterotrophs obtain organic nutrients via feeding (e.g. amoeba)
• Saprotrophs release digestive enzymes onto non-living organic matter and absorb the products (e.g. fungi)

Microorganisms can also be categorised according to their mechanism of respiration:

• Obligate anaerobes respire anaerobically and can only grow in the absence of oxygen
• Aerotolerant anaerobes respire anaerobically but can grow in the presence of oxygen
• Facultative anaerobes can respire anaerobically or aerobically depending on oxygen availability
• Obligate aerobes only respire aerobically and cannot survive in the absence of oxygen