Microbiology | Recommended microbes
Bacteria

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Bacteria

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Fungi

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Viruses

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Other microbes

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Unsuitable microbes

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BACTERIUM

EDUCATIONAL USE, INTEREST
and SUITABILITY

EASE OF USE  and MAINTENANCE

Acetobacter aceti

Of economic importance as it causes spoilage in beers and wines, by oxidising ethanol to ethanoic (acetic) acid, carbon dioxide and water.

However, this is utilised deliberately in the production of vinegar.

Needs special medium and very frequent subculturing to maintain viability.

Agrobacterium tumefaciens

Causes crown gall disease in plants, by transferring a tumour-inducing (Ti) plasmid. 'Disabled' forms of this plasmid are used as vectors in the genetic modification of dicotyledonous plants.

Grows on nutrient agar, but requires 2-3 days' incubation.

Alcaligenes eutrophus

In the absence of nitrogen, it produces intracellular granules of poly--hydroxybutyrate (PHB) used in the production of biodegradable plastics (e.g., ICI's 'Biopol').

Grows on nutrient agar.

Azotobacter vinelandii

A free-living nitrogen fixer, producing a fluorescent, water-soluble pigment.

Grows on a nitrogen-free medium.

Bacillus megaterium

Has very large cells; produces lipase, protease and also PHB (see Alcaligenes); Gram-positive staining.

Grows on nutrient agar.

Bacillus stearothermophilus

Thermophilic species which grows at 65 C; produces lipase and protease. Also used to test the efficiency of autoclaves.

Grows on nutrient agar.

Bacillus subtilis [1]

General-purpose, Gram-positive bacterium. Produces amylase, lipase and protease.

Grows on nutrient agar.

Cellulomonas sp.

Produces extra-cellular cellulase.

Grows on nutrient agar but also used with agar containing carboxymethylcellulose.

Chromatium sp.

A photosynthetic, anaerobic bacterium.

Requires special medium and light for good growth.

Erwinia carotovora

(= E. atroseptica)

Produces pectinase which causes rotting in fruit and vegetables. Useful for studies of Koch's postulates.

Grows on nutrient agar.

Escherichia coli [1]

K12 strain: general-purpose, Gram-negative bacterium.

B strain: susceptible to T4 bacteriophage

Grows on nutrient agar.

Janthinobacterium (= Chromobacterium) lividum [2]

Produces violet colonies. Grows best at 20 C.

Needs frequent subculture; will grow on nutrient agar but special medium recommended. Bacterium

Lactobacillus spp.

Ferment glucose and lactose, producing lactic acid.

L. bulgaricus is used in the production of yoghurt.

Requires special medium and frequent subculturing to maintain viability.

Leuconostoc mesenteroides

Converts sucrose to dextran, which is used as a blood plasma substitute.

Requires special medium (same as that required for Lactobacillus).

Methylophilus methylotrophus

Requires methanol as energy source; was used for the production of 'Pruteen' single-cell protein.

Requires special medium containing methanol.

Micrococcus luteus (= Sarcina lutea)

Produces yellow colonies; useful in the isolation of the bacterium from impure cultures. Also used to simulate the effects of disinfectants, mouthwashes and toothpastes on more harmful organisms.

Grows on nutrient agar.

Photobacterium phosphoreum

Actively-growing, aerated cultures show bioluminescence; grows in saline conditions.

Requires a medium containing sodium chloride.

Pseudomonas fluorescens

Produces a fluorescent pigment in the medium.

Grows on nutrient agar.

Rhizobium leguminosarum

A symbiotic, nitrogen fixer; stimulates the formation of nodules on the roots of legumes but special conditions are needed for N-fixation in culture.

Grows on yeast malt agar; some authorities recommend buffering with chalk to maintain viability.

Rhodopseudomonas palustris

A photosynthetic, anaerobic, red bacterium. Also grows aerobically in the dark.

Requires light and a special medium, growing atypically on nutrient agar.

Spirillum serpens

Of morphological interest.

May grow on nutrient agar but requires very frequent subculturing to maintain viability.

Staphylococcus albus (= epidermidis) [3]

A general-purpose, Gram-positive bacterium, producing white colonies.

Grows on nutrient agar.

Streptococcus (= Enterococcus) faecalis

Of morphological interest, forming pairs or chains of cocci.

Nutrient agar with added glucose can be used but grows better on special medium, as for Lactobacillus.

Streptococcus (= Lactococcus) lactis

Can grow on nutrient agar with added glucose; some authorities recommend buffering with chalk to maintain viability.

Streptococcus thermophilus

Ferments glucose and lactose, producing lactic acid; used in the production of yoghurt. Grows at about 50C.

Can grow on nutrient agar with added glucose; some authorities recommend frequent subculturing to maintain viability.

Streptomyces griseus

Responsible for the earthy odour of soil. Grows to form a fungus-like, branching mycelium with aerial hyphae bearing conidia. Produces the antibiotic streptomycin, although a suitable strain is required to demonstrate this convincingly.

Grows on nutrient or glucose nutrient agar but better on special medium which enhances formation of conidia.

Thiobacillus ferrooxidans

Involved in the bacterial leaching of sulphur-containing coal. Oxidises iron (II) and sulphur. Demonstrates bacterial leaching of coal samples containing pyritic sulphur.

Requires special medium.

Vibrio (= Beneckea) natriegens

A halophile, giving very rapid growth. Prone, however, to thermal shock with a sudden drop in temperature.

Requires medium containing sodium chloride.

Vibrio spp.

Of morphological interest, with typical shape, better shown than by V. natriegens but ensure that a safe species is used.

Grows on nutrient agar.

NOTES

1.

Some strains of Bacillus subtilis and Escherichia coli have been associated with health hazards. Reputable suppliers should ensure that safe strains are provided.

2.

Can be used in place of Chromobacterium violaceum or Serratia marcescens (both of which should not be used in schools) for some investigations.

3.

Staphylococcus albus (epidermidis) has been known to infect debilitated individuals and those taking immuno-suppressive drugs.

Copyright National Centre for Biotechnology Education, 2006 | www.ncbe.reading.ac.uk