Optimum Temperature for Growth
of Bacteria

Since bacteria grow in many environments from artic oceans to hot springs, it is not surprising that the optimum growth temperatures vary. Bacteria from the human gut grow well at body temperature (37 C) but bacteria from plants may be killed at that temperature. Hospital incubators are often set at 37 C. It is safer for the home experimenter to work with non-pathogenic bacteria from plants, fruit, soils, and water and these usually grow best at room temperature. Therefore, the home experimenter seldom needs an incubator. Be sure to keep your cultures out of the reach of childern and uninformed adults. Since the home or school may not have incubators, you may select ambient temperatures that are available in your school or home. Thus, you may set your cultures in the furnace room, refrigerater (if food will not be contaminated), in a cold unheated room, on a hot high shelf, on a cold floor (where childern can't touch them).

Make 6 identical plates and streak the same 8 bacteria on each plate then incubate each plate at a different temperature. Here are some suggested temperatures

The reason for incubating some plates at an extreme temperature and then moving them to room temperature is to learn whether they are killed at the high temperature. You should inspect the plates and record growth every 12 or 24 hours because some bacteria grow at temperature extremes but slowly.

choice of species for this experiment. Thus if you wish to use anaerobes such as Clostridium, you would need to use deep tubes of reduced medium. Page LINK may help you select media for the species of bacteria you have available for this experiment.

1. Chromobacterium lividum 5. Bacillus stearothermophilus
2. Escherichia coli B 6. Pseudomonas fluorescens
3. Bacillus subtilis 168 7. Xanthomonas campestris
4. Photobacterium phosphoreum 8. Paracoccus denitrificans

A suggested pattern for streaking the 8 bacteria species on each plate by using sterile 5 mm wide paper strips dipped into liquid cultures or suspensions of the bacteria. Be sure to mark the top edge of the plate with tape.

Temperatures: Optimum, Minimum, Maximum

Optimum = Temperature at which the bacterium grows most rapidly
Minimum = Temperature below which no growth occurs
Maximum = Temperature above which no growth occurs

Psychrophilic = Cold loving; optimum growth at 15 - 20C
Mesophilic = middle living; optimum growth at 30 - 37 C
Thermophilic = heat loving; optimum growth at 50 - 60 C

Psychrophiles are commonly isolated from cold waters and bottoms of lakes and oceans. Many grow well at 0 - 4C and some at -7 if solutes added to depress freezing point.

Mesophiles are the the most common bacteria. Saprophytes grow best around 30 and the parasitic species aaround 37C. Every species grows over a wide range. Saprophytic have a wider range than parasitic species. Two species may have an optimum at 37, but one may grow from 5 to 45 and the othr may only grow from 25 to 40.

Thermophiles were first found in hot springs and heating piles of hay and manure. They are fairly widespread in nature. They present a problem in pasteurizing milk because they grow at the temperatures intended to kill. Some cause canned foods to spoil because they produce highly thermo-resistant spores.

Bacteria isolated from soil and plants often grow best at 20 to 30C. Bacteria isolated from hot rotting grass or hay are often thermophilic and grow best at 45C, 55C, or 65C. Therefore, if one is canning fruits or vegetables with inadequate heating by the cold-pack method in a water boiler, it is common for spoilage to occur. The cold-pack method is suitable for acid foods such as tomatoes or pickles which contain enough vinegar, but if certain acid-tolerant thermophiles such as Bacillus stearothermophilus are present spoilage is likely. Spoilage of cold-pack tomatoes by Bacillus stearothermophilus causes and off flavor called "flat-sour" but causes no harm to humans eating the tomatoes. I believe I have eaten dozens of cans of such spoiled tomatoes and never knew the difference.

put a table here giving the optimum and rang e for about 50 or 100 speciec. Divide by psy, meso, therm Enter them by optimum and later insrt the p,m, t headings.
sci name | optimum | range| habitat
bUILD THis table and then order by temperaure from a print out.

Temperatur optimums of common Bacteria
Species Optimum Range habitat, comments
Paracoccus denitrificans 30 5 - 37 soil, aerobic, H or organo

    Bacillus coagulans

Bacillus stearothermophilus ? 30 - 75 soil; flat sour canning

Microbiological Safety Precautions

See our safety page.

Put a link here to a safety page on isolating your own bacteria.

If you isolate your own bacteria for experiments, avoid environments where pathogens are common. But if you isolate bacteria from your own mouth, perhaps they are not causing you harm. It should be safer to isolate bacteria from plant leaves, and perhaps soil. However, Staphylococcus aureus from plants can cause skin infections, and Clostridium tetani (lockjaw = tetnaus) Clostridium perfrigens?? (gas gangrene) are from soil and are serious pathogens.

Written by Harold Eddleman, Ph. D., President, Indiana Biolab, 14045 Huff St., Palmyra IN 47164
Suggestions, corrections, and comments are appreciated: Contact Harold Eddleman (indbio@disknet.com).
Revision # 3 completed 1998 January 23.