Mutualism in Continuous Culture
Our group studied B. polymixa and P. vulgaris in continuous culture
(H.T. Yeoh, H.R. Bungay, and N.R. Kreig, "A microbial interaction involving
combined mutualism and inhibition", Can. Jour. Microbiol. 14: 491 1968).
The former required biotin and the latter required niacin. Each could supply the
needs of the other. However, a protein was produced that strongly inhibited one
of the organisms. Such protein factors when made by E. coli are called "colicins".
This toxicity stopped the growth of one organisms and prevented it from making
the vitamin needed by the other organism. Each washed out until the toxic protein
was diluted enough for growth and mutualism to resume. Electronic counts of
total organisms are shown versus time in the figure:
coulter.gif
Total Counts with Electronic Coulter Counting
Counting on Petri dishes verified the behavior discovered by electronic counting:
mix.gif
Plate Counts
Adding the enzyme chymotrypsis destroyed the toxic protein, and mutualism was observed:
chymo.gif
Chymotrypsin injected into medium and then into reservoir
Computer Simulations
If you have trouble understanding this applet, take a look at some older figures:
Simulation of uncomplicated mutalism in
continuous culture
Mutualisms with inhibition
Computer simulation of mutualism complicated by one organism excreting an inhibitor for the other
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Competition in a pH Auxostat
