Abstract
Normal strains of
Bacterium lactis aerogenes
and of
Escherichia coli
only utilize d-arabinose after a long lag (A
-
), but can become adapted to use it freely (A
+
). In a medium not containing d-arabinose the A
+
and A
-
types can compete for predominance as more or less independent strains. The result of the competition in the examples studied never depended upon the initial proportions of the two types (as certain selective mechanisms would suggest) but simply upon the relative extent to which each strain had been previously acclimatized to the specific minimal medium used for the competitive growth. According to the previous history either type could be initially selected, or an even balance preserved for a considerable time. Superposed on the selection of the A
+
or of the A
-
cells there was a certain tendency for the A
+
cells to lose their adaptation to d-arabinose. It was very slight with
Bact. lactis aerogenes
and much more marked with
E. coli
.
Cited by
2 articles.
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