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Epistatic effects of promoter and repressor functions of the Tn 10 tetracycline‐resistance operon on the fitness of Escherichia coli
Author(s) -
LENSKI R. E.,
SOUZA V.,
DUONG L. P.,
PHAN Q. G.,
NGUYEN T. N. M.,
BERTRAND K. P.
Publication year - 1994
Publication title -
molecular ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.619
H-Index - 225
eISSN - 1365-294X
pISSN - 0962-1083
DOI - 10.1111/j.1365-294x.1994.tb00113.x
Subject(s) - biology , operon , genetics , repressor , escherichia coli , epistasis , tetracycline , trp operon , gene , gal operon , lac operon , gene expression , antibiotics
Abstract We have been studying the effects of expression of plasmid‐borne, Tn 10 ‐encoded, tetracycline resistance on the fitness of Escherichia coli K12. We previously demonstrated large reductions in fitness resulting from induced or constitutive expression of the resistance protein; however, any residual expression by the repressed operon was so slight that possession of an inducible resistance function imposed essentially no burden in the absence of antibiotic. Here, we demonstrate two distinct disadvantages for inducible genotypes relative to isogenic constitutive constructs. During the transition from antibiotic‐free to antibiotic‐containing media, the inducible genotype experiences a longer lag phase prior to growth. In the sustained presence of antibiotic, full induction of the resistance function in the inducible genotype is prevented by the continued action of its repressor. However, these disadvantages may be reduced by increasing the strength of the promoter for the resistance gene in the inducible genotype. Simultaneous consideration of the mode of gene regulation (i.e. constitutive or inducible) and the strength of the resistance‐gene promoter (i.e. maximum level of expression) indicates an adaptive landscape with very strong epistasis and, perhaps, multiple fitness peaks.