Abstract
Summary
Ethionine resistance in E. coli ATCC 9637 occurs at a high frequency and requires the constant presence of the analogue to maintain resistance. Resistant cells exhibited a lag phase 6 to 8 hours longer than sensitive cell controls when cultured in a glucose salts medium. This extended lag was reduced to that of sensitive cell controls by ethionine, methionine, homocysteine or cystathionine. A similar prolonged lag occurred when sensitive cells, previously grown in the presence of methionine, homocysteine or cystathionine, were inoculated in basal glucose salts media. The extended lag in all cases tested was due to the rapid death of a significant portion of the initial inoculum during the first hour of incubation. Resistant cells were repressed for cystathionine synthetase to the same degree as sensitive cells grown in media containing methionine. The data indicate that ethionine resistance in this strain occurs by an induced ability to convert ethionine to methionine via homocysteine, which results in repression of cystathionine synthetase. The viability loss apparently occurred in inocula repressed for de novo methionine synthesis due to metabolic imbalances brought about by the rapid growth conditions employed in this study.
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