Escherichia coli Females Defective in Conjugation and in Adsorption of a Single-Stranded Deoxyribonucleic Acid Phage

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We predicted that, among mutants resistant to infection by single-stranded deoxyribonucleic acid viruses, there would be some also resistant to “infection” by single-stranded conjugal deoxyribonucleic acid. Approximately 5% of the Escherichia coli K-12 females selected for resistance to phage ST-1 were defective as recipients in conjugation. These spontaneous mutants fell into two classes. Type A accepted both plasmid and chromosomal markers at greatly reduced frequencies (<10−6 of normal for at least one strain), formed “rough” colonies, and (unlike their parent) were nonflagellated. Type B strains accepted both chromosomal and plasmid markers at reduced frequencies (10−2 to 10−1 of normal), were temperature sensitive for growth, and showed increased susceptibility towards antibiotics and deoxycholate. Both classes of mutants also were resistant to certain female-specific viruses.

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