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Coliphage HK243: Biological and Physicochemical Characteristics

Coliphage HK243 can form plaques on Escherichia coli C and K‐12, but not B. The plaques are 1–2 mm in diameter and are opaque areas which clear upon exposure to chloroform vapor. During one‐step growth, the eclipse and the latent periods are 20 and 30 min, respectively. Phage‐infected cells continue to produce cell‐free plaque‐forming units for as long as 80 min after the end of the latent period, although at high multiplicities of infection (MOI) most cells lyse. No lysogenic bacteria have been found among survivors, so HK243 is considered a virulent phage. Some of the cells surviving a high MOI challenge are maltose negative and resistant to both HK243 and coliphage lambda. This fact has made possible the isolation of lambda‐resistant mutants of lambda‐lysogens. However, no serological cross‐reaction between the phages lambda and HK243 has been detected. Genetic data involving three essential loci and a locus controlling plaque morphology suggest a circular linkage map. The virions are tadpole‐shaped with an icosahedral head 68 nm long which is attached to a flexible tail 131 nm long. The phage has a linear, duplex DNA genome of molecular weight approximately 44 × 106 and a base composition of 33% adenine, 31% thymine, 16% guanine, and 20% cytosine.