Isolation and characterization of Corynebacterium diphtheriae nontandem double lysogens hyperproducing CRM197

Abstract

Phage β197/(tox-), which codes for CRM197, a nontoxic protein immunochemically indistinguishable from diphteria toxin, was UV induced from a culture of the C7(β197)(tox-) strain. A total of 191 C7(β197)(tox-) lysogens were isolated and selected according to the halo produced on TYE agar containing antidiphtheria toxin serum and were further characterized by Southern blots of their chromosomal DNA. Most of the isolates turned out to the monolysogens, but some tandem and nontandem double lysogens were also found. The nontandem double lysogens were stable and capable of giving high yields of CRM197, up to threefold higher than monolysogens. They are, therefore, suitable for large-scale industrial production.