The Production and Selection of a Family of Strains in Penicillium chrysogenum

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Abstract
A group of superior variants of P. chrysogenum Thom, tracing their origin from P. chrysogenum strain X-1612, is described, including methods employed in obtaining, testing, and maintaining the improved stocks. Greatly enhanced ability to produce penicillin, elimination of yellow pigment, and increased efficiency in utilization of penicillin precursors have been realized in the "Wisconsin Family" of strains. A long series of populations, each stemming from a variant of the generation preceding, has provided the basis for selection; and the quality of the stock was built up gradually over a period of ten years. Spontaneous variation occurred in populations grown from untreated conidia, but some of the most significant improvements were obtained following treatment of spores with ultraviolet radiation (2750 A and 2534-37 A) and with the nitrogen mustard, methyl-bis ([beta]-chloro-ethyl) amine. A more or less progressive decline in the vegetative and reproductive vigor of the strains has accompanied the increase in capacity to produce the antibiotic.