Abstract
Lactose-utilizing mutants (D type) were isolated from Streptomyces olivaceus by a prolonged culture on the lactose-Bennett's agar. The D type could also be induced from the lactose-non-utilizing type (F type), but the reverse mutation could not be detected. The D type was found morphologically distinguishable from the original F type in giant colonies. The lag phase between glucose- and lactose-utilizing phases which was found previously with the original type on lactose-enriched media could not be found with the D type. A new morphological mutant (B type) with characteristic black reverse was isolated from an aged culture stock of Stm. olivaceus No. G.
