The genetic location of prophage on the chromosome of Streptomyces coelicolor.

HE genetic structure of Streptomyces coelicolor A3 (2), the only strain among the actinomycetes for which a genetic map has been constructed, was studied in detail by HOPWOOD (1967) and SERMONTI (1 969). For genetic analysis, HOPWOOD and SERMONTI utilized the capacity of mutant strains of A3 (2) to undergo genetic recombination. To enlarge the possibilities of genetic analysis of the actinomycetes by using a temperate actinophage and to genetically analyze the actinophage in a suitable host, an actinophage from S. coelicolor strain A3 (2) was isolated ( LOMOVSKAYA, MKRTUMIAN and GOSTIMSKAYA 1970). The actinophage was designated +C31; it was isolated from a culture of S. coelicolor A3 (2) on the indicator strain, Actinomyces coelicolor 66. The spontaneous rate of actinophage induction was very low. It was possible to increase it by a factor of 10 or 100 when germinated spores were treated with ultraviolet (UV) light and then with N-methyl-N’-nitro-N-nitrosoguanidine. LOMOVSKAYA (1970) suggested that such a low spontaneous rate of actinophage +C31 induction could result from a defective lysogenic nature of A3 (2). If so, actinophage +C31 must be a mutant of an induced defective prophage that had acquired the ability to grow on the indicator strain. The actinophage +C31 appeared to be a temperate phage which produces large turbid plaques and causes formation of true lysogenic cultures in indicator cultures and in cultures cured of prophage. The actinophage +C31 could be adsorbed on strain A3 (2) but failed to reproduce. The present communication solves the question of whether the prophage is located on the A3(2) chromosome or not. Lysogeny segregates among the recombinants in crosses between lysogenic and nonlysogenic strains in precisely the same way as other genetic markers do. Hence. it was possible to locate the prophage on the A3 (2) linkage map.