The strain F of bacteriophages which attack the typical strain of amylase-producing bacteria, Bac. subtilis var. amyloliquefaciens FUKUMOTO K 49, had been investigated by Watanabe in our institute. During succeeding study, two mutants of F were isolated. A mutant Fs forms clear but very small plaque which is closely similar to that of NH_2OH-mutant of F introduced by Watanabe.8 Another mutant Ftb produces turbid plaque of about the same size with the original clear one of F. However, electron-microscopic examination showed that their shape, especially the characteristic cylindrical head, resembles completely to that of F. The virulent activity of both Fs and Ftb against the host K 49 was neutralized by anti-F-serum, demonstrating that they must be mutants derived from the strain F. In addition, much difference was not observed among velocity constants for neutralization, K, of the original strain F as well as both mutants against anti-F-serum, contrary to that of NH_2OH-mutant whose K value is about 53 per cent of the original one. This suggests that at least Fs and Ftb are much nearer relation of F than NH_2OH-mutant. As for the growth of the original strain F in the host cell, it had been already elucidated by Watanabe that latent period is about 30 minutes, rise period from about 30 minutes to about 60 minutes and mean burst size about 80-90 under the optimum condition at 37℃ and pH = 7. Although the condition of multiplication for Fs and Ftb had not been examined, one step growth curves of them were estimated under the same condition according to Watanabe's procedure for F. It was disclosed that Fs multiplied with latent period of about 45 minutes, rise period from about 45 minutes to about 70 minutes and mean burst size of about 65-70. On the other hand, progeny phages of Ftb were released until about 65 minutes after latent period of about 35 minutes with a remarkably low burst size of only about 6. This estimation indicates that both mutants Fs and Ftb multiply with less efficiency than the original strain F. Furthermore, resistant strains of the host K 49 against mutants Fs and Ftb were obtained with higher rate than that for F.
アミラーゼ生産菌Bac.subtilis var. amyloliquefaciens FUKUMOTO K49いわゆる福本菌を侵すバクテリオファージF株と形態的には差はないが,異なつたプラークを生ずる2種のファージを分離し,これがいずれも変異株であることをF株の抗血清に対する中和反応によつて確めた.その1つ(Fs)は原株Fのものより非常に小さい透明なプラークを生ずるものであつて,潜伏期約45分,上昇期約45分~約70分の間とFのものより多少長いが放出価は65~70と若干低い値をもつことを一段増殖試験によつて確めた.これに対して他の1つ(Ftb)は原株のものと同様の大きさであるが,白濁不透明のプラークを生じ,潜伏期約35分,上昇期約35分~約65分の問とFとほとんど差はないが,放出価約6と異常に低い値を示した.しかも,この両変異株に対する福本菌の抵抗株は原ファージFに対するものよりも高い率で獲得されやすいことを認めた.