NORTHROP J H
J Gen Physiol. 1957 May 20;40(5):653-61. doi: 10.1085/jgp.40.5.653.
Cultures of megatherium 899a, growing under different conditions, were exposed to ultraviolet or white light. 1. Cultures exposed to ultraviolet light and then to white light continue to grow at the normal rate. Cultures exposed to ultraviolet light and then placed in the dark grow at the normal rate for varying lengths of time, depending on conditions, and then lyse with the liberation of from 5 to 1000 phage particles per cell, depending on the culture medium. 2. Increasing the time of exposure to ultraviolet light results in an increase in the fraction of cells which lyse in the dark. The lysis time decreases at first, remains constant over a wide range of exposure, and then increases. The lysis can be prevented by visible light after short exposure, but not after long exposures. 3. The time required for lysis is independent of the cell concentration. 4. Effect of temperature. After exposure to ultraviolet the cell concentration increases about 4 times at 20 degrees , 30 degrees , or 35 degrees C., but only 1.5 to 2.0 times at 40-45 degrees . This is due to the fact that the growth rate of the culture reaches a maximum at 38 degrees while the lysis rate increases steadily up to 45 degrees . 5. Terramycin decreases the growth rate and lysis rate in proportion. 6. At pH 5.1, the cultures continue to grow slowly in the dark after exposure to ultraviolet light. 7. Megatherium sensitive cells infected with T phage lyse more rapidly than ultraviolet-treated 899a, and visible light does not affect the lysis time. The results agree with the assumption that exposure to ultraviolet results in the production of a toxic (mutagenic) substance inside the bacterial cell. This substance is inactivated by white light.
在不同条件下生长的大地懒899a培养物，被暴露于紫外线或白光下。1. 先暴露于紫外线下然后再暴露于白光下的培养物继续以正常速率生长。先暴露于紫外线下然后置于黑暗中的培养物，根据条件不同，会在不同长度的时间内以正常速率生长，然后裂解，每个细胞释放出5到1000个噬菌体颗粒，这取决于培养基。2. 增加紫外线暴露时间会导致在黑暗中裂解的细胞比例增加。裂解时间起初减少，在广泛的暴露范围内保持恒定，然后增加。短时间暴露后可见光可防止裂解，但长时间暴露后则不能。3. 裂解所需时间与细胞浓度无关。4. 温度的影响。暴露于紫外线后，在20℃、30℃或35℃时细胞浓度增加约4倍，但在40 - 45℃时仅增加1.5到2.0倍。这是因为培养物的生长速率在38℃时达到最大值，而裂解速率一直稳定增加直至45℃。5. 土霉素按比例降低生长速率和裂解速率。6. 在pH 5.1时，培养物在暴露于紫外线下后在黑暗中继续缓慢生长。7. 被T噬菌体感染的大地懒敏感细胞比经紫外线处理的899a裂解得更快，并且可见光不影响裂解时间。这些结果与以下假设一致，即暴露于紫外线会导致细菌细胞内产生一种有毒（致突变）物质。这种物质会被白光灭活。
