Zusman D R, Krotoski D M, Cumsky M
J Bacteriol. 1978 Jan;133(1):122-9. doi: 10.1128/jb.133.1.122-129.1978.
The rates of DNA synthesis during the cell-division cycle were measured in Myxococcus xanthus growing in three different media permitting a twofold variation in doubling time. In all three media, simple DNA cycles were observed. Synthesis of DNA occurred during 85% of the cell-division cycle, independent of generation time, from 5 to 11 h. Cells were observed to contain one bacterial nucleoid at birth that later divided synchronously midway through the cell cycle. Nucleoid segregation appeared to begin before chromosome replication was completed. The DNA content of exponential-phase bacteria was determined to be about 20 +/- 3 X 10(-9) microgram per cell; newborn bacteria contained about 14 +/- 2 X 10(-9) microgram of DNA per cell. Exponential-phase bacteria showed about a 50% increase in DNA in the presence of chloramphenicol (50 microgram/ml). The number of randomly segregating chromosomes present in exponential-phase bacteria was determined by following the fate of prelabeled DNA during outgrowth in nonradioactive media. The results are consistent with a model in which cells are born with exactly one complete unreplicated chromosome. The molecular weight of such a chromosome is about 8.4 +/- 1.2 X 10(9).
在三种不同培养基中生长的黄色粘球菌，其细胞分裂周期中的DNA合成速率被测定，这三种培养基使得细菌的倍增时间有两倍的差异。在所有这三种培养基中，均观察到简单的DNA周期。DNA合成发生在细胞分裂周期的85%期间，与世代时间无关，时间范围为5至11小时。观察到细胞在出生时含有一个细菌类核，该类核随后在细胞周期的中途同步分裂。类核分离似乎在染色体复制完成之前就开始了。指数生长期细菌的DNA含量被测定为约每细胞20±3×10⁻⁹微克；新生细菌每细胞含有约14±2×10⁻⁹微克的DNA。在氯霉素（50微克/毫升）存在的情况下，指数生长期细菌的DNA显示约增加50%。通过追踪预标记DNA在非放射性培养基中生长过程中的命运，确定了指数生长期细菌中随机分离的染色体数量。结果与一个模型一致，即细胞出生时恰好含有一条完整的未复制染色体。这样一条染色体的分子量约为8.4±1.2×10⁹。
