CHANGES OF PLOIDY DURING THE AZOTOBACTER-VINELANDII GROWTH-CYCLE
CHANGES OF PLOIDY DURING THE AZOTOBACTER-VINELANDII GROWTH-CYCLE
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DOI：
10.1128/jb.176.13.3911-3919.1994
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发表时间：
1994-07-01
影响因子：
3.2
通讯作者：
CASADESUS, J
中科院分区：
文献类型：
--
作者：
MALDONADO, R;JIMENEZ, J;CASADESUS, J
通过脉冲场电泳分离用很少切割的核酸内切酶 SpeI 和 SwaI 消化的片段计算得出，Azotobacter vinelandii 染色体的大小约为 4,700 kb。通过流式细胞术对每个细胞的 DNA 含量进行的调查表明，A. vinelandii 在丰富培养基中的生长周期中存在倍性变化。早期指数期细胞的倍性水平与大肠杆菌或鼠伤寒沙门氏菌相似（每个细胞可能大约有四个染色体），但在生长过程中观察到每个细胞的 PNA 含量持续增加。晚期指数期细胞每个细胞可能含有 >40 条染色体，而处于早期稳定期的细胞可能每个细胞含有 >80 条染色体。在后期稳定期培养物中，每个细胞的 DNA 含量甚至更高，每个细胞可能超过 100 个染色体当量。当高多倍体细菌群体分离出低倍体细胞时，在旧的稳定期培养物中观察到巨大的变化。后者细胞的 DNA 含量与囊肿相似，表明该过程可能反映了囊肿分化的开始。当旧的稳定期培养物稀释到新鲜培养基中时，也会形成低倍性细胞。在指数期培养物中添加利福平会导致 DNA 含量快速增加，表明 A. vinelandii 在每次细胞分裂时启动多轮染色体复制。在基本培养基中的生长不会导致快速生长期间观察到的倍性的惊人变化；这一观察结果表明，A. vinelandii 的多倍体可能不存在于实验室之外。
The size of the Azotobacter vinelandii chromosome is similar to 4,700 kb, as calculated by pulsed-field electrophoretic separation of fragments digested with the rarely cutting endonucleases SpeI and SwaI. Surveys of DNA content per cell by flow cytometry indicated the existence of ploidy changes during the A. vinelandii growth cycle in rich medium. Early-exponential-phase cells have a ploidy level similar to that of Escherichia coli or Salmonella typhimurium (probably ca. four chromosomes per cell), but a continuous increase of PNA content per cell is observed during growth. Late-exponential-phase cells may contain >40 chromosomes per cell, while cells in the early stationary stage may contain >80 chromosomes per cell. In late-stationary-phase cultures, the DNA content per cell is even higher, probably over 100 chromosome equivalents per cell. A dramatic change is observed in old stationary phase, cultures, when the population of highly polyploid bacteria segregates cells with low ploidy. The DNA content of the latter cells resembles that of cysts, suggesting that the process may reflect the onset of cyst differentiation. Cells with low ploidy are also formed when old stationary-phase cultures are diluted into fresh medium. Addition of rifampin to exponential-phase cultures causes a rapid increase in DNA content, indicating that A. vinelandii initiates multiple rounds of chromosome replication per cell division. Growth in minimal medium does not result in the spectacular changes of ploidy observed during rapid growth; this observation suggests that the polyploidy of A. vinelandii may not exist outside the laboratory.