Sánchez-Romero María A, Mérida-Floriano Ángela, Casadesús Josep
Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain.
Front Microbiol. 2020 Dec 4;11:599931. doi: 10.3389/fmicb.2020.599931. eCollection 2020.
Quantitative PCR analysis shows that the virulence plasmid of serovar Typhimurium (pSLT) is a low-copy-number plasmid, with 1-2 copies per chromosome. However, fluorescence microscopy observation of pSLT labeled with a fluorescent tag reveals cell-to-cell differences in the number of foci, which ranges from 1 to 8. As each focus must correspond to ≥1 plasmid copy, the number of foci can be expected to indicate the minimal number of pSLT copies per cell. A correlation is found between the number of foci and the bacterial cell volume. In contrast, heterogeneity in the number of loci appears to be independent of the cell volume and may have stochastic origin. As a consequence of copy number heterogeneity, expression of a pSLT-bone reporter gene shows high levels of cell-to-cell variation, especially in actively dividing cultures. These observations support the notion that low-copy-number plasmids can be a source of gene expression noise in bacterial populations.
定量PCR分析表明，鼠伤寒血清型（pSLT）的毒力质粒是一种低拷贝数质粒，每条染色体有1 - 2个拷贝。然而，用荧光标签标记的pSLT的荧光显微镜观察显示，病灶数量在细胞间存在差异，范围为1至8个。由于每个病灶必须对应≥1个质粒拷贝，因此病灶数量有望表明每个细胞中pSLT拷贝的最小数量。在病灶数量与细菌细胞体积之间发现了相关性。相比之下，基因座数量的异质性似乎与细胞体积无关，可能源于随机因素。由于拷贝数异质性，pSLT - 骨报告基因的表达在细胞间表现出高水平的变异，尤其是在活跃分裂的培养物中。这些观察结果支持了低拷贝数质粒可能是细菌群体中基因表达噪声来源的观点。
