Borrelia burgdorferi, the tick-transmitted spirochete agent of Lyme disease, has a highly segmented genome with a linear chromosome and various linear or circular plasmids. Here, by imaging several chromosomal loci and 16 distinct plasmids, we show that B. burgdorferi is polyploid during growth in culture and that the number of genome copies decreases during stationary phase. B. burgdorferi is also polyploid inside fed ticks and chromosome copies are regularly spaced along the spirochete’s length in both growing cultures and ticks. This patterning involves the conserved DNA partitioning protein ParA whose localization is controlled by a potentially phage-derived protein, ParZ, instead of its usual partner ParB. ParZ binds its own coding region and acts as a centromere-binding protein. While ParA works with ParZ, ParB controls the localization of the condensin, SMC. Together, the ParA/ParZ and ParB/SMC pairs ensure faithful chromosome inheritance. Our findings underscore the plasticity of cellular functions, even those as fundamental as chromosome segregation.

伯氏疏螺旋体（Borrelia burgdorferi）是由蜱传播的莱姆病螺旋体，其基因组高度分段，具有线性染色体和各种线性或环状质粒。在这里，通过对几个染色体位点和 16 个不同质粒进行成像，我们表明伯氏疏螺旋体在培养物中生长期间是多倍体，并且在稳定期基因组拷贝数减少。伯氏疏螺旋体在喂食的蜱体内也是多倍体，并且在生长的培养物和蜱中，染色体拷贝沿着螺旋体的长度规则地间隔开。这种模式涉及保守的 DNA 分配蛋白 ParA，其定位由潜在的噬菌体衍生蛋白 ParZ（而不是其通常的伙伴 ParB）控制。ParZ 结合其自己的编码区并充当着丝粒结合蛋白。当 ParA 与 ParZ 一起工作时，ParB 控制凝缩蛋白 SMC 的定位。ParA/ParZ 和 ParB/SMC 对共同确保染色体的忠实遗传。我们的研究结果强调了细胞功能的可塑性，甚至是像染色体分离这样基本的功能。