Kneubehl Alexander R, Lopez Job E
Department of Pediatrics, Baylor College of Medicine , Houston, Texas, USA.
Department of Molecular Virology and Microbiology, Baylor College of Medicine , Houston, Texas, USA.
Microbiol Spectr. 2023 Sep 22;11(5):e0089523. doi: 10.1128/spectrum.00895-23.
spirochetes, causative agents of Lyme disease and relapsing fever (RF), have uniquely complex genomes, consisting of a linear chromosome and both circular and linear plasmids. The plasmids harbor genes important for the vector-host life cycle of these tick-borne bacteria. The role of plasmids from Lyme disease causing spirochetes is more refined compared to RF because of limited plasmid-resolved genome assemblies for the latter. We recently addressed this limitation and found that three linear plasmid families (F6, F27, and F28) were syntenic across all the RF species that we examined. Given this conservation, we further investigated the three plasmid families. The F6 family, also known as the megaplasmid, contained regions of repetitive DNA. The F27 was the smallest, encoding genes with unknown function. The F28 family encoded the putative expression locus for antigenic variation in all species except and . Taken together, this work provides a foundation for future investigations to identify essential plasmid-localized genes that drive the vector-host life cycle of RF . IMPORTANCE spp. spirochetes are arthropod-borne bacteria found globally that infect humans and other vertebrates. RF borreliae are understudied and misdiagnosed pathogens because of the vague clinical presentation of disease and the elusive feeding behavior of argasid ticks. Consequently, genomics resources for RF spirochetes have been limited. Analyses of plasmids have been challenging because they are often highly fragmented and unassembled in most available genome assemblies. By utilizing Oxford Nanopore Technologies, we recently generated plasmid-resolved genome assemblies for seven spp. found in the Western Hemisphere. This current study is an in-depth investigation into the linear plasmids that were conserved and syntenic across species. We identified differences in genome structure and, importantly, in antigenic variation systems between species. This work is an important step in identifying crucial plasmid-localized genetic elements essential for the life cycle of RF spirochetes.
螺旋体是莱姆病和回归热（RF）的病原体，其基因组具有独特的复杂性，由一条线性染色体以及环状和线性质粒组成。这些质粒携带对这些蜱传细菌的媒介-宿主生命周期至关重要的基因。与回归热螺旋体相比，引起莱姆病的螺旋体中质粒的作用更为明确，因为后者的质粒解析基因组组装有限。我们最近解决了这一局限性，发现三个线性质粒家族（F6、F27和F28）在我们研究的所有回归热螺旋体物种中是同线的。鉴于这种保守性，我们进一步研究了这三个质粒家族。F6家族，也称为大质粒，包含重复DNA区域。F27是最小的，编码功能未知的基因。F28家族在除[具体物种1]和[具体物种2]之外的所有物种中编码假定的抗原变异表达位点。综上所述，这项工作为未来的研究奠定了基础，以确定驱动回归热螺旋体媒介-宿主生命周期的必需质粒定位基因。重要性 疏螺旋体属螺旋体是全球发现的节肢动物传播细菌，可感染人类和其他脊椎动物。回归热疏螺旋体是研究不足且误诊的病原体，因为疾病的临床表现模糊，argasid蜱的摄食行为难以捉摸。因此，回归热螺旋体的基因组学资源有限。回归热螺旋体质粒的分析一直具有挑战性，因为它们在大多数可用的基因组组装中往往高度碎片化且未组装。通过利用牛津纳米孔技术，我们最近为在西半球发现的七种疏螺旋体属物种生成了质粒解析基因组组装。本研究是对跨物种保守且同线的线性质粒的深入研究。我们确定了物种之间基因组结构的差异，重要的是，还确定了抗原变异系统的差异。这项工作是确定回归热螺旋体生命周期所需的关键质粒定位遗传元件的重要一步。
