Table_2_The Distinctive Evolution of orfX Clostridium parabotulinum Strains and Their Botulinum Neurotoxin Type A and F Gene Clusters Is Influenced by Environmental Factors and Gene Interactions via Mobile Genetic Elements.XLSX

Of the seven currently known botulinum neurotoxin-producing species of Clostridium, C. parabotulinum, or C. botulinum Group I, is the species associated with the majority of human botulism cases worldwide. Phylogenetic analysis of these bacteria reveals a diverse species with multiple genomic clades. The neurotoxins they produce are also diverse, with over 20 subtypes currently represented. The existence of different bont genes within very similar genomes and of the same bont genes/gene clusters within different bacterial variants/species indicates that they have evolved independently. The neurotoxin genes are associated with one of two toxin gene cluster types containing either hemagglutinin (ha) genes or orfX genes. These genes may be located within the chromosome or extrachromosomal elements such as large plasmids. Although BoNT-producing C parabotulinum bacteria are distributed globally, they are more ubiquitous in certain specific geographic regions. Notably, northern hemisphere strains primarily contain ha gene clusters while southern hemisphere strains have a preponderance of orfX gene clusters. OrfX C. parabotulinum strains constitute a subset of this species that contain highly conserved bont gene clusters having a diverse range of bont genes. While much has been written about strains with ha gene clusters, less attention has been devoted to those with orfX gene clusters. The recent sequencing of 28 orfX C. parabotulinum strains and the availability of an additional 91 strains for analysis provides an opportunity to compare genomic relationships and identify unique toxin gene cluster characteristics and locations within this species subset in depth. The mechanisms behind the independent processes of bacteria evolution and generation of toxin diversity are explored through the examination of bacterial relationships relating to source locations and evidence of horizontal transfer of genetic material among different bacterial variants, particularly concerning bont gene clusters. Analysis of the content and locations of the bont gene clusters offers insights into common mechanisms of genetic transfer, chromosomal integration, and development of diversity among these genes.

目前已知的7种产肉毒神经毒素的梭菌属（Clostridium）物种中，副肉毒梭菌（C. parabotulinum），即肉毒梭菌I群（C. botulinum Group I），是全球范围内与绝大多数人类肉毒中毒病例相关的菌种。对该类细菌的系统发育分析表明，该物种具有丰富的遗传多样性，包含多个基因组进化枝。其所产生的神经毒素同样具有多样性，目前已发现超过20种毒素亚型。在基因组序列高度相似的菌株中存在不同的bont基因（botulinum neurotoxin genes），而在不同细菌变异株或物种中却存在相同的bont基因/基因簇，这说明这些基因是独立演化而来的。神经毒素基因与两类毒素基因簇之一相关联：一类包含血凝素（hemagglutinin, ha）基因，另一类则包含orfX基因。这些基因既可定位于细菌染色体，也可存在于大型质粒等染色体外遗传元件中。尽管产肉毒神经毒素的副肉毒梭菌在全球范围内均有分布，但在某些特定地理区域的分布更为广泛。值得注意的是，北半球的菌株主要携带ha基因簇，而南半球菌株则以orfX基因簇占绝对优势。携带orfX基因簇的副肉毒梭菌菌株是该物种的一个亚群，其基因组中包含高度保守的bont基因簇，且这些基因簇可携带多种不同的bont基因。尽管针对携带ha基因簇的菌株已有大量研究，但针对携带orfX基因簇菌株的相关研究则相对较少。近期研究完成了28株携带orfX基因簇的副肉毒梭菌菌株的全基因组测序，另有91株菌株可供分析，这为深入比较该亚群的基因组亲缘关系、识别其独特的毒素基因簇特征与定位提供了契机。本研究通过分析菌株来源地域相关的细菌亲缘关系，以及不同细菌变异株之间的遗传物质水平转移证据（尤其是针对bont基因簇的相关证据），探究了细菌演化与毒素多样性产生的独立机制。对bont基因簇的序列内容与整合位置进行分析，可为这类基因的常见遗传转移机制、染色体整合过程以及多样性演化提供新的研究视角。