Department of Biology, Center for Evolutionary and Theoretical Immunology, Parasite Division Museum of Southwestern Biology, University of New Mexico, Albuquerque, New Mexico, United States of America.
Center for Biotechnology Research and Development, Kenya Medical Research Institute, Nairobi, Kenya.
PLoS Negl Trop Dis. 2023 Mar 24;17(3):e0011208. doi: 10.1371/journal.pntd.0011208. eCollection 2023 Mar.
Biomphalaria pfeifferi is the world's most widely distributed and commonly implicated vector snail species for the causative agent of human intestinal schistosomiasis, Schistosoma mansoni. In efforts to control S. mansoni transmission, chemotherapy alone has proven insufficient. New approaches to snail control offer a way forward, and possible genetic manipulations of snail vectors will require new tools. Towards this end, we here offer a diverse set of genomic resources for the important African schistosome vector, B. pfeifferi.
METHODOLOGY/PRINCIPAL FINDINGS: Based largely on PacBio High-Fidelity long reads, we report a genome assembly size of 772 Mb for B. pfeifferi (Kenya), smaller in size than known genomes of other planorbid schistosome vectors. In a total of 505 scaffolds (N50 = 3.2Mb), 430 were assigned to 18 large linkage groups inferred to represent the 18 known chromosomes, based on whole genome comparisons with Biomphalaria glabrata. The annotated B. pfeifferi genome reveals a divergence time of 3.01 million years with B. glabrata, a South American species believed to be similar to the progenitors of B. pfeifferi which undertook a trans-Atlantic colonization < five million years ago.
CONCLUSIONS/SIGNIFICANCE: The genome for this preferentially self-crossing species is less heterozygous than related species known to be preferential out-crossers; its smaller genome relative to congeners may similarly reflect its preference for selfing. Expansions of gene families with immune relevance are noted, including the FReD gene family which is far more similar in its composition to B. glabrata than to Bulinus truncatus, a vector for Schistosoma haematobium. Provision of this annotated genome will help better understand the dependencies of trematodes on snails, enable broader comparative insights regarding factors contributing to susceptibility/ resistance of snails to schistosome infections, and provide an invaluable resource with respect to identifying and manipulating snail genes as potential targets for more specific snail control programs.
比氏巴蜗牛是世界上分布最广、最常被牵连的曼氏血吸虫病病原体的中间宿主蜗牛物种。在控制曼氏血吸虫病传播的努力中，仅化疗已被证明是不够的。控制蜗牛的新方法提供了前进的道路，而对蜗牛载体的可能遗传操作将需要新的工具。为此，我们在这里为重要的非洲血吸虫病载体比氏巴蜗牛提供了一套多样化的基因组资源。
方法/主要发现：主要基于 PacBio 高保真长读，我们报告了比氏巴蜗牛（肯尼亚）的基因组组装大小为 772Mb，比已知的其他扁蜗牛血吸虫病载体的基因组小。在总共 505 个支架（N50 = 3.2Mb）中，根据与光滑双脐螺的全基因组比较，将 430 个支架分配到 18 个大连锁群中，这些连锁群被推断为代表 18 个已知的染色体。注释的比氏巴蜗牛基因组揭示了与光滑双脐螺的分化时间为 301 万年，光滑双脐螺是一种南美的物种，被认为与比氏巴蜗牛的祖先相似，它在 500 万年前进行了跨大西洋的殖民化。
结论/意义：这个优先自交的物种的基因组比已知的优先异交的相关物种的基因组杂合度低；与同属物种相比，其较小的基因组可能同样反映了它对自交的偏好。注意到与免疫相关的基因家族的扩张，包括 FReD 基因家族，它在组成上与光滑双脐螺的相似性远远超过与布氏豆螺的相似性，布氏豆螺是埃及血吸虫病的载体。提供这个注释的基因组将有助于更好地了解吸虫对蜗牛的依赖性，能够更广泛地了解导致蜗牛对血吸虫感染易感性/抗性的因素，并为识别和操纵蜗牛基因作为更具体的蜗牛控制计划的潜在目标提供宝贵的资源。
