Abstract：
The catastrophic loss of aquatic life in the Central European Oder River in 2022, caused by a toxic bloom of the haptophyte microalga Prymnesium parvum (in a wide sense, s.l.), underscores the need to improve our understanding of the genomic basis of the toxin. Previous morphological, phylogenetic, and genomic studies have revealed cryptic diversity within P. parvum s.l. and uncovered three clade-specific (types A, B, and C) prymnesin toxins. Here, we used state-of-the-art long-read sequencing and assembled the first haplotype-resolved diploid genome of a P. parvum type B from the strain responsible for the Oder disaster. Comparative analyses with type A genomes uncovered a genome-size expansion driven by repetitive elements in type B. We also found conserved synteny but divergent evolution in several polyketide synthase (PKS) genes, which are known to underlie toxin production in combination with environmental cues. We identified an approximately 20-kbp deletion in the largest PKS gene of type B that we link to differences in the chemical structure of types A and B prymnesins. Flow cytometry and electron microscopy analyses confirmed diploidy in the Oder River strain and revealed differences to closely related strains in both ploidy and morphology. Our results provide unprecedented resolution of strain diversity in P. parvum s.l. and a better understanding of the genomic basis of toxin variability in haptophytes. The reference-quality genome will enable us to better understand changes in microbial diversity in the face of increasing environmental pressures and provides a basis for strain-level monitoring of invasive Prymnesium in the future.
摘要：
2022年中欧奥得河水生生物的灾难性损失，是由无糖微藻Prymnesiumparvum的有毒水华引起的（从广义上讲，s.l.),强调需要提高我们对毒素基因组基础的理解。以前的形态学，系统发育，和基因组研究揭示了P.parvums.l.内的隐秘多样性。并发现了三个特定的进化枝(A型，B,和C）普里米尼辛毒素。这里,我们使用了最先进的长读数测序技术,并从造成Oder灾难的菌株中组装了第一个单倍型解析的B型小疟原虫二倍体基因组.与A型基因组的比较分析揭示了由B型重复元件驱动的基因组大小扩展。我们还发现了几个聚酮合成酶（PKS）基因的保守性，但进化不同。已知它们是毒素产生与环境线索相结合的基础。我们在B型最大的PKS基因中发现了大约20kbp的缺失，我们将其与A型和B型普鲁尼汀的化学结构差异联系起来。流式细胞术和电子显微镜分析证实了奥得河菌株的二倍体，并揭示了与紧密相关的菌株在倍性和形态上的差异。我们的结果提供了前所未有的解析P.parvums.l.中的菌株多样性，并更好地理解了haptophytes中毒素变异性的基因组基础。参考质量的基因组将使我们能够更好地了解面对不断增加的环境压力时微生物多样性的变化，并为将来对侵袭性Prymnesium的菌株水平监测提供基础。
