Cylindrospermopsis and Raphidiopsis (C/R group) are closely related species responsible for cyanobacterial blooms worldwide. Paralytic shellfish toxins (PSTs) and cylindrospermopsins (CYNs) have been identified in different C/R group strains. However, the evolutionary relationship between PST- and CYN-producing strains has not been systematically evaluated. In this study, C/R group strains and their toxin biosynthesis genes were evaluated by phylogenetic analysis and sequence comparison. None of the tested strains are able to produce PSTs and CYNs simultaneously. The C/R group strains were clustered into five clades, including two non-toxic, two CYN-producing and one PST-producing clades. A high degree of similarity was observed for rpoC1 (> 96%) and ITS-L (> 97%) sequences within each clade with the exception of the ITS-L (87% to 100%) region in CYN-producing R. curvata, which has been shown to contain variable sequence insertions. Genomic analysis revealed that sxtY and sxtZ could be found in both toxic and non-toxic strains. The transposase gene IS4 was only observed in strains from the PST-producing clade. The sxt and cyr gene clusters share five gene families with similar functions. The amino acid sequences of the adenylyl-sulfate kinase genes, sxtO and cyrN, are more similar (45% to 81%) than other pairs of genes (8.0% to 40%). SxtO and CyrN proteins from C/R group strains forms an independent clade on the phylogenetic tree with a high degree of sequence similarity (78% to 100%). In conclusion, PST- and CYN- producing C/R group species can be classified into different clades based on their phylogenetic profile. The sxtO and cyrN genes have probably diverged from a single ancestral adenylyl-sulfate kinase gene, and may be specifically used for toxin biosynthesis in C/R group species.

圆柱精子和蚜虫（C / R组）是密切相关的物种，在世界范围内负责蓝藻繁殖。在不同的C / R组品系中已鉴定出麻痹性贝类毒素（PSTs）和cylindrospermopsins（CYNs）。但是，尚未系统评估产生PST和CYN的菌株之间的进化关系。在这项研究中，C / R组菌株及其毒素生物合成基因通过系统发育分析和序列比较进行了评估。所有测试菌株均不能同时产生PST和CYN。C / R组菌株分为五个进化枝，包括两个无毒，两个CYN产生和一个PST产生。观察到rpoC1的高度相似每个进化枝中的（> 96％）和ITS-L（> 97％）序列，但在CYN产生的R. curvata中，ITS-L（87％至100％）区域除外，该区域已显示含有可变序列插入。基因组分析表明，在有毒和无毒菌株中均可发现sxtY和sxtZ。转座酶基因IS4仅在来自产生PST的进化枝的菌株中观察到。该SXT和CYR基因簇共享类似职能的五项基因家族。腺苷酸硫酸盐激酶基因sxtO和cyrN的氨基酸序列与其他成对的基因（8.0％至40％）相似（45％至81％）。来自C / R组菌株的SxtO和CyrN蛋白以高度的序列相似性（78％至100％）在系统发育树上形成独立的进化枝。总之，可以将产生PST和CYN的C / R组物种根据其系统发育概况分为不同的进化枝。的sxtO和cyrN基因可能已经从单一祖腺苷酸硫酸盐激酶基因发散，并且可以具体地用于在C / R组物种毒素的生物合成。