Abstract：
Microseira wollei, a globally distributed freshwater bloom-forming benthic cyanobacterium, is known for its production of cyanotoxins and taste and odor (T&O). While CYN (Cylindrospermopsin)-producing populations of M. wollei are confined to Australia, PST (Paralytic shellfish toxins)-producing populations have been exclusively documented in North America. In this study, four benthic cyanobacterial strains, isolated from West Lake in China, were identified as M. wollei based on morphological and phylogenetic analyses. Detection of sxtA gene and UPLC-MS/MS analysis conclusively confirmed the PST-producing capability of M. wollei CHAB5998. In the phylogenetic tree of 16S rDNA, M. wollei strains formed a monophyletic group with two subclades. Notably, non-PST-producing Chinese strains clustered with Australian strains in Clade II, while all other strains, including PST-producing ones, clustered in Clade I. Additionally, CHAB5998 contains ten PST variants, of which STX, NEO, GTX2, GTX3, GTX5 and C1 were identified for the first time in M. wollei. Sequence analysis of PST biosynthetic gene cluster (sxt) genes indicated potential base variations, gene rearrangements, insertions, and deletions in the strain CHAB5998. Also, sxt gene has a longer evolutionary history in M. wollei than that in cyanobacteria from Nostocales. Multiple recombination breakpoints detected in sxt genes and the inconsistency in the topology of the phylogenetic trees between sxt and 16S rDNA suggested that multiple horizontal gene transfers (HGT) have occurred. Overall, the present study marks the first documented occurrence of PST-producing M. wollei outside of North America and identifies it as the first toxic freshwater benthic cyanobacterium in China. This revelation implies that benthic cyanobacteria may pose a higher environmental risk in China than previously acknowledged.
摘要：
MicroseiraWollei,全球分布的淡水水华形成底栖蓝细菌，以其产生的氰基毒素和味道和气味（T＆O）而闻名。虽然产生CYN（Cylindrospermopsin）的M.wollei种群仅限于澳大利亚，产生PST（麻痹性贝类毒素）的种群在北美仅有记录。在这项研究中,四种底栖蓝细菌菌株，与中国的西湖隔绝，根据形态学和系统发育分析鉴定为M.wollei。sxtA基因的检测和UPLC-MS/MS分析最终证实了M.wolleiCHAB5998的PST生产能力。在16SrDNA的系统发育树中，M.wollei菌株形成了一个具有两个亚进化枝的单系群。值得注意的是,非PST生产的中国菌株与澳大利亚菌株聚集在CladeII中，而所有其他菌株，包括生产PST的，聚集在CladeI中，此外，CHAB5998包含十个PST变体，其中STX,NEO,GTX2、GTX3、GTX5和C1在沃利分枝杆菌中首次被鉴定。PST生物合成基因簇（sxt）基因的序列分析表明潜在的碱基变异，基因重排,插入,和CHAB5998菌株中的缺失。此外，sxt基因在M.wollei中的进化史比来自Nocales的蓝细菌更长。在sxt基因中检测到多个重组断点，并且sxt和16SrDNA之间的系统发育树拓扑结构不一致表明已经发生了多个水平基因转移（HGT）。总的来说,本研究标志着在北美以外首次有记录的产生PST的M.wollei的发生，并将其确定为中国第一个有毒的淡水底栖蓝细菌。这一发现表明，底栖蓝藻在中国可能构成比以前公认的更高的环境风险。
