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首页> 外文期刊>Applied Microbiology >Evolutionary Acquisition and Loss of Saxitoxin Biosynthesis in Dinoflagellates: the Second “Core” Gene, sxtG
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Evolutionary Acquisition and Loss of Saxitoxin Biosynthesis in Dinoflagellates: the Second “Core” Gene, sxtG

机译：鞭毛藻中毒素毒素生物合成的进化获得和丧失：第二个“核心”基因sxtG

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Saxitoxin and its derivatives are potent neurotoxins produced by several cyanobacteria and dinoflagellate species. SxtA is the initial enzyme in the biosynthesis of saxitoxin. The dinoflagellate full mRNA and partial genomic sequences have previously been characterized, and it appears that sxtA originated in dinoflagellates through a horizontal gene transfer from a bacterium. So far, little is known about the remaining genes involved in this pathway in dinoflagellates. Here we characterize sxtG , an amidinotransferase enzyme gene that putatively encodes the second step in saxitoxin biosynthesis. In this study, the entire sxtG transcripts from Alexandrium fundyense CCMP1719 and Alexandrium minutum CCMP113 were amplified and sequenced. The transcripts contained typical dinoflagellate spliced leader sequences and eukaryotic poly(A) tails. In addition, partial sxtG transcript fragments were amplified from four additional Alexandrium species and Gymnodinium catenatum . The phylogenetic inference of dinoflagellate sxtG , congruent with sxtA , revealed a bacterial origin. However, it is not known if sxtG was acquired independently of sxtA . Amplification and sequencing of the corresponding genomic sxtG region revealed noncanonical introns. These introns show a high interspecies and low intraspecies variance, suggesting multiple independent acquisitions and losses. Unlike sxtA , sxtG was also amplified from Alexandrium species not known to synthesize saxitoxin. However, amplification was not observed for 22 non-saxitoxin-producing dinoflagellate species other than those of the genus Alexandrium or G. catenatum . This result strengthens our hypothesis that saxitoxin synthesis has been secondarily lost in conjunction with sxtA for some descendant species.
机译：虎毒素及其衍生物是由几种蓝细菌和鞭毛藻产生的有效神经毒素。 SxtA是saxitoxin生物合成中的初始酶。鞭毛鞭毛完整的mRNA和部分基因组序列已被表征，似乎sxtA通过细菌水平基因转移起源于鞭毛鞭毛。迄今为止，关于鞭毛鞭毛虫中与该途径有关的其余基因知之甚少。在这里，我们表征sxtG，一种氨基转移酶基因，该基因被假定为编码毒素的第二步。在这项研究中，来自亚历山大港CCMP1719和亚历山大港CCMP113的整个sxtG转录物被扩增和测序。成绩单包含典型的鞭毛剪接的前导序列和真核poly（A）尾巴。另外，从另外四个亚历山大种和裸子草中扩增了部分sxtG转录物片段。与sxtA一致的鞭毛藻sxtG的系统发育推断揭示了细菌起源。但是，尚不清楚sxtG是否独立于sxtA获得。相应的基因组sxtG区域的扩增和测序揭示了非规范内含子。这些内含子显示出较高的种间差异和较低的种内差异，表明存在多个独立的获取和损失。与sxtA不同，sxtG还从未知的合成saxitoxin的亚历山大菌种中扩增得到。然而，除了亚历山大（Alexandreum）属或连翘菌（G. catenatum）属的那些之外，未观察到22种非沙门氏菌生产的鞭毛藻物种的扩增。这一结果加强了我们的假设：对于某些后代物种，毒素与sxtA一起次生丧失。

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