Department of Biotechnology, Sangmyung University, Seoul 03016, South Korea.
Department of Biotechnology, Sangmyung University, Seoul 03016, South Korea; Key Laboratory of Marine Ecosystem and Biogeochemistry, State Oceanic Administration & Second Institute of Oceanography, Ministry of Natural Resources, PR China.
Harmful Algae. 2020 Mar;93:101777. doi: 10.1016/j.hal.2020.101777. Epub 2020 Mar 10.
In the present study, we extensively characterized potential toxin-related genes, including polyketide synthase (PKS), saxitoxin (STX) and fatty acid synthase (FAS) from the non-toxin producing marine dinoflagellate Cochlodinium polykrikoides, comparing to those of a toxigenic dinoflagellate Alexandrium pacificum. RNA sequencing revealed 50 and 271 PKS contigs from C. polykrikoides and A. pacificum, respectively. According to domain constitute and amino acid alteration, we further classified the dinoflagellate type I PKS genes into 4 sub-groups. Type III PKS was first identified in C. polykrikoides. Interestingly, we detected a large number (242 and 288) of homologs of 18 sxt genes from two studied dinoflagellates. Most of the eight key genes (sxtA, sxtB, sxtD, sxtG, sxtH/T, sxtI, sxtS and sxtU) for STX synthesis were detected in both dinoflatellates, whereas a core STX biosynthesis gene sxtG was not detected in C. polykrikoides. This may partially explain the absence of saxitoxin production in C. polykrikoides. In addition, we identified several type I and type II FAS genes, including FabD, FabF, FabG, FabH, FabI, and FabZ, whereas FabB was not found in C. polykrikoides. Overall, the numbers of the toxin-related genes in C. polykrikoides were less than that of A. pacificum. Phylogenetic analyses showed that type I PKS/FASs of dinoflagellates had close relationships with apicomplexans and bacteria. These suggest that the toxin-related PKS and sxt genes are commonly present in toxigenic and non-toxin producing dinoflagellates, and may be involved not only in the toxin synthesis, but also in other related molecular metabolic functions.
在本研究中，我们广泛表征了潜在的毒素相关基因，包括非产毒海洋甲藻旋沟藻中的聚酮合酶（PKS）、石房蛤毒素（STX）和脂肪酸合酶（FAS），并与产毒甲藻亚历山大藻中的相应基因进行了比较。RNA 测序显示，旋沟藻和亚历山大藻分别有 50 个和 271 个 PKS 基因簇。根据结构域组成和氨基酸变化，我们进一步将甲藻 I 型 PKS 基因分为 4 个亚组。旋沟藻中首次鉴定出 III 型 PKS。有趣的是，我们从两种研究的甲藻中检测到大量（242 和 288）18sxt 基因的同源物。STX 合成的 8 个关键基因（sxtA、sxtB、sxtD、sxtG、sxtH/T、sxtI、sxtS 和 sxtU）在两种甲藻中都有检测到，而核心 STX 生物合成基因 sxtG 在旋沟藻中未检测到。这可能部分解释了旋沟藻中没有产生石房蛤毒素的原因。此外，我们鉴定了几个 I 型和 II 型 FAS 基因，包括 FabD、FabF、FabG、FabH、FabI 和 FabZ，而旋沟藻中没有 FabB。总的来说，旋沟藻中的毒素相关基因数量少于亚历山大藻。系统发育分析表明，甲藻的 I 型 PKS/FAS 与顶复门和细菌密切相关。这些表明，毒素相关的 PKS 和 sxt 基因普遍存在于产毒和非产毒甲藻中，它们不仅参与毒素合成，还可能参与其他相关的分子代谢功能。
