Ecotoxicity Reference Laboratory, Risk Assessment Science Collaboration Office, Center for Health and Environmental Risk Research, National Institute for Environmental Studies (NIES), Tsukuba, Ibaraki, Japan.
Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies (NIES), Tsukuba, Ibaraki, Japan.
PLoS One. 2020 Nov 9;15(11):e0241889. doi: 10.1371/journal.pone.0241889. eCollection 2020.
Raphidocelis subcapitata is one of the most frequently used species for algal growth inhibition tests. Accordingly, many microalgal culture collections worldwide maintain R. subcapitata for distribution to users. All R. subcapitata strains maintained in these collections are derived from the same cultured strain, NIVA-CHL1. However, considering that 61 years have passed since this strain was isolated, we suspected that NIVA-CHL1 in culture collections might have acquired various mutations. In this study, we compared the genome sequences among NIVA-CHL1 from 8 microalgal culture collections and one laboratory in Japan to evaluate the presence of mutations. We found single-nucleotide polymorphisms or indels at 19,576 to 28,212 sites per strain in comparison with the genome sequence of R. subcapitata NIES-35, maintained at the National Institute for Environmental Studies, Tsukuba, Japan. These mutations were detected not only in non-coding but also in coding regions; some of the latter mutations may affect protein function. In growth inhibition test with 3,5-dichlorophenol, EC50 values varied 2.6-fold among the 9 strains. In the ATCC 22662-2 and CCAP 278/4 strains, we also detected a mutation in the gene encoding small-conductance mechanosensitive ion channel, which may lead to protein truncation and loss of function. Growth inhibition test with sodium chloride suggested that osmotic regulation has changed in ATCC 22662-2 and CCAP 278/4 in comparison with NIES-35.
盔形胶鞘藻是最常用于藻类生长抑制测试的物种之一。因此，世界上许多微藻培养物保藏库都保存盔形胶鞘藻，以供用户分发。这些保藏库中保存的所有盔形胶鞘藻菌株都源自同一培养株，即 NIVA-CHL1。然而，考虑到自该菌株分离以来已经过去了 61 年，我们怀疑保藏库中的 NIVA-CHL1 可能已经获得了各种突变。在这项研究中，我们比较了来自 8 个微藻培养物保藏库和日本一个实验室的 NIVA-CHL1 的基因组序列，以评估突变的存在。与日本筑波的国立环境研究所（National Institute for Environmental Studies）保存的盔形胶鞘藻 NIES-35 的基因组序列相比，我们发现每个菌株的基因组序列中有 19576 到 28212 个位点存在单核苷酸多态性或插入/缺失。这些突变不仅发生在非编码区，也发生在编码区；其中一些后者突变可能会影响蛋白质功能。在 3,5-二氯苯酚的生长抑制测试中，9 个菌株的 EC50 值差异了 2.6 倍。在 ATCC 22662-2 和 CCAP 278/4 菌株中，我们还检测到编码小电导机械敏感离子通道的基因发生突变，这可能导致蛋白质截断和功能丧失。氯化钠生长抑制测试表明，与 NIES-35 相比，ATCC 22662-2 和 CCAP 278/4 的渗透调节已经发生了变化。
