Louisiana State University, Baton Rouge, LA, USA; Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia.
Gulf Coast Research Laboratory, University of Southern Mississippi, Ocean Springs, MS, USA.
J Invertebr Pathol. 2018 Sep;157:125-135. doi: 10.1016/j.jip.2018.05.007. Epub 2018 May 19.
We report a new microsporidium from a key species of the estuarine communities of the Gulf States, the Riverine grass shrimp, Palaemonetes paludosus. A milky-white shrimp was found in the Mobile Bay Delta, a large, oligohaline-freshwater wetland in Alabama, USA. Light microscopy of smears and thick sections of the abdominal tissues demonstrated infection with microsporidian spores enclosed in sporophorous vesicles (SVs) in sets of eight. Broadly oval spores measured 2.9 ± 0.06 × 1.7 ± 0.03 µm (2.5-3.3 × 1.6-1.9 µm, n = 11). SVs with a persistent membrane ranged from 4.4 to 5.6 µm in diameter. Subcuticular epithelium and underlying musculature were packed with sporonts, sporoblasts, and spores. Electron microscopy demonstrated diplokaryotic meronts that gave rise to sporont mother cells with a large single nucleus. The meront plasma membrane turned into a SV envelope, and the sporont wall segregated internally. The sporont nucleus underwent meiosis followed by two mitotic divisions accompanied by internal budding to produce four sporonts, each dividing in two uninucleate sporoblasts. Eight-spore SVs were filled with fibrillary-tubular secretions. Spores possessed 90-110-nm thick envelopes (exospore, 40-60 nm + endospore, 30-50 nm), a triangle-shaped nucleus, isofilar polar filament of 10-13 coils arranged in two-three rows, bipartite polaroplast, and a mushroom-shaped polar disk. The SSU rDNA sequence of the novel species was deposited in GenBank under Accession number MG 708238. SSU rDNA-based phylogenetic analysis indicated that the Riverine grass shrimp microsporidium was a new species and placed it in one branch with two species of Potaspora, xenoma-forming microsporidia from freshwater perciform fishes. Because morphological and developmental characters of the novel species did not fit the diagnosis of the genus Potaspora, and, based on SSU rDNA-inferred phylogenetic analyses, different host specificity, pathogenesis, and ecological considerations, we erect here the new genus Apotaspora for the Riverine grass shrimp microsporidium and name the new species Apotaspora heleios. Grouping together fish and crustacean parasites on SSU rDNA phylogenetic trees suggests that polyxenous life cycles might be a common feature of extinct and/or extant members of the studied lineage of the Microsporidia.
我们报道了一种来自海湾州河口群落关键物种的新型微孢子虫，即河虾 Palaemonetes paludosus。在美国阿拉巴马州的大型寡盐水生湿地莫比尔湾三角洲，发现了一只乳白色的虾。对腹部组织的涂片和厚切片进行的光学显微镜检查显示，受感染的微孢子虫孢子被包在孢子囊（SVs）中，每个 SVs 中有 8 个孢子。宽椭圆形孢子的大小为 2.9 ± 0.06 µm × 1.7 ± 0.03 µm（2.5-3.3 µm×1.6-1.9 µm，n=11）。具有持久膜的 SVs 的直径范围为 4.4 至 5.6 µm。皮下上皮和下面的肌肉组织充满了孢子母细胞、孢子母细胞和孢子。电子显微镜显示双核成孢期，随后是有一个大单核的孢子母细胞。成孢期的质膜变成了 SV 包膜，孢子囊壁在内部分离。孢子母细胞核经历减数分裂，随后进行两次有丝分裂，伴随着内部出芽，产生四个孢子母细胞，每个孢子母细胞分裂成两个单核孢子母细胞。八个孢子的 SVs 充满了纤维管状分泌物。孢子具有 90-110nm 厚的包膜（外膜，40-60nm+内膜，30-50nm），三角形的核，排列成两到三排的 10-13 匝的等丝状极丝，二分体极粒体和蘑菇形极盘。新物种的 SSU rDNA 序列已在 GenBank 中以注册号 MG708238 提交。基于 SSU rDNA 的系统发育分析表明，河虾微孢子虫是一个新物种，与来自淡水鲈形目鱼类的两种形成 Xenoma 的 Potaspora 微孢子虫一起处于一个分支中。由于新物种的形态和发育特征不符合 Potaspora 属的诊断标准，并且基于 SSU rDNA 推断的系统发育分析，不同的宿主特异性、发病机制和生态考虑，我们在这里为河虾微孢子虫建立了一个新属 Apotaspora，并将新物种命名为 Apotaspora heleios。在 SSU rDNA 系统发育树上将鱼类和甲壳类寄生虫分组在一起表明，多宿主生活史可能是研究微孢子虫谱系中已灭绝和/或现存成员的一个共同特征。
