Contents lists available at ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/jip The diversity of microsporidian parasites infecting the Holarctic amphipod Gammarus lacustris from the Baikal region is dominated by the genus Dictyocoela Polina Drozdova a , Ekaterina Madyarova a,b , Mariya Dimova a , Anton Gurkov a,b , Kseniya Vereshchagina a,b , Renat Adelshin a,c , Maxim Timofeyev a,b, ⁎ a Irkutsk State University, Karl Marx str. 1, 664003 Irkutsk, Russia b Baikal Research Centre, Lenin str. 21, 664003 Irkutsk, Russia c Irkutsk Anti-Plague Research Institute of Siberia and Far East, Trilissera str. 78, 664047 Irkutsk, Russia ARTICLE INFO Keywords: Host specifcity Microsporidia Dictyocoela Gammaridae ABSTRACT Microsporidia are a highly diverse group of single-celled eukaryotic parasites related to fungi and infecting hosts belonging to all groups of eukaryotes, including some protists, invertebrate and vertebrate animals. We in- vestigated the diversity of microsporidia in the Holarctic amphipod species Gammarus lacustris from mostly, but not limited to, water bodies in the Lake Baikal region. Ribosomal DNA sequencing and host transcriptome sequencing data from various works show that this species is predominantly infected by representatives of the genus Dictyocoela and probably has some features underlying this specifc interaction. 1. Introduction Microsporidia are a highly diverse group of single-celled eukaryotic parasites. They are related to Cryptomycota (or rozeliids) and Aphelidea, and these groups form the ARM clade, or the Opisthosporidia super- phylum, which is a sister group to Fungi (Ascomycota, Basidiomycota, Zygomycota, and Chytridiomycota) (Karpov et al., 2014). Diferent re- presentatives of this group infect hosts belonging to all major groups of eukaryotes, from some groups of protists to vertebrates, including hu- mans (Stentiford et al., 2013). The diversity of the microsporidia is of particular interest because it can shed light on the early evolution of eukaryotes and fundamental issues of parasitism and host specifcity. Aquatic organisms host almost half the described microsporidian genera, and there are about 50 mi- crosporidian genera that infect aquatic arthropods (Stentiford et al., 2013). At least twelve of these genera have been found in amphipods (Malacostraca: Amphipoda), based on the DNA sequences deposited to NCBI (Bojko and Ovcharenko, 2019). Among those, the three most di- verse genera infecting amphipods include Dictyocoela with seven known species, Nosema with fve species, and Cucumispora with three species (reviewed in Bojko and Ovcharenko, 2019). Generally, diferent mi- crosporidian genera have been found in each gammarid host deeply screened for microsporidia (e.g., Haine et al., 2004; Kuzmenkova et al., 2008; Krebes et al., 2010; Grabner, 2017; Quiles et al., 2019). The genus Gammarus Fabricius, 1775 is the most diverse epigean genus of freshwater amphipods in the eastern Holarctic region, in- cluding over 200 species (Väinölä et al., 2007). Gammarus lacustris Sars, 1863 is the only non-local species with very broad geographic range throughout the Northern Hemisphere (Väinölä et al., 2007; Hou et al., 2011). In this report, we summarize the distribution of microsporidia in G. lacustris, mostly from the Baikal region, with several samples from other regions. 2. Materials and methods The microsporidian small subunit (SSU) rDNA sequences used in this work were retrieved from NCBI Genbank (Tables S1 and S2; de- scribed in Hogg et al., 2002; Haine et al., 2004; Terry et al., 2004; Krebes et al., 2010; Ryan and Kohler, 2010; Grabner et al., 2015; Ironside and Alexander, 2015; Ironside and Wilkinson, 2017; Bacela- Spychalska et al., 2018; Quiles et al., 2019; Wilkinson et al., 2011). Sampling and sequencing detail for the data obtained in this work (KT956061-62, KT956055, MH753357-60) are provided in Text S1. In addition, raw RNA sequencing (RNA-seq) data were retrieved from SRA (Table S2; described in Drozdova et al., 2019; Naumenko et al., 2017; Jin et al., 2019). Search for the reads matching microsporidian SSU rRNA in RNA-seq samples was performed using k-mer matching with bbduk (Bushnell, https://doi.org/10.1016/j.jip.2020.107330 Received 20 September 2019; Received in revised form 13 January 2020; Accepted 18 January 2020 ⁎ Corresponding author. E-mail address: m.a.timofeyev@gmail.com (M. Timofeyev). Journal of Invertebrate Pathology 170 (2020) 107330 Available online 21 January 2020 0022-2011/ © 2020 Elsevier Inc. All rights reserved. T