Humic-acid-driven escape from eye parasites revealed by RNA-seq and target-specific metabarcoding
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Parasites & Vectors Open Access
RESEARCH
Humic‑acid‑driven escape from eye parasites revealed by RNA‑seq and target‑specific metabarcoding Kristina Noreikiene1*† , Mikhail Ozerov2,3,4†, Freed Ahmad2, Toomas Kõiv5, Siim Kahar1, Riho Gross1, Margot Sepp5, Antonia Pellizzone2,6, Eero J. Vesterinen4,7, Veljo Kisand8 and Anti Vasemägi1,3*
Abstract Background: Next generation sequencing (NGS) technologies are extensively used to dissect the molecular mechanisms of host-parasite interactions in human pathogens. However, ecological studies have yet to fully exploit the power of NGS as a rich source for formulating and testing new hypotheses. Methods: We studied Eurasian perch (Perca fluviatilis) and its eye parasite (Trematoda, Diplostomidae) communities in 14 lakes that differed in humic content in order to explore host-parasite-environment interactions. We hypothesised that high humic content along with low pH would decrease the abundance of the intermediate hosts (gastropods), thus limiting the occurrence of diplostomid parasites in humic lakes. This hypothesis was initially invoked by whole eye RNA-seq data analysis and subsequently tested using PCR-based detection and a novel targeted metabarcoding approach. Results: Whole eye transcriptome results revealed overexpression of immune-related genes and the presence of eye parasite sequences in RNA-seq data obtained from perch living in clear-water lakes. Both PCR-based and targetedmetabarcoding approach showed that perch from humic lakes were completely free from diplostomid parasites, while the prevalence of eye flukes in clear-water lakes that contain low amounts of humic substances was close to 100%, with the majority of NGS reads assigned to Tylodelphys clavata. Conclusions: High intraspecific diversity of T. clavata indicates that massively parallel sequencing of naturally pooled samples represents an efficient and powerful strategy for shedding light on cryptic diversity of eye parasites. Our results demonstrate that perch populations in clear-water lakes experience contrasting eye parasite pressure compared to those from humic lakes, which is reflected by prevalent differences in the expression of immune-related genes in the eye. This study highlights the utility of NGS to discover novel host-parasite-environment interactions and provide unprecedented power to characterize the molecular diversity of cryptic parasites. Keywords: Diplostomidae, Host-parasite interaction, Humic substances, Metabarcoding, Perca fluviatilis, RNA-seq
*Correspondence: [email protected]; [email protected] † Kristina Noreikiene and Mikhail Ozerov contributed equally to this work 1 Chair of Aquaculture, Institute of Veterinary Medicine and Animal Sciences, Estonian University of Life Sciences, Kreutzwaldi 46, 51006 Tartu, Estonia 3 Department of Aquatic Resources, Institute of Freshwater Research, Swedish University of Agricultural Sciences, 17893 Drottningholm, Sweden Full list of author information is available at the end of the article © The Author(s) 2020. This art
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