A non-lethal method for detection of Bonamia ostreae in flat oyster (Ostrea edulis) using environmental DNA

Louise Von Gersdorff Jørgensen,Per Walter Kania,Kurt Buchmann,Sussie Dalvin,Heidi Mathiessen,Lone Madsen,Mikkel Kehler Villadsen,Johan Wedel Nielsen,Bent Vismann

doi:10.1038/s41598-020-72715-y

Louise Von Gersdorff Jørgensen, Per Walter Kania + Show 7 more

Open Access

https://doi.org/10.1038/s41598-020-72715-y

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Abstract

Surveillance and diagnosis of parasitic Bonamia ostreae infections in flat oysters (Ostrea edulis) are prerequisites for protection and management of wild populations. In addition, reliable and non-lethal detection methods are required for selection of healthy brood oysters in aquaculture productions. Here we present a non-lethal diagnostic technique based on environmental DNA (eDNA) from water samples and demonstrate applications in laboratory trials. Forty oysters originating from Limfjorden, Denmark were kept in 30 ppt sea water in individual tanks. Water was sampled 6 days later, after which all oysters were euthanized and examined for infection, applying PCR. Four oysters (10%) were found to be infected with B. ostreae in gill and mantle tissue. eDNA purified from the water surrounding these oysters contained parasite DNA. A subsequent sampling from the field encompassed 20 oysters and 15 water samples from 5 different locations. Only one oyster turned out positive and all water samples proved negative for B. ostreae eDNA. With this new method B. ostreae may be detected by only sampling water from the environment of isolated oysters or isolated oyster populations. This non-lethal diagnostic eDNA method could have potential for future surveys and oyster breeding programs aiming at producing disease-free oysters.

Highlights

Production of European flat oysters (Ostrea edulis) for human consumption has decreased from 32,995 tons in 1961 to 3120 tons in 2016 mostly due to diseases caused by the parasites Bonamia ostreae and Marteilia refringens[1]
The parasitic disease bonamiosis caused by the protist B. ostreae is a major reason for the decline
The present study evaluates a non-lethal water sampling method detecting B. ostreae DNA in water containing B. ostreae infected European flat oyster

Summary

Introduction

Production of European flat oysters (Ostrea edulis) for human consumption has decreased from 32,995 tons in 1961 to 3120 tons in 2016 mostly due to diseases caused by the parasites Bonamia ostreae and Marteilia refringens[1]. Environmental DNA (eDNA) released from the oysters to the environment can be detected and serve to demonstrate presence or former presence of specific organisms associated with the o ysters[17,18,19,20]. Using this methodology, sampling of the organism itself is unnecessary. Oysters infected with B. ostreae will discharge remnants of the parasite to the environment and detection of the eDNA in water will thereby represent a non-lethal sampling technique. In order to select resistant and healthy oysters for breeding purposes, the B. ostreae infection status of the oyster must be determined by non-lethal techniques

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