Oral immunostimulation of the oyster Ostrea edulis: Impacts on the parasite Bonamia ostreae

doi:10.1016/j.fsi.2015.01.019

Fish & Shellfish Immunology

Volume 45, Issue 1, July 2015, Pages 43-51

https://doi.org/10.1016/j.fsi.2015.01.019 Get rights and content

Highlights

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We studied the oral administration of immunostimulants in the oyster Ostrea edulis.
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Immune response enhanced after oral administration of encapsulated stimulants.
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Encapsulated immunostimulants boosted the response of Bonamia ostreae infected oysters.
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Prevalence of B. ostreae decreased after stimulation with encapsulated zymosan.

Abstract

Bioactive compounds were orally administered to the native European oyster Ostrea edulis to evaluate the immune response and the progression of infection of the protozoan parasite Bonamia ostreae. The immunostimulants lipopolysaccharide and zymosan directly administrated to the water column induced an increase in lysozyme activity and the percentage of granulocytes in naïve oysters over a period of 7 days. In another set of experiments, zymosan and curdlan were microencapsulated in alginate and also administered to the water column to naïve and B. ostreae infected O. edulis. Oyster mortality, prevalence and intensity of infection and several immune parameters were evaluated up to 28 days post-administration. Lysozyme activity, nitric oxide production and the expression of galectin, lysozyme and superoxide dismutase increased after 24 h in both infected and uninfected oysters. Zymosan immunostimulated oysters displayed a decrease in the prevalence of B. ostreae infection not attributed to mortalities but which could be associated to the enhanced ability of immunostimulants to evoke an enhanced immune response in the oysters and reduce infection.

Introduction

Ostrea edulis, the European native oyster, is the natural host of the parasite Bonamia ostreae [1]. Mass mortalities have been associated with this parasite during the last few decades [2], [3] causing important losses in O. edulis production and the introduction of an exotic and resistant species, the Pacific oyster, Crassostrea gigas [4]. Larvae, spat, juveniles and adults, especially oysters older than 2 years, are susceptible to the disease [5], [6], [7], [8].

Although B. ostreae can be found extracellularly, it is considered an intracellular parasite, mainly invading the haemocytes [1], the circulating cells involved in defense in invertebrates [9], [10]. Haemocyte immune function is activated through the recognition of pathogen associated molecular patterns (PAMPs) such as lipopolysaccharide (LPS), the major component of the membrane of Gram-negative bacteria, and (1,3)-β-glucans, the main compound of zymosan and curdlan that can be obtained from yeast and bacteria [11], [12], [13], [14], [15], [16], [17], [18], [19].

The immune response can be evaluated at a functional level by the determination of the total or differential haemocyte counts, the production of oxidative reactive species such as nitric oxide (NO) and lysozyme activity in the serum against bacterial peptidoglycan [20], [21], [22], [23], [24]. The molecular basis of the immune response complements the information obtained by functional assays. Several studies based on suppression subtractive hybridization libraries, microarray technology or new generation sequencing methods have enriched the database available on bivalves, improving the knowledge of host pathogen interactions [25], [26], [27], [28], [29], [30].

Recent studies have concluded that B. ostreae can modulate the host immune response for its own benefit, through the inhibition of the respiratory burst and phagocytosis [21], [31], [32]. At a molecular level, B. ostreae modifies the expression pattern of immune related genes such as galectin, superoxide dismutase (SOD) and filamin [33], [34].

To our knowledge, strategies to fight bonamiosis have been focused on the selection of resistant oyster strains [35], [36], [37]. However, no information is available to date regarding disease control. The development of environmentally friendly agents is one of the main concerns currently in aquaculture management. The use of probiotics has been successfully applied in fish and shellfish culture to improve health, growth and survival [38], [39], [40], [41], [42], [43], [44], [45], [46], [47]. Following the World Health Organization and the Food and Agricultural Organization definition, probiotics are live microorganisms, which when administered in adequate amounts confer health benefits on the host [48]. Although with some controversy, several authors have concluded that inactivated cells, subcellular components and extracellular products are also effective [49]. Probiotics and diets are usually microencapsulated in innocuous polymers, such as alginate, to be immobilized and chemically protected [50]. Previous studies carried out in our laboratory concluded that alginate microcapsules can be used as a suitable delivery vehicle in the oyster O. edulis [51].

In the present work, we studied the effect of immunostimulants, with and without alginate protection on the immune response of the oyster O. edulis. We also evaluated the effect of alginate encapsulated zymosan and curdlan on the development of bonamiosis over a one month period.

Section snippets

Oysters and holding conditions

European flat oysters, naïve or naturally infected with B. ostreae, were obtained from two commercial shellfish farms located in Loch Ryan (Scotland) and Lough Foyle (Ireland), respectively. An initial sample of 60 individuals from each stock was collected to evaluate the initial prevalence of B. ostreae infection. Oysters were acclimatized for 5 days at 12 °C before the experiment commenced and were fed daily with 2 ml of Shellfish Diet 1800 (Reed Mariculture) consisting of a heteromorphic mix

Alginate microcapsules

Microcapsules of zymosan and curdlan ranged from 50 to 100 μm and were easily observed by light microscopy. Their appearance was circular to ovoid. Compared to control microcapsules (Fig. 1A), the engulfed immunostimulants provided a more cloudy aspect to zymosan (Fig. 1B) and curdlan (Fig. 1C) microcapsules. Both immunostimulants could be easily distinguished from the conservative media.

Oyster mortality

No oyster mortality was observed in naïve oysters exposed to unencapsulated zymosan and LPS in the column

Discussion

The effect of the immunostimulants administered by oral route on the immune status of the oyster O. edulis was investigated in this study. The direct administration of LPS and zymosan in water induced an increase in the number of circulating granulocytes and lysozyme activity of O. edulis. These results showed that oral administration of immunostimulants can enhance the defenses of the oyster O. edulis. To our knowledge, this is the first time that water borne administration has been

Acknowledgements

The authors would like to thank the shellfish growers who contributed material for the study. The project BEADS (Bioengineered micro-encapsulation of active agents delivered to shellfish) was funded by the Seventh EU Framework Programme (FP7-SME-2010-1-262649).

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Citation Excerpt :
In this study, an increased CgLys expression was detected in oysters fed the Δmnn9-containing diet 50A50Y compared to those fed the 100A control. Similarly, following β-glucan stimulation, higher Lys activity was reported in Ostrea edulis at 24 h and 48 h [13], in Fenneropenaeus chinensis (during 48 h) [55], as well as higher Lys expression in Ruditapes philippinarum gills after 3 h and 6 h [24]. To avoid self-damage against reactive oxygen species, the host relies on effective antioxidant defense systems that involve antioxidant enzymes such as SOD and catalase [11].
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Full length articleOral immunostimulation of the oyster Ostrea edulis: Impacts on the parasite Bonamia ostreae

Highlights

Abstract

Introduction

Section snippets

Oysters and holding conditions

Alginate microcapsules

Oyster mortality

Discussion

Acknowledgements

Aquaculture

Eur J Cell Biol

Fish Shellfish Immunol

Dev Comp Immunol

Fish Shellfish Immunol

Fish Shellfish Immunol

Dev Comp Immunol

Fish Shellfish Immunol

J Invertebr Pathol

J Invertebr Pathol

J Invertebr Pathol

Gene

Gene

Fish Shellfish Immunol

Gene

Fish Sellfish Immunol

Int J Parasitol

Gene

Dev Comp Immunol

Aquaculture

Aquaculture

J Exp Mar Biol Ecol

Aquaculture

Aquaculture

Aquaculture

Aquaculure

Fish Shellfish Immunol

Aquaculture

Aquaculture

J Invertebr Pathol

J Invertebr Pathol

Fish Shellfish Immunol

Anal Biochem

Anal Biochem

Fish Shellfish Immunol

Methods

J Drug Del Sci Tech

J Exp Mar Biol Ecol

Int J Parasitol

Full length article
Oral immunostimulation of the oyster Ostrea edulis: Impacts on the parasite Bonamia ostreae