Selenium enrichment in the marine microalga Nannochloropsis oceanica

Bárbara O Guimarães,Kieke De Boer,Pieter Gremmen,Anemoon Drinkwaard,Rick Wieggers,René H Wijffels,Maria J Barbosa,Sarah D'Adamo

doi:10.1016/j.algal.2021.102427

Bárbara O Guimarães, Kieke De Boer + Show 6 more

Open Access

https://doi.org/10.1016/j.algal.2021.102427

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Abstract

Se-enriched ingredients have recently gained interest in the aquaculture industry as feed supplements due to their positive effects on fish health, growth, and potential effects on animal welfare. This study aims to assess which inorganic selenium (Se) species is suitable to produce Se-enriched Nannochloropsis oceanica (N. oceanica) biomass for aquafeed applications. The effective concentration for 50% growth inhibition (EC50) and Se bioaccumulation of the two inorganic forms of Se, sodium selenite (Na2SeO3), and sodium selenate (Na2SeO4), were assessed at different concentrations after twelve days of cultivation. Toxicity results showed that selenate, EC50 = 32.93 μM, had a greater negative effect on cell growth than selenite, EC50 = 163.82 μM. Total intracellular Se was analysed by inductively coupled plasma - optical emission spectrometry (ICP-OES) and high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), which revealed that selenite was better accumulated by N. oceanica. Further investigation at 30 μM of selenite in the growth medium resulted in Se bioaccumulation with a minor effect on cell growth and reached a Se intracellular content of 0.131 gSe/kgbiomass after 12 days. Thus, 30 μM of selenite was selected for batch pilot-scale cultivation in a 1500 L tubular photobioreactor. Total Se accumulated in the biomass at pilot-scale was in the same order of magnitude compared with flasks (0.104–0.159 gSe/kgbiomass). The results from this pilot-scale study are fundamental for a proof of concept from laboratory to pilot-scale production and they represent a critical bridging step for the potential use of Se-enriched N. oceanica in aquafeed.

Highlights

Selenium (Se) deficiency in fish can interfere with growth, cause greater fish mortality and hinder the fish immune response [1]
Cell growth was monitored to determine the effective concentration for 50% growth inhibition (EC50)
The dose-response effect was evaluated for sodium selenate, EC50 = 32.93 μM (2.60 mgSe/ L) and sodium selenite, EC50 = 163.82 μM (12.94 mgSe/L), revealing that selenite is less harmful for the growth of N. oceanica

Summary

Introduction

Selenium (Se) deficiency in fish can interfere with growth, cause greater fish mortality and hinder the fish immune response [1]. It is challenging to naturally meet Se dietary requirements in aquaculture, and efforts to mitigate this issue include adding mineral additives to aquafeed such as mineral mixes containing a higher supply of inorganic Se [3]. Studies have focused on understanding the bioavailability of different Se sources used in aqua feed, including inorganic Se [5], organic Se (in the form of selenome thionine) [5], Se-enriched yeast [3], and Se-enriched microalgae [6,7]. Microalgae are considered an important aquafeed ingredient since they are the primary producers of (polyunsaturated fatty acids) PUFAs in the ocean and contain, carbohydrates, proteins, vitamins, essential amino acids, minerals and pigments which are essential to meet fish nutritional demands [8,9,10]. Studies have shown that microalgae play a crucial nutritional role in early development stages of finfish and for molluscs (such as oysters) during all stages of development [11,12]

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