Effect of sulphur on selenium accumulation and speciation in Nannochloropsis oceanica

Abstract

• Sulphur deplete and limiting conditions result in more Se accumulation in N. oceanica . • The dominant Se species in N. oceanica is selenomethionine (SeMet) (>97 %). • Se speciation in N. oceanica is SeMet > SeCys 2 > SeMeSeCys > Se. • Selenium enrichment in N. oceanica does not affect total fatty acids accumulation. Sulphur (S) and selenium (Se) are chemically similar. Once Se is taken up, it substitutes S in S-containing amino acids. This study investigated the effect of S on selenite accumulation in the microalga Nannochloropsis oceanica . [0–28 mM] S concentrations and selenite concentrations of 0 and 30 μM were tested. S concentrations of ≤ 3 mM led to decreased cell growth whereas cultures with ≥ 4 mM were not growth limited. Se accumulation increased up to 8-fold when using S ≤ 2 mM and decreased with S 28 mM. The average relative abundance of organic Se species was selenomethionine (SeMet) 98.2 %, selenocystine (SeCys 2 ) 1.4 % and selenomethyl selenocysteine (SeMeSeCys) 0.4 %. Total fatty acids were not affected by S limitation or Se presence. This is the first study on the effect of S on selenite accumulation, organic Se speciation of N. oceanica and its potential as an organic Se-enriched food/feed ingredient.