Lipid and fatty acid yield of nine stationary-phase microalgae: Applications and unusual C24–C28 polyunsaturated fatty acids

Abstract

Nine microalgal species from the classes Bacillariophyceae, Cryptophyceae, Prymnesiophyceae and Dinophyceae were isolated from Australian waters, cultured to stationary phase and analyzed for their lipid and fatty acid composition and yield. Five species (Pavlova pinguis, Heterocapsa niei, Proteomonas sulcata, Navicula jeffreyi and Thalassiosira pseudonana) produced high proportions of triacylglycerol (TAG: 22-57% total lipid). An unidentified Navicula-like diatom (CS-786), despite having a low TAG content, had the highest EPA yield (5.8 mg L −1 ), due to high biomass and a high relative proportion of EPA. Heterocapsa niei had the highest DHA yield (2.9 mg L −1 ), due to a high cellular lipid and DHA content (171 pg cell −1 and 13.7 pg cell −1 , respectively) despite its relatively low biomass. The desirable PUFA composition and yield of both diatom CS-786 and H. niei make them potential candidates for optimization of biomass and PUFA production for use as live-feeds in aquaculture. In addition, H. niei may have potential as a source of DHA for other uses. Low proportions (<1.2%) of 24:6(n − 3) accompanied by trace proportions of 24:5(n − 6) were detected in most strains, while 28:8(n − 3) was found in dinoflagellates and also in the prymnesiophyte P. pinguis. All non-diatomaceous species contained 26:7(n − 3) in minor quantities. This is the first time these unusual C 24 and C 26 PUFA have been reported in microalgae and the first report of C 28 PUFA in a microalga other than dinoflagellates. Possible biosynthetic reasons why these might occur in stationary phase cultures are considered and the likely dietary transfer of these PUFA to higher aquatic life is discussed.

Growth phase significantly decreases the DHA-to-EPA ratio in marine microalgae

“…Although many studies have demonstrated accumulation of (neutral) lipids in starved cultures of microalgae, relatively little was known about the effect of growth phase on EPA and DHA accumulation. Our study confirms previous results that the absolute amounts of EPA and DHA, but also the total fatty acid content varies considerably between species (Volkman et al 1989;Viso and Marty 1993;Tonon et al 2002;Mansour et al 2005;Patil et al 2007;Boelen et al 2013). Consequently, high interspecific variability in their nutritional value exists.…”

The place of diatoms in the biofuels industry

“…Reports range from 4 to 32% C14:0 of the total FA composition for diatoms [98,103,104]. C16 FAs are highly represented in diatoms and C16:0 and C16:1 combined can represent 65-70% of the total FA, with C16:1 being predominant.…”

“…Diatoms are unusually highly enriched for eicosapentaenoic acid (EPA; C20:5, w-3), which is not prevalent in chlorophytes [98,103,104]. Fish do not naturally produce EPA, but obtain it from algae they ingest, to which diatoms should contribute significantly.…”

“…Fish do not naturally produce EPA, but obtain it from algae they ingest, to which diatoms should contribute significantly. Docosahexaenoic acid (DHA) levels in diatoms are less than EPA, on the order of 5% of total lipid [98,103,104]. Diatoms contain a rich variety of carotenoids in the form of b-carotene, as well as a number of oxygenated derivatives called xanthophylls.…”

Crecimiento y composición bioquímica de <i>Thalassiosira pseudonana</i> (Thalassiosirales: Thalassiosiraceae) bajo cultivo semi-continuo en diferentes medios y niveles de irradiancias

“…Algunos ensayos realizados previamente, demostraron que la tasa de renovación utilizada en esta investigación era satisfactoria, coincidiendo con lo expuesto por Otero et al (1997), lo cual permitió obtener durante la fase de estabilización en ambos medios de cultivo a 180μE/m 2 .s, densidades celulares superiores y tasas específicas de crecimiento similares a las reportadas por Mansour et al (2005). A pesar de que el crecimiento de T. pseudonana en Humus a 60 y 120μE/m 2 .s fue bajo, el efecto combinado de éste, con el incremento de la irradiancia permitió la mayor producción de biomasa.…”