Morphophysiological analyses of Neochloris oleoabundans (Chlorophyta) grown mixotrophically in a carbon-rich waste product

Abstract

Neochloris oleoabundans is considered one of the most promising oil-rich microalgae because of its ability to store lipids under nitrogen starvation. However, high biomass densities, required for applications on medium to large scale, are not reached in this condition of growth. As previous studies on other microalgae have shown that mixotrophy allows to obtain higher biomass in comparison to autotrophic cultures, we performed morphophysiological analyses in order to test the mixotrophic growth capability of N. oleoabundans. A carbon-rich manure derived from the apple vinegar production (AWP) was added to the medium. Cells were also cultivated under nutrient starvation (tap water), to observe the expected lipids accumulation, and combining AWP to water, to test the potential of this waste in a low-cost culture system. The results highlighted that AWP in the medium allowed to obtain the highest final cell density. Moreover, starch granules were stored inside chloroplast at the beginning of the experiment. The presence of AWP did not induce variations on light harvesting complex II (LHCII)-photosystem II (PSII) assembly, even if an interesting promotion of pigment synthesis in cells was observed. On the other hand, in starved cells, chloroplast degeneration, pigment content decrease, altered LHCII-PSII assembly and accumulation of high amount of lipid globules were observed, irrespective of the presence of AWP. The results suggest that mixotrophy promotes growth in N. oleoabundans and open up the possibility of using waste products from agri-food industries for this purpose. After growth, cells could be transferred under nutrient starvation to induce lipid accumulation.

Transcriptomic analysis of the oleaginous microalga Neochloris oleoabundans reveals metabolic insights into triacylglyceride accumulation

“…Although starch synthase and AGPase encoding genes were repressed in –N, the gene encoding for α-amylase, responsible for the hydrolysis of starch to glucose monomers, was also repressed. The concomitant accumulation of starch and lipids under nitrogen limitation has been reported in the nonoleaginous C. reinhardtii [44,45] and recently reported for N. oleoabundans [46]. This contrasts with recent reports in Micractinium pusillum where carbohydrate content was reduced and TAG production was increased under nitrogen limitation [19].…”

Membrane Proteomic Insights into the Physiology and Taxonomy of an Oleaginous Green Microalga

“…The majority of the membrane proteins (41%) were located in the chloroplast, not surprising as this organelle occupies most of the microalga's cell volume (Giovanardi et al, 2013). Despite this, most of the cellular compartments were represented in the membrane proteome, including the lipid droplets (LDs), which are structures induced by nitrogen deprivation (Davis et al, 2012;Popovich et al, 2012;Giovanardi et al, 2013). Cytoplasmic proteins comprised only 9% of the membrane proteome (Supplemental Fig.…”

“…E. oleoabundans is a highly versatile organism, as it can grow in freshwater, wastewater (Levine et al, 2011;Wang and Lan, 2011;Yang et al, 2011;Olguín et al, 2015), and in culture media with salt concentrations up to seawater levels (Arredondo-Vega et al, 1995;Baldisserotto et al, 2012;Popovich et al, 2012). Moreover, it is able to grow under phototrophic, mixotrophic (Giovanardi et al, 2013;Baldisserotto et al, 2016), and heterotrophic (Wu et al, 2011;Morales-Sánchez et al, 2013) conditions. Owing to its high lipid content and growth versatility, E. oleoabundans is an organism of biotechnological interest.…”

A multidomain enzyme, with glycerol‐3‐phosphate dehydrogenase and phosphatase activities, is involved in a chloroplastic pathway for glycerol synthesis in Chlamydomonas reinhardtii

“…Microalgae, photosynthetic eukaryotic microorganisms, can convert CO 2 to a variety of products, including high value chemicals, pharmaceuticals, and biofuel precursors (Borowitzka, 1998;Pulz and Gross, 2004;Spolaore et al, 2006;Giovanardi et al, 2013). Some microalgal species can accumulate high quantities of nonpolar lipids, mainly triacylglycerols, and can potentially be used as feedstock for the production of edible oils and biofuels (Morales-S anchez et al, 2014;Gimpel et al, 2015).…”