Arginine culture generates triacylglycerol by triggering nitrogen starvation responses during robust growth inChlamydomonas

Abstract

Under nitrogen (N) starvation, microalgae increase carbon storage in the form of lipid droplets while also downregulating photosynthesis and eventually terminating growth. To improve lipid yield, we asked whether lipid droplets and N starvation responses can be induced without limiting growth or photosynthesis. In the chlorophyte Chlamydomonas reinhardtii, gametogenesis is induced either by N starvation or by growth with arginine as the sole N source. We showed that arginine cultures supported robust phototrophic growth, constitutively turned on N starvation-induced genes, and increased lipid droplets. The lipids accumulated in arginine cultures exhibited strong enrichment of saturated and monounsaturated fatty acids, a preferred characteristic of biodiesel precursors. The diatom Phaeodactylum tricornutum also accumulated lipid droplets in arginine culture without growth impairment. We document a system wherein N starvation responses are induced without compromising photosynthesis or growth, thereby suited to the producing valuable chemicals and biofuel precursors without requiring stressors in microalgae.

The bHLH family NITROGEN‐REPLETION INSENSITIVE1 represses nitrogen starvation‐induced responses in Chlamydomonas reinhardtii

“…According to the hypothetical signaling that senses the cytosolic ammonium concentration to regulate N starvation‐induced responses, nitrate or arginine feeding may provoke N starvation responses (Figure 5b). In accordance with this prediction, arginine‐fed cells were shown to derepress N starvation responses, including gametogenesis, TAG accumulation, and N starvation marker gene expression, without significant growth defects (Munz et al., 2020). By contrast, nitrate feeding suppressed N starvation responses in C. reinhardtii (Pozuelo et al., 2000).…”

“…NIT1 promoter is turned on by N starvation in an nit2-null background Previous studies using NIT1 promoter-reporter constructs focused on nitrate-dependent activation and ammoniumtriggered repression of nitrate assimilation genes in NIT2 wild-type backgrounds. We recently reported that NIT1 was >100-fold upregulated under N starvation conditions in the 137c laboratory strain harboring a nit2 mutation (Munz et al, 2020). Therefore, we sought to use a NIT1 promoter-reporter system to identify mutants defective in regulating N starvation-specific responses in the absence of NIT2-dependent regulation.…”

Mixotrophic cultivation of Chlorella vulgaris in sugarcane molasses preceding nitrogen starvation: Biomass productivity, lipid content, and fatty acid analyses

“…Nitrogen starvation has been extensively studied to increase lipid contents of the algal biomass. [54][55][56][57] However, the accumulation of neutral lipids during photoautotrophic cultivations resulted in cessation of microalgal growth. Thus the biomass productivity became decreased.…”

Análise integrativa de proteômica, metabolômica e lipidômica para estudo da acumulação de lipídios neutros na microalga >i<Chlamydomonas reinhardtii>/i<

“…Diferentemente do observado no presente estudo, Munz et al(2020) verificou acúmulo de lipídios neutros em C. reinhardtii quando a cultura foi suplementada com 8 mM de Arg em condição mixotrófica. No entanto, considerando que uma molécula de Arg possui 4 vezes mais N do que uma molécula de amônio, o estudo deMunz et al (2018) torna-se questionável devido ao excesso de N adicionado e à ausência de um controle com a mesma proporção de N. Este desbalanço na razão nitrogênio/carbono (N/C) pode afetar tanto o crescimento, quanto acúmulo de lipídios neutros. Portanto, acreditamos que mais experimentos com diferentes concentrações de Arg e de amônio devam ser realizados para confirmar o efeito da suplementação de Arg no acúmulo de lipídios neutros.…”

“…Portanto, acreditamos que mais experimentos com diferentes concentrações de Arg e de amônio devam ser realizados para confirmar o efeito da suplementação de Arg no acúmulo de lipídios neutros. Rota de anabolismo e catabolismo de Arg e via de síntese de Óxido Nítrico (NO) e Poliaminas: Representação dos metabólitos e proteínas em condição de privação de N (Baseado em ChlamyCyc,Munz et al, 2018 e Winter et al 2015. Metabólitos indicados por fontes em vermelho aumentaram sua concentração relativa entre 0.5h a 8h.…”