Hormesis effects of phosphorus on the viability of Chlorella regularis cells under nitrogen limitation

Liang Fu,John C Crittenden,Qingcheng Li,Ge Yan,Dandan Zhou

doi:10.1186/s13068-019-1458-z

Liang Fu, John C Crittenden + Show 3 more

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https://doi.org/10.1186/s13068-019-1458-z

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Abstract

BackgroundPhosphorus (P) is an essential element of microalgae, which is either required for anabolism or for energy metabolism. When employing a nitrogen limitation strategy to trigger microalgal intracellular lipid accumulation, P supplementation was always simultaneously applied to compensate for the accompanied growth inhibition.ResultsThis study identified that P exerts hormesis effects on microalgae. Slight excess of P (≤ 45 mg L−1) under nitrogen limitation condition stimulated the cell growth of Chlorella regularis and achieved a 10.2% biomass production increase. This also improved mitochondrial activity by 25.0% compared to control (P = 5.4 mg L−1). The lipid productivity reached 354.38 mg (L d)−1, which increased by 39.3% compared to control. Such an improvement was caused by the intracellularly stored polyphosphate energy pool. However, large excess of P (250 mg L−1) inhibited the cell growth by 38.8% and mitochondrial activity decreased by 71.3%. C. regularis cells showed obvious poisoning status, such as enlarged size, plasmolysis, deformation of cell walls, and disorganization of organelles. This is probably because the over-accumulated P protonated the amide-N and disrupted membrane permeability.ConclusionsThese results provide new insight into the roles of P in microalgae lipid production: P does not always play a positive role under nitrogen limitation conditions.

Highlights

Phosphorus (P) is an essential element of microalgae, which is either required for anabolism or for energy metabolism
Nitrogen limitation is the most popular approach to increase the microalgal lipid content, because it is able to up-regulate the key enzymes on the lipid biosynthesis pathways: malic enzymes become more activated for catalyzing pyruvate synthesis and reduced nicotinamide adenine dinucleotide phosphate (NADPH) formation and both acetyl-CoA and adenosine triphosphate (ATP)
C. regularis was inoculated into the modified BG11 media, which resulted in an initial cell density of 1.5 × 107 cell mL−1 for further heterotrophic at 28 °C, 160 rpm, in the dark (ZWY-240, Zhicheng Shanghai, China)

Summary

Introduction

Phosphorus (P) is an essential element of microalgae, which is either required for anabolism or for energy metabolism. Slight excess of P (≤ 45 mg L−1) under nitrogen limitation condition stimulated the cell growth of Chlorella regularis and achieved a 10.2% biomass production increase. This improved mitochondrial activity by 25.0% compared to control (P = 5.4 mg L−1). Microalgae are a promising feedstock for biodiesel [1, 2] In their studies on microalgae bioenergy technologies in the past 40 years, researchers have endeavored to explore strategies for enhancing biomass production and lipid accumulation [3, 4], which taken together, determines microalgal lipid production.

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