Application of high-salinity stress for enhancing the lipid productivity of Chlorella sorokiniana HS1 in a two-phase process

Abstract

Increased lipid accumulation of algal cells as a response to environmental stress factors attracted much attention of researchers to incorporate this stress response into industrial algal cultivation process with the aim of enhancing algal lipid productivity. This study applies high-salinity stress condition to a two-phase process in which microalgal cells are initially grown in freshwater medium until late exponential phase and subsequently subjected to high-salinity condition that induces excessive lipid accumulation. Our initial experiment revealed that the concentrated culture of Chlorella sorokiniana HS1 exhibited the intense fluorescence of Nile red at the NaCl concentration of 60 g/L along with 1 g/L of supplemental bicarbonate after 48 h of induction period without significantly compromising cultural integrity. These conditions were further verified with the algal culture grown for 7 days in a 1 L bottle reactor that reached late exponential phase; a 12% increment in the lipid content of harvested biomass was observed upon inducing high lipid accumulation in the concentrated algal culture at the density of 5.0 g DW/L. Although an increase in the sum of carbohydrate and lipid contents of harvested biomass indicated that the external carbon source supplemented during the induction period increased overall carbon assimilation, a decrease in carbohydrate content suggested the potential reallocation of cellular carbon that promoted lipid droplet formation under high-salinity stress. These results thus emphasize that the two-phase process can be successfully implemented to enhance algal lipid productivity by incorporating high-salinity stress conditions into the pre-concentrated sedimentation ponds of industrial algal production system.

Eukaryote microbes potential for bioflocs in the swamp aquaculture

“…This happened as Chlorella can easily grow either in freshwater or brackishwater. High salinity level in the brackishwater induces lipid formation in Chlorella cells (Kakarla et al, 2018), making Chlorella retain the osmoregulation process with the lipid protection on the cell walls.…”

Transcriptomic responses associated with carbon and energy flows under high salinity stress suggest the overflow of acetyl-CoA from glycolysis and NADPH co-factor induces high lipid accumulation and halotolerance inChlorellasp. HS2

“…While high salinity stress strongly influences the viability and biochemical composition of algal crops and thus the economic feasibility of entire algal biorefinery (Kakarla et al, 2018; Laurens et al, 2017; Oh et al, 2019), this study was set out to elucidate transcriptional responses that give rise to the salt tolerance of highly-productive Chlorella sp. HS2.…”

“…For instance, Kakarla et al supplemented 60 g/L of NaCl into concentrated Chlorella cultures for 48 hr and reported ca. 58% increase in algal lipid productivity, supporting the possibility of deploying high salinity stress as a promising post-treatment for the cultivation systems targeting to produce algal lipids (Kakarla et al, 2018). Moreover, while high salinity stress could act as an effective method of crop protection in reducing freshwater cyanobacterial or ciliate contaminants, it was successfully demonstrated to facilitate algal harvesting by enlarging cellular diameter and increasing algal settling rates (Church et al, 2017; Lee et al, 2016; von Alvensleben, Stookey, Magnusson, & Heimann, 2013).…”

“…Notably, industrial algal cultivation platforms require continuous provision of nutrient salts with some studies demonstrating the utilization of saline wastewater sources enriched with nitrogenous and phosphorus nutrients as growth media to drive down the costs of commercial operation of algal cultivation systems (Yun, Cho, Lee, Heo, et al, 2018; Yun, Smith, & Pate, 2015; Zhu et al, 2013). In addition, the direct application of salinity stress for algal cultivation systems has been demonstrated as an effective abiotic inducer of high lipid accumulation and an environmental barrier inhibiting the proliferation of undesirable alien invaders in cultivation systems (Church et al, 2017; Kakarla et al, 2018; Lee, Nam, Yang, Han, & Chang, 2016). For instance, Kakarla et al supplemented 60 g/L of NaCl into concentrated Chlorella cultures for 48 hr and reported ca.…”

Evaluation of the operational conditions in the production and morphology of Chlorella sp.

“…In contrast, studies carried out by Sang-Il et al (2019), showed that by evaluating different operating conditions such as the intensity of LED lights (blue, red, and white) on the cultivation of microalgae like D. salina, different beta-carotene productivity were obtained (Sang-Il et al, 2019). The responses of microalgae could include enhanced metabolism due to increased nutrient (Seung Won et al, 2010) Additional studies showed that Chlorella strain hyper-accumulates lipids under high-salinity stress condition; however, it was found that the high-salinity condition significantly limited the production of algal biomass (Kakarla et al, 2018).…”