Isolation and identification of oleaginous microalgae isolated from the salt-discharging channel and cultivation for lipid production

Abstract: Soil salinization is currently improved via flood irrigation and salt-washing drainage for the main crop cultivation in a typical arid desert region of Xinjiang, China. As such, most produced saline-alkali water is discharged directly through the salt-discharging channel. Loss of water resources has posed a serious threat to the local soil and ecological environment. Oleaginous microalgae offer an attractive alternative to generate biofuel in the saline-alkali land unsuitable for farming, such as desert and mudflat in recent years. However, little attention has been paid to the cultivation of oleaginous microalgae in the salt-discharging channel water with high salinity and nutrient deficiency. In this study, one species of oleaginous microalga (WY205), identified as Chlorella sp, was isolated from the salt-discharging channel water. A systematic examination was made to explore the effects of supplementation with organic carbon sources on microalgae growth and lipid accumulation. An attempt was also made to investigate the salt-tolerance, the growing and lipid producing stability of oleaginous microalga. The results showed that the addition of organic carbon sources improved significantly the growth rate and lipid yield of microalgae. Since the accumulation of microalgae lipid followed the type of growth coupling, the logistic equation and Gaden growth model were selected to describe the algal growth and kinetics of lipid generation in the salt-discharging channel water. The maximum biomass (3.03 g/L) and the highest lipid yield (1.26 g/L) were predicted at the supplementation of 2.5 g/L glucose, which were 1.35 and 2.21 times more than those treated without sugar, respectively. When the Na+ was added up to 5 g/L (equivalent to NaCl 12.72 g/L), the content of microalgae lipid reached 44.90%, while the lipid yield achieved the maximum, 21.69% higher than that of the original water from the salt-discharging channel (Na+ concentration was 2.64 g/L). Even when the Na+ concentration enhanced to 10 g/L (equivalent to NaCl 25.43 g/L), the content of microalgae lipid reached 59.71%, whereas, the lipid yield began to decline, 10.84% higher than that of the original water from the salt-discharging channel, due to the large reduction of biomass. This indicated the high salt-tolerance of oleaginous microalgae. There was no significant change in the biomass and lipid yield of alga strain after 60 days of semi-continuous culture using undiluted salt-discharging channel water for 3 cycles plus 2 times concentrated water sample for another 3 cycles (10 days for each cycle). The content of microalgae lipid maintained higher than 30% in all cycles, exhibiting good adaptability and stability. In further optimization, the culture conditions of microalgae can be extended to the growth monitoring on a large-scale in subsequent studies. The finding can provide a promising technical reference to cultivate oleaginous microalgae for resource utilization of salt-discharging channel water.