Enhanced accumulation of alpha-linolenic acid rich lipids in indigenous freshwater microalga Desmodesmus sp.: The effect of low-temperature on nutrient replete, UV treated and nutrient stressed cultures

•Freshwater microalga Desmodesmus sp. produced ALA-rich lipids under low temperature, UV treatment and nutrient stress.•Low temperature led to a 1.8 fold increase in ALA fraction of total fatty acids.•UV treated cultures at low temperature showed a 2.6 fold increase in lipid content.•UV treated cultures at low temperature showed maximum ALA content of biomass. The indigenous microalga, Desmodesmus sp. produced alpha-linolenic acid (ALA) rich lipids in response to low temperature and UV treatment. Incubation at 5 °C showed a 1.5 fold increase in lipid content (34% w/w) with 44% ALA fraction of total fatty acids. The UV treatment (UV 60 min) exhibited a 1.4 fold increase in biomass productivity and 1.6 fold increase in lipid content (37% w/w) with ALA fraction as 31% of total fatty acids. The nitrogen stress enhanced the lipid content (39% w/w) with a reduced ALA fraction (18%) of total fatty acids. The UV treated cultures (UV 40 and 60 min) on incubation at 5 °C showed maximum lipid accumulation (59 to 62% w/w) with ALA fraction of total fatty acids as 39 to 42%. The incubation of nutrient-replete and UV treated cultures at low-temperature could therefore be used for the production of ALA-rich lipids in microalgae.