Beneficial effect of urea utilization in response to high temperature in Arthrospira platensis C1

Nitrogen sources are essential to the growth and biochemical composition of cyanobacteria. This study evaluated the impact of high temperature on the growth and biochemical composition of Arthrospira platensis C1 grown on media containing urea as an alternative nitrogen source. The cell biomass of A. platensis C1 in culture medium with 29 mM urea-N was comparable to that of the control (29 mM nitrate-N) at the control temperature (35 ◦C). However, urea-grown cells produced a higher amount of carbohydrates (52.09 ± 6.93 % DW) but lower levels of protein (38.52 ± 1.27 % DW) and pigments (chlorophyll a; 0.87 ± 0.07 % DW; and phycocyanin; 5.75 ± 0.72 % DW). Interestingly, increasing the culture temperature from 35 ◦C to 42 ◦C had less impact on urea-grown cells than on nitrate-grown cells. Cells cultivated in 29 mM urea-N produced more protein (43.40 ± 2.95 % DW) and phycocyanin (8.12 ± 0.46 % DW) contents after 24 h of exposure to 42 ◦C compared to cells grown at 35 ◦C. Moreover, the transcriptional response of urea-grown cells to high temperature revealed an increase in the transcript levels of genes involved in urea uptake, phycocyanin, carbon-lipid mechanisms, and transcriptional regulation of C/N homeostasis following exposure to 42 ◦C. The findings suggest that urea is an excellent nitrogen source for outdoor cultivation to maintain growth potential and high protein and pigment levels, especially at high temperatures.