Effects of salt concentration and trophic mode on glucosylglycerol and phycocyanin production by Arthrospira maxima

Arthrospira maxima is an excellent cyanobacterial strain for phycocyanin production, while it has also recently been employed to produce a high-value product called glucosylglycerol that can be used as a cosmetic and food ingredient. In this study, the effect of NaCl-induced salt stress on cell growth, glucosylglycerol (GG) and phycocyanin (PC) production by A. maxima was investigated. The results suggested that the addition of NaCl effectively induced GG synthesis in cyanobacteria. The GG content increased from 0 % to the highest level of 15.29 % with increasing NaCl concentrations from 0 to 900 mM. However, the highest GG yield (174.54 mg L⁻¹) was obtained at 600 mM NaCl as a higher NaCl concentration significantly reduced the biomass concentration. Furthermore, the PC content decreased from 17.44 to 9.72 %, and the PC yield sharply reduced from 333.63 to 80.00 mg L⁻¹, indicating that increasing salt concentration adversely affected PC production. Consequently, the NaCl concentration of 300 mM was considered a suitable option for simultaneous production of PC and GG, under which both the high yields of GG (149.00 mg L⁻¹) and PC (249.05 mg L⁻¹) were achieved. Moreover, trophic mode markedly influenced GG synthesis in A. maxima. Photoautotrophic cells accumulated as much as 15.77 % GG in cyanobacterial cells, whereas only 6.28 % GG accumulated in mixotrophic cells, resulting in a significantly lower GG yield. In conclusion, the application of salt stress was an effective approach to producing GG under the photoautotrophic mode, and a medium salt concentration was the optimal option to simultaneously achieve high productivities of GG and PC. This study lays a foundation for efficient co-production of PC and GG, facilitating the high-value utilization of Arthrospira maxima.