Synergistic effect of alkane and membrane lipid alteration in Synechococcus elongatus PCC 7942 under salt and light stresses.

Salinity and light markedly influence cyanobacterial viability. High salinity disrupts the osmotic balance, while excess light energy affects redox potential in the cells. Regulating the ratio of saturated and unsaturated alka(e)ne and fatty acids in cyanobacteria is thought to have crucial roles in coping with these stresses by regulating membrane fluidity. In Synechococcus elongatus PCC 7942 (Syn7942), alkane is produced from fatty acid metabolites using acyl-acyl carrier protein reductase (Aar) and aldehyde-deformylating oxygenase (Ado) enzymes. However, the role of alka(e)nes and their correlation with fatty acid-related compounds, especially under salinity stress, is not yet fully understood. This study explored the significance of the natural alka(e)ne biosynthesis pathway using Syn7942. The role of alka(e)ne was assessed using single and double knockout mutants of the aar and/or ado genes in this biosynthetic process. The alka(e)ne levels and membrane lipid content exhibited an inverse relationship, correlating with cell fluidity under high-salinity and high-light conditions. The absence of alka(e)ne resulted in a severe growth phenotype of Δado and Δaar/Δado under high-salinity conditions and less severe under high-light conditions. In addition, feeding with C15:0 and/or C17:0 alkanes complemented the growth phenotype with different accumulation profiles. The Δaar mutant exhibited higher resistance to high salinity than the Syn7942 WT, indicating the importance of Ado for survival at high salinity. Overall, lipid-related compounds, especially alka(e)nes, markedly contribute to cell integrity maintenance under high-salinity conditions by regulating membrane rigidity and fluidity.