Role of ERA protein in enhancing glyceroglycolipid synthesis and phosphate starvation tolerance in Synechococcus elongatus PCC 7942

Abstract

Glyceroglycolipids are the primary thylakoid membrane lipids in cyanobacteria. Their diverse bioactivities have led to extensive utilization in the biomedical industry. In this study, we elucidated the role of ERA (E. coli Ras-like protein) in augmenting glyceroglycolipid synthesis and bolstering stress resilience in Synechococcus elongatus PCC 7942 during phosphate starvation. Notably, the ERA overexpression strain (ERA OE) outperformed the wild-type (WT) strain under phosphate-starved conditions, displaying an average 13.9 % increase in biomass over WT during the entire growth period, peaking at 0.185 g L⁻¹ of dry cell weight on day 6. Lipidomic analysis using UHPLC-MS/MS techniques revealed that ERA OE exhibited a higher total glyceroglycolipid content compared to WT under phosphate starvation, representing a 7.95 % increase over WT and constituting a maximum of 5.07 % of dry cell weight on day 6. Transcriptomic analysis identified a significant up-regulation of the gldA gene (encoding glycerol dehydrogenase) involved in glycerolipid metabolism due to overexpression of ERA during phosphate starvation. These findings suggest a potential mechanism by which ERA regulates glyceroglycolipid synthesis through the up-regulation of GldA, thereby enhancing phosphate starvation tolerance in S. elongatus PCC 7942. Furthermore, lipidomic analysis revealed that ERA facilitated the production of glyceroglycolipid molecules containing C16:1 and C18:1 fatty acids. Additionally, ERA redirected lipid flux and promoted glyceroglycolipid accumulation while attenuating triacylglycerol production under phosphate starvation. This study represents the first demonstration of pivotal role of ERA in enhancing glyceroglycolipid synthesis and phosphate starvation tolerance in cyanobacteria, offering new insights into the effective utilization of glyceroglycolipids in various applications.