Effect of overexpression of sll1848 and/or slr1510/sll1848 genes on lipid content in cyanobacterium synechocystis sp. PCC 6803

Abstract

In this work, sll1848-overexpressing (OE+C) and slr1510/sll1848 overexpressing (OE+XC) strains of Synechocystis sp. PCC 6803 were successfully constructed. The effects of nutrient-modified conditions on growth rate, chlorophyll a and carotenoid contents, oxygen evolution rate, transcript level of genes related to fatty acid biosynthetic pathway, total lipid and unsaturated lipid contents of cells WT, control WT+pE, OE+C and OE+XC strains were studied. The alignment of the amino acid sequences of the putative Sll1848 protein of Synechosystis sp. PCC 6714 and of Synechococcus sp. PCC 7002 showed the identities of 89% and 56.4%, respectively to that of Synechocystis sp. PCC 6803. However, it showed low identity with 1-acyl-sn-glycerol-3-phosphate acyltransferase of Arabidopsis thaliana plant with about 18.7%. The cultivated cells of four strains in BG11 medium could confirm that two overexpressing strains had insignificant changes on their growth, pigment contents and oxygen evolution rate when compared to WT and control WT+pE. Importantly, the total lipid contents of those OE+C and OE+XC strains were significantly higher than WT of about 1.24 fold and 1.49 fold, respectively when compared to WT. The maximum level of total lipid content under normal condition was 24.3% w/dcw observed in OE+XC strain whereas its maximum unsaturated lipid content was 1.3% w/dcw. Additionally, the total lipid content could be further enhanced by nutrient-modified condition. The nitrogen deficiency condition could increase total lipid contents of OE+C and OE+XC strains to 26.5 and 32.7% w/dcw, respectively, whereas unsaturated lipid contents of both strains were increased to 2.0 and 2.4% w/dcw, respectively. Interestingly, 0.4% acetate supplementation significantly induced the total lipid content of OE+XC up to 39% w/dcw whereas its unsaturated lipid content was increased to 1.6% w/dcw. Double overexpression of slr1510/sll1848 genes of OE+XC strain showed up-regulation on both sll1848 and slr1510 mRNA levels. In addition, AccA and lipA mRNA levels were slightly induced in OE+XC strain. The results suggest that transcript levels of sll1848 and slr1510 mRNA were related to the total lipid content in OE+XC strain, especially under 0.4% acetate supplementation. Altogether, the enhancement of lipid production in Synechocystis sp. PCC 6803 was achieved by overexpressing sll1848 and slr1510/sll1848 genes. The higher production of lipid content also occurred by nitrogen deficiency and acetate supplementation.