# _Synechococcus elongatus_ PCC 7942 as a Platform for Bioproduction of Omega-3 Fatty Acids
## 3 Results
To test the ability of Se7942 to produce SDA, we used a previously engineered ALA-producer strain expressing _desA_ and _desB_ genes from Ss7002 [33], in which we expressed the _desD_ gene from Ss6803 generating MSM_D\({}_{\text{AB}}\)_F\({}_{\text{F}}\)D\({}_{\text{D}}\) that should be able to transform ALA into SDA (Figure 2). As expected, these modifications led to the production of SDA up to 5.73% (Figure 5). In addition, other changes were observed in the FA profile of MSM_D\({}_{\text{AB}}\)_F\({}_{\text{F}}\)D  
\begin{table}
\begin{tabular}{c c c c c} \hline
**FA (\%) 1** & **MSM\_D\({}_{\text{AB}}\)** & **MSM\_D\({}_{\text{AB}}\)**\_F\({}_{\text{F}}\)** & **MSM\_D\({}_{\text{AB}}\)**\_F\({}_{\text{G}}\)** & **MSM\_D\({}_{\text{AB}}\)**\_F\({}_{\text{G}}\)** & **MSM\_D\({}_{\text{AB}}\)**\_F\({}_{\text{FZ}}\)** \\ \hline C14:0 & 1.56 \(\pm\) 0.40 \({}^{\text{a}}\) & 0 \(\pm\) 0 \({}^{\text{b}}\) & 1.03 \(\pm\) 0.15 \({}^{\text{c}}\) & 0.53 \(\pm\) 0.06 \({}^{\text{d}}\) & 0.82 \(\pm\) 0.05 \({}^{\text{c}}\) \\ C16:0 & 70.44 \(\pm\) 4.14 \({}^{\text{a}}\) & 65.19 \(\pm\) 2.58 \({}^{\text{a}}\) & 69.17 \(\pm\) 6.52 \({}^{\text{a}}\) & 57.68 \(\pm\) 1.16 \({}^{\text{b}}\) & 50.46 \(\pm\) 1.50 \({}^{\text{b}}\) \\ C16:1 & 16.22 \(\pm\) 2.95 \({}^{\text{a}}\) & 13.04 \(\pm\) 2.43 \({}^{\text{a}}\) & 16.4 \(\pm\) 1.41 \({}^{\text{a}}\) & 14.90 \(\pm\) 1.81 \({}^{\text{a}}\) & 42.33 \(\pm\) 2.16 \({}^{\text{b}}\) \\ C18:0 & 2.73 \(\pm\) 0.47 \({}^{\text{a}}\) & 0 \(\pm\) 0 \({}^{\text{b}}\) & 4.94 \(\pm\) 0.63 \({}^{\text{c}}\) & 13.65 \(\pm\) 0.93 \({}^{\text{d}}\) & 2.46 \(\pm\) 0.52 \({}^{\text{a}}\) \\ C18:1 & 0 \(\pm\) 0 \({}^{\text{a}}\) & 0 \(\pm\) 0 \({}^{\text{a}}\) & 0.06 \(\pm\) 0.03 \({}^{\text{a}}\) & 0.07 \(\pm\) 0.07 \({}^{\text{a}}\) & 3.29 \(\pm\) 0.28 \({}^{\text{b}}\) \\ C18:2 & 0 \(\pm\) 0 in comparison to the profile shown by MSM_DAB_FF as follows (i) a significant reduction in C16:0 FA, suggesting that this FA is used in the production of SDA; (ii) a significant rise in C14:0, C18:0, and C18:2 FAs, indicating that elongation reactions are highly active in MSM_DAB_FFDD; (iii) an absence of \(\gamma\)-linolenic acid (GLA), another product of DesD activity can be used to produce SDA; (iv) no statistical changes in C18:3 (ALA) levels between both strains, indicating that DesD has greater affinity to linoleic acid (LA) than to ALA as substrate. Our previous results demonstrated that _find_ deletion improves ALA production in Se7942 [33]. To test if this deletion might have a beneficial effect on SDA production, this modification was introduced in the MSM_DAB_FFDD strain, generating MSM_DAB_FFDD_AD (Figure 2). The amounts of SDA decreased significantly in the new strain, albeit no other significant changes were observed in the FA profile of this strain (Table 2). These results might indicate that _find_ deletion has a detrimental effect on SDA production, but the nature of this negative effect is unclear. Stearidonic Acid Production Is Improved by Increasing the Induction Time of the Genes Involved in Its Synthesis  
Since the synthetic pathway for SDA production implemented in Se7942 requires the overproduction of several enzymes, we hypothesized that longer post-induction times could yield increased production of SDA. To test this hypothesis, we analyzed the SDA produced at various times after induction (i.e., 24 h, 48 h, 72 h, and 96 h). Interestingly, \begin{table}
\begin{tabular}{c c c} \hline \hline
**FA (\%) 1** & **MSM\_DAB\_FFDD** & **MSM\_DAB\_FFDD\_DD\_AD** \\ \hline C14:0 & \(0.14\pm 0.24\) & \(0.71\pm 0.39\) \\ C16:0 & \(56.57\pm 0.73\) & \(55.65\pm 5.82\) \\ C16:1 & \(14.39\pm 1.96\) & \(18.29\pm 4.07\) \\ C18:0 & \(2.22\pm 0.94\) & \(0.71\pm 0.78\) \\ C18:1 & \(1.67\pm 1.45\) & \(3.38\pm 1.03\) \\ C18:2 & \(1.16\pm 0.44\) & \(0.95\pm 0.76\) \\ C18:3 & \(18.12\pm 3.40\) & \(19.40\pm 4.26\) \\ C18:4 & \(5.73\pm 0.58\) & \(0.92\pm 1.08\) \\ \hline \hline \end{tabular} 1  
\end{table} 
Table 2: FA profile of SDA-producer strains. Figure 5: SDA production in Se7942.