The aquatic food chain has been dependent on microalgal species as a primary source of polyunsaturated fatty acids (PUFAs). Delta-6 desaturase plays a crucial role in the biosynthesis of essential long-chain PUFAs, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In fish, PUFAs are indispensable for growth and development. PUFAs play a significant role in major structural components of cellular membranes and as precursors of physiologically active molecules such as hormones and eicosanoids.
Fishes are incapable of synthesizing all required PUFAs de novo and therefore depend largely on dietary sources to meet their physiological requirements. Consequently, vast variety of fishes rely on microalgal organisms within the food chain as their primary PUFA source. Delta-6 desaturase catalyzes the conversion of linoleic acid (LA) to γ-linolenic acid (GLA), a key rate-limiting step in the biosynthetic pathway leading to the production of EPA and DHA. Based on this pivotal role, we propose delta-6 desaturase-rich Synechocystis sp. PCC 6803 substr. Kazusa as a promising candidate that could be utilized as a functional aquafeed ingredient.
The delta-6 desaturase protein (accession number Q08871.1) from Synechocystis sp. PCC 6803 substr. Kazusa, comprising 359 amino acids, was retrieved from the NCBI database. In silico analysis of its physicochemical properties using ProtParam revealed an isoelectric point of 6.80, a molecular weight of 41,424.96 Da, an instability index of 37.55, an aliphatic index of 98.05, and a GRAVY value of 0.187. Conserved domain (CD) analysis identified the DesA (COG3239) domain spanning amino acid residues 3 to 358, confirming its functional identity.
Three-dimensional structural modeling of the protein was performed using AlphaFold2. Among the five predicted models, model 1 exhibited a mean local distance difference test (LDDT) score of 93.28, indicating high structural accuracy. Furthermore, phylogenetic analysis using the neighbor-joining method revealed that, among 19 homologous proteins, the delta-6 desaturase from Kamptonema formosum was the closest evolutionary relative, supported by a strong bootstrap value.
Collectively, these findings suggest that delta-6 desaturase-rich Synechocystis sp. PCC 6803 substr. Kazusa holds significant potential as a sustainable aquafeed resource. Its incorporation into fish diets may enhance PUFA availability, thereby supporting optimal growth, development, and health of cultured fish, and playing a massive role in the advancement and sustainable growth of aquaculture industry.