Biochemical Composition and Fatty Acid Content of Filamentous Nitrogen-Fixing Cyanobacteria

Abstract

The biochemical composition and fatty acid content of twelve strains of filamentous, heterocystous, nitrogen‐fixing cyanobacteria have been determined. When grown under diazotrophic conditions, protein, carbohydrate, lipid, and nucleic acids comprised 37–52%, 16–38%, 8–13%, and 8–11% of the dry weight, respectively. The presence of a combined nitrogen source resulted in an increase in the protein content of the cells and a decrease in the levels of lipids and carbohydrates, although biomass productivity was not affected significantly. Biochemical composition also changed during culture growth, with the highest levels of proteins and lipids occurring as the culture entered stationary phase, whereas the highest levels of carbohydrate and nucleic acids were found during the exponential phase. Total fatty acid levels in the strains assayed ranged between 3 and 5.7% of the dry weight. With regard to fatty acid composition, all strains showed high levels of polyunsaturated fatty acids (PUFAs) and saturated fatty acids (SAFAs), with values of 24–45% and 31–52% of total fatty acids, respectively, whereas the levels of monounsaturated fatty acids (MUFAs) were in general lower (11– 32%). Palmitic acid (16:0) was the most prevalent SAFA, whereas palmitoleic (16:1n‐ 7) and oleic acid (18:1n‐9) were the most abundant MUFAs in all the strains. Among PUFAs, γ‐linolenic acid (GLA, 18:3n‐6) was present at high levels (18% of total fatty acids) in Nostoc sp. (Chile) and at lower levels (3.6% of total fatty acids) in Anabaenopsis sp. The presence of GLA has not been previously reported in these genera of cyanobacteria. The rest of the strains exhibited high levels (12–35% of total fatty acids) of α‐linolenic acid (ALA, 18:3n‐3). Linoleic acid (18:2n‐6) was also present at a substantial level in most of the strains. Eicosapentaenoic acid (EPA, 20:5n‐3) was also detected in Nostoc sp. (Albufera). Some filamentous nitrogen‐fixing cyanobacteria therefore represent potential sources of commercially interesting fatty acids.