BIOCHEMICAL-COMPOSITION AND FATTY-ACID CONTENT OF FILAMENTOUS NITROGEN-FIXING CYANOBACTERIA

The biochemical composition and fatty acid content of twelve strains o f filamentous, heterocystous, nitrogen-fixing cyanobacteria have been determined. When grown under diazotrophic conditions, protein carbohyd rate, lipid, and nucleic acids comprised 37-52%, 16-38%, 8-13%, and 8- 11% of the dry weight, respectively. The presence of a combined nitrog en source resulted in an increase in the protein content of the cells and a decrease in the levels of lipids and carbohydrates, although bio mass productivity was: not affected significantly. Biochemical composi tion also changed during culture growth, with the highest levels of pr oteins and lipids occurring as the culture entered stationary phase, w hereas 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 fa tty 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 lev els of monounsaturated fatty acids (MUFAs) were in general lower (11-3 2%). Palmitic acid (16:0) was the most prevalent SAFA, whereas palmito leic (16:1n-7) and oleic acid (18:1n-9) were the most abundant MUFAs i n all the strains. Among PUFAs, gamma-linolenic acid (GLA, 18:3n-6) wa s present at high levels (18% of total fatty acids) in Nostoc sp. (Chi le) 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 (12-3 5% of total fatty acids) of alpha-linolenic acid (ALA, 18:3n-3). Linol eic 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 fat ty acids.