DETERMINATION OF FATTY ACID PROFILE AND EFFECT OF MIXOTROPHIC GROWTH IN SELECTED CYANOBACTERIAL STRAINS

Microalgae are photosynthetic microorganisms used in the nutrition of humans and animals (especially in aquaculture) due to the production of vitamins, proteins,  polyunsaturated fatty acids,  antioxidants, etc. Among microalgae, cyanobacteria (blue-green algae) are particularly recognized as the producers of different nutritive and biotechnologically valuable compounds. Although fatty acids of the microalgal origin are today available in the form of dietary supplements and are incorporated into various food products, microalgae are still an insufficiently explored source of these nutrients. In the present study, fatty acid compositions off our cyanobacterial strains belonging to the Nostoc and Anabaena genera have been analysed Furthermore, since in photoautotrophic cultures, the biomass production of microalgae is mostly low, the present study reviews the effect of the mixotrophic mode of nutrition (besides CO2 cells use organic matters as a carbon source) on the biomass production of the selected cyanobacteria. The analyses of fatty acid methyl esters (FAMES) were carried out by gas chromatography coupled with flame ionization detection (GC-F1D) after 42 days of the cyanobacterial  cultivation. The  results  showed that the most significant constituents of these strains are 16 carbon (16:0 and 16:1 types) chain fatty acids, linoleic acid (18:2n6c) and a-linolenic acid (18:3n3). Oleic acid (18:1n9c) was also present in significant amounts, while myristic acid (14:0) and stearic acid (18:0) were present in small amounts. Erucic acid (22:1n9) was present in traces only in the strain Nostoc 2S₁, while caproic acid (6^:0) and myristoleic acid (14:1) were present only in the strains Nostoc S₈ and Nostoc 2S₁. For the purpose of determining the mixotrophic growth, the strains were cultured at different glucose concentrations (1.5 and 3 g/l) for 42 days, and the biomass  production was determined periodically by spectrophotometrically measuring of the chlorophyll a concentration. The only strain which grew better in the autotrophic culture was Anahaena LC₁B, with the maximum production of only 0.1 g/l. In all the other strains, the biomass production  of mixotrophic cultures surpassed 1 g/l, at the lower concentration of glucose (1.5 g/1). The most productive strain was Nostoc 2S₃8 which, after 28 days with 1.43 g^/1, had 18 times higher production in comparison with the autotrophic culture. The strains Nostoc S₈ and Nostoc 2S1 were the most productive after 42 days, with 1.05 and 1.48 g/l, which was 1.32 and 4.84 times higher production than in the autotrophic cultures respectively. Taking into account the aspects of biomass production in mixotrophic cultures with glucose and fatty acid composition, among the tested cyanobacterial strains, Nostoc 2S₃B has the greatest biotechnological potential.