Overproduction of γ-Linolenic and Eicosapentaenoic Acids by Algae

Abstract

The pharmaceutical interest and limited availability of y-linolenic acid (GLA) and eicosapentaenoic acid (EPA) prompted the search for genetic means for increasing the production of these fatty acids from algal sources. Cell lines of Spirulina platensis and Porphyridium cruentum resistant to the growth inhibition of the herbicide Sandoz 9785 were selected by serial transfers of the culture in the presence of increasing concentrations of the herbicide. The resistant cell lines of S. platensis overproduced GLA and those of P. cruentum overproduced EPA and were stable for at least 50 generations in the absence of the inhibitor.The recent pharmaceutical interest in the polyunsaturated fatty acids, EPA2 and GLA (7,17) and the limitations of their current availability (2, 5) triggered the search for potential new sources for these fatty acids. We (1,5) have previously demonstrated that the marine red microalga Porphyridium cruentum and the cyanobacterium Spirulina platensis are among the best producers of EPA and GLA, respectively. Strain selection and manipulation of physiological and environmental conditions brought about an increased content of these polyunsaturated fatty acids (1, 2, 4-6). Yet, the inherent limitation ofthese approaches prompted us to look for genetic means that could result in even higher contents of EPA and GLA.A possible approach for increasing the content of particular cell metabolites is the use of inhibitors of specific steps in biosynthetic pathways or analogs of specific products. Generally, such inhibitors and analogs inhibit growth as well. Thus, resistance to the inhibitor could be achieved by overproduction of the inhibited metabolites. It was indeed shown in higher plants that some lines selected for resistance to the growth inhibition are overproducers of the metabolite in question (8,10,15 ence of proline analogs (12). Similar results were obtained in the cyanobacterium Nostoc (9) and the alga Nannochloris bacilaris (13).Several herbicides of the substituted pyridazinone family were shown to inhibit fatty acid desaturation. Of these, SAN 9785 is the most effective inhibitor of w3 desaturation (11), and its effect on reduction of 18:3w3 levels in the glycolipids of higher plants and algae was widely studied. Recently, we (1) found this herbicide to be an effective inhibitor also for A6 desaturation of linoleic acid in Spirulina. Although SAN 9785 has a certain inhibitory effect on photosynthesis, it was shown that the effect on fatty acid desaturation is a direct inhibition of the desaturase ( 16).In the present paper, we describe the successful selection of P. cruentum and S. platensis cell lines that display stable resistance to the growth inhibition of SAN 9785. These cell lines over produced EPA and GLA, respectively. To the best of our knowledge, this is the first report of a fatty acid overproduction in either higher or lower plants induced by perturbation of fatty acid metabolism. MATERIALS AND METHODS Organisms and Culture ConditionsSpirulina platensis strain 2340 wa...

Antibacterial potential of γ-linolenic acid from Fischerella sp. colonizing Neem tree bark

“…The amount of total fatty acids in the cyanobacterium (3.38% of dry wt) is quite in the range (2.4-4.8%) reported in different Spirulina strains although in the latter case, GLA content varied from 8-31.7% of the fatty acid (Cohen et al 1987). GLA (12.5% of total fatty acid) as measured presently, is in the range of other cyanobacteria such as Synechocystis PCC 6803 (13-26%; Wada & Murata 1990) and Spirulina (21%) (Cohen et al 1992). Interestingly, a comparable level of GLA i.e.…”

“…GLA overproduction in the herbicide-resistant S. platensis could reach only 2% (23.6% of total fatty acid) (Cohen et al 1992). The latter investigators observed that GLA content in three Spirulina strains (optimum growth 35°C) was maximum at 30 or 35°C thus suggesting that temperature conditions optimum for general growth, also favoured GLA synthesis.…”

“…GLA is also reported in fungi such as Mortierella ramanniana (Hansson & Dosta´lek 1988), Mucor sp. (Shin & Shin 1988), Cunninghamella japonica (Galanina et al 1988), Entomophthora exitalis (Kendrick & Ratledge 1992) as well as in the cyanobacteria, Spirulina (Nichols & Wood 1968;Pelloquin et al 1970;Hudson & Karris 1974;Cohen et al 1992), Synechocystis (Wada & Murata 1990), Microcystis and green alga Scenedesmus (Piorreck et al 1984). Therefore, microalgae seem to be the prospective GLA resource.…”

Culture Conditions stimulating high γ-Linolenic Acid accumulation by Spirulina platensis

“…An alternative promising source for GLA production is Spirulina platensis (4,6). Unlike fungi, which should be grown in sophisticated bioreactors, the cyanobacteria can be grown in large open ponds (2,17).…”

Increasing γ-linolenic acid content in Spirulina platensis using fatty acid supplement and light–dark illumination

“…As the fatty acid composition is largely affected by environmental conditions, many studies have already been carried out based on varying the nutritional and physical conditions (Chojnacka and Noworyta 2004;Cohen et al 1987;Costa et al 2004;Mahajan and Kamat 1995), mutating to increase the GLA content (Cohen et al 1992;Tanticharoen et al 1994), and adding exogenous nutrients to the medium (Khoomrung et al 2008;Narayan et al 2005;Quoc et al 1994). In a previous study, the growth and GLA content of S. platensis were enhanced when culturing under dark conditions and using a mixotrophic culture with a high concentration of a glucose-tolerant mutant (Choi et al 2008).…”