Potential use of substituted pyridazinones for selecting polyunsaturated fatty acid overproducing cell lines of algae

The effects of the herbicides SAN 9785 and norflurazon on growth and fatty acid composition of the cyanobacterium Spirulina platensis, the marine microalga Porphyridium cruentum and the freshwater alga Monodus subterraneus were studied. Norflurazon was more effective than SAN 9785 in causing growth inhibition of S. platensis cultures; changes in fatty acid composition confirmed that this compound is a potent inhibitor of DELTA6-desaturation. SAN 9785 inhibited the growth of S. platensis concomitantly causing a reduction in the amount of the fatty acids 18:3omega6 and 18:2omega6 and an increase in 18: 1 and 18: 0, thus indicating an inhibitory effect of this herbicide on the DELTA6-desaturation system. Similar growth inhibition was observed in P. cruentum. In this alga, the herbicide also inhibited the formation of 20:5omega3, apparently by blocking the desaturation of 18:2 to 18:3omega3 in one pathway of eicosapentaenoic acid biosynthesis. However, in M. subterraneus SAN 9785 reduced growth, but caused an increase in the proportion of 20:5omega3 indicating a possible alternative pathway for the formation of 20:5omega3 in this alga. SAN 9785 was therefore considered to be useful for the selection of cell lines which overproduce the valuable fatty acids 18:3omega6 and 20:5omega3 in S. platensis and P. cruentum, respectively.