DIFFERENTIATION OF FREE-LIVING ANABAENA AND NOSTOC CYANOBACTERIA ON THE BASIS OF FATTY-ACID COMPOSITION

The cellular fatty acids of free-living, nitrogen-fixing cyanobacteria belonging to the genera Anabaena and Nostoc were analyzed to differentiate the genera. The fatty acid compositions of 10 Anabaena strains and 10 Nostoc strains that were grown for 12 days on BG-11(0) medium were determined by gas-liquid chromatography-mass spectroscopy. Of the 53 fatty acids detected, 17 were major components; the average level for each of these 17 fatty acids was at least 0.9% of the total fatty acids (in at least one of the genera). These fatty acids included (with mean percentages in the Anabaena and Nostoc strains, respectively) the saturated fatty acids 16:0 (30.55 and 23.23%) and 18:0 (0.77 and 1.27%); several unsaturated fatty acids, including 14:1 cis-7 (2.50 and 0.11%), 14:1 cis-9 (3.10 and 3.41%), a polyunsaturated 16-carbon (sites undetermined) fatty acid with an equivalent chain length of 15.30 11.20 and 1.03%), 16:4 cis-4 (0.95 and 0.87%), 16:3 cis-6 (2.16 and 1.51%), 16:1 cis-7 (1.44 and 0.36%), 16:1 cis-9 (6.53 and 18.76%), 16:1 trans-9 (4.02 and 1.35%), 16:1 cis-11 (1.62 and 0.42%), 18:2 cis-9 (10.16 and 12.44%), 18:3 cis-9 (18.19 and 17.25%), 18:1 cis-9 (4.01 and 5.10%), and 18:1 trans-9 (0.92 and 1.94%); and the branched-chain fatty acids iso-16:0 (2.50 and 1.14%) and iso-15:1 (0.34 and 2.05%). Among the fatty acids or classes of fatty acids that were significantly different in the genera Anabaena and Nostoc, and thus of taxonomic value (with ranges in the Anabaena and Nostoc strains, respectively), were 16:0 (27.39 to 34.72 and 18.50 to 26.10%) and the total saturated, straight-chain, even-carbon fatty acids (class A) (29.06 to 36.61 and 21.06 to 28.62%); in addition, the ratios of class C fatty acids (unsaturated straight-chain fatty acids) to class A fatty acids were significantly different (1.52 to 2.13 and 2.25 to 3.47). On the basis of these parameters, Anabaena variabilis isolate ATCC 29413 has the fatty acid characteristics of a Nostoc strain and should be considered for reclassification as Nostoc variabilis; ana strain ATCC 27895, which was originally placed in the species Anabaenopsis circularis, should be retained in the genus Nostoc.