Fatty acids of Azotobacter vinelandii ATCC 12837 were determined at various times during aerobic vegetative growth at 30 degrees C to provide baseline data for studying the effects of chemical agents on the organism's survival and fatty acid biosynthesis. Palmitate (16:0) was the highest at 36.7 +/- 4.3 mol% (mean +/- SD) after the first 5 h in fresh culture, decreasing slightly to 33.4 +/- 2.6 mol% at 49 h. The other fatty acids were therefore each normalized as a ratio of 16:0. At 5 h, as a ratio of 16:0, myristate. (14:0) was 0.14 +/- 0.06, palmitoleate (16:1c Delta(9-10)) 0.13 +/- 0.06, oleate (18:1c Delta(9-10)) 0.21 +/- 0.12, cis-vaccenate (18:1c Delta(11-12)) 0.30 +/-0.17 and stearate (18:0) 0.68 +/- 0.02. As the growth phase advanced to 49 h, 14:0 and 16:1c Delta(9-10) increased, 18:1c Delta(9-10) decreased and cis-vaccenate reciprocally increased, whereas 18:0 decreased. These suggest that the saturated fatty acid biosynthesis pathway yielded 16:0 and 18:0 in the 5-h lag period. By desaturation, 18:0 formed the unsaturated fatty acid (UFA) 18:1c Delta(9-10). As the culture aged, the anaerobic UFA biosynthesis pathway formed 16:1c Delta(9-10), which was elongated to 18:1c Delta(11-12). These fatty acid alterations represent a homeoviscous adaptation, modulating the microbe's membrane lipid viscosity for optimal cellular function.