Effects of oxygen tension on the lipid composition of Azotobacter chroococcum

Lipid content and composition were determined in Azotobacter chroococcum grown, under nitrogen-fixing conditions, in continuous culture with intense aeration under atmospheres containing between 5 and 40% O2. Total lipid content remained almost constant at approximately 9% of dry weight. Phospholipid content was maximal at 20% O2 where it accounted for 92% of total lipid, and was minimal at 40% O2. Phosphatidylethanolamine was the only species of phosphatide detected in this fraction. Neutral lipid content was minimal at 20% O2 and maximal at 40% O2 where it represented approximately 30% of the total lipid. Glycolipid remained between 2 and 13% of total lipid throughout. The principal fatty acids of A. chroococcum were hexadecanoic (C16:0), hexadecenoic (C16:1), and octadecenoic acid (C18:1) at all O2 tensions, but C18:1 increased at the expense of C16:1 at higher O2 tensions, particularly in free fatty acid and phospholipid fractions. [U-14C]acetate was readily incorporated into lipid at both 20 and 40% O2, but total incorporation was much greater at 20% O2.