Classes of Anabaena variabilis mutants with oxygen-sensitive nitrogenase activity.

Mutants of Anabaena variabilis deficient in the envelope glycolipids of heterocysts have no or very low nitrogenase activity when assayed aerobically. Revertants capable of aerobic growth on N2 have increased quantities of these glycolipids. Among mutants which require fixed nitrogen for growth in air and which have a normal complement of glycolipids, one expresses high nitrogenase activity at low oxygen tension. Three others show high nitrogenase activity only in the presence of dithionite and are therefore impaired in electron transfer.