2 MUTATIONS THAT BLOCK HETEROCYST DIFFERENTIATION HAVE DIFFERENT EFFECTS ON AKINETE DIFFERENTIATION IN NOSTOC-ELLIPSOSPORUM

Evident differentiation of Vegetative cells into heterocysts in Anabae na sp. strain PCC 7120 is prevented by insertions in genes hetR and he tP. Nostoc ellipsosporum possesses single copies of genes that hybridi ze with hetR and hetP. In mutant NE2 of H ellipsosporum, in which hetR is interrupted by an insert, and in a double recombinant of wild-type N. ellipsosporum with a plasmid that bears an interrupted copy of het R, neither heterocysts nor akinetes are formed. When an intact copy of hetR from Anabaena sp. strain PCC 7120 was added to NE2 the ability t o form both heterocysts and akinetes was restored. In contrast to the hetR mutant, a hetP mutant of N. ellipsosperum could form akinetes, bu t heterocyst formation was blocked. Use of luxAB, encoding luciferase, as a reporter, and use of luxC, luxD and luxE to generate aldehyde (a substrate for the luciferase reaction), permitted visualization of th e expression of hetR at the level of single cells; hetR was expressed in akinetes.