Manipulation of Pattern of Cell Differentiation in a Mutant of sp. PCC 7120 by Overexpressing Alone or with .

In the filamentous cyanobacterium, sp. PCC 7120, single heterocysts differentiate at semi-regular intervals in response to nitrogen stepdown. HetR is a principal regulator of heterocyst differentiation, and and are two genes that are regulated directly by HetR. In a mutant generated from the IHB (Institute of Hydrobiology) substrain of PCC 7120, heterocyst formation can be restored by moderate expression of and The resulting heterocysts are located at terminal positions. We used a tandem promoter, PP to express and strongly in the mutant. Co-expression of and enabled the mutant to form multiple contiguous heterocysts at both terminal and intercalary positions. Expression of , alone resulted in terminally located heterocysts, whereas expression of , alone produced enlarged cells in strings. In the absence of HetR, formation of heterocysts was insensitive to the peptide inhibitor, RGSGR.