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Strain UCD 311 is a transposon-induced mutant of Nostoc sp. strain ATC C 29133 that is unable to fix nitrogen in air but does so under anoxic conditions and is able to establish a functional symbiotic association with the hornwort Anthoceros punctatus. These properties of strain UCD 311 are consistent with previous observations that protection against oxygen inactivation of nitrogenase is physiologically provided within A. punctatus tissue. Upon deprivation of combined nitrogen, strain UCD 311 clearly differentiates heterocysts and contains typical heterocyst-specific glycolipids; it also makes apparently normal akinetes upon phosphate starvation. Sequence analysis adjacent to the point of the transposon insertion revealed an open reading frame designated devR. Southern analysis established that similar sequences are present in other heterocyst-forming cyanobacteria. devR putatively encodes a protein of 135 amino acids with high similarity to the receiver domains of response regulator proteins characteristics of two-component regulatory systems. On the basis of its size and the absence of other functional domains, DevR is most similar to CheY and Spo0F. Reconstruction of the mutation with an interposon vector confirmed that the transposition event was responsible for the mutant phenotype. The presence of wild-type devR on a plasmid in strain UCD 311 restored the ability to fix nitrogen in air. While devR was not essential for differentiation of akinetes, its presence in trans in Nostoc sp. strain ATCC 29133 stimulated their formation to above normal levels in aging medium. On the basis of RNA analysis, devR is constitutively expressed with respect to the nitrogen source for growth. The devR gene product is essential to the development of mature heterocysts and may be involved in a sensory pathway that is not directly responsive to cellular nitrogen status.

journal of bacteriology

The devR gene product is characteristic of receivers of two-component regulatory systems and is essential for heterocyst development in the filamentous cyanobacterium Nostoc sp. strain ATCC 29133