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J. Bacteriol., 04 1996, 2037-2043, Vol 178, No. 7
EL Campbell, KD Hagen, MF Cohen, ML Summers and JC Meeks
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.
Copyright © 1996, American Society for Microbiology
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
Section of Microbiology, Division of Biological Sciences, University of California, Davis, California 95616, USA.
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