The trpE gene negatively regulates differentiation of heterocysts at the level of induction in Anabaena sp. strain PCC 7120.
Levels of 2-oxoglutarate (2-OG) reflect nitrogen status in many bacteria. In heterocystous cyanobacteria, a spike in the 2-OG level occurs shortly after the removal of combined nitrogen from cultures and is an integral part of the induction of heterocyst differentiation. In this work, deletion of one of the two annotated trpE genes in Anabaena sp. strain PCC 7120 resulted in a spike in the 2-OG level and subsequent differentiation of a wild-type pattern of heterocysts when filaments of the mutant were transferred from growth on ammonia to growth on nitrate. In contrast, 2-OG levels were unaffected in the wild type, which did not differentiate under the same conditions. An inverted-repeat sequence located upstream of trpE bound a central regulator of differentiation, HetR, in vitro and was necessary for HetR-dependent transcription of a reporter fusion and complementation of the mutant phenotype in vivo. Functional complementation of the mutant phenotype with the addition of tryptophan suggested that levels of tryptophan, rather than the demonstrated anthranilate synthase activity of TrpE, mediated the developmental response of the wild type to nitrate. A model is presented for the observed increase in 2-OG in the trpE mutant.
Department of Microbiology, University of Hawaii, Honolulu, Hawaii, USA.
Patrick
P
Videau
Department of Microbiology, University of Hawaii, Honolulu, Hawaii, USA.
Loralyn M
LM
Cozy
Department of Microbiology, University of Hawaii, Honolulu, Hawaii, USA.
Jasmine E
JE
Young
Department of Microbiology, University of Hawaii, Honolulu, Hawaii, USA.
Blake
B
Ushijima
Department of Microbiology, University of Hawaii, Honolulu, Hawaii, USA.
Reid T
RT
Oshiro
Department of Microbiology, University of Hawaii, Honolulu, Hawaii, USA.
Orion S
OS
Rivers
Department of Molecular Biosciences and Bioengineering, University of Hawaii, Honolulu, Hawaii, USA.
Andrew H
AH
Burger
Department of Microbiology, University of Hawaii, Honolulu, Hawaii, USA Department of Molecular Biosciences and Bioengineering, University of Hawaii, Honolulu, Hawaii, USA scallaha@hawaii.edu.
Sean M
SM
Callahan
D017033:Anabaena / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial
D001426:Bacterial Proteins