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Journal of Bacteriology, September 1998, p. 4644-4649, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Expression of glnB and a glnB-Like Gene (glnK) in a Ribulose Bisphosphate Carboxylase/Oxygenase-Deficient Mutant of Rhodobacter sphaeroides

Yilei Qian1 and F. Robert Tabita1,2,*

The Biochemistry Program1 and The Department of Microbiology and Plant Molecular Biology/Biotechnology Program,2 The Ohio State University, Columbus, Ohio 43210-1292

Received 2 February 1998/Accepted 18 June 1998

In a ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO)-deficient mutant of Rhodobacter sphaeroides, strain 16PHC, nitrogenase activity was derepressed in the presence of ammonia under photoheterotrophic growth conditions. Previous studies also showed that reintroduction of a functional RubisCO and Calvin-Benson-Bassham (CBB) pathway suppressed the deregulation of nitrogenase synthesis in this strain. In this study, the derepression of nitrogenase synthesis in the presence of ammonia in strain 16PHC was further explored by using a glnB::lacZ fusion, since the product of the glnB gene is known to have a negative effect on ammonia-regulated nif control. It was found that glnB expression was repressed in strain 16PHC under photoheterotrophic growth conditions with either ammonia or glutamate as the nitrogen source; glutamine synthetase (GS) levels were also affected in this strain. However, when cells regained a functional CBB pathway by trans complementation of the deleted genes, wild-type levels of GS and glnB expression were restored. Furthermore, a glnB-like gene, glnK, was isolated from this organism, and its expression was found to be under tight nitrogen control in the wild type. Surprisingly, glnK expression was found to be derepressed in strain 16PHC under photoheterotrophic conditions in the presence of ammonia.

* Corresponding author. Mailing address: Department of Microbiology, The Ohio State University, 484 West 12th Ave., Columbus, OH 43210-1292. Phone: (614) 292-4297. Fax: (614) 292-6337. E-mail: Tabita.1{at}osu.edu.

Journal of Bacteriology, September 1998, p. 4644-4649, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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