The Calvin cycle enzyme phosphoglycerate kinase of Xanthobacter flavus required for autotrophic CO2 fixation is not encoded by the cbb operon.

AUTOR(ES)

Meijer, W G

RESUMO

During autotrophic growth of Xanthobacter flavus, energy derived from the oxidation of hydrogen methanol or formate is used to drive the assimilation of CO2 via the Calvin cycle. The genes encoding the Calvin cycle enzymes are organized in the cbb operon, which is expressed only during autotrophic growth. Although it has been established that the transcriptional activator CbbR is required for the expression of the cbb operon, it is unclear whether CbbR is the only factor contributing to the regulation of the cbb operon. This paper describes the isolation of X. flavus mutants which were affected in the regulation of the cbb operon. One of the mutant strains was subject to an enhanced repression of the cbb operon promoter by the gluconeogenic substrate succinate and in addition failed to grow autotrophically. The rate of growth of the X. flavus mutant on succinate-containing medium was lower than that of the wild-type strain, but rates of growth on medium supplemented with gluconate were identical. A genomic library of X. flavus was constructed and was used to complement the mutant strain. The nucleotide sequence of the DNA fragment required to restore autotrophic growth of the X. flavus mutant was determined. One open reading frame that displayed extensive similarities to phosphoglycerate kinase-encoding genes (pgk) was identified. The X. flavus mutant lacked phosphoglycerate kinase activity following growth on gluconate or succinate. Introduction of the pgk gene into the X. flavus mutant partially restored the activity of phosphoglycerate kinase. Induction of the cbb operon of the X. flavus wild-type strain resulted in a simultaneous and parallel increase in the activities of ribulose-1,5-biphosphate carboxylase and phosphoglycerate kinase, whereas the latter activity remained absent in the X. flavus pgk mutant. It is concluded that X. flavus employees a single phosphoglycerate kinase enzyme and this is not encoded within the cbb operon.

Documentos Relacionados

• CbbR, a LysR-type transcriptional activator, is required for expression of the autotrophic CO2 fixation enzymes of Xanthobacter flavus.
• The LysR-Type Transcriptional Regulator CbbR Controlling Autotrophic CO2 Fixation by Xanthobacter flavus Is an NADPH Sensor
• Regulation of CO2 assimilation in Ralstonia eutropha: premature transcription termination within the cbb operon.
• Malonyl-Coenzyme A Reductase from Chloroflexus aurantiacus, a Key Enzyme of the 3-Hydroxypropionate Cycle for Autotrophic CO2 Fixation
• Induction of the gap-pgk operon encoding glyceraldehyde-3-phosphate dehydrogenase and 3-phosphoglycerate kinase of Xanthobacter flavus requires the LysR-type transcriptional activator CbbR.