GlpR Represses Fructose and Glucose Metabolic Enzymes at the Level of Transcription in the HaloarchaeonHaloferax volcanii

In this study, a DeoR/GlpR-type transcription factor was investigated for its potential role as a global regulator of sugar metabolism in haloarchaea, usingHaloferax volcanii as a model organism. Common to a number of haloarchaea and Gram-positive bacterial species, the encodingglpR gene was chromosomally linked with genes of sugar metabolism. InH. volcanii ,glpR was cotranscribed with the downstream phosphofructokinase (PFK;pfkB ) gene, and the transcript levels of thisglpR-pfkB operon were 10- to 20-fold higher when cells were grown on fructose or glucose than when they were grown on glycerol alone. GlpR was required for repression on glycerol based on significant increases in the levels of PFK (pfkB ) transcript and enzyme activity detected upon deletion ofglpR from the genome. Deletion ofglpR also resulted in significant increases in both the activity and the transcript (kdgK1 ) levels of 2-keto-3-deoxy-d- gluconate kinase (KDGK), a key enzyme of haloarchaeal glucose metabolism, when cells were grown on glycerol, compared to the levels obtained for media with glucose. Promoter fusions to a β-galactosidasebgaH reporter revealed that transcription ofglpR-pfkB andkdgK1 was modulated by carbon source and GlpR, consistent with quantitative reverse transcription-PCR (qRT-PCR) and enzyme activity assays. The results presented here provide genetic and biochemical evidence that GlpR controls both fructose and glucose metabolic enzymes through transcriptional repression of theglpR-pfkB operon andkdgK1 during growth on glycerol.