Construction of a Rhodobacter sphaeroides Strain That Efficiently Produces Hydrogen Gas from Acetate without Poly(β-Hydroxybutyrate) Accumulation: Insight into the Role of PhaR in Acetate Metabolism

Abstract

This study provides a novel approach for increasing the yield of photofermentative H 2 production from acetate by purple nonsulfur phototrophic bacteria. This study further suggests that polyhydroxyalkanoate is not only a storage substance for carbon and energy in bacteria, but may also act as a signaling molecule that mediates bacterial metabolic adaptations to specific environments.

Pleiotropic Effects of PhaR Regulator in Bradyrhizobium diazoefficiens Microaerobic Metabolism

“…If we assume that these genes do not encode active PHB synthases [1], the only active PHB synthase (PhaC1) was not controlled by PhaR. Therefore, the reduced PHB content in the phaR mutant cells (Figure 1) can be explained based on the following observations: (i) higher PHB degradation by overexpression of phaZ1/PhaZ1 ( [40], this work), (ii) higher expression levels of phaC2 and phaC5 that do not code active PHB synthases ( [1], this work), and/or (iii) formation of lessactive heterodimers PhaC1/PhaC2 rather than fully active homodimers PhaC1/PhaC1, due to higher phaC2 transcription and a constant transcription of phaC1 ( [1,2,22,41], this work) (Figure 3B). In addition, since PHB is not synthesized, PhaR would be free to bind to DNA and exert its activity as a transcriptional regulator rather than PHB modulator.…”