Abstract
The ability of bacteria to produce polyhydroxyalkanoates such as poly(3-hydroxybutyrate) (PHB) enables provision of a carbon storage molecule that can be mobilized under demanding physiological conditions. However, the precise function of PHB in cellular metabolism has not been clearly defined. In order to determine the impact of PHB production on global physiology, we have characterized the properties of a ΔphaC1 mutant strain of the diazotrophic bacterium Herbaspirillum seropedicae. The absence of PHB in the mutant strain not only perturbs redox balance and increases oxidative stress, but also influences the activity of the redox-sensing Fnr transcription regulators, resulting in significant changes in expression of the cytochrome c-branch of the electron transport chain. The synthesis of PHB is itself dependent on the Fnr1 and Fnr3 proteins resulting in a cyclic dependency that couples synthesis of PHB with redox regulation. Transcriptional profiling of the ΔphaC1 mutant reveals that the loss of PHB synthesis affects the expression of many genes, including approximately 30% of the Fnr regulon.
Highlights
Herbaspirillum seropedicae SmR1 is a nitrogen-fixing bacterium able to interact with important crops (Chubatsu et al, 2011; Pedrosa et al, 2011)
The sequence data for all libraries analyzed in this study are Accumulation of PHB Is Physiologically Important for the Synthesis of c-Type Cytochromes In H. seropedicae SmR1, the production of PHB is mainly dependent upon the PHA synthase encoded by phaC1
Whilst the phaC1 gene is likely to form an operon with phaB1 (Hsero_2998), analysis of transcripts mapping to the phaC1 (Hsero_2999) neighborhood, suggests that in-frame deletion of phaC1 does not affect the expression of immediate downstream genes, including phaB1 (Hsero_2998) and phaR (Hsero_2997) (Supplementary Figure 2; see Supplementary Table 2)
Summary
Herbaspirillum seropedicae SmR1 is a nitrogen-fixing bacterium able to interact with important crops (Chubatsu et al, 2011; Pedrosa et al, 2011). For total RNA extraction, H. seropedicae SmR1 (wild-type) and phaC1 strains were grown to an optical density of approximately 1.0 (late-log phase), when high levels of PHB production occur (Tirapelle et al, 2013).
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