Exploring new approaches to enhance polyhydroxybutyrate accumulation in Paracoccus denitrificans

Area of Science:

• Microbiology
• Biochemistry
• Metabolic Engineering

Background:

• Polyhydroxybutyrate (PHB) is a microbial polyester with diverse applications.
• Understanding the metabolic pathways and regulatory mechanisms of PHB production is crucial for optimizing its yield.
• Paracoccus denitrificans is a versatile bacterium with potential for biopolymer synthesis.

Purpose of the Study:

• To investigate the effect of various organic carbon substrates on PHB production in Paracoccus denitrificans.
• To elucidate the role of specific enzymes and regulatory proteins, such as propionyl-CoA synthetase and FnrP, in PHB metabolism.
• To explore the influence of environmental factors, like ion availability and nutrient limitation, on PHB accumulation.

Main Methods:

• Cultivation of Paracoccus denitrificans on eight different organic carbon substrates.
• Measurement of PHB content using analytical techniques.
• Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) to analyze gene expression.
• Construction and analysis of FnrP mutant strains.
• Transmission electron microscopy (TEM) for visualizing PHB granules.
• Membrane inlet mass spectrometry (MIMS) to study metabolic pathways.
• Enzyme assays to determine citrate synthase activity and regulation.

Main Results:

• Crotonate supported the highest PHB accumulation during aerobic cultivation.
• PHB production on butyrate was enhanced by HCO₃⁻ addition.
• Propionyl-CoA synthetase likely catalyzes butyrate and crotonate activation.
• FnrP plays a role in regulating PHB metabolism, with FnrP mutants showing increased PHB accumulation under anaerobic conditions.
• The FnrP mutant exhibited an impaired denitrification pathway.
• Citrate synthase activity was modulated by NAD⁺/NADH ratio and specific ions (Na⁺, K⁺, NH₄⁺).
• Potassium (K⁺) limitation during aerobic growth resulted in elevated PHB accumulation.

Conclusions:

• Paracoccus denitrificans can efficiently produce PHB from various substrates, with crotonate being particularly effective.
• The FnrP protein and ion availability are key factors influencing PHB production and metabolic regulation in this bacterium.
• Further research into these pathways could optimize PHB yields for biotechnological applications.