Potassium deficiency results in accumulation of ultra-high molecular weight poly-β-hydroxybutyrate in a methane-utilizing mixed culture

To investigate the effect of various single nutrient deficiencies on poly-β-hydroxybutyrate (PHB) biosynthesis in a methane-utilizing mixed culture (dominant species Methylocystis sp. GB 25 DSM 7674). Poly-β-hydroxybutyrate accumulation experiments were performed in 7 and 70 l bioreactors and initiated by potassium, sulfur or iron deficiency. After 24 h the PHB content reached levels of 33·6%, 32·6% and 10·4% respectively. Interestingly a polymer with an ultra-high average-weight molecular weight (Mw) of 3·1 MDa was accumulated under potassium-limited conditions. When sulfur and iron were lacking Mw were lower by 20·6 and 41·6%. Potassium-deficiency experiments were furthermore characterized by a maximum specific PHB formation rate 0·08 g g⁻¹residual biomass (R) h⁻¹ and a yield coefficient of 0·45 g PHB g⁻¹ CH₄. Biosynthesis of an ultra-high Mw PHB in a methane-utilizing mixed culture can be induced by potassium deficiency. This study greatly extends the knowledge in the field of bacterial biopolymer formation with gaseous substrates. The special system used here combines the use of methane a low-cost substrate available from natural and renewable sources with the possibility of employing a mixed-culture in an open system for the synthesis of a high-value product.