Journal of Applied Microbiology, Vol.105, No.4, 1054-1061, 2008
Potassium deficiency results in accumulation of ultra-high molecular weight poly-beta-hydroxybutyrate in a methane-utilizing mixed culture
Aims: To investigate the effect of various single nutrient deficiencies on poly-beta-hydroxybutyrate (PHB) biosynthesis in a methane-utilizing mixed culture (dominant species Methylocystis sp. GB 25 DSM 7674). Methods and Results: Poly-beta-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 (M-w) of 3.1 MDa was accumulated under potassium-limited conditions. When sulfur and iron were lacking M-w 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(-1)residual biomass (R) h(-1) and a yield coefficient of 0.45 g PHB g(-1) CH4. Conclusions: Biosynthesis of an ultra-high M-w PHB in a methane-utilizing mixed culture can be induced by potassium deficiency. Significance and Impact of the Study: 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.
Keywords:methanotrophic bacteria;Methylocystis sp GB25;poly-beta-hydroxybutyrate;potassium deficiency;ultra-high molecular weight PHB