Autotrophic biosynthesis of polyhydroxyalkanoate by Ralstonia eutropha from non-combustible gas mixture with low hydrogen content

Objectives To autotrophically produce polyhydroxyalkanoate (PHA) by Ralstonia eutropha without the risk of gas explosion, the feasibility of using a non-combustible gas mixture with low hydrogen content was investigated. Results A non-combustible gas mixture (H-2: O-2: CO2: N-2 = 3.6: 7.6: 12.3: 76.5) was used for a 144-hour flask cultivation of two R. eutropha strains. Initially, using strain H16, the production conditions for poly(3-hydroxybutyrate) [P(3HB)] were explored by examining nutrient deficiency. Of these, a nitrogen source-deficient culture medium yielded the highest polymer content of 70 wt% in cells. Next, to produce PHA copolymer, the recombinant strain 1F2 was cultured under the nitrogen source-deficient autotrophic condition. As a result, the accumulation of 3HB-based copolymer containing of 1.2 mol% 3-hydroxyvalerate unit and 1.2 mol% 3-hydroxy-4-methylvalerate unit was observed with 57 wt% of the cell content. Conclusions The use of a non-combustible gas with low hydrogen content is beneficial for PHA production in eliminating the risk of explosion due to hydrogen leakage.