Autotrophic Growth of Paracoccus denitrificans in Aerobic Condition and the Accumulation of Biodegradable Plastics from CO 2

Abstract

The cell growth on H 2 and O 2 as the energy source and CO 2 as the sole carbon source in the autotrophic culture condition was tested for the gram-negative bacteria Paracoccus spp. The aerobic growth in the autotrophic condition was only observed in Paracoccus denitrificans NBRC13301 and P.pantotrophus NBRC102493. Both strains were sensitive to O 2 in particular the growth of P.pantotrophus was completely inhibited at the concentrations above 2% O 2. P.denitrificans grew until 15% O 2 however the optimum O 2 concentration was 5%. The growth characteristic of P.denitrificans was investigated by pH-controlled batch culture with supplying the gas mixture of H 2 , O 2 and CO 2. The specific growth rate was 0.12 h-1 at 5% O 2 , 30°C and pH7.0. The growth was much slower than other hydrogen-oxidizing bacteria however P.denitrificans accumulated biodegradable plastic, polyhydroxybutyrate, PHB with the content of 57.3% w/w in the cell under nitrogen limitation. Under DO limitation, the cell concentration increased to 25 g/L without accumulating PHB if NH 3 solution as the nitrogen source was fed sufficiently.