Production of biomass and extracellular 5-aminolevulinic acid by Rhodopseudomonas palustris KG31 under light and dark conditions using volatile fatty acid

Abstract

Kinetic parameters for growth and extracellular 5-aminolevulinic acid (ALA) production of Rhodopseudomonas palustris KG31 under light and dark conditions in a medium containing volatile fatty acids (VFA) as the carbon sources were estimated using a Gompertz model. The lag phase for growth and the maximum specific growth rate under microaerobic-light cultivations were 7.29-12.49 h and 0.038-0.094 h(-1), respectively, whereas under aerobic-dark cultivations, they were 2.03-14.25 h and 0.016-0.022 h(-1), respectively. The lag phase for extracellular ALA production and the maximum specific extracellular ALA production rate under microaerobic-light cultivations (15.72-24.74 h and 0.222-0.299 h(-1), respectively) were better than those obtained under aerobic-dark cultivations (24.57-44.84 h and 0.103-0.215 h(-1), respectively). The biomass and the extracellular ALA yields of 39.66-56.25 gDCW/l/mol C, and 148.47-245.75 μM/mol C, respectively, under microaerobic-light cultivations were higher than of those obtained under aerobic-dark conditions. An enhancement of extracellular ALA production under aerobic-dark conditions revealed that the ALA yield was markedly increased 8-fold (48.36 μM) by the addition of 10mM succinate, 4.5mM glycine, and 15 mM levulinic acid (LA). By controlling dissolved oxygen (DO) and pH values, a maximum extracellular ALA yield of 66.38 μM was found. The degradation rate of ALA in the culture broth was closely related to the pH value.