Production of 5-aminolevulinic acid by methanogens

Abstract

The possibility of 5-aminolevulinic acid (ALA) accumulation in a culture medium was studied using Methanosarcina barkeri growing on a methanol minimal medium. To effect the accumulation of ALA in the culture medium, some ALA analogues were tested as inhibitors of ALA dehydratase. It was found that ALA was accumulated when either levulinic acid or 4,6-dioxoheptanoic acid (DOH) was added, with the latter being more effective, even at a much lower concentration. It was also found that in M. barkeri 2-oxoglutarate reacted as a precursor on the formation of ALA, the production of ALA increasing to 83 μM from 73 μM with the addition of 30 mM of 2-oxoglutarate compared with the control experiment. The continuous production of ALA from methanol in fixed-bed reactors of M. barkeri was tested, resulting in a maximum production rate of 400 μmol/ l/d compared with 200 μmol/ l/d by Methanobacterium thermoautotrophicum growing on a H 2 and CO 2 minimal medium.