Production of Endotoxin-Free Microbial Biomass for Food Applications by Gas Fermentation of Gram-Positive H2-Oxidizing Bacteria

The production of edible microbial biomass in bioreactors is an attractive alternative to agriculture, which is a major consumer of fresh water, an emitter of greenhouse gases, and a cause of eutrophication. This study examines microbial food production by gas fermentation of two endotoxin-free Gram-positive H-2-oxidizing autotrophic bacterial strains, Nocardioides nitrophenolicus KGS-27 and Rhodococcus opacus DSM 43205. The supply of the gaseous substrates H-2 and O-2 by in situ water electrolysis was investigated as an alternative to providing them from an external source. N. nitrophenolicus KGS-27 produced <= 9.9 +/- 2.0 mg of biomass L-1 h(-1) and was not affected by in situ water electrolysis, which potentially produces growth-inhibiting reactive oxygen species. With R. opacus DSM 43205, in turn, electrolysis slowed growth considerably and resulted in a volumetric productivity of 2.6 +/- 0.8 mg of biomass L-1 h(-1), which was a quarter of what was obtained with the gases supplied externally. The macromolecular compositions of biomasses produced by the two cultivation modes using the two bacterial strains were rather similar containing approximately 33-37% protein, 28-56% carbohydrates, and 4-5% fatty acids of the cell dry weight. Relatively high protein concentrations and balanced amino acid profiles, comparable to those of casein and soy protein, were achieved with both strains.