Novel single cell protein substrate

In the process for manufacture of single cell protein comprising bacteria and fungus by growing a microorganism on fossil fuel carbon source the improvement which comprises using as the carbon source an oxidation-nitration product of lignite which is manufactured by subjecting a slurry of lignite in aqueous nitric acid to a temperature of from about 15.degree. C. to about 200.degree. C. for about 0.5 to about 15 hours, separating the solids, extracting the resulting solids with acetone, recovering the acetone-insoluble fraction, and dissolving the acetone-insoluble solid in base and neutralizing the solution to between pH 6.5 and pH 8.0.