Decomposition of Lignin by Soil Bacteria and Complex Formation between Autoxidized Lignin and Organic Nitrogen Compounds

SUMMARY: Several bacteria able to decompose native lignin prepared according to Brauns (1939) were isolated from soil; they were aerobic, Gram-negative, motile or non-motile, non-endospore forming rods belonging to the genera Pseudomonas and Flavobacterium. The decomposition was studied in a neutral medium containing the lignin as a suspension of fine particles and solidified with silica gel. 20–30% of the lignin added to the medium was decomposed by the bacteria. Independently of the biological decomposition, a non-biological transformation of lignin occurred during the later stage of the incubation when the medium dried out. The products of the non-biological transformation were dark brown, soluble in water but insoluble in ethanol. They reacted readily with nitrogen compounds in peptone, forming complexes containing about 2·5% nitrogen, half of which was α-amino nitrogen. The relation of these complexes to soil humic acid is discussed.