The strain of Pseudomonas putida was tested in terms of the degradation ability of organic matter of lignites and subbituminous coals. The conversion degree to water soluble products and structural characteristics of bioextracts and bioresidues by elemental analysis and infrared spectroscopy were assessed. Oxidizing pretreatment with nitric acid essentially enhanced the biodegradability resulting in similar to 90% solubilization of lignites and similar to 40% of subbituminous coals, The bioextracts precipitated from supernatants were solids of high contribution 40-70% of oxygen functionalities and increased nitrogen content. The extent of bioresidue organic matter alteration increased with conversion depth, The enhanced hydrogen content was most characteristic feature of the residues. (C) 2002 Elsevier Science B.V. All rights reserved.