Influence of cultural parameters on the depolymerization of a soluble lignite coal polymer by Pseudomonas cepacia DLC-07

Abstract

A lignite coal-depolymerizing bacterium, Pseudomonas cepacia DLC-07, was grown in liquid media containing water soluble lignite coal. The coal substrate was soluble at pH 5.5, but had not been preoxidized with nitric acid. Bacterial coal depolymerization was monitored by high performance liquid chromatography (HPLC). Cells were grown on soluble coal in three media: mineral salts broth, peptone broth, and Sabouraud dextrose broth (SDB). In some experiments, media were supplemented with specific coal substructure model compounds, or a mixture of compounds, which served as potential inducers of coal-degradative enzymes. In one experiment, peptone broth contained Kraft lignin instead of coal. Uninoculated controls were included in all experiments. P. cepacia DLC-07 depolymerized coal in all experiments, but depolymerization was greatest in peptone-coal broth. Of ten coal substructure models examined, indole and p-coumaric acid measurably affected depolymerization. Their presence in SDB led to the appearance of distinctive peaks in HPLC chromatograms. P. cepacia further polymerized Kraft lignin into a product of higher molecular weight than the starting substrate. Spectrometric analyses showed that coal depolymerization was associated with attack on ester and ether bonds in the coal.