Biodegradation of wood in crude oil-polluted soil

A field investigation (April–November) in Nigeria showed that biodegradation of obeche (Triplochiton scleroxylon) wood blocks was initially retarded in crude oil-contaminated soil but later became enhanced as indicated by loss of compression resistance. Further indication of this pattern was the detection of soft-rot cavities and basidiomycete fungi after 2–3 months exposure when compared to control blocks in uncontaminated soil. Laboratory tests with Pleurotus sp., Trametes sp., Gloeophyllum sp. (basidiomycetes) and Chaetomium sp. (soft-rot fungus) confirmed that degradation of crude oil-coated obeche blocks was markedly retarded without the presence of hydrocarbon-degrading bacteria. The filtrate of hydrocarbon-degrading Pseudomonas sp. grown in mineral salt/crude oil medium for 3–4 weeks supported growth of the test fungi better than in carboxymethyl cellulose medium but less than in potato dextrose broth. Similarly, wood blocks immersed in the filtrate became significantly more susceptible to fungal degradation. Pseudomonas sp. from stationary phase growth in crude oil medium depleted residual sugar in basidiomycete-degraded sawdust with a concomitant marked increase in its population. It may be concluded that readily metabolizable products of crude oil degradation by soil organisms and the removal of residual sugar which may have prevented catabolite repression of cellulases, culminated in increased attack on the wood by soil-borne wood-decomposing organisms.