Biodegradation of wood in crude oil-polluted soil Bernard Onyekweli Ejechi Department of Microbiology, Delta State University, Abraka, Nigeria (E-mail: ejechiben@yahoo.co.uk) Received 9 December 2002; accepted 21 May 2003 Keywords: Basidiomycetes, biodegradation, crude oil, soft-rot, wood Summary 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. Introduction Environmental conditions influence the type of organ- isms that dominate wood degradation processes at any point in time (Kaarik 1974). For instance while bacteria are the major agents of wood decay under waterlogged anoxic conditions, the microfungi dominate in areas with low oxygen and basidiomycetes thrive only when oxygen is abundant (Blanchette 2000). In addition, the presence of other metabolizable substrates may influ- ence the course of decomposition of wood by diverting attention away from the wood, increasing the popula- tion of the wood inhabitants or release of degradation products that may promote or inhibit the activities of wood-inhabiting organisms. Spillages of crude petroleum or its refined products commonly occur in the soil of Nigeria’s Niger Delta region with over 5 million inhabitants due to pipe-line leakages, vandalism, tanker accidents, and during oil exploration activities. Forest residue, felled log and service timbers in contact with soil (e.g. platform houses along the Niger delta creeks, farmhouses, warehouses, wooden fences and transmission poles) are often con- taminated by these spillages. Microorganisms are the major agents of degradation of these petroleum hydro- carbons to innocuous products: biomass, energy, CO 2 and H 2 O (Margesin 2000). However, many incompletely oxidized products like organic acids, esters, alcohols, aldehydes etc., accumulate (Davis 1967). These products may inhibit or promote the growth of some wood- attacking bacteria and fungi. It is desirable to understand how the degradation of petroleum contaminants by soil microorganisms affects the course of decay of timbers in contact with petro- leum-contaminated soil, because the service-life of the timbers may be affected. For example more prominent signs of decay such as occurrence of basidiocarps was observed in service-timbers located in petroleum-con- taminated soil than in comparative uncontaminated soil. A field and laboratory investigation of degradation of wood blocks in crude oil-contaminated soil by soft-rot and basidiomycete fungi was undertaken during the wet season (April–November) to ascertain the pattern and rate of decay. Materials and methods Field work An area measuring 20 · 20 m in the rain forest near the University campus (Abraka, Nigeria) was cleared and demarcated for the experiment. Obeche (Triplochiton scleroxylon K. Schum) wood blocks measuring World Journal of Microbiology & Biotechnology 19: 799–804, 2003. 799 Ó 2003 Kluwer Academic Publishers. Printed in the Netherlands.