Lignocellulose biodegradation: Fundamentals and applications

Natural pastures are one of South Africa’s most important agricultural resources for it provides the cheapest source of animal feed (Aucamp & Danckwerts 1989). Natural grazing is threatened by expansion of the Karoo (semi-desert region) into grasslands, overgrazing, poisonous plants, poor grazing management practices, and bush densification. Finally, expanding human activities (agriculture, housing, and industrialization) places a demand on already overburdened natural grazing resources. Therefore, the use and re-use of lignocellulosic wastes for animal feed will become a South African reality in the near future. Sadly, much lignocellulose waste is often disposed of by biomass burning, which is not restricted to underdeveloped countries alone, but is considered a global phenomenon (Levine 1996). This scenario does not only apply to South Africa alone, for some or all of the listed problems are common in many parts of the world today. The problem of increasing the utility of lignocellulose wastes has been known for decades. In addition to the growing demand for traditional applications (paper manufacture, biomass fuels, composting, animal feed, etc.), novel markets for lignocellulosics have been identified in recent years. The intensity of research and the magnitude of capital investment in this field increased vastly once commercial viability seemed probable for many of these new applications. The most ambitious of these has been the conversion of lignocellulose to alternative energy carriers (e.g. fuel ethanol, acetone and butanol) (Kaylen et al. 2000; Lee 1997; Mitchell 1998; Wheals et al. 1999). The pulp and paper industry discovered lignocellulose biotechnology could improve process efficiency through savings in money and energy (Breen & Singleton 1999; Scott et al. 1998). Others aimed at improving digestibility of nutritionally poor forages by exposing these lignocellulosics to white-rot fungi (Agosin & Odier 1985; Karunanandaa et al. 1992). The complete and successful utilization of lignocellulose by man remains a daunting task, whatever the intended application. Defeating the barriers, which prevent commercial exploitation of lignocellulose, will be the key to its successful application in biotechnological endeavors. This review will not focus on current or new chemical and physical lignocellulose processing technologies (and their problems). Rather, the aim is to summarize the current knowledge available on lignocellulose biodegradation, and add value to that knowledge by discussing ways to integrate natural processes into low cost, low technology biotechnological applications.