The degradation of plant cell walls by ruminants is of major economic importance in the developed as well as developing world. Rumen fermentation is unique in that efficient plant cell wall degradation relies on the cooperation between microorganisms that produce fibrolytic enzymes and the host animal that provides an anaerobic fermentation chamber. Increasing the efficiency with which the rumen microbiota degrades fiber has been the subject of extensive research for at least the last 100 years. Fiber digestion in the rumen is not optimal, as is supported by the fact that fiber recovered from feces is fermentable. This view is confirmed by the knowledge that mechanical and chemical pretreatments improve fiber degradation, as well as more recent research, which has demonstrated increased fiber digestion by rumen microorganisms when plant lignin composition is modified by genetic manipulation. Rumen microbiologists have sought to improve fiber digestion by genetic and ecological manipulation of rumen fermentation. This has been difficult and a number of constraints have limited progress, including: (a) a lack of reliable transformation systems for major fibrolytic rumen bacteria, (b) a poor understanding of ecological factors that govern persistence of fibrolytic bacteria and fungi in the rumen, (c) a poor understanding of which glycolyl hydrolases need to be manipulated, and (d) a lack of knowledge of the functional genomic framework within which fiber degradation operates. In this review the major fibrolytic organisms are briefly discussed. A more extensive discussion of the enzymes involved in fiber degradation is included. We also discuss the use of plant genetic manipulation, application of free-living lignolytic fungi and the use of exogenous enzymes. Lastly, we will discuss how newer technologies such as genomic and metagenomic approaches can be used to improve our knowledge of the functional genomic framework of plant cell wall degradation in the rumen.

Opportunities to improve fiber degradation in the rumen: microbiology, ecology, and genomics

Lignocellulose is the most abundant biomass available on Earth. It has attracted considerable attention as an alternate feed stock and energy resource because of the large quantities available and its renewable nature. The potential uses of lignocelluloses are in pulp and paper industries, production of fuel alcohol and chemicals, protein for food, and feed using biotechnological means. The current industrial activity of lignocellulosic biomass fermentation is limited mainly because of the difficulty in economic bioconversion of these materials to value-added products. Considerable improvement in many processes related to lignocellulose biotechnology appeared during the last decade. Current uses of lignocellulosic biomass, process constraints, and areas of future research are discussed here.

Lignocellulose Biotechnology: Current and Future Prospects

Two cultivated mushroom species, namely, Lentinula edodes and Pleurotus florida and two wild growing species Lentinus cladopus and Pleurotus djamor were studied for their mineral contents such as Ca, Mg, Na, K, Fe, Zn, Mn, Cu, Ni, Se, Pb, and Cd by Inductive Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and also Atomic Absorption Spectroscopy, (AAS). Phosphorus was estimated by spectrophotometric method. K, Ca, Na, and P were in higher concentrations ranging from 59.3 mg to 3634 mg, 8.27 mg–174.9 mg, 22.2 mg–327.4 mg, and 100.5 mg–769.9 mg/100 g dry weight respectively in the four mushroom species studied. Fe, Zn, Mg and Se were ranging from 6.27 mg to 35.3 mg, 1.58 mg–9.44 mg, 21.1 mg–40.7 mg and 0.048 mg–0.182 mg/100 g dry weight, respectively, amongst the mushroom species analyzed. However, Ni, Cu, and Mn contents showed relatively lower concentrations, whereas Pb and Cd were below detectable level. The mushrooms were safe for consumption, in accordance with the permissible tolerance limits of the estimated toxic metals. Implications of the mineral contents on mushroom nutritional value are highlighted.

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Mineral Composition of Four Edible Mushrooms

The cultivation of Pleurotus pulmonarius was carried out on different substrate: cotton waste (A) leaves of Cymbopogon citratus (B) and leaves of Panicum maximum Jacq. (C). The mushroom had a varied chemical composition; nevertheless they contained a good composition for to be used as a good source of protein for human kind. The results showed the higher protein content (29.19%) and fibre (9.0%) for the mushroom that were cultivated on cotton peel. The substrate composition and the residue composition after the mushroom harvest were: Protein for the substrate "A" (10.63% and 9.35%), "B" (7.87% and 4.24%) and "C" (7.55% and 5.90 %); Lipids "A" (4.17% and 2.03%), "B"(2.77% and 3.20%) and "C" (0.91% and 2.05%); Fibres "A" (49.02% and 37.02%), "B" (28.40% and 23.26%) and "C" (37.50% and 26.66%) respectively. The substrate "A" showed 0.048% of iron and "C" 0.14% of magnesium, 0.31% of potassium and 0.26% of calcium. In the substrate "B" the quantity of the minerals were very low in comparison to the other substrates. The residues after the harvest of mushroom could be used as fertiliser or as complement in the composition for animal feed.

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Chemical composition of Pleurotus pulmonarius (Fr.) Quél., substrates and residue after cultivation

Nutritional characterisation of Pleurotus ostreatus (Jacq. ex Fr.) P. Kumm. produced using paper scraps as substrate.

Publisher Summary Basidiomacromycetes represent a circumscribed group of higher fungi of the class Basidiomycetes, wherein the basidia bearing the exogenously produced basidiospores represent the fertile layer (hymenium), which in turn is lined up, encroached, and covered by tufts of tissues to form distinct objects of the Earth's beauty, namely the basidiocarps. Genetic incompatibility factors (bipolarhetrapolar) allow these fungi fungi great diversity in their ability to grow over a range of conditions: fermented or unfermented; pasteurized or unpasteurized; sterilized or unsterilized; on soft woods or hardwoods; on cereal straws or oil crop residues, or plantation crop residues. Moreover, Basidiomacromycetes display an array of physiological properties that have a range of useful applications. Edible species represent the best examples: they grow over a range of lignocellulosic substrates to yield fruiting bodies, and the degarded substrates can in turn be used in a number of useful ways. The search for new species of basidiomacromycetes and research on new and different ways to use these fungi should be a matter of priority. It is a task that requires much intelligence and perseverance. Increasing the list of their applications depends on prolonged and continued research. It can take the ingenuity of mankind, coupled with nature's mercy, to unravel the untapped potentialities of the basidiomacromycetes.

Mysore Nanjarajurs Shashireka

Papers

Biopotentialities of the basidiomacromycetes.