Biodegradation of lignin present as lignocellulose in crop residues and forest wastes is of significance for the terrestrial energy rich carbon cycle. However, no studies on this important aspect, either with respect to the degradation of important agro-forestal wastes or the ability of fungal isolates capable of causing biodegradation in them, have been carried out in Pakistan. The lack of knowledge on thee aspects relevant to the bio-resources in Pakistan provided the basis for the study reported here.
Sugar-cane bagasse and wheat straw being the major crop residues in Pakistan were sued as the substrate for the biodegradation of lignin. In a minor additional study for biodegradation of lignin in wood, sheesham wood an important wood plant in the plantations in Pakistan and bamboo wood, was also investigated.
As the Biodegrading organisms were used six basidiomycete species, five of which were from the Mycoflora of Pakistan, isolated locally . The species investigated for the purpose were: Trametes versicolor, Termetomyces sp. Polyporus sulphureus, Bjerkandera adjusta, Schizophyllum commune and Peniophora gigantea.
Solid state fermentation of sugar-cane bagasse and wheat straw with T. versicolor was followed at 7 day intervals for 35 days.
According to the screening of the five white rot and one brown basidioymcetes, with respect to their ligninolytic activity on sugar-cane bagasse carried over a period of 21 days, their relative ability as to the efficiency to remove lignin was T. Versicolor (39.5%), Termetomyces sp. (27.0%) B. adusta (22.6%) S. commune(21.8%), P. gigantean(21.6%) and P. sulphureus(15.7%).
The ligninolytic activities of the six fungi investigated, however, did not correspond with the cellulose degradation note during the same period of 21 days of fermentation of sugar-cane bagasse, which was noted in the following descending order: P. sulphureus (21.2%) S. commune(18.8%), P. gigantean (16.8%) , B. adusta (13.8%), S. Termetomyces. sp.(14.4%) T. versicolor (11.8%).
Major degradation of lignin in wheat straw 11.7% of the total 17.1% occurring in 35 days) was noted during the first 14 days, while in the case of sugar-cane bagasse it was observed in 21 days (16.9% of the total 21.3% occurring in 35 days). For one unit of cellulose lost in 14 days in wheat straw the lignin loss was 1.2, while in 21 days in sugar-cane baggass the lignin loss was 1.4 These ratios therefore also represented the most economical lignin removal at the least loss of cellulose.
All the fungi tested for their ability to degrade wheat straw and sugar-cane bagasse were able to colonize the unamended substrates. The substrates on amendment with different sugars at different concentration were noted, affect the degradation process varyingly. The variations were observed in respect to the degree of total organic matter, lignin and cellulose losses in the two substates amended with various sugars and their concentrations. No. uniform pattern was, however, evident.
All fungi test could colonize the native substrate sued the highest degradation rate of lignin was fund with T. versicolor on supplementation with 5% glucose which was 39.5% and with Termetomyces sp. 27.0%.
A further increase in the amount of glucose or replacement of glucose with sucrose upto 15%, in the medium showed a slight decrease in the lignin degradation which indicates that lignin degradation was at the best only at a marginal carbon/energy source for maintenance of metabolism.
Ligninolytic activity and reticulo-rumen digestibility are strongly dependent on fungal species. T. versicolor and Termetomyces sp. Showed good lignin degradation and thus also caused increased reticulo-rumen digestibility of the sugar-cane bagasse. B. adusta, S. commune and P. gignatea degraded lignin only to a small extent, while P. sulphureus behaved as brown not basidiomycete. These low level of lignin degradation are well reflected in the little to no augmentation of digestion relevant with non-amended substrates
Biodegradation study on wheat straw after incubation with T. versicolor and fermentation for 14 days is reported. Wheat straw when subjected to solid state fermentation with or without supplementation with extraneous carbon and nitrogen was found necessary for accelerated preferential degradation of lignin over cellulose. Glucose was noted to be a better supplementation than beet pulp molasses as a carbon source for the delignification under nitrogen starved conditions
Solid state fermentation of sheesham wood and bamboo wood with T. versicolor for a 14-days fermentation period after supplementation with 5% glucose removed 12.3% and 18.1% lignin. In the presence of glucose T. versicolor selectively remove lignin without degradation of cellulose in bamboo wood.
T. versicolor and termetoymyces sp. Showed good lignin degradation and increased reticulo- rumen digestibility at 5% glucose under nitrogen starved condition, whereas nitrogen source suppressed ligninolytic activity