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Sixty-two fungal isolates were screened for lignin peroxidase production. The most potent isolates for lignin peroxidase production were identified using the DNA sequence of the internal transcribed spacer (ITS) region as Phanerochaete chrysosporium and Pleurotus ostreatus. The pretreatment of rice straw with P. chrysosporium, Pl. ostreatus, or lignin peroxidase for use in the biopulping process was studied. Great variations in the loss of pulp yield and kappa number were recorded with different fungal and enzyme treatments. Pretreatment of rice straw with P. chrysosporium for 25 days resulted in a substantial decrease in pulp yield (by 9.1%) and kappa number (by 25.6%). Losses of pulp yield and kappa number were considerably lower with lignin peroxidase treatment (3.7 and 14.1%, respectively). However, the pretreatment of rice straw with the Pl. ostreatus isolate caused moderate pulp yield losses (5.8%) and preferential lignin degradation (kappa number losses of 34.6%). This indicated that the Pl. ostreatus isolate might be superior to both the isolate of P. chrysosporium and lignin peroxidase for use in the biopulping process or other processes in which preferential lignin degradation is desired. [ABSTRACT FROM AUTHOR]