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This study reports the isolation and optimization of cellulase-producing bacteria from the gastrointestinal tract of South African goats for the pretreatment of lignocellulosic biomass in bioenergy applications. Among the isolates, three strains, Bacillus KC50, Bacillus KC70, and Proteus mirabilis KC94, were identified by 16S rDNA sequencing. To our knowledge, this is the first report of cellulolytic optimization in P. mirabilis derived from a goat rumen. Enzyme production was optimized under varying pH, temperature, and incubation conditions. P. mirabilis KC94 exhibited robust enzyme activity at pH 7 and 35 °C, with stability across a broader range than the Bacillus strains. Peak activity occurred at 84 hours of incubation, reflecting strain-specific metabolic adaptation. The presence of organic solvents and surfactants inhibited enzyme activity, whereas mild oxidative stress induced by H₂O₂ stimulated cellulase production. Amplification of GH39, GH45, and GH48 genes revealed KC94’s strong genetic potential for efficient lignocellulose degradation. These findings highlight the biotechnological potential of rumen-derived cellulolytic bacteria, particularly P. mirabilis KC94, for advancing sustainable bioenergy systems.