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Lignocellulose liquefaction by bacterial treatment is a quite challenging task yet. The microstructural changes and liquefaction efficiency of hydrothermal associated Bacillus sp. AY8 treated lingo-cellulosic straw have been focused in this study. The straws (5%) of rice, barley, and wheat were treated at 170°C, 180°C and 190°C for 30 min in biomass digester. The optimum hydrothermal treatment conditions to complete liquefaction of rice, wheat, and barley straws with Bacillus sp. AY8 were obtained at 180°C, 190°C and 190°C for 30 min, respectively. In minimal nutrient media, the Bacillus sp. AY8 degraded aromatic dyes and lignin derivatives when those were utilised as sole carbon and energy sources by the strain. The scanning electron microscopy exhibited the porous structure of the rice straw due to the loss of lignin and other impurities. Moreover, Fourier transformed infrared spectroscopy demonstrated that the lignin-associated peaks at 1516 and 1325 cm-1 intensities were almost disappeared due to the removal of lignin wrapping on the surface of cellulose fibers of treated samples. The crystalline index of the rice straw was 78.30, 63.69, 57.16, and 36.10 on 0, 4, 6, and 8 days treatment respectively with Bacillus sp. AY8. The liquefaction of lignocelluloses was observed likely due to a combination of extracellular enzymes of Bacillus sp. AY8. The Bacillus sp. AY8 treated rice straw yielded maximum 73.5% reducing sugar after 72 h in saccharification. This is the first report that suggests hydrothermal associated bacterial pretreatment to liquefy lignocellulose that has opened a new route of biomass pretreatment.