We studied a new strategy for pretreatment of rice straw (RS) to enhance enzymatic hydrolysis under mild condition. This approach uses the synergy of sodium carbonate (Na2CO3) and the bacterial strain Cupriavidus basilensis B-8 (hereafter B-8). After synergistic Na2CO3 and B-8 pretreatment (SNBP), the reducing sugar yield varied from 335.3 mg/g to 799.6 mg/g under different conditions. This increased by 13-31% over Na2CO3 pretreatment (284.2-719.2 mg/g) and 3.42-8.15 times over the untreated RS (98 mg/g). Moreover, the composition of RS was changed significantly through decreases in lignin and hemicellulose. We confirmed this change by compositional analysis and physicochemical characterization of the structure of RS before and after pretreatment. We also elaborated a mechanism for SNBP to better explain RS changes and bacterial effects on enzymatic hydrolysis.