The major problem for industrial application of bioflocculants is its high production cost. Here, a novel bacterium Pseudomonas boreopolis G22, which can secret a cellulase-free xylanase and simultaneously produce bioflocculants (MBF-G22) through directly converting untreated biomass, was isolated. The bioflocculants' production of G22 was closely related to its xylanase activity, hydrolysis ability of biomass and the hemicellulose loss caused by G22. The optimal fermentation conditions with the highest bioflocculants' yield (3.75 mg g(-1) dry biomass) were obtained at the fermentation time of 96 h, incubation temperature of 30 degrees C, inoculum concentration of 1.0% and biomass concentration of 1.0% in an initial pH value of 7.0. MBF-G22 mainly consisted of polysaccharides (63.3%) with a molecular weight of 3.982x10(6) Da and showed the highest flocculating efficiency of 97.1% at a dosage of 3.5 mg L-1. In addition, MBF-G22 showed high flocculating efficiency of microalgae (95.7%) at a dosage of 80 mg L-1.