We have simulated the effects of fracture characteristics on the reduction of effective permeability of fractured rocks due to in-situ bacteria growth. A solute is injected continuously to provide food for the growth of in-situ bacteria. We used a power law for fracture length distribution and a fBm for fracture aperture spatial distribution. The results show that in-situ bacteria growth reduces the permeability hyperbolically, but the porosity of backbone fracture does not change significantly. It shows that the reduction of the permeability proceeds faster for smaller values of length exponent and for larger values of Hurst exponent. The fracture length distribution has a stronger effect on the speed of permeability reduction than the aperture spatial distribution. The time needed to reduce permeability is inversely proportional to the hydraulic gradient.