In recent years, the use of engineered metal nanoparticles (NPs) has raised concerns over their ecotoxic effects. Thus, it is important to study the effects of NPs on environmentally important microbes that involve in bioremediation. In this study, we evaluated the impact of aluminum, iron, nickel, zinc and their oxide NPs (nAl, nFe, nNi, nZn and their oxides) on three different dibenzofuran (DF) degrading bacteria (Agrobacterium sp., PH-08, Stenotrophomonas sp. PH-09, and Sphingomonas wittichii RW1). NPs (0.01 to 1 g/L) treated bacterial cells were checked for cytotoxicity, genotoxicity, growth, biodegradation, and catabolic enzyme activities. In aqueous system, higher toxicity (range, 36 - 77.5%) was observed with the cells treated with nAl, nZn and nNi at 0.5 g/L than nFe and iron oxide NPs (<30%). High levels of reactive oxygen species (ROS), glutathione, catalase, death and DNA damage in cells treated with nAl, nNi, nZn and their oxides suggest that these NPs can induce oxidative stress and cell death. Moreover, DF biodegradation and catechol dioxygenase activities were significantly inhibited (range 63 - 95 %) in bacteria treated with these NPs for 6 h; whereas, nFe showed weak inhibition while iron oxide NPs were nearly non-toxic. Impact of NPs on DF degradation by RW1 in soil system revealed that only nAl and nNi showed effective inhibition.