In sediments, the bioavailability and toxicity of Ni are strongly influenced by its sorption to manganese (Mn) oxides, which largely originate from the redox metabolism of microbes. However, microbes are concurrently susceptible to the toxic effects of Ni, which establishes complex interactions between toxicity and redox processes. This study measured the effect of Ni on growth, pellicle biofilm formation and oxidation of the Mn-oxidizing bacteria Pseudomonas putida GB-1. In liquid media, Ni exposure decreased the intrinsic growth rate but allowed growth to the stationary phase in all intermediate treatments. Manganese oxidation was 67% less than control for bacteria exposed to 5 μM Ni and completely ceased in all treatments above 50 μM. Pellicle biofilm development decreased exponentially with Ni concentration (maximum 92% reduction) and was replaced by planktonic growth in higher Ni treatments. In solid media assays, growth was unaffected by Ni exposure, but Mn oxidation completely ceased in treatments above 10 μM of Ni. Our results show that sublethal Ni concentrations substantially alter Mn oxidation rates and pellicle biofilm development in P. putida GB-1, which has implications for toxic metal bioavailability to the entire benthic community and the environmental consequences of metal contamination.