Sublethal metal toxicity shuts off biofilm development and manganese oxidation in Pseudomonas putida GB-1

Abstract:

Nickel is a widespread pollutant in streams that can impair diversity and ecological functions. In sediments, the bioavailability and toxicity of nickel are strongly influenced by its sorption to metal oxides, such as manganese oxides. The presence of manganese oxides in sediments is largely determined by the redox metabolism of microbes. However, microbes are concurrently susceptible to the toxic effects of nickel, which can lead to energetic trade-offs and result in decreased rates of redox reactions, ultimately modifying the availability of metal oxides. The sensitivity of benthic microbes to nickel toxicity and their influence on nickel bioavailability establishes potential emergent feedbacks between toxicity and redox processes. This study assessed the effect of nickel on growth, biofilm formation and oxidation of the manganese-oxidizing bacteria Pseudomonas putida GB-1. Bacteria were incubated for 32h in liquid media amended with 100µM of manganese and dosed with nickel at concentrations of 0, 5, 10, 25, 50, 75, 125 and 250µM. Triplicate cultures were sampled every 4h or at the end of experiment to measure growth (optical density and protein concentration), manganese oxidation (leucoberbelin blue dye), and biofilm formation (crystal violet). Nickel exposure hindered bacterial growth at 250µM but allowed for growth to stationary phase in all intermediate treatments, though the intrinsic growth rate decreased as nickel concentration increased. Manganese oxidation was 67% less (relative to control) for bacteria exposed to 5µM nickel, and completely ceased in all treatments above 50µM. Biofilm development decreased exponentially with nickel concentration (up to 92%) and was replaced by planktonic growth in the 75 and 125µM nickel treatments. Nickel treatments 25–250µM showed over 60% decrease in biofilm formation and did not have visible evidence of manganese oxidation. Bacteria incubated with up to 10µM nickel developed less prominent biofilm compared to control but oxidized manganese efficiently. Our results show that sublethal concentrations of nickel alter manganese oxidation rates and biofilm development, which has implications for toxic metal bioavailability to the entire benthic community.