Cupriavidus metallidurans: a species-non-specific and multifaceted plant growth-promoting bacteria.

Here we report growth promoting effects of Cupriavidus metallidurans on plants, and provide evidence for the underlying mechanisms of the growth promoting effects. In a series of greenhouse experiments on tomato, maize, and wheat, complemented with genetic analysis of Arabidopsis mutants, we tested the effects of the bacteria on seed germination, root and shoot growth, metal uptake, gas exchange parameters, and stomatal and xylem traits in maize, wheat, and tomato plants. Results showed that the bacteria substantially accelerate seed germination, increase shoot and root biomass, enhance photosynthetic performance, acidify the rhizosphere, increase metal uptake, and modulate stomatal and xylem traits. Analysis of Arabidopsis mutants impaired in auxin or ethylene perception and signaling revealed that the growth promoting effects of the bacteria and accelerating seed germination is independent of auxin and ethylene. We conclude that the bacteria acidify the rhizosphere and thereby increase metal uptake. It increases stomatal density and xylem area leading to increased stomatal conductance and hydraulic conductivity, leading to increased photosynthesis. Altogether, our data suggest C. metallidurans as a plant growth-promoting bacteria with striking abilities to manipulate different plant traits including stomatal density and xylem structure.