Soil Amoebae Affect Iron and Chromium Reduction through Preferential Predation between Two Metal-Reducing Bacteria

Area of Science:

• Soil Ecology
• Microbial Ecology
• Biogeochemical Cycles

Background:

• Soil protists are crucial for ecosystem functions but their role in heavy metal cycling is understudied.
• Understanding protist-microbe interactions is key to deciphering soil metal transformations.

Purpose of the Study:

• To investigate how protist predation affects iron (Fe) and chromium (Cr) reduction by soil bacteria.
• To explore the impact of *Dictyostelium discoideum* predation on metal-reducing bacteria.

Main Methods:

• Utilized *Dictyostelium discoideum* as a model protist.
• Co-cultured protists with Fe(III)-reducing (*Shewanella decolorationis* S12) and Cr(VI)-reducing (*Brevibacillus laterosporus*) bacteria.
• Assessed bacterial biomass, activity, and metal reduction rates.

Main Results:

• *D. discoideum* predation reduced *S. decolorationis* biomass but stimulated its Fe(III) reduction activity.
• *D. discoideum* could not prey on *B. laterosporus* alone, but did when *S. decolorationis* was present, decreasing Cr(VI) reduction.
• Protist predation selectively altered bacterial activity impacting Fe and Cr cycling.

Conclusions:

• Protists significantly influence heavy metal cycling through selective predation on metal-reducing bacteria.
• This study highlights the complex ecological interactions governing biogeochemical processes in soil.
• Protist predation represents a novel mechanism affecting soil Fe and Cr biogeochemistry.