The three roles are:

1. Decomposers: Inset image is of Rhizobium. Bacteria of the genes Rhizobium often live symbolically within nodules attached to roots of legumes such as clover, where they convert atmospheric nitrogen into a form that is useable by plants.
2. Producers: Inset image of Cyanobacteria. Cynobacteria in the genes Anaboena form filamentous chains in ponds and oter aquatic environments, where they perform photosynthesis.
3. Nitrogen fixers: Inset image of actinomycetes. Bacteria called actinomycetes are present in soil and in rotting plant material such as fallen logs, where they decompose complex organic molecules into simpler molecules.