Pathogens are the bad guys they cause disease in plants. Bacteria are common throughout the soil, but tend to be most abundant in or adjacent to plant roots, an important food source. Actinomycetes are a broad group of bacteria that form thread-like filaments in the soil. They are responsible for the distinctive scent of freshly exposed, moist soil. Why They Are Important Bacteria are important in the carbon cycle.
Bacteria are important decomposers in grassland environments.
When one group becomes dominant where it shouldn't be, there is also a shift in the rest of the system. The shift from bacterial to fungal dominance, for instance, can enhance the conditions favoring weed invasions on rangelands. Bacteria are particularly important in nitrogen cycling. Free-living bacteria fix atmospheric nitrogen, adding it to the soil nitrogen pool. Other nitrogen-fixing bacteria form associations with the roots of leguminous plants such as lupine, clover, alfalfa, and milkvetches.