Define the role of Bacteria in soil flora

The most abundant soil organisms are primitive, very minute, unicellular organisms devoid of chlorophyll. Bacteria are most abundant in soil with an average mass of about 1.5 x 10^{- 12}g.  Some 300 to 3000 kg of live bacteria are present in every hectare of surface soil. Most of the bacterial cells remain adsorbed on the clay particles and humus part of soil. Their number   in a soil depends upon the type of soil and the climatic conditions. Bacteria, in general, prefer near neutral to slightly alkaline medium, between pH 6.5 to 8.00 for their growth. Soil bacteria may be heterotrophic, obtaining their energy and carbon from complex organic substances or autotrophic, obtaining their energy from the oxidation of the organic compounds, their carbon from the carbon dioxide, their nitrogen and other minerals from inorganic compounds.