2015 Elsevier Inc. All rights reserved. This chapter describes microbial aspects of Earth's living skin, which is a major habitat for environmental microorganisms. Both surface soils and subsurface vadose zones are discussed with respect to their solid, liquid and gaseous phases. Soil and vadose zones are also characterized with respect to their potential as a microbial environment. The major classes of microbes in soil are described including: indigenous bacteria; actinomycetes; fungi, algae; and protozoa. Similar information is also provided for both shallow and deep subsurface environments. Characteristics of soil bacteria, actinomycetes and fungi are provided in terms of their relative diversity similarities, functions and requirements for life within earth.
