Bacteria change the surface of the Earth. All kinds of bacteria reside in the biosphere, and although sometimes they may cause damage, they also help in cleaning the surface of the Earth and in the circulation of various substances. Chemolithoautotrophic bacteria in particular have a unique and intimate relationship with inorganic substances and human beings. This book covers in detail advances in the biochemistry and physiology of several chemolithoautotrophic bacteria as well as their relationship to certain environments. Included are recent findings regarding the oxidation mechanisms of ammonia, nitrite, sulfur compounds, and ferrous iron by special bacteria. The characteristics of many cyhromes are described to further advance the understanding of bacterial oxidation systems of inorganic compounds. Applications of bacteria, such as in sewage treatment and in biohydometallurgy, among others, are detailed, and bacteria considered closest to the origins of life are discussed in the final chapter.