ABSTRACT
This chapter presents the proteobacteria, a vast phylum of Gram negative prokaryotes from which proto-mitochondria originated. It focuses on the functional properties of anaerobic deltaproteobacteria that define their energy metabolism and are linked to their phylogenesis. The name ‘proteobacteria’ stands for ‘protean group of bacteria of diverse properties’, from the mythological god Proteus, capable of assuming many different shapes. Initially, proteobacteria comprised the four subdivisions of alpha, beta, gamma and delta. Epsilonproteobacteria and deltaproteobacteria are often considered together as the oldest group of proteobacteria, since they include obligate anaerobes which utilize sulfur compounds for their energy metabolism. Phylogenetically, the delta class has been generally positioned at the root of the whole phylum of proteobacteria. The epsilon class is the second smallest of the phylum proteobacteria, but comprises ecophysiologically diverse organisms varying from human pathogens to dominant microbes of hydrothermal vents in the oceans.
