ABSTRACT
Most thinking about microbial evolution is couched in terms of molecular evolutionary trees, the subject matter of a discipline called phylogeny. The evolutionary steps to Chl biosynthesis in a corrinand heme-possessing diazotrophic cell are few in number and simple in nature. The nature of that main exergonic reaction, which has driven the evolutionary process forward in uninterrupted continuity since the origin of the first cells, is a central topic of investigation in the field of physiology or, more specifically, bioenergetics. The physiological view of microbial evolution was, of course, replaced in the 1980s by a gene centered view of microbial evolution that was constructed around the ribosomal RNA tree of life, also called the universal tree or the three domain tree. Fermentations are an altogether problematic starting point for physiological evolution. The main problem with the concept that fermentations came first concerns substrate.
