Heterotrophic Feeding

Abstract

Much has been written on the evolution of metabolism and it would be superfluous to consider more than the barest introduction in this context. Most biologists accept that a simple form of heterotrophy was the means by which the earliest forms of life, the primitive prokaryotes, obtained energy to grow and replicate, utilizing preformed nucleotides and amino acids. That they did so in an anaerobic atmosphere is also accepted. As these early microbes proliferated one can visualize the situation whereby their metabolic requirements exceeded the supply of organic substrates produced abiotically in the ‘primeval soup’. Some of these primitive organisms (early chemoautotrophs) then evolved the capacity to fix atmospheric carbon dioxide. Evidence that phosphoglycede acid, phosphoglyceraldehyde and ribulose, all products of the Dark Reaction (see Chapter 4), could have been produced by primitive microbes, comes from the existence of similar metabolic pathways in anaerobic prokaryotes alive today. These carbon dioxide fixation pathways resulted in the accumulation of oxygen in the Precambrian atmosphere, preparing the way for aerobic heterotrophs to flourish, from prokaryotes through to eukaryotic micro-organisms.