Is electron equivalence between substrate and product preferable to C-mol equivalence in representations of microbial anabolism applicable to “origin of life” environmental conditionsʔ

This research compares two techniques for constructing sets of equations representing the growth of a microorganism on a given substrate. Each anabolic equation represents a defined initial and a final state. The initial state comprises all necessary mineral nutrients and one organic source of carbon and energy. The final state comprises the microbial cells that have grown, and any additional organic or inorganic products of the growth process. The cells are represented by a unit-carbon formula of the form CHhOoNnPpSs, where the subscripts represent the proportions of the respective elements relative to carbon, which has a unit value. Vitamins, trace elements, and substances that are not covalently bound within the cells are not included in these equations. One technique for constructing growth-process equations is to assume that all available electrons in the cells or other products can only have come from the anabolic substrate. In addition, the quantity of electrons in the products and that in the quantity of the carbon and energy source that forms them are made equivalent. A second technique assumes that all the carbon in the cells or other products can only have come from the anabolic substrate. Here, the quantity of carbon in the products and that in the carbon and energy source that forms them is made equivalent. No O2 is included in any anabolic equation constructed by the first technique. Instead, CO2 is either produced or consumed, depending on the degree of reduction of the substrate relative to the product. Using the second technique, O2 is either produced or consumed in any equation, depending on the degree of reduction of the substrate relative to the product. This latter could not occur in an anoxic, “origin of life” environment.