Species-independent maintenance energy and natural population sizes

A general strategy to estimate the size of an active microbial community based on catabolic rates was developed. Tijhuis et al. (Biotechnol. Bioeng. 42, 1993, 509-519) calculated from chemostat experiments maintenance energy consumption rates by multiplication of the maintenance substrate consumption rate with the standard free energy of the catabolic reaction. They showed that the maintenance energy can generally be described as species-independent by an Arrhenius equation. In the present communication, it is shown that the theory is applicable for different microbial culture systems. For a given environmental situation, the maximal microbial population size is obtained when the free energy conserved is consumed solely for maintenance of the cell. The free energy conservation rate per volume together with the species-independent description of maintenance energy enables calculations of the maximal population size corresponding to a catabolic rate and of maintenance substrate consumption rates for microbial cultures.