Effect of macromolecular composition of microorganisms on the thermodynamic description of their growth.

Most models describing bacterial growth, including the original mosaic non-equilibrium thermodynamic (MNET) description, do not take into account that the macromolecular composition of the cells varies with growth rate. The MNET description of bacterial growth is extended to account for such a variation in macromolecular composition of the cells in order to make the MNET description more generally applicable. Klebsiella aerogenes NCTC 418 was cultured in a chemostat under glucose- or ammonia-limited conditions to determine the macromolecular composition at varying growth rate. The dilution rate has a strong influence on the macromolecular composition of the cells. Under glucose-limited conditions an increase of the RNA content of the cells was observed with increasing growth rate. The RNA content of the cells was much lower under ammonia-limited conditions of the cells than under glucose-limited conditions but also showed an increase with increasing growth rates. Under ammonia-limited conditions, the polysaccharide content strongly decreased with increasing growth rate. The other cellular components changed relatively less with changing growth rate. It is shown that the slope of the line relating catabolism to anabolism varies very little due to variation of the macromolecular cell composition with growth rate, at least under the tested conditions.