A bioenergetic model has been developed to examine growth kinetics associated with bacterial utilization of dissolved organic matter (DOM), NH4+, and NO3-. A set of 11 metabolic reactions are used to govern the incorporation, oxidation, and N remineralization of DOM and DIN associated with bacterial growth. For each reaction, free energies and electron transfer requirements are calculated based on the C, H, O, and N composition of the substrates and their concentration in the environment. From these reactions, an optimization problem is constructed in which bacterial growth rate is maximized subject to constraints on energetics, electron balances, substrate uptake kinetics, and bacterial C:N ratio. The optimization approach provides more information on bacterial growth kinetics than Monod-type models that are typically employed to describe bacterial growth. Batch simulations are run to examine bacterial carbon yield and growth rate, N remineralization or immobilization, and substrate preferences as resource concentrations and compositions are varied. Results from the model agree well with observations in the literature, which indicates that the model premise, that bacteria allocate resources to maximize growth rate, may be an accurate overall decription of bacterial growth. Simulations indicate that bacterial growth rate and yield are strongly correlated to the oxidation state of the labile DOM, as determined from its bulk elemental composition. Furthermore, the model demonstrates that bacterial growth can not always be explained by a single constraint (such as the C:N ratio of substrate), since several constraints are often active simultaniously and continuously change with environmental conditions.
Keywords: Bioenergetic, DOM, DOC, optimization, bacterial yield, bacterial growth rate, modeling.