MODELING BACTERIAL UTILIZATION OF DISSOLVED ORGANIC-MATTER - OPTIMIZATION REPLACES MONOD GROWTH-KINETICS

A bioenergetic model has been developed to examine growth kinetics ass ociated 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 dissolved inorganic N associated with bacterial growth. For each reaction, free energies and electron transfer requirements are calculated based on t he C, H, O, and N composition of the substrates and their concentratio n in the environment. From these reactions, an optimization problem is constructed in which bacterial growth rate is maximized subject to co nstraints on energetics, electron balances, substrate uptake kinetics, and bacterial C:N ratio. The optimization approach provides more info rmation on bacterial growth kinetics than do the Monod-type models tha t are typically used to describe bacterial growth. Simulations are ran to examine bacterial C yield and growth rate, N remineralization or i mmobilization, and substrate preferences as resource concentrations an d compositions are varied. Results from the model agree well with obse rvations in the literature, which indicate that the premise of the mod el, that bacteria allocate resources to maximize growth rate, may be a n accurate overall description of bacterial growth. Simulations indica te that bacterial growth rate and yield are strongly correlated to the oxidation state of the labile DOM, as determined from its bulk elemen tal composition. Furthermore, the model demonstrates that bacterial gr owth cannot always be explained by a single constraint (such as the C: N ratio of substrate), since several constraints are often active simu ltaneously and continuously change with environmental conditions.