Consumption and release of dissolved organic carbon by marine bacteria in a pulsed-substrate environment: from experiments to modelling.

To investigate the effects of episodic occurrence of dissolved organic carbon(DOC) in the natural environment, bacterial degradation of labile DOC was studied under laboratory-controlled conditions followed by modelling. A single labile DOC compound was periodically added to the experimental culture and its degradation by a monospecific marine bacterial strain was followed. The measured variables were DOC and bacterial biomass determined from the particulate organic carbon values. Experimental dynamics showed a repetition of 2 successive patterns after each DOC pulse:(1) substrate consumption and bacterial growth in the first few hours after substrate addition, followed by(2) bacterial reduction(organic carbon-related) and associated non-labile DOC release within the next few hours. Based on these experimental results, the Dynamic Energy Budget theory was applied for the first time to such conditions to develop a mechanistic model that comprised 7 parameters and 4 state variables in which bacterial biomass was fractionated into reserve and structure compartments. The model was constructed by accounting for a constant specific maintenance rate and comprised 2 different cell maintenance fluxes, one fuelled from cell reserves when substrate was abundant and one from reserves and cell structures when starvation occurred. This new model of bacterial degradation adequately matched experimental measurements and accurately reproduced the accumulation of non-labile DOC in the culture during the experiment. This model can easily be implemented in an aquatic biogeochemical model and could provide better understanding of the role of bacteria in carbon cycling in fluctuating environments. © Inter-Research 2009