Spatially explicit simulations of a microbial food web

A mechanistic model of a simplified microbial food web was implemented based on spatially explicit transport of nutrients and energy sources by molecular diffusion. Individual organisms were simulated to interact in a two-dimensional arena consisting of 70 x 70 interconnected hexagonal compartments each of 2 nl in volume. Release of dissolved organic matter in conjunction with predation events resulted in patches of increased concentration lasting long enough to be consumed completely by bacteria before being dispersed. Individual bacteria encountered concentrations of dissolved organic matter varying up to 100-fold within time scales significant for growth. The simulations also predicted that given a chemotactic response to nutrient gradients, bacteria could grow 50% faster on average when gathered in loose cluster; within patches. Extending the scenario to the three-dimensional case and looking at a 1-ml volume, patch-generating events were estimated to occur several times per hour and spread to within a few millimeters in radius before being eroded by bacteria. The erosion time scale is probably longer than the time between patch appearances resulting in patches overlapping and creating a markedly inhomogeneous microenvironment. In such a scenario, foraging strategies enabling bacteria and predators to respond to elevated concentrations of food could represent a significant adaptive advantage.