Dynamic models of multi-trophic interactions in microbial food webs

Completely mechanistic mathematical models have been developed to examine the dynamic behavior of bioavailability-limited substrate utilization in a competitive microbial system experiencing protozoan predation pressure in continuously mixed open-flow (CMFR) and batch reactors to examine the effects of various processes on the bioremediation process. Mechanistic processes incorporated into the models include: (1) growth inhibition of one bacterial species, (2) selective predation by protozoa using a novel "contact-complex" formation mechanism, (3) adoption of defense mechanisms by bacteria against predation, (4) incorporation of spatial refuge provided by sediment particles, (5) heterotrophic consumption of non-living organic carbon exudates produced by bacteria and protozoa and (6) bioavailability limited microbial substrate utilization. Sensitivity analyses were performed by simulation of the multi-parameter non-steady state models to focus research on the parameters that affect the overall process of bioremediation most significantly. The results of the simulations demonstrate that growth inhibition, selective predation by protozoa and the adoption of defense mechanisms all allow the two prey species and predator to co-exist in the system resulting in enhanced substrate removal. The biokinetic parameters that control the overall substrate utilization rate are dilution rate (CMFR only), prey and predator endogenous decay rate and the predator growth rate. Also, the CMFR is more dynamic compared to the batch reactor system. The results suggest that a more "biodiverse" microbial community enhances the bioremediation process. In addition, abiotic studies were performed to better understand bioavailability limitations and the role pore transport plays in the bioremediation process using naphthalene and phenanthrene in low organic carbon ( foc) engineered particles. The results indicate that sorption non-linearity does not significantly affect bioavailability of the substrate (assuming either local equilibrium or first order micropore domain resistance for intra-particle pore transport) in low foc geosorbents (such as in the test system or aquifer material). In contrast, in high foc geosorbents (such as surface soils and sediments), sorption non-linearity will result in greatly decreased bioavailability and much greater remediation time scales. These results help us understand how various model parameters and bioavailability limitations affect remediation outcomes, and hopefully leading towards better management of the contaminated soils and sediments.