Title

Modeling microbial growth and coexistence on heterogeneous and unsaturated rough surfaces

Date of Completion

January 2006

Keywords

Biology, Microbiology|Environmental Sciences|Engineering, Environmental

Degree

Ph.D.

Abstract

Rich diversity of microbial species in the vadose zone is believed to be promoted by complexity of resource and micro-environments and by heterogeneity of aquatic habitats in unsaturated soils that limit diffusion pathways and form physically isolated niches capable of supporting diverse species within small soil volumes. The role of heterogeneity in media structure and aqueous phase distribution in controlling of substrate diffusion, microbial growth and competition was investigated by numerical simulations in this study. Hybrid methods, which incorporate Reaction Diffusion Method (RDM) and Individual Based Models (IBM), were used to capture the transport and reactive behaviors of both the continuous substrate, and the discrete microbial cells. The hybrid model was developed for general qualitative evaluation of microbial coexistence affected by spatial heterogeneity, then extended to investigate microbial growth and competition on rough surfaces. Two approaches, namely the rough surface network model and the patched surface model were developed for the purpose of experimental study in micro-models and practical simulation in real soils, respectively. Numerical results revealed the complicated impact of media structure and matric potential on microbial growth in unsaturated media. Although lower matric potential suppressed microbial growth, in some cases, it protected microbial diversity. Spatial heterogeneity could also increase the chance of coexistence. The effective diffusion coefficient of the media may serve as an important indicator to evaluate the capacity of the porous media to support microbial activities.^