Genetic factors driving attachment of bacteria to environmental particles

Abstract

<p>Modeling the fate and transport of bacteria in water bodies is important for reducing outbreaks of water-borne diseases. However, limited understanding of microbial-particle interactions has led to the diminished accuracy of modeling efforts. The collective work from this thesis attempts to identify genetic factors involved in the attachment of the aquatic fecal indicator organism E. coli to sediment particles. Seventy eight distinct E. coli strains isolated from sediment and water of a local stream were tested for cell properties and attachment propensity to three model particles under environmentally relevant conditions. The results demonstrate that isolates from sediment and the overlying water column possess different cell properties and that attachment ability is influenced by both strain type (genotype) and particle type. We proceeded to analyze the roles of surface structures in bacteria-particle interactions through proteomic analysis and molecular manipulations. We found species-wide variation of outer membrane protein A (OmpA) among our E. coli collections and the five different versions of OmpA differ primarily on the extracellular loops. Moreover, the polymorphism of OmpA is associated with heterogeneity in cell surface properties and attachment ability to an organic particle, corn stover. We further characterized the five versions of OmpAs through constructing strains differing only in OmpA sequence and conducting property measurements and attachment assays. The results confirmed that OmpA plays a major role in determining cell properties such as zeta potential and hydrophobicity, as well as attachment to environmental particles. Through investigation of the distribution of different OmpA among our E. coli collections, we found that isolates from sediment are more diverse than those from the water column, in terms of the OmpA patterns. Moreover, we found that E. coli with the same O antigen type encode the same pattern of OmpA, with rare exceptions. Apart from OmpA, we also studied the roles of outer membrane protein X (OmpX), flagella, and extracellular polysaccharides in attachment of E. coli to particles. In summary, the findings of our work should provide new insights into the mechanisms of bacterial attachment in the environment and outer membrane proteins study.</p>