The Ecological Significance of Bacteriophages in SoilEPA Grant Number: U916129
Title: The Ecological Significance of Bacteriophages in Soil
Investigators: Williamson, Kurt E.
Institution: University of Delaware
EPA Project Officer: Zambrana, Jose
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $98,008
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Fellowship - Microbiology , Academic Fellowships , Biology/Life Sciences
The objectives of this research project are to determine: (1) the optimal conditions for extracting phages from soils; and (2) what makes a soil phage a soil phage. The importance of bacteriophages in marine environments has been clearly established over the past decade. Phages may control the abundance of bacteria, control the composition of bacterial communities, and influence bacterial genetic diversity. In contrast to the increasing number of marine investigations, few studies have examined the role of phages in soils, and of these few, almost all have been limited by their reliance on cultured phage isolates. The key to accessing the wide range of culture-independent analyses at our disposal is the efficient recovery of representative phage communities from soils.
Four techniques were compared to determine the most effective method of extracting autochthonous viruses from two Delaware agricultural soils. The best method was used for an initial characterization of virus communities within soil samples using transmission electron microscopy. Beef extract and glycine buffer were most effective in eluting viable phages; however, extraction efficiency varied significantly with phage strain. Overall, potassium citrate buffer eluted the highest numbers of virus-like particles by direct counts, but specific soil-eluant combinations had a significant effect on extraction efficiency. No single method will be optimal for extracting all phage from all soils; thus, it is imperative to assess multiple extraction techniques before undertaking ecological studies of soil bacteriophage communities. Transmission electron micrographs indicate that there are significant differences between the two soil viral communities.
Much of the current modeling of phage dynamics in soils is derived from wastewater management studies. Enteric phages often are used to track the movement and elimination of pathogens in wastewater as it infiltrates soil. Enteric phages, however, are presumably adapted to the chemical and physical hazards of animal digestive tracts and may not be reliable models of autochthonous soil phage dynamics. What are the genetic and phenotypic determinants of phages that are native to soils? Unpredictable wetting and drying cycles are one of the largest environmental hazards that soil environments present. How do soil-dwelling phages deal with the stresses created by wetting and drying, and how are phage community dynamics affected by the concomitant stresses on the bacterial host population? Molecular approaches such as pulsed-field electrophoresis and isoelectric focusing will be used to examine soil phage communities. It is hoped that phage community changes can be linked to changes in the host (bacterial) community, yielding greater insight into the role and impact of bacteriophages in soil ecosystems.