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Impacts of Phage Predation on Microbial Dynamics in Temperate Ecosystems

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Author: Helsley, Kaitlin R.
Advisor: Williamson, Kurt E.
Committee Members: Forsyth, Mark H.; Allison, Lizabeth; Peterson, Beverly
Issued Date: 7/17/2012
Subjects: Bacteriophage
Soil microbial dynamics
Terrestrial viruses
Phage predation
URI: http://hdl.handle.net/10288/16754
Description: In marine ecosystems, virus-mediated microbial mortality results in cell lysis and release of cellular contents, freeing dissolved organic nutrients. This nutrient recycling facilitates competition within diverse bacterial assemblages. In contrast, little is known about the role of phage predation in terrestrial ecosystems. A single study done in Barrow, Alaska found phage predation to be a key factor controlling bacterial population dynamics. By applying the methods used in the Arctic experiment to a temperate environment, the goal of this study was to examine the impact of phage predation in temperate soil ecosystems. Upland and wetland field sites were established in the College Woods on the William & Mary campus and PVC soil collars were installed at each site. Five days post installment, each collar received one of four treatments, done in six replicates: acetate (C), nutrients (N, P, K), Tea extract + ferrous sulfate (antiphage, "TeaF"�), or sterile water (control). Upon treatment, microbial respiration of each collar was measured for eight consecutive days using an infrared gas analyzer. At day three and day eight, selected collars were harvested for direct count analysis of microbial cells and virus particles, as well as microbial biomass carbon. At both the wetland and upland sites, treatment of soil with the antiphage solution had no significant impact on microbial respiration or abundance. Nutrient amendment also failed to significantly impact microbial dynamics. Acetate treatment at the upland site, however, resulted in a significant increase in microbial respiration, but not in microbial biomass carbon or abundance. Furthermore, TeaF did not appear to exhibit virucidal activity in temperate soils, as it has been documented to exert in Arctic soils. Two field tests examining the effects of varying volumes of TeaF treatment on autochthonous phage were conducted to explore this disparity. Results indicated that TeaF lacks virucidal capacity in temperate soils and appears to facilitate a washout effect on soil viral populations that is also produced by water. Further studies are necessary to understand the impacts of phages on microbial dynamics within terrestrial soils. This early study neither defends nor rejects the idea that bacteriophage serve as significant drivers of bacterial mortality. Thus, despite their abundance in soils, impacts of phages on soil microbial dynamics remain unknown.
Degree: Bachelors of Science in Biology

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