Bioremediation in the vadose zone is unpredictable because of poor
understanding of factors influencing microbial growth in this environment. A
lab-scale experimental system was developed to examine, noninvasively,
interactions between microbial growth, water flow, and solute transport in
unsaturated porous media. Measurements of microbial colonization, and its impact
on hydrology, were facilitated by using the luxCDABE-containing reporter
bacterium Pseudomonas fluorescens HK44 and digital CCD imaging. Experiments
were conducted in glass-walled two-dimensional flow cells (45 x 50 x 1 cm)
packed with silica sand. Several bioengineering problems associated with chamber
design and function required solution before microbial experiments were
successful. These included: choice of materials for chamber components;
development of sterilization, packing, and inoculation protocols; and development
of procedures for data collection and chamber maintenance during experiments
lasting several days. Bacterial growth was mapped daily by quantifying development of salicylate-induced bioluminescence. A model relating the rate of
increase in light emission after induction successfully predicted microbial densities
over four orders of magnitude (R��=0.95) provided that sufficient oxygen for the
bioluminescence reaction was available. Total model-predicted growth during a
one-week experiment agreed with potential growth calculated from the
mass-balance of the system and previously established kinetic parameters
(predicted, 1.2x10���� cells; calculated, 1.7x10���� cells). Although the rate of
expansion of the colonized zone (and predicted populations in newly colonized
regions) remained relatively constant, the proportion of the daily potential growth
remaining within the chamber declined over time. Monitoring of bioluminescence
revealed the development of an (hypothesized) anaerobic zone associated with
microbial growth in the unsaturated porous media. Water content and flow streams
were measured using light transmission. Accumulation of microbial growth
modified the hydrologic properties of the sand causing up to 50% decrease in
saturation within the colonized zone, diversion of flow around the colonized zone,
and lowering (5 cm) of the capillary fringe height. Apparent solute velocity
through the colonized region was reduced from 0.39 cm min����� (R��=0.99) to 0.25
cm min����� (R��=0.99). These experiments provide proof-of-concept for combining
light transmission and bioluminescence technologies to study interactions between
microbial growth and hydrology in unsaturated porous media. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32412 |
| Date | 20 August 2001 |
| Creators | Yarwood, Rockie R. |
| Contributors | Bottomley, Peter J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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