Liv Fevang's thesis
by
Liv Fevang, MSE
University of Texas at Austin, 1997
Supervisor: Mukul M. Sharma
Paul Majors
The transport and growth of microorganisms in the subsurface is of
relevance to microbial ecology in aquifers and sediments and to the in-situ
biodegradation of organic contaminants. In many instances, biofilm growth is the
dominant mechanism by which cell populations colonize subsurface environments
There is currently no direct method for monitoring in-situ such bacteria
populations.
In this project we introduce the use of nuclear magnetic resonance imaging
(NMRI) techniques as a methodology for the detection and visualization of
biofilms. Ultimately the techniques are to be applied to bioflm growth in porous
media.
The objective of the first part of this work was to verify optically that
NMRI techniques could be used to detect biofilms. The resolution of the NMR
technique was also investigated by running experiments with bacterial colonies on
agar, centrifuged cells in test tubes and varying free cell concentration. NMR
velocity images of flow in bioreactors were also conducted.
It was found that semi-quantitative relaxation weighted NMR images of
biofilms compare well with optical images. Attempts to quantitatively image
biofilms were less successful, due in part to the limitations of available data
analysis routines.
The spatial resolution experiments showed the E. coli colonies on agar
with diameters as small as 1 mm and heights as small as 0.2 mm could be
detected and measured with reasonable accuracy using NMRI technique.
These limits correspond with the resolution of the NMRI apparatus used in this
study and are therefore, not inherent.
Dilute concentrations of free E. coli cells (as opposed to cells within a
biofilm) could not be detected easily, indicating that the NMR method might not
be a suitable method for detecting free cells of this particular strain.
NMR velocity profiles compare very well with calculated velocities. However,
no effect of biofilm growth on the velocity distribution was detected.
The second part of this work involved the investigation of the effect of
different substrates and flow velocities on bacterial adhesion and biofilm growth.
These studies show that biofilms develop sooner and cover a greater percentage
of the flow area when the nutrient flow rate is low, thus indicating that it is easier
for the cells to adhere when the shear forces are small. The same trend was
detected for both PlexiglasTM and albumen coated Plexiglas. By adding albumen
the surface charge density is reduced, and the surface also becomes more
hydrophilic. Both factors should, and do, reduce bacterial adhesion.
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