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Transport of Bacterial Endospores in Silica Sand. Sibylle Tesar, Fulbright Scholar Dr. Barbara Williams, Faculty Dr. Robin Nimmer, Res. Supp. Sci. Angelina Cernick, Undergraduate Kristina Beaulieau, NSF REU. Department of Biological and Agricultural Engineering University of Idaho.

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transport of bacterial endospores in silica sand

Transport of Bacterial Endospores in Silica Sand

Sibylle Tesar, Fulbright Scholar

Dr. Barbara Williams, Faculty

Dr. Robin Nimmer, Res. Supp. Sci.

Angelina Cernick, Undergraduate

Kristina Beaulieau, NSF REU

Department of Biological

and Agricultural Engineering

University of Idaho

outline
Research Goals – transport mechanisms / endospores

Background – transport mechanisms / endospores

Research Questions – preliminary

Methods – sporulation / saturated column tests / breakthrough curves / depth distribution data

Preliminary Results

Preliminary Conclusions

Future Work – B. cereus, other microbes

Outline
research goals spore transport in porous media
Mechanistic Goal: Contribute to the lively debate of attachment versus straining

Microbe-specific goal: Bacterial endospore

Practical Applications

Drinking water protection - groundwater

Shallow recharge

Septic drainfield setbacks

Surface water filtration

Riverbank or riverbed filtration

Research Goals – Spore Transport in Porous Media
outline1
Research Goals – transport mechanisms / endospores

Background – transport mechanisms / endospores

Research Questions – preliminary

Methods – sporulation / saturated column tests / breakthrough curves / depth distribution data

Preliminary Results

Preliminary Conclusions

Future Work – B. cereus, other microbes

Outline
terminology mechanisms for retention
Attachment – adhesion – sorption

Function of collision, collector efficiency, sticking efficiency

Mechanical filtration – complete retention of particles that are larger than all of the soil pores (formation of filter cake)

Straining – physical trapping in geometric corners

Particles can be smaller than smallest pore openings

Requires grain-grain contact

Only occurs in some fraction of soil pore space, transport occurs elsewhere

Terminology – Mechanisms for Retention

Bradford et al, WRR, 2006

background
Clean-bed Filtration Theory

Depends on mechanism of attachment / detachment

Deviation from Clean Bed Filtration Theory

Unfavorable attachment condition; neg-neg

Fine sand and large colloids (dp/d50 .005)

Background
explanations for deviation from cft
Attachment w/ porous media charge variability – Johnson and Elimelech, 1995

Attachment w/ heterogeneity in surface charge characteristics of colloids – Li et al, 2004

Attachment w/ deposition of colloids in a secondary energy minimum – Tufenkji et al. 2003, Redman et al., 2004

All of the above – Tufenkji and Elimelech, 2005

Attachment w/ straining – Foppen et al, 2005, Bradford et al, 2006a, b

Explanations for Deviation from CFT
theory cont

Theory (cont.)

Aqueous Phase Colloid Mass Balance Equation- Bradford et al., 2003

Where:

θw = volumetric water content [-]

t = time [T]

C = colloid concentration in the aqueous phase [N L-3]

JT = total colloid flux [N L-2 T-1]

EattSW = colloid attachment mass transfer between solid/water phases [N L-3 T-1]

EstrSW = colloid straining mass transfer between solid/water phases [N L-3 T-1]

research goals endospore transport
Endospore-forming bacteria have two viable modes

Vegetative cell (growing)

Endospore (dormant) – formed as survival mechanism

Endospores have the potential to be more mobile than their vegetative cell counterparts

smaller size

potentially less adhesion

Research Goals – Endospore Transport
bacterial endospores
Formed as a survival mechanism

Cryptobiotic – no sign of life - dormant mode

Bacterial Endospores

http://www.textbookofbacteriology.net/

differences between endospores and vegetative cells in bacillus species
Differences between endospores and vegetative cells in Bacillus species

http://www.textbookofbacteriology.net

in terms of physical passage through the pore space
In terms of physical passage through the pore space…

…the spore has a “shorter” aspect

ratio than the vegetative cell.

  • B. cereus spore properties:
    • Food poisoning pathogen
    • Length: 1-2 mm, Width: 0.5-0.75 mm
    • Hydrophobic
    • Isoelectric point: pH ~3
outline2
Research Goals – transport mechanisms / endospores

Background – transport mechanisms / endospores

Research Questions – preliminary

Methods – sporulation / saturated column tests / breakthrough curves / depth distribution data

Preliminary Results

Preliminary Conclusions

Future Work – B. cereus, other microbes

Outline
preliminary research questions
Do spores obey CFT, exhibiting more retention in higher ionic strength solution or does spore transport deviate from CFT theory as do other negatively charged particles (unfavorable attachment)?

Future: Do vegetative cells and endospores have a different charge?

Future: Do vegetative cells exhibit more attachment than endospores?

Preliminary Research Questions
outline3
Research Goals – transport mechanisms / endospores

Background – transport mechanisms / endospores

Research Questions – preliminary

Methods – sporulation / saturated column tests / breakthrough curves / depth distribution data

Preliminary Results

Preliminary Conclusions

Future Work – B. cereus, other microbes

Outline
materials sand properties

Materials: Sand Properties

Saturated conductivity: Ksat = 1.8x10-4 m/sec

Dry bulk density:

rb = 1.65 g/cm3

Porosity:

n = 0.34

dp/d50 .0017

breakthrough c c o of b cereus spores as a function of ionic strength
Breakthrough (C/Co) of B. cereus spores as a function of ionic strength

Artificial groundwater

DDI

column dissection1
Column Dissection
  • Drain column to field capacity, in the flow direction.
  • Dissect into seven 2 cm increments
  • STR 1:Gently place sand, allowing bridging and loose packing, in a funnel that has been plugged with Scotchbritetm pad
  • STR 2: Wash off the strained bacteria by pouring the solution (the solution used in that particular experiment) over the sand into a graduated cylinder
  • ATT: To remove the attached bacteria, place a known amount of 2% Tweentm 80 solution into a beaker containing the sand. Stir then sonicate.
  • Used optical density (OD) measurements in addition to plate counting to enumerate.

(Tween and sonication proven not to affect germination efficiency)

depth distribution data
Depth Distribution Data

“Strained” spores in AGW run

depth distribution data1
Depth Distribution Data

“Attached” spores in AGW run

depth distribution data2
Depth Distribution Data

Strained and attached fractions combined

outline4
Research Goals – transport mechanisms / endospores

Background – transport mechanisms / endospores

Research Questions – preliminary

Methods – sporulation / saturated column tests / breakthrough curves / depth distribution data

Preliminary Results

Preliminary Conclusions

Future Work – B. cereus, other microbes

Outline
preliminary conclusions
Breakthrough curvedata are consistent with CFT – higher ionic strength, more retention

Depth distribution data show deviation from CFT – not exponential with depth

Preliminary Conclusions
outline5
Research Goals – transport mechanisms / endospores

Background – transport mechanisms / endospores

Research Questions – preliminary

Methods – sporulation / saturated column tests / breakthrough curves / depth distribution data

Preliminary Results

Preliminary Conclusions

Future Work – B. cereus, other microbes

Outline
future work
Compare attachment/straining of spores versus vegetative cells

Column experiments

Micromodels and photographs

Wet AFM

Compare zeta potential

pH and more ionic strength effects

Different endospore bacteria, such as S. pasteurii, for biomineralization

Future Work
acknowledgements
Dr. Ron Crawford, Director, Environmental Biotechnology Institute, UI

Nick Benardini, PhD Candidate, MMBB

Elizabeth Scherling, MS, BAE

Dr. Markus Tuller, PSES

David Christian, Research Support Sci.

Acknowledgements
funding acknowledgements
Fulbright Scholars Program

USDA Hatch

UI URO Seed Grant Program

NSF REU program

Funding Acknowledgements
references
Bradford, S.A., J. Šimůnek, M. Bettahar, M. vanGenuchten, and S.R. Yates. 2003. Modeling colloid attachment, straining, and exclusion in saturated porous media. Environmental Science and Technology 37: 2242-2250.

Bradford, S.A., J. Šimůnek, M. Bettahar, M.Th. vanGenuchten, and S.R. Yates. 2006a. Significance of straining in colloid deposition: evidence and implications. Water Resources Research, 42:doi:10.1029/2005WR004791.

Bradford, S.A., J. Šimůnek, and S.L. Walker. 2006b. Transport and straining of E. coli 0157:H7 in saturated porous media. Water Resources Research (in review).

Li, X., TD. Scheibe, and W.P. Johnson. 2004. Apparent decreases in colloid deposition rate coefficient with distance of transport under unfavorable deposition conditions: a general phenomenon. Environ. Sci. Technol., 38: 5616-5625.

Redman, J.A., S.L. Walker, and M. Elimelech. 2004. Bacterial adhesion and transport in porous media: Role of the secondary energy minimum, Environ. Sci. Technol., 38:1777-1785.

Tufenkji, N., J.A. Redman, and M. Elimelech. 2003. Interpreting deposition patterns of microbial particles in laboratory-scale column experiments, Environ. Sci. Technol., 37: 616-623.

Tufenkji, N., Elimelech, M. 2005. Breakdown of colloid filtration theory: Role of the secondary energy minimum and surface charge heterogeneities. Langmuir 21: 841-852.

References
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