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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 attachment versus straining – 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 attachment versus straining

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


Strained versus mechanically filtered
Strained versus Mechanically Filtered attachment versus straining

dp/d50 .005


Background

Clean-bed Filtration Theory attachment versus straining

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 – attachment versus strainingJohnson 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.) attachment versus straining

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 attachment versus straining

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 attachment versus straining

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 attachment versus strainingBacillus species

http://www.textbookofbacteriology.net


Differences between endospores and vegetative cells in bacillus species1
Differences between endospores and vegetative cells in attachment versus strainingBacillus species


In terms of physical passage through the pore space
In terms of physical passage through the pore space… attachment versus straining

…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 attachment versus straining – 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, attachment versus strainingexhibiting 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 attachment versus straining – 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 attachment versus straining

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

Dry bulk density:

rb = 1.65 g/cm3

Porosity:

n = 0.34

dp/d50 .0017


Method constant head sand column
Method: Constant Head, Sand Column attachment versus straining


Breakthrough c c o of b cereus spores as a function of ionic strength
Breakthrough (C/C attachment versus strainingo) of B. cereus spores as a function of ionic strength

Artificial groundwater

DDI


Column dissection
Column Dissection attachment versus straining


Column dissection1
Column Dissection attachment versus straining

  • 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 attachment versus straining

“Strained” spores in AGW run


Depth distribution data1
Depth Distribution Data attachment versus straining

“Attached” spores in AGW run


Depth distribution data2
Depth Distribution Data attachment versus straining

Strained and attached fractions combined


Outline4

Research Goals attachment versus straining – 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 curve attachment versus strainingdata 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 attachment versus straining – 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 Institute, UI

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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