Bacterial adhesion in aquatic system
Encyclopedia
Bacterial adhesion involves the attachment (or deposition) of bacteria on the surface (solid, gel layer, etc.). This interaction plays an important role in natural system as well as in environmental engineering.
The attachment of biomass on the membrane
surface will result to membrane fouling
, which can significantly reduce the efficiency of the treatment system using membrane filtration process in wastewater treatment plants . The low adhesion of bacteria to soil is essential key for the success of in-situ bioremediation
in groundwater treatment . However, the contamination of pathogens in drinking water could be linked to the transportation of microorganisms in groundwater and other water sources .
Controlling and preventing the adverse impact of the bacterial deposition on the aquatic environment need a deeply understanding about the mechanisms of this process. DLVO theory
has been used extensively to describe the deposition of bacteria in many current researches .
describes the interaction potential between charged surfaces. It is the sum of electrostatic double layer, which can be either attractive of repulsive, and attractive Van der Waals interactions of the charge surfaces . DLVO theory is applied widely in explaining the aggregation and deposition of colloidal and nano particles such as Fullerene C60 in aquatic system. Because bacteria and colloid particles both share the similarities in size and surface charge, the deposition of bacteria also can be describe by the DLVO theory . The prediction is based on sphere-plate interaction for one cell and the surface.
The electrostatic double layer interactions could be describes by the expression for the constant surface potential
Where ε0is the vacuum permittivity, εr is the relative dielectric permittivity
of water, ap is the equivalent spherical radius of the bacteria, κ is the inverse of Debye length
, h is the separation distance between the bacterium and the collector surface; ψp and ψc are the surface potentials of the bacterial cell and the collector surface. Zeta potential
at the surface of the bacteria and the collector were used instead of the surface potential.
The retarded Van der Waals
interaction potential was calculated using the expression from Gregory, 1981 .
With A is Hamaker constant
for bacteria-water-surface collector (quartz) = 6.5 x 10−21 J and λ is the characteristic wavelength of the dielectric and could be assumed 100 nm, a is the equivalent radius of the bacteria, h is the separation distance from the surface collector to the bacteria.
Thus, the total interaction between bacteria and charged surface can be expressed as follow
surface . The deposition of bacteria on the surface was observed and estimated through an inverted microscope
and recorded at regular intervals (10 s or 20 s) with a digital camera.
Flow flied at the stagnation point flow http://www.yale.edu/env/alexis_folder/alexis_research_2b.jpg
Many bacterial stains have been used for the experiments. They are:
All of the bacterial strains have negative zeta potential at experimental pH (5.5 and 5.8) and less become negative at higher ionic strength in both mono and divalent salt solutions .
Ultra pure quartz surface collectors have been used extensively due to their surface homogeneity, which is an important factor for applying DLVO theory
. The quartz surface originally has negative potential. However, the surface of the collectors was usually modified to have positive surface for the favorable deposition experiments .
In some experiments, the surface collector was coated with an alginate layer with negative charge for simulating the real conditioning film in natural system .
The presences of divalent electrolyte (Ca2+) can neutralize the charge surface of bacteria by the binding between Ca2+ and the functional group on the oocyst surface . This resulted to an observable bacterial deposition despite of the very high electrostatic repulsive energy from the DLVO prediction.
The motility of bacteria also has a significant effect on the bacterial adhesion. Monmotile and motile bacteria showed different behavior in deposition experiments . At the same ionic strength, motile bacteria showed greater adhesion to the surface than nomotile bacteria and motile bacteria can attach to the surface of the collector at high repulsive electrostatic force . It was suggested that the swimming energy of the cells could overcome the repulsive energy or they can adhere to regions of heterogeneity on the surface. The swimming capacity increase with the ionic strength and 100mM is the optimal concentration for the rotation of flagella .
Despite the electrostatic repulsion energy from DLVO calculation between the bacteria and surface collector, the deposition could occur due to other interaction such as the steric impact of the presence of flagella on the cell environment and the strong hydrophobicity of the cell .
The attachment of biomass on the membrane
Biological membrane
A biological membrane or biomembrane is an enclosing or separatingmembrane that acts as a selective barrier, within or around a cell. It consists of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content...
surface will result to membrane fouling
Membrane fouling
Membrane fouling is a process where solute or particles deposit onto a membrane surface or into membrane pores in a way that degrades the membrane's performance. It is a major obstacle to the widespread use of this technology. Membrane fouling can cause severe flux decline and affect the quality of...
, which can significantly reduce the efficiency of the treatment system using membrane filtration process in wastewater treatment plants . The low adhesion of bacteria to soil is essential key for the success of in-situ bioremediation
Bioremediation
Bioremediation is the use of microorganism metabolism to remove pollutants. Technologies can be generally classified as in situ or ex situ. In situ bioremediation involves treating the contaminated material at the site, while ex situ involves the removal of the contaminated material to be treated...
in groundwater treatment . However, the contamination of pathogens in drinking water could be linked to the transportation of microorganisms in groundwater and other water sources .
Controlling and preventing the adverse impact of the bacterial deposition on the aquatic environment need a deeply understanding about the mechanisms of this process. DLVO theory
DLVO theory
The DLVO theory is named after Derjaguin and Landau, Verwey and Overbeek.The theory describes the force between charged surfaces interacting through a liquid medium....
has been used extensively to describe the deposition of bacteria in many current researches .
Prediction of bacterial deposition by classical DLVO theory
DLVO theoryDLVO theory
The DLVO theory is named after Derjaguin and Landau, Verwey and Overbeek.The theory describes the force between charged surfaces interacting through a liquid medium....
describes the interaction potential between charged surfaces. It is the sum of electrostatic double layer, which can be either attractive of repulsive, and attractive Van der Waals interactions of the charge surfaces . DLVO theory is applied widely in explaining the aggregation and deposition of colloidal and nano particles such as Fullerene C60 in aquatic system. Because bacteria and colloid particles both share the similarities in size and surface charge, the deposition of bacteria also can be describe by the DLVO theory . The prediction is based on sphere-plate interaction for one cell and the surface.
The electrostatic double layer interactions could be describes by the expression for the constant surface potential
Where ε0is the vacuum permittivity, εr is the relative dielectric permittivity
Permittivity
In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how...
of water, ap is the equivalent spherical radius of the bacteria, κ is the inverse of Debye length
Debye length
In plasma physics, the Debye length , named after the Dutch physicist and physical chemist Peter Debye, is the scale over which mobile charge carriers screen out electric fields in plasmas and other conductors. In other words, the Debye length is the distance over which significant charge...
, h is the separation distance between the bacterium and the collector surface; ψp and ψc are the surface potentials of the bacterial cell and the collector surface. Zeta potential
Zeta potential
Zeta potential is a scientific term for electrokinetic potential in colloidal systems. In the colloidal chemistry literature, it is usually denoted using the Greek letter zeta, hence ζ-potential...
at the surface of the bacteria and the collector were used instead of the surface potential.
The retarded Van der Waals
Van der Waals
-People:* Fransje van der Waals , Dutch medical physician* Johannes Diderik van der Waals , Dutch physicist-Physics:* the Van der Waals force, named after the physicist* the Van der Waals equation, named after the physicist...
interaction potential was calculated using the expression from Gregory, 1981 .
With A is Hamaker constant
Hamaker Constant
The Hamaker constant A can be defined for a Van der Waals body-body interaction:A=\pi^2\times C \times \rho_1 \times \rho_2where \rho_1 and \rho_2 are the number of atoms per unit volume in two interacting bodies and C is the coefficient in the particle-particle pair interaction.The Hamaker...
for bacteria-water-surface collector (quartz) = 6.5 x 10−21 J and λ is the characteristic wavelength of the dielectric and could be assumed 100 nm, a is the equivalent radius of the bacteria, h is the separation distance from the surface collector to the bacteria.
Thus, the total interaction between bacteria and charged surface can be expressed as follow
Experimental method
Radial stagnant point flow (RSPF) system has currently been used for the experiment of bacterial adhesion with the verification of DLVO theory. It is a well-characterized experimental system and is useful for visualizing the deposition of individual bacteria on the uniform charge, flat quartzQuartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
surface . The deposition of bacteria on the surface was observed and estimated through an inverted microscope
Inverted microscope
An inverted microscope is a microscope with its light source and condenser on the top, above the stage pointing down, while the objectives and turret are below the stage pointing up. It was invented in 1850 by J. Lawrence Smith, a faculty member of Tulane University...
and recorded at regular intervals (10 s or 20 s) with a digital camera.
Flow flied at the stagnation point flow http://www.yale.edu/env/alexis_folder/alexis_research_2b.jpg
Many bacterial stains have been used for the experiments. They are:
- Cryptosporidium parvumCryptosporidium parvumCryptosporidium parvum is one of several protozoal species that cause cryptosporidiosis, a parasitic disease of the mammalian intestinal tract....
oocysts , having 3.7 μm equivalent spherical diameter. - Escherichia coliEscherichia coliEscherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
, having 1.7 μm equivalent spherical diameter. - Pseudomonas aeruginosaPseudomonas aeruginosaPseudomonas aeruginosa is a common bacterium that can cause disease in animals, including humans. It is found in soil, water, skin flora, and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also in hypoxic atmospheres, and has, thus, colonized many...
, having 1.24 μm equivalent spherical diameter.
All of the bacterial strains have negative zeta potential at experimental pH (5.5 and 5.8) and less become negative at higher ionic strength in both mono and divalent salt solutions .
Ultra pure quartz surface collectors have been used extensively due to their surface homogeneity, which is an important factor for applying DLVO theory
DLVO theory
The DLVO theory is named after Derjaguin and Landau, Verwey and Overbeek.The theory describes the force between charged surfaces interacting through a liquid medium....
. The quartz surface originally has negative potential. However, the surface of the collectors was usually modified to have positive surface for the favorable deposition experiments .
In some experiments, the surface collector was coated with an alginate layer with negative charge for simulating the real conditioning film in natural system .
Result
It was concluded that bacterial deposition mainly occurred in a secondary energy minimum by using DLVO theory . DLVO calculation predicted an energy barrier 140kT at 31.6 mM ionic strength to over 2000kT at 1mM ionic strength. This data was not in agreement with the experimental data, which showed the increasing deposition with increasing ionic strength . Therefore, the deposit could occur at secondary minimum having the energy from 0.09kT to 8.1kT at 1mM and 31.6 mM ionic strength, respectively . The conclusion was further proven by the partial release of deposited bacteria when the ionic strength decreased. Because the amount of released bacteria was less than 100%, it was suggested that bacteria could deposit at primary minimum due to the heterogeneity of the surface collector or bacterial surface. This fact was not covered in classical DLVO theory .The presences of divalent electrolyte (Ca2+) can neutralize the charge surface of bacteria by the binding between Ca2+ and the functional group on the oocyst surface . This resulted to an observable bacterial deposition despite of the very high electrostatic repulsive energy from the DLVO prediction.
The motility of bacteria also has a significant effect on the bacterial adhesion. Monmotile and motile bacteria showed different behavior in deposition experiments . At the same ionic strength, motile bacteria showed greater adhesion to the surface than nomotile bacteria and motile bacteria can attach to the surface of the collector at high repulsive electrostatic force . It was suggested that the swimming energy of the cells could overcome the repulsive energy or they can adhere to regions of heterogeneity on the surface. The swimming capacity increase with the ionic strength and 100mM is the optimal concentration for the rotation of flagella .
Despite the electrostatic repulsion energy from DLVO calculation between the bacteria and surface collector, the deposition could occur due to other interaction such as the steric impact of the presence of flagella on the cell environment and the strong hydrophobicity of the cell .