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 A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...

surface will result in

membrane fouling Membrane fouling is a process whereby a solution or a particle is deposited on a membrane surface or in membrane pores in a processes such as in a membrane bioreactor, reverse osmosis, forward osmosis, membrane distillation, ultrafiltration, microf ...

, which can significantly reduce the efficiency of the treatment system using membrane filtration process in wastewater treatment plants.Alexis J. de Kerchove and Menachem Elimelech, Impact of Alginate Conditioning Film on Deposition Kinetics of Motile and Nonmotile Pseudomonas aeruginosa Strains, Applied and Environmental Microbiology, Aug. 2007, p. 5227–5234. The low adhesion of bacteria to soil is essential key for the success of in-situ

bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...

in groundwater treatment.Jeremy A. Redman, Sharon L. Walker and Menachem Elimelech, Bacterial adhesion and transport in porous media: role of the secondary energy minimum, Environ. Sci. Technol. 2004, 38, 1777-1785. However, the contamination of

pathogens In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

in drinking water could be linked to the transportation of microorganisms in groundwater and other water sources.Alexis J. de Kerchove, Paweł Weronski, and Menachem Elimelech, Adhesion of Nonmotile Pseudomonas aeruginosa on “Soft” Polyelectrolyte Layer in a Radial Stagnation Point Flow System: Measurements and Model Predictions, Langmuir 2007, 23, 12301-12308. 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 The DLVO theory (named after Boris Derjaguin and Lev Landau, Evert Verwey and Theodoor Overbeek) explains the aggregation of aqueous dispersions quantitatively and 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.Zachary A. Kuznar and Menachem Elimelech, Adhesion kinetics of Viable Cryptosporidium parvum Oocysts to Quartz Surfaces, Environ. Sci. Technol. 2004, 38, 6839-6845.Alexis J. de Kerchove and Menachem Elimelech, Calcium and Magnesium Cations Enhance the Adhesion of Motile and Nonmotile Pseudomonas aeruginosa on Alginate Films, Langmuir 2008, 24, 3392-3399.Sharon L. Walker, Jeremy A. Redman, and Menachem Elimelech, Role of Cell Surface Lipopolysaccharides in Escherichia coli K12 Adhesion and Transport, Langmuir 2004, 20, 7736-7746.

Prediction of bacterial deposition by classical DLVO theory

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

V_= \pi \varepsilon_0\varepsilon_ra_p\bigg\

Where ε₀is the vacuum permittivity, ε_r is the relative dielectric

permittivity In electromagnetism, the absolute permittivity, often simply called permittivity and denoted by the Greek letter ''ε'' (epsilon), is a measure of the electric polarizability of a dielectric. A material with high permittivity polarizes more in ...

of water, a_p is the equivalent spherical radius of the bacteria, κ is the inverse of

Debye length In plasmas and electrolytes, the Debye length \lambda_ (also called Debye radius), is a measure of a charge carrier's net electrostatic effect in a solution and how far its electrostatic effect persists. With each Debye length the charges are in ...

, h is the separation distance between the bacterium and the collector surface; ψ_p and ψ_c are the surface potentials of the bacterial cell and the collector surface.

Zeta potential Zeta potential is the electrical potential at the slipping plane. This plane is the interface which separates mobile fluid from fluid that remains attached to the surface. Zeta potential is a scientific term for electrokinetic potential in coll ...

at the surface of the bacteria and the collector were used instead of the surface potential. The retarded

Van der Waals interaction In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and the ...

potential was calculated using the expression from Gregory, 1981 .

V_=-\frac   \bigg 1+ \frac   \bigg

With A is

Hamaker constant The Hamaker constant ''A'' can be defined for a van der Waals (vdW) body–body interaction: :A=\pi^2C\rho_1\rho_2, where \rho_1 and \rho_2 are the number densities of the two interacting kinds of particles, and ''C'' is the London coefficient in ...

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

V_= \pi \varepsilon_0\varepsilon_ra_p\bigg\-\frac   \bigg 1+ \frac   \bigg

Current experimental result

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

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

surface. The deposition of bacteria on the surface was observed and estimated through an

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 membe ...

and recorded at regular intervals (10 s or 20 s) with a digital camera. Flow flied at the stagnation point flow https://web.archive.org/web/20090418224617/http://www.yale.edu/env/alexis_folder/alexis_research_2b.jpg Many bacterial stains have been used for the experiments. They are: *''

Cryptosporidium parvum ''Cryptosporidium parvum'' is one of several species that cause cryptosporidiosis, a parasitic disease of the mammalian intestinal tract. Primary symptoms of ''C. parvum'' infection are acute, watery, and nonbloody diarrhea. ''C. parvum'' in ...

'' oocysts, having 3.7 μm equivalent spherical diameter. *''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

'', having 1.7 μm equivalent spherical diameter. *''

Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic–facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. aerugi ...

'',Alexis J. de Kerchove and Menachem Elimelech, Bacterial swimming motility enhances cell deposition and surface coverage, Environ. Sci. Technol. 2008, 42, 4371–4377. 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

. 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 Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Its colour ...

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 In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules pe ...

of 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 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 the primary minimum due to the heterogeneity of the surface collector or bacterial surface. This fact was not covered in classical DLVO theory.
The presence of divalent electrolytes (Ca²⁺) can neutralize the charge surface of bacteria by the binding between Ca²⁺ and the functional group on the oocyst surface. This resulted in an observable bacterial deposition despite the very high electrostatic repulsive energy from the DLVO prediction. The motility of bacteria also has a significant effect on the bacterial adhesion. Nonmotile and motile bacteria showed different behavior in deposition experiments. At the same ionic strength, motile bacteria showed greater adhesion to the surface than nonmotile 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 interactions such as the steric impact of the presence of flagella on the cell environment and the strong hydrophobicity of the cell.

References

{{DEFAULTSORT:Bacterial Adhesion In Aquatic System Physical chemistry Colloidal chemistry