Bacterial Adhesion Process Research Articles

Mechanistic study of the pyrite–solution interface during the oxidative bacterial dissolution of pyrite (FeS 2) by using electrochemical techniques

The beneficiation of mineral substances through biotechnology forms the objective and basis of the present study of the pyrite bacterial leaching (bioleaching) process. The use of ferrous and sulfide oxidizing bacteria in bioleaching processes is a recent technique that has found industrial applications in copper, uranium, cobalt and gold extraction. To pursue its application and extend it to the upgrading of other ores, its technical and economic viability must be continually demonstrated and optimized through credible technological innovations in terms of scale-up and better control of biochemical activity. This is what this work aims to achieve by improving our knowledge of the intimate mechanisms governing the action of microorganisms during pyrite bacterial oxidative dissolution. The substrate used is formed of finely ground pyrite. The cultures (classical nutritive medium without ferrous iron) are batch-prepared and kept at a temperature of 35°C, agitated and aerated. The bacterial population used comprises three species: Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans. Specific equipment was developed and adapted for the study, including the design of special pyrite electrodes and the use of electrochemical methods for corrosion and interface investigations. These tools served to identify and monitor the electrochemical reactions occurring during bioleaching, both in solution and on the surface of the pyrite electrodes. The work consisted in relating the observations of the changes in certain key electrochemical parameters to the presence of Fe 2+ and Fe 3+ ions in solution. The electrochemical behavior of pyrite during bioleaching was studied by continuous measurement of certain electrochemical parameters in different situations, both natural and induced. The overall chemical process of pyrite bioleaching was determined and subdivided into distinct elementary stages. The key factors of each elementary stage and their respective roles were identified. This made it possible, for each stage, to differentiate the electrochemical reactions occurring in solution and at the interfaces, which, when combined, lead to overall reactions that advance the bioleaching of pyrite. The results completely contradict the theory of direct dissolution of the pyrite by the bacteria and indicate that (i) the ferric ion hence remains the only powerful oxidant of pyrite during its bacterial leaching, (ii) the only role of the bacteria is (re)generation of ferric ions in solution, and (iii) the process of bacterial adhesion or contact or attack no longer has the same meaning as was hitherto attributed.

Adhesion of Alcaligenes denitrificans to Polymeric Materials: The Effect of Divalent Cations

The influence of surface characteristics of the microorganisms and the substrate materials, such as electrokinetic potential and hydrophobicity, in the adhesion process was investigated in a previous work [1]. As neither surface charge nor hydrophobicity can fully explain the process of bacterial adhesion, the effect of divalent cations was experimentally studied. Adhesion assays were performed in sodium phosphate buffer saline (PBS) medium and in a medium with the same ionic strength containing Ca2 +, Mg2 + and Fe2 +. In the presence of divalent cations, contrary to what happened in PBS, adhesion was more favourable to the more negatively charged polymeric material. This points out a strong contribution of ion bridging in culture medium. In the absence of divalent cations, a higher hydrophobicity of the support is required in the process of adhesion.

Concise review of mechanisms of bacterial adhesion to biomaterial surfaces.

This article reviews the mechanisms of bacterial adhesion to biomaterial surfaces and the factors affecting the adhesion. The process of bacterial adhesion includes an initial physicochemical interaction phase (phase one) and a late molecular and cellular interaction phase (phase two), which is a complicated process affected by many factors, including the characteristics of the bacteria themselves, the target material surface, and the environmental factors, such as the presence of serum proteins or bactericidal substances.

Processes of bioadhesion on stainless steel surfaces and cleanability: A review with special reference to the food industry

Biofouling of equipment surfaces in the food industry is due initially to physico-chemical adhesion processes, and subsequently to the proliferation of microbes within an extracellular polymer matrix. Two physico-chemical theories can be applied to predict simple cases of bacterial adhesion. However, these models are limited in their applicability owing to the complexity of bacterial surfaces and the surrounding medium. Various factors that can affect the bacterial adhesion process have been listed, all directly linked to the solid substratum, the suspension liquid or the microorganism. For stainless steel surfaces, it is important to take into account the grade of steel, the type of finish, surface roughness, the cleaning procedures used and the age of the steel. Regarding the suspension fluid within which adhesion takes place, pH, ionic composition and the presence of macromolecules are important variables. In addition, the adhering microorganisms have extremely complex surfaces and many factors must be taken into account when conducting adhesion tests, such as the presence of cell appendages, the method of culture, the contact time between the microorganism and the surface, and exopolymer synthesis. Research on biofilms growing on stainless steel has confirmed results obtained with other materials, regarding resistance to disinfectants, the role of the extracellular matrix and the process by which the biofilm forms. However, it appears that the bactericidal activity of disinfectants on biofilms differs according to the type of surface on which they are growing. The main cleaners and disinfectants used in the food industry are alkaline and acid detergents, peracetic acid, quaternary ammonium chlorides and iodophors. The cleanability and disinfectability of stainless steel surfaces have been compared with those of other materials. According to the published research findings, stainless steel is comparable in its biological cleanability to glass, and significantly better than polymers, aluminium or copper. Moreover, microorganisms in a biofilm developing on a stainless steel surface can be killed with lower concentrations of disinfectant than those on polymer surfaces.

Bacterial adhesion onto apatite minerals —electrokinetic aspects

The role of the electrokinetic properties of Streptococcus sanguis and Actinomyces naeslundii in determining their adhesion to apatite minerals is examined. It is shown that bacterial adhesion onto a mineral surface takes place even when both the surfaces are negatively charged, and that the adhered layer is resistant to washing. Also, the mineral fines after exposure to bacteria exhibit zeta potential values which are in between those of the mineral and the bacteria, but lie closer to that of the mineral. In the absence of salivary proteins, the inorganic species present in saliva alter the magnitude of the surface charge but do not affect the bacterial adhesion process. Dissolved apatite mineral species (in supernatant solutions) are also shown to decrease the magnitude of the zeta potential of the bacteria. The observed adsorption of negatively charged bacteria onto negatively charged minerals suggests that electrostatic interactions are not the primary factors determining adhesion.

Monitoring microbiol adhesion and biofilm formation by attenuated total reflection/Fourier transform infrared spectroscopy

A major problem in accurately defining bacterial adhesion mechanisms and processes occurring in biofilms on surfaces is the lack of techniques that nondestructively provide on-line information about the microorganisms, their extracellular polymers, and metabolites. The attenuated total reflectance (ATR) technique of Fourier transform infrared spectroscopy (FT-IR) is ideally suited to monitor molecular interactions at the solution/internal reflection element (IRE) interface, and we report its application to biofilm research. Two methodologies were utilized to obtain the ATF/FT-IR spectra of living Caulobacter crescentus cells attached to germanium crystals. Initially, spectra of attached bacteria in high purity water produced molecular details of the attachment process without spectral interferences from components of the medium. A growth medium, utilized in the second method, allowed direct examination of the infrared absorption bands associated with the actively growing microorganisms on the surface of the IRE in the spectral region of 2000 to 1200 cm −1. Using the amide II band as a marker for biofilm biomass, the detection limit was determined to be approximately 5 × 10 5 cells·cm −2. These results proved that the ATR-FT/IR methodologies can be utilized to provide chemical information from bacteria and bacterial products located within approximately 1 μm of the surface without spectral interferences due to components of the medium.

The role of adhesion in the migration of bacteria along intrauterine contraceptive device polymer monofilaments

Abstract Using an in vitro model simulating the female genital tract, it was demonstrated that bacterial adhesion to intrauterine contraceptive device (IUD) tails is of importance in the transmission of bacteria along such surfaces. The process of bacterial adhesion to polymer monofilaments was subsequently investigated. Organisms were seen to adhere reversibly at first and then to produce polymeric material to achieve stronger, irreversible adhesion. Using scanning electron microscopy, the extent of bacterial adhesion was shown to be dependent upon several factors including the bacterial species and the microrugosity of the threads. A greater number of bacteria were found adhering to the monofilaments when there was no agitation of the washing or dehydrating solutions compared to the standard preparatory techniques.

Improved Method for Determining Bacterial Filtration Rates in Zooplankton

Filtration rates were determined for a natural population of zooplankton grazers (Bosmina longirostris [Müll.], Cyclops vicinus vicinus [Ulianine], Acanthodiaptomus denticornis [Wierz.], and Daphnia longispina [Müll.]) by using H-labeled bacteria as food for these organisms. There was a relationship between filtration rates of the major zooplankton grazers and the prevailing algal and bacterial composition in the lake water. Low filtration rates were obtained in the presence of colonial and filamentous cyanobacteria. The rapid process of bacterial adhesion to the external organs of grazers can result in an overestimation of filtration rates. By using the simple method presented here, filtration rates, with simultaneous correction for bacterial adhesion, can be quickly determined.

In vitro and in vivo inhibition of lectin mediated adhesion of Pseudomonas aeruginosa by receptor blocking carbohydrates.

In vitro and in vivo experiments with Balb/c mice and Pseudomonas aeruginosa ATCC 27853 supported our hypothesis that bacterial lectins play an important role in the organotropy of infectious diseases. In vitro and in vivo adhesion of P. aeruginosa was mediated by N-acetylneuraminic acid (NANA) receptors. Blocking of the binding sites (lectins) on the bacterial surfaces with competitive specific carbohydrates (NANA) completely prevented the bacterial adhesion process in vitro. In vivo the number of adherent organisms in various organs decreased dramatically in the presence of NANA, whereas non-related carbohydrates (e.g. D-galactose) just showed negligible effects. Additionally, the application of NANA-treated organisms protected the animals from septicemia and death. Therefore, blocking of bacterial lectin receptors with specific carbohydrates might be of clinical relevance to prevent bacterial attachment to organ cells.

Lectin mediated adhesion of Streptococcus pneumoniae and its specific inhibition in vitro and in vivo

According to our hypothesis, bacterial lectins play an important role in the organotropy of infectious diseases which is analogous to the metastasis of tumor cells. As a model for proving this, we investigated the specific lectin of Streptococcus pneumoniae, which has N-acetyl-D-glucosamine/D-galactose (GlcNAc-Gal) specificity. In vitro, after incubation with Streptococcus pneumoniae, cryotome sections of various organs from Balb/c-mice showed remarkable quantitative differences of bacterial adhesion to the organ cells. Whereas lungs and meninges were closely settled with bacteria, attachment to other organs (e. g. liver, spleen, brain) was lacking. In vitro lectin-blocking by GlcNAc completely prevented the adherence of Streptococcus pneumoniae to lungs and meninges. Other non-related carbohydrates (e. g. D-mannose, D-xylose) showed no effect. During in vivo experiments with Balb/c-mice, intratracheal application of Streptococcus pneumoniae led to a diffuse settlement of the lung. However, bacterial lectin-blocking with intratracheal GlcNAc administration completely inhibited adhesion to the organ cells of the lung. Therefore blocking of bacterial adhesins with competitive specific monosaccharides can completely prevent bacterial adhesion processes, a fact, which opens therapeutical aspects.

The nature of the adhesion of Corynebacterium rathayi to the cuticle of the infective larva of Anguina agrostis

The relationship between Corynebacterium rathayi and the infective second stage ‘dauer” larva (DL 2) of Anguina agrostis has been studied with particular regard to the nature and extent of bacterial adhesion to the nematode. Viability of the 1-year-old DL 2 was high, the number of dead specimens per gall only ranging from 5.1% to 8.3%. The DL 2 were exposed to C. rathayi either from cultures or galls and the numbers with and without adhering bacteria were counted. A total of 22,917 DL 2 from 15 galls were examined, the mean number of DL 2 per gall being 1,528. The mean percentage per gall of DL 2 with bacteria adhering was 42%. However there was much variability (from 0 to 98%). The significance of galls with DL 2 that did not succumb to bacterial adhesion is discussed. The sequence of events associated with the process of bacterial adhesion to the nematode cuticle was examined with the aid of the electron microscope. The process involves fusion of the glycocalyx with the bacterial capsule followed by thickening and, at times, displacement of the epicuticle together with changes in the main body of the cuticle. The possible nature of the process of adhesion is discussed.