The physiological role of EPS depends on the ecological niches and the natural environment in which microorganisms have been isolated. In this chapter, data on EPS production and the effect of EPS on corrosion of steel produced by Lactobacillus sp. are presented and discussed. Lactobacillus plantarum Ts was obtained from the Collection of Department of Biology, Shumen University. It was tested for its ability to produce exopolysaccharides when cultivated in a medium containing 10% sucrose. It could be underlined that 10% sucrose in the medium stimulated the process of protection of corrosion. Also, the biofilm in vitro in the combined cultivation of Staphylococcus aureus and the Lactobacillus plantarum Ts probiotic bacterium on the surface of different metal materials for fixed dental prostheses was investigated [unpublished results]. The structure of layer over steel plates was analyzed by scanning electron microscopy (SEM) JSM 5510. In our opinion, more detailed research is needed to be done in the future, and the possibilities should be analyzed for the creation of a thin biofilm from a probiotic bacterium or an exopolysaccharide this bacterium has produced, which would protect the implants against the growth of a pathogenic biofilm.
- microbial biofilms
According to Reyes et al. reported one of the most complex topics within bacterial anatomy and physiology is that of exopolysaccharides (EPSs). These molecules have various structures and functions and also provide different types of advantages to their producing microorganisms, including surface variability, resistance to innate and acquired immunity mechanisms, the ability to adhere to different surface and cell types, and resistance to antibiotic activity .
Exopolysaccharides (EPSs) are a term first used by Sutherland  “to describe high-molecular-weight carbohydrate polymers produced by marine bacteria.” EPSs can be found as in capsular material or as dispersed slime in the surrounding environment with no obvious association to any one particular cell .
Many microorganisms produce exopolysaccharides as a strategy for growing, adhering to solid surfaces, and surviving adverse conditions.
Considerable progress has been made in discovering and developing new microbial EPSs that possess novel industrial significance .
Bacterial EPSs by Reyes  are “believed to play an important role in the environment by promoting survival strategies such as bacterial attachment to surfaces and nutrient trapping, which facilitate processes of biofilm formation and development. These microbial biofilms have been implicated in corrosion of metals, bacterial attachment to prosthetic devices, fouling of heat exchange surfaces, toxicant immobilization, and fouling of ship hulls.” Corrosion of metals is one of the most serious and challenging problems faced by industries worldwide. Biofilms composed of a secreted polymeric substance containing microbial population have shown to inhibit corrosion in metals [5, 6]. Fang et al. and Chongdar et al. reported that “kinetics of corrosion processes of metals, mineral, and polymeric materials can be influenced by biofilms. Products of their metabolic activities including enzymes, exopolymers, organic and inorganic acids, as well as volatile compounds such as ammonia or hydrogen sulfide can affect cathodic and/or anodic reactions, thus altering electrochemistry at the biofilm/metal interface. This phenomenon is often referred to as ‘biocorrosion’ or ‘microbially influenced corrosion’. Microbiologically, influenced corrosion has been documented for metals exposed to sea water, fresh water, demineralized water, process chemicals, food stuffs, soils, aircraft fuels, human plasma, and sewage” [7, 8].
In this paper, data on EPS production and the effect of EPS on corrosion of steel produced by
2. Materials and methods
3. Results and discussion
Corrosion process causes great economic losses in various industries, shipbuilding, jewelry, archaeological monuments, railway, water channels, and all countries of the world. For handling this problem are normally applied different physical and chemical methods, but they often prove toxic. A perspective in this regard can be the application example of exopolysaccharides produced by the so-called good bacteria–probiotics. The presence of EPS associated with bacterial cells can be recognized by the formation of colonies in mucous solid medium. Therefore, the presence of a translucent or creamy material involving a mucoid colony is indicative of EPS production potential. When cultivated in a medium with high content of saccharides such as 10% sucrose solutions, strain
When they develop microbial biofilm, the organisms are much more resistant and treating them is much more difficult. For investigation of the microbial biofilm, using different methods had been proposed, but in our work, we used the method by using the staining congo red.
“Qualitative assessment of biofilm formation is the microorganisms are grown in agar with 5% sucrose and congo red” . Positive results are indicated by black colonies with a dry crystalline consistency. When cultivated in a medium with high content of saccharides such as 10% sucrose solutions, with 5% congo red, strain
In the presence of high concentrations of sugars (as in our case 10% sucrose), lactic acid bacteria synthesize extracellular exopolysaccharide (Figure 1A), which is displayed as mucoid colonies on agar medium. By adding the staining congo red, the exopolysaccharides produced by lactic acid bacteria are displayed in black (Figure 1B).
Our studies also show that the use of sugar supplementation (sucrose was normally used though similar results were obtained using 5% glucose) is essential for the detection of slime production using the congo red medium. “The congo red method is rapid, sensitive, and reproducible and has the advantage that colonies remain viable on the medium” .
Similar experiments have also been demonstrated by other authors [14, 15]. Homopolysaccharides produced by generally recognized as safe (GRAS) lactic acid bacteria are often synthesized by a single extracellular sucrose enzyme, using only sucrose as substrate . The structure of the layer over the steel plates was analyzed by scanning electron microscopy. The results from this procedure are shown in Figure 2.
Microscope techniques provide information about the morphology of microbial cells and colonies, their distribution on the surface, and the nature of corrosion products (crystalline or amorphous). They can also reveal the type of attack (e.g., pitting or uniform corrosion) by visualizing changes in microstructure and surface features after removal of the covering and corrosion products (Figure 2).
The pictures in Figure 2B show that there is a biofilm formed on the steel surface which is an indicator of the good adhesive capacity of
Microorganisms can interact with the metal surfaces differently. Most often they form biofilms on contacting surfaces, but can also react with various metals to form complex compounds. For this reason, we think that different techniques have to be used to clarify the corrosion process influenced by microorganisms. When the corrosion process starts, the surface of metals is deposited large quantities of ferrousions, which are very harmful for all steel materials. If lactic acid bacteria can immobilized in the microbial biofilm, these ferrousions that could explain why exopolysaccharides produced by these bacteria protect the metal surface from corrosion. Similar to our van Geel-Schutten “biofilm of a polysaccharide-producing culture”, delta marina was found to act as a strong corrosion inhibitor with almost complete passivation of mild steel, reducing the corrosion rate by 95% .
In our previous studies [9–11, 17–20], it was shown that the presence of high concentration of lactose (5 to 15%), high concentration of sucrose 4%, mixed sucrose 4 and 2% maltose, mixed sucrose 5 and 5% maltose, mixed 5% sucrose and 5% fructose, and mixed 5% sucrose and 5% fructose, high concentration of lactose, sucrose and fructose (10%) the strains
In recent years, the development of new technologies in medicine and dentistry leads to the production of various medical materials and prostheses.On these materials, however, when introduced in the human body, are deposited large number of microorganisms. According to van Geel-Schuten, ‘biofilms are a major cause of systemic infections (e.g., nosocomial infections) in humans . It is known that the human body consists about 3–4 kg microorganisms–mostly useful–but there are also the so- called ‘pathogens’. In surgery, the probability of contamination with microorganisms and especially with
The search for biomaterials that are able to provide for the optimal resistance to the infection can be based only on the deep understanding of the interactions between bacteria and biomaterials’ .
The adhesion in the combined cultivation of
The results obtained from the SEM analysis of the adhesion ability of the tested microorganisms on the different metals are shown in Figure 3. When a combined culture is used on the surface of the steel plates, only the probiotic bacterium adheres.
The results obtained from the SEM analysis of the adhesion ability of the tested microorganisms on the different dental prostheses are shown in Figure 4.
The ability of microorganisms to adhere to the surface of various surfaces is determined by various physicochemical interaction of forces, such as–Lifshitz –van der Waals forces, Brownian motion forces, and electrostatic forces. These results are discussed by other authors [21, 22]. On the other hand, the microbial adhesion may be due to the presence of specific active group sin the microbial exopolysaccharides.
After adhesion to biomaterials, most microorganisms start secreting slime and embed themselves in a slime layer, the glycocalix, which is an important virulence factor for BCI and which explains the extraordinary prevalence of slime producing
According to “the updated paradigm for biocompatibility”, as redrawn by Williams, a biomaterial should perform its designed function eliciting the most appropriate tissue response .
The various metabolic ways and the various end metabolic products of the two types of bacteria:
In our opinion, more detailed research is needed to be done in the future and the possibilities should be analyzed for the creation of a thin biofilm from a probiotic bacterium or an exopolysaccharide this bacterium has produced, which would protect the implants against the growth of a pathogenic biofilm.
On the other hand, conduction of more detailed studies on the application of exopolysaccharides and the development of nanolayers as potential inhibitors of the corrosion process are needed.
Support from the Research Fund of the Konstantin Preslavsky University of Shumen (Project No. RD-08-66/02. 02. 2016, Department of Biology).
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