Bacterial Cell Surface Tension Attachment and Implications for Bioremediation - Article Example

Bacterial Cell Surface Tension Attachment and Implications for Bioremediation ABSTRACT The bacterial cell surface attachment of two bacterial species, Bacillus subtilis and Pseudomonas putida, was assayed by means of bacterial aggregation in different solutions. These included full strength liquid broth with and without 10% v/v glucose, ½ strength nutrient broth and PYE also with and without 10% vv glucose. All the suspensions were phosphate buffered in seeking to establish bacterial affinity to hexadecane and polystyrene surfaces. The bacterial microbes showed relatively higher affinity to hexadecane materials compared to their affinity to polystyrene surfaces that were tested. There was no significant relationship between the culturing of the bacteria with their attachment to the different material that was being tested. The environments under which the bacterial species were cultured had significant influence on the level of attachment of different bacterial species to various surfaces. These results present essential in seeking to establish the variance of species adherence to hexadecane. INTRODUCTION The attachment of microbial cells to solids and hydrophobic liquids is an important prerequisite in the degradation of chemicals that are recalcitrant because of extremely low solubility. Bacterial adsorption at interfaces is a physical and chemical process that, for the majority of micro-organisms, does not involve the expenditure of metabolic energy. The attachment process involves non-specific interactions between the cell surface, the solid or hydrophobic liquid and the bulk liquid phase(Abbasnezhad et al. 2011). Many factors influence bacterial attachment at solid/liquid and liquid/liquid interfaces. Environmental factors such as pH, temperature and the presence of cat-ions, anions and organic molecules in the bulk liquid phase all directly affect the attachment process, as does the nature of the solid or the hydrophobic liquid(Mceldowney & Fletcher 1986). Microbial factors are equally important in determining the extent of bacterial attachment to surfaces, and the characteristics of the cell surface have a considerable impact on attachment. Microbial cell surfaces are complex and consist of a variety of macromolecules, which vary with the microbial type. The macro-molecular composition of bacterial cell surfaces, also, differs with growth substrate, growth phase and growth rate. Such variations alter the charge and hydrophobic characteristics of bacterial surfaces(Rosenberg et al. 1980). Differences in cell surface characteristics between microbial type and growth condition contribute considerably to variations in attachment at solid or liquid interfaces. One way of characterising microbial surfaces is to measure the relative hydrophobicity and hydropholicity of the cells(Tsuneda et al. 2003). This can be achieved through a variety of techniques one of which is by measuring the adherence of bacteria in suspension to a hydrophobic liquid (the MATH test). The higher the attachment to the hydrophobic liquid, the more hydrophobic the cells(Krepsky et al. 2003). The research aims to achieve the following: Estimate the relative hydrophobicity of different microbial cells; Examine the variability of hydrophobicity for selected micro-organisms with growth condition; Determine the effect of cell hydrophobicity on attachment to a hydrophobic solid surface. MATERIAL AND METHODS Materials The experiment consisted of two species of bacterial organisms which were cultured under different conditions. The species used for the experiments were Bacillus subtilis and Pseudomonas putida. The species used for the experiments were cultured under the following six conditions. A sample of each species was cultured under each of the listed conditions; hence a total of 12 samples were available for the experiment full strength nutrient broth full strength nutrient broth plus 10% v/v glucose ½ strength nutrient broth ½ strength nutrient broth plus 10% v/v glucose PYE (0.5% w/v bacteriological peptone, 0.3% w/v yeast extract, pH 7) PYE plus 10% v/v glucose Method This research is based on a laboratory experiment performed on two different bacterial species cultured under different conditions in the laboratory. The research included two experiments that were measuring different variables for all the samples provided for the experiment. Each sample was subjected to both of these experiments to test the effects of growth conditions on the characteristics of the different bacteria. The first experiment tested the bacterial attachment to polystyrene surface using all the bacterial strains cultured in the laboratory. The second experiment tested for hydrophobicity of the bacterial cells through measuring the percentage of adherence to hexadecane. Greater adherence to hexadecane indicated higher hydrophobicity of the bacterial cells. RESULTS Evidently, the experiment focussed on 12 groups of microbes cultured in different media. The first experiment sought to find out the attachment of bacteria cultured under different conditions to polystyrene surfaces. The graph below represents average results of the attachment of the bacterial species to polystyrene surfaces as tested by the experiment. Figure 1 attachment of bacteria to polystyrene surfaces Figure 2 standard deviation of attachment of bacteria to polystyrene surfaces The highest recorded average value of attachment is at 3.41, with 0 being the lowest recorded reading. Bacillus subtilis Bacteria species cultured under the PYE with glucose environment has the highest level of attachment to polystyrene surfaces, while there is no bacterial attachment for the same species cultured under full strength with glucose. The Pseudomonas putida species presents relatively high values of attachment to the polystyrene surfaces. The highest value in this species is 57.46 with the lowest value being 1.79. These values were recorded for species cultured in ½ strength nutrient broth and ½ strength nutrient broths with glucose, respectively. Bacterial attachment to polystyrene surfaces is generally high within the Pseudomonas putida species compared to Bacillus subtilis. The percentage of adherence to hexadecane among the Bacillus species of bacteria has significant differences through the differently cultured bacteria. The second experiment included testing the adherence of bacteria species to hexadecane solutions which would be utilised in establishing hydrophobicity. The adherence is expressed as a percentage. The highest recorded value is 33.88, with the lowest value being 2.25. These values have been recorded for cultures growing under ½ full strength with glucose and PYE, respectively. Adherence to hexadecane among the Pseudomonas putida species is recorded at 44.50 and 1.29 for the highest and lowest values. These values have been recorded for bacteria cultured under full strength with glucose and ½ strength with glucose, respectively. The figure below shows the average values of percentage of adherence to hexadecane as recorded from the experiment. Figure 3. Adherence of bacteria to hexadecane Figure 4 standard deviation of adherence to hexadecane DISCUSSION Evidently, as the results reveal, there is lack of correlation between the hydrophobicity levels exhibited by the two species assayed in the experiment. With no evidence suggesting the existence of a relationship between the species, it becomes critical to highlight the contribution of the genetic structure exhibited by cells (van Merode et al. 2006). This serves as a valid explanation for the salient difference evident in the hydrophobicity levels observed in the experiment. Pseudomonas genus has a relatively higher hydrophobicity compared to the Bacillus genus. Pseudomonas genus shows much resistance and increased adherence to hexadecane hence higher hydrophobicity. Higher hydrophobicity of pseudomonas results in their higher attachment to polystyrene surfaces as recorded from the experiment. Different species exhibit varying surface features that determine the potential of the organism to interact with the environment and other microorganisms. This augments the findings that the assayed species exhibited varied levels of hydrophobicity. As many experts in this field have highlighted, bacterial growth conditions exert salient effects on the hydrophobicity traits of the bacterial species used in the experiment. This is evident from the adherence results indicated above. The level of nutrient concentration is critical in determining the level of hydrophobicity. There is evidence suggesting that nutrients affect the electrophoretic mobility of microbial species. Nutrient concentration within the bacterial cell has been established as affecting the hydrophobicity of cells because of the variance in nutrient concentration in the cell and outside the cell. Cells exhibit high hydrophobicity in seeking to control water concentration within the cell. As evidenced by the experiential results, glucose has a significant influence on the hydrophobicity and the attachment of cells to polystyrene surfaces. Cells cultured under glucose enhanced environments recorded lower attachment to polystyrene materials in both species, than the organisms cultured in environments without glucose. The presence of glucose within the cells significantly reduces the attachment of bacteria to polystyrene surfaces. This reduced affinity to polystyrene surfaces is associated with the presence of acidity upon the surface of the cell. The acidity or basic properties of the cell membranes have a fundamental role in the attachment of bacterial cells to different surfaces (Zeraik & Nitschke 2012). The presence of glucose within the cells changes the properties of the cell membranes, resulting in a relative change in the attachments, under the influence of glucose. Evidently, there is lack of a salient interrelationship between the general attachments exhibited and the growth conditions for the microbes. Genetic composition serves as a primary determinant and not the food substrates within their cells. The environmental effects on the attachment would result from the changing properties of the cell membranes, which have a fundamental role in attachment of the cells to different surfaces (Palmer et al. 2007). A cell capacity to become attached to a surface depends on the physical properties of the cell membrane. The environment defining the culturing of the microbes accounts cultured result in the cell membranes having different properties, hence different attachment characteristics, based on the culturing environment. There is no significant relationship in the attachment to polystyrene surfaces with the surface hydrophobicity. Higher attachment of pseudomonas genus is attributed to the hydrophobic characteristics of the bacterial cell membranes. Research done using Bacillus cereus indicated existence of such relationship on stainless steel (Penga et al. 2001). The adhesion characteristics of the materials directly influence these findings. The internal condition of the cell membrane affects the movement of water molecules through the membrane, consequently affecting the hydrophobicity of the various bacterial cells. The environment under which the strains have been cultured affects the properties of the cell membrane through the different pH of the food substrates provided. This leads to the observed differences in the hydrophobicity of same strains, cultured under different environments. Many materials have been tested for hydrophobicity characteristics against bacterial microorganisms when seeking to further research in bioremediation (Mceldowney 2000; Basson et al. 2008). Understanding the characteristics of the materials remains essential in establishing the best materials for manufacturing waste holding material within the food microbiology sector(Kubotaa et al. 2008). Understanding microbe adherence to different materials becomes fundamental in enhancing contamination that could result from microbes being held at waste containers. Utilisation of stainless steel material containers when undertaking bioremediation would be discouraged when compared to plastic, polystyrene materials (Piepera & Reinekeb 2000). The plastic materials exhibit lower levels of adhesion with the bacterial microorganisms. References Abbasnezhad, H., Gray, M. & Foght, J.M., 2011. Influence of adhesion on aerobic biodegradation and bioremediation of liquid hydrocarbons. Applied microbiology and biotechnology, 92(4), pp.653–675. 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FEMS Microbiology Letters, 223(2), pp.287–292. Zeraik, A.E. & Nitschke, M., 2012. Influence of growth media and temperature on bacterial adhesion to polystyrene surfaces. Brazilian Archives of Biology and Technology, 55(4), pp.569–576.  Read More