Ardiyan Harimawan

Bacteria attachment to surfaces – AFM force spectroscopy and physicochemical analyses

Understanding bacterial adhesion to surfaces requires knowledge of the forces that govern bacterial-surface interactions. Biofilm formation on stainless steel 316 (SS316) by three bacterial species was investigated by examining surface force interaction between the cells and metal surface using atomic force microscopy (AFM). Bacterial-metal adhesion force was quantified at different surface delay time from 0 to 60s using AFM tip coated with three different bacterial species: Gram-negative Massilia timonae and Pseudomonas aeruginosa, and Gram-positive Bacillus subtilis. The results revealed that bacterial adhesion forces on SS316 surface by Gram-negative bacteria is higher (8.53±1.40 nN and 7.88±0.94 nN) when compared to Gram-positive bacteria (1.44±0.21 nN). Physicochemical analysis on bacterial surface properties also revealed that M. timonae and P. aeruginosa showed higher hydrophobicity and surface charges than B. subtilis along with the capability of producing extracellular polymeric substances (EPS). The higher hydrophobicity, surface charges, and greater propensity to form EPS by M. timonae and P. aeruginosa led to high adhesive force on the metal surface.

Adhesion of B. subtilis spores and vegetative cells onto stainless steel--DLVO theories and AFM spectroscopy.

Interactions between the bacterium Bacillus subtilis (either as vegetative cells or as spores) and stainless steel 316 (SS-316) surfaces were quantified using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and extended DLVO (xDLVO) approach in conjunction with live force spectroscopy using an Atomic Force Microscope (AFM). The xDLVO approach accounts for acid-base (polar) interactions that are not considered in the classical DLVO theory. AFM results revealed that spores manifested stronger attraction interactions to stainless steel compared to their vegetative cells counterparts due to lower energy barrier as predicted by both the theoretical approaches as well as the higher hydrophobicity on the spore surfaces. Both DLVO and xDLVO theories predict that vegetative cells manifest weaker attachment on the surfaces compared to spores. Results of AFM force measurement corroborate these findings; spores recorded significantly higher adhesion force (2.92±0.4 nN) compared to vegetative cells (0.65±0.2 nN). The adhesion of spores presents greater challenges in biofilm control owing to its stronger attachment and persistence when the spores are formed under adverse environmental conditions.

Investigation of extracellular polymeric substances (EPS) properties of P. aeruginosa and B. subtilis and their role in bacterial adhesion

Extracellular polymeric substances (EPS) matrix in biofilm poses important functions such as a diffusion barrier to antimicrobial agents so that biofilm cells are more difficult to completely eliminate. Therefore, biofilm cells exhibit enhanced resilience unlike planktonic cells, and are more difficult to completely eliminate. In order to obtain a comprehensive understanding of bacterial adhesion to surfaces, knowledge of the composition and conformational properties of EPS produced during growth and biofilm formation is required, since their adhesive and conformational properties remain poorly understood at molecular level. Present study has provided further insights into identifying compositional and conformational properties of EPS produced by planktonic and biofilm cells of B. subtilis and P. aeruginosa. Various spectroscopy analyses showed that EPS produced by the two different species were chemically dissimilar. More proteinaceous compounds were present in EPS from B. subtilis, while EPS from P. aeruginosa were characterized by greater carbohydrate components. However, relative proportions of polysaccharides and/or proteins constituents varied with the growth mode of the bacteria. AFM was then used to probe the adhesive nature of EPS produced by the bacteria by using Single Molecule Force Spectroscopy (SMFS). Comparison of the two bacterial species indicated that the presence of polysaccharides promoted the adhesion strength of the EPS while proteins had lesser adherence effects. Comparison of the two growth modes for the same bacterial strain also indicated that greater EPS production and enhanced cellular adhesion are associated with biofilm growth.

Effect of MgO to Fatty Acid Molar Ratio on the Production of Magnesium Salt of Fatty Acid from Palm Fatty Acid Distillates (PFAD) for Food Additives

Palm Fatty Acid Distillate (PFAD), a by-product of CPO industry, contains approx. 82%-wt of free fatty acids, which can be utilized as raw material for Magnesium Salts of Fatty Acids (Mg-PFAD). The objectives of the experiment were to produce Mg-PFAD salts through saponification-fusion reaction of PFAD at low temperature and ambient pressure and investigate the effect of MgO to fatty acid molar ratio on reaction conversion and yield. Next, washing Mg-PFAD salts with ethanol was able to facilitate the recovery of vitamin E (tocopherol and tocotrienol) from PFAD. Composition of Mg-PFAD were determined by AAS and GC analysis. Based on the data, yield of Mg-PFAD was increased by the increased of MgO to PFAD molar ratio. Mg-content of the product was within the standard according to FAO reference (4-5%-wt). Reaction was completed within 5-7 min after the addition of H2O (as catalyst).Fresh Water and salt are the most important necessities in human life. The scarcity and the difficulty to get fresh water and salt became main problems that emerge in many places such as for people who live in coastal areas and small islands where their main source of water and salt is the sea water. In order to obtain fresh water, people needs to process seawater into fresh water and salt. The term of fresh water used here means water which is free from dirt, bacteria, and other substances that are harmful for human health. To process the sea water into fresh water and salt has been done by distillation technic. The distillation technic requires heat to evaporate seawater before condensed and produce clean water. Heat for distillation process can be derived from a variety of sources, one of them is solar energy. The purpose of this study is to compare between a flat plate with one slope cover and two slope cover to produce fresh water and salt. The distilled water was tested in laboratory to determine whether the quality of water and salt after distillation meets the consumable requirements. The working principle of the distillator is by filled the basin with sea water and then heated with solar power. The water will be evaporated and due to the different of temperature between inside and out side of cover so that the condensation accurs at inside of cover. The condensed water will flow through surface of glass cover and then the distilled freshwater gathered in storage. The process will continue until water runs out and creates salt crystals in the basin. Solar distillation testing by using one slope cover with a size of 140 cm x 220 cm produce 3,482 ml / day of clean water and 322 grams of salt / 4 days at average intensity of 697 W/m2. While solar distillation by using two-slope cover with size of 80 cm x 50 cm produce 1,551 ml clean water/day and 199.9 grams of salt / 4 days.

Influence of incubation temperature on biofilm formation and corrosion of carbon steel by Serratia marcescens

Microbial induced corrosion (MIC) or biocorrosion is one type of corrosion, directly or indirectly influenced by microbial activities, by forming biofilm and adhering on the metal surface. When forming biofilm, the microorganisms can produce extracellular products which influence the cathodic and anodic reactions on metal surfaces. This will result in electrochemical changes in the interface between the biofilm and the metal surface, leading to corrosion and deterioration of the metal. MIC might be caused by various types of microorganism which leads to different corrosion mechanism and reaction kinetics. Furthermore, this process will also be influenced by various environmental conditions, such as pH and temperature. This research is aimed to determine the effect of incubation temperature on corrosion of carbon steel caused by Serratia marcescens in a mixture solution of synthetic seawater with Luria Bertani medium with a ratio of 4:1. The incubation was performed for 19 days with incubation temperature ...

Equilibrium and kinetic modelling of cadmium (II) biosorption by Dried Biomass Aphanothece sp. from aqueous phase

The Biosorption of cadmium (II) ions on dried biomass of Aphanothece sp.which previously grown in a photobioreactor system with atmospheric carbon dioxide fed input, was studied in a batch system with respect to initial pH, biomass concentration, contact time, and temperature. The biomass exhibited the highest cadmium (II) uptake capacity at 30oC, initial pH of 8.0±0.2 in 60 minute and initial cadmium (II) ion concentration of 7.76 mg/L. Maximum biosorption capacities were 16.47 mg/g, 54.95 mg/g and 119.05 mg/g at range of initial cadmium (II) 0.96–3.63 mg/L, 1.99–8.10 mg/L and 6.48–54.38 mg/L, respectively. Uptake kinetics follows the pseudo-second order model while equilibrium is best described by Langmuir isotherm model. Isotherms have been used to determine thermodynamic parameter process (free energy change, enthalpy change and entropy change). FTIR analysis of microalgae biomass revealed the presence of amino acids, carboxyl, hydroxyl, sulfhydryl and carbonyl groups, which are responsible for biosorption of metal ions. During repeated sorption/desorption cycles, the ratio of Cd (II) desorption to biosorption decreased from 81% (at first cycle) to only 27% (at the third cycle). Nevertheless, due to its higher biosorption capability than other adsorbent, Aphanothece sp appears to be a good biosorbent for removing metal Cd (II) ions from aqueous phase.