טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentFarber Yair
SubjectDegradation of Ormosils and Silicate Minerals by the
Silicate Bacterium: Bacillus mucilaginosus
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Robert Armon
Full Thesis textFull thesis text - English Version


Abstract

The major mineral mass of the earth’s crust are silicates (minerals that contain one or more central silicone atoms) that are subject to continuous abiotic and biotic degradation. Previous studies showed that certain bacteria are involved and directly promote degradation of silicates in order to release caged elements (e.g. phosphorus, iron, magnesium, etc.). These elements are necessary to support a variety of biological processes required by bacterial cells. Biotic degradation of silicate is based on several mechanisms in which different components such as organic acids, ligands, siderophores and EPS (extracellular polysaccharides) are involved. Bacillus mucilaginosus bacterium, genotypically similar to other strains from the genus Bacillus, is a soil bacterium capable to degrade silicate minerals and also to produce abundant EPS.

The primary goal of this research was to find out if Bacillus mucilaginosus is able to biodegrade ormosils materials (organically modified silicates made by sol-gel technique). Ceramic or glassy materials obtained by sol-gel process have an important advantage from the biological aspect. These materials can be produced at room temperature while typical industrial ceramics and glasses are manufactured at elevated temperatures (> 1000ºC). Throughout this study, it could be concluded that apparent ormosil films biodegradation is feasible by Bacillus mucilaginosus and that its mechanism is related to iron stress (lack of free soluble iron). Iron stress also accelerates biodegradation of various natural silicate mineral chips, as revealed by this study results. The method used to demonstrate ormosil degradation is unique. The method was developed by entrapping iron into ormosil thin film matrices through sol-gel process and iron release tracked by use of confocal laser scanning microscopy (CLSM). Local surface degradation (similar to etching) can lead in the future to nano-drilling techniques of organically modified silicate surfaces.

Another objective of the present research was to identify silicate degrading enzymes involved in the biodegradation mechanism. Although this task was unsuccessful, it was found that Bacillus mucilaginosus is capable to utilize chitin, probably by owing the enzyme chitinase. Such chitinase expression is interesting because other researchers assumed that enzymes capable of breaking down mineral structure would be analogous to chitinase.

Finally, bacterial silicate precipitation, the opposite phenomenon to silicate degradation, was also demonstrated. Bacillus mucilaginosus was used as a model and a new fluorescent method was developed based on Rhodamine 123 dye coupled with epifluorescent microscopy. Utilizing this fluorescent method it was possible to reveal clay precipitation on bacterial cell surface.