טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentTardi-Ovadia Rinat
SubjectMicrobial Characterization of Bacillus mucilaginosus
Involved in Silicate Degradation and its Impact
on a Sol-Gel Matrix
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Robert Armon
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

The main goal of the present study was to characterize microbially and biochemically the silicate bacterium B. mucilaginosus which was first discovered by Aleksandrov in 1950, and still the systematic position of this strain remains unclear. Due to its ability to decompose silicate-containing minerals, sol-gel matrices were used as an artificial simulation for ferric containing minerals in nature. It was found that the growth kinetics of B. mucilaginosus in nitrogen source containing medium and in the absence of nitrogen source showed a diauxic growth curves. Effect of salinity degree on B. mucilaginosus growth showed that the optimal concentration for bacterial growth in the presence and absence of nitrogen in medium was 0% and 0.4% respectively. The negative stain of the microbial capsule showed a change in morphology as a function of the media composition; in the absence of nitrogen cells intensively produced a larger capsule with increase in viscosity and elasticity of the colonies and a better cell attachment to solid medium. It was found that the preferred environment for bacterial growth is solid medium (reversible sporulation in solid medium as opposed to irreversible in liquid medium). In contradiction to the literature B. mucilaginosus (sub strain 1480D) can use amino acids as carbon source. No resistance to antibiotics was found except for colistin 10 μg. It was also found that

 B. mucilaginosus is biochemically similar to B. circulans. Due to the formation of cracking in monolith sol gel on exposure to water vapor and solvent it was difficult to study the interactions between bacteria and sol gel matrices and to match a suitable quantitative and qualitative method. In order to solve this problem, thin films of sol gel by spin-coating of the pyrex dishes with the desirable sol-gel mixture were selected. The sol gel films (doped with 10% Ferric citrate versus undoped) functioned as a solid medium, an external liquid medium provided the initial requirements for growth.  The films that were found to be the most suitable for interaction study were hydrophobic sol-gel (no cracking occurred). We can’t conclude from the interaction study about different interaction with doped and undoped sol-gel films. It is possible that in order to have a significant conclusion about cell interaction, a longer period of time is required; it is also possible that the structural differences between sol-gel matrix and silicate minerals influenced the efficacy of the mechanisms responsible for biological weathering.