I Saadi

Publications of I Saadi

• Effect of flagella expression on adhesion of Achromobacter piechaudii to chalk surfaces.

  Authors: A Nejidat, I Saadi, Z Ronen

  Journal of applied microbiology. 01/2009; 105(6):2009-14.

  AIMS: To examine flagella role and cell motility in adhesion of Achromobacter piechaudii to chalk. METHODS AND RESULTS: Transmission electron microscopy revealed that stationary cells have thickerAIMS: To examine flagella role and cell motility in adhesion of Achromobacter piechaudii to chalk. METHODS AND RESULTS: Transmission electron microscopy revealed that stationary cells have thicker and longer flagella than logarithmic cells. SDS-PAGE analysis showed that flagellin was more abundant in stationary cells than logarithmic ones. Sonication or inhibition of flagellin synthesis caused a 30% reduction in adhesion to chalk. Preincubation of chalk with flagella extracts reduced adhesion, by 50%. Three motility mutants were isolated. Mutants 94 and 153 were nonmotile, expressed normal levels of flagellin, have regular flagella and exhibited reduced adhesion. Mutant 208 expressed low levels of flagellin, no flagella and a spherical cell shape but with normal adhesion capacity. CONCLUSIONS: Multiple cell surface factors affect the adhesion efficiency to chalk. Flagella per se through physical interaction and through cell motility contribute to the adhesion process. The adhesion behaviour of mutant 208 suggests that cell shape can compensate for flagellar removal and motility. SIGNIFICANCE AND IMPACT OF THE STUDY: Physiological status affects bacterial cell surface properties and hence adhesion efficiency to chalk. This interaction is essential to sustain biodegradation activities and thus, remediation of contaminated chalk aquifers.

• Degradation of 2,4,6-tribromophenol by bacterial cells attached to chalk collected from a contaminated aquifer.

  Authors: A Nejidat, I Saadi, Z Ronen

  Journal of applied microbiology. 02/2004; 96(4):844-52.

  AIM: To investigate the factors governing the adhesion and activity of the 2,4,6-tribromophenol (TBP) degrading bacterium Achromobacter piechaudii TBPZ-N61 on chalk from a contaminated aquifer.AIM: To investigate the factors governing the adhesion and activity of the 2,4,6-tribromophenol (TBP) degrading bacterium Achromobacter piechaudii TBPZ-N61 on chalk from a contaminated aquifer. METHODS AND RESULTS: Adhesion kinetics of TBPZ-N61 to grey and white chalk from a polluted fractured chalk aquifer was tested in a batch system. Both grey and white chalk contain ca 80% CaCO3, while grey chalk contains more organic matter (2.4%) than the white chalk (0.3%) and also contains Dolmite and Clinoptilolite. Adhesion of the bacterial cells to the chalk particles (<0.2 mm) occurred rapidly (96% of the cells within 15 min). Langmuir-fitted adhesion isotherms suggest that cells in the stationary phase, which are more hydrophobic, adhere to both grey and white chalk more efficiently than cells in the logarithmic growth phase. Increasing the pH (from 6.7 to 8.1) caused a significant reduction in cell adhesion to the chalk. Activity of attached cells was evaluated in both batch and column experiments. Logarithmic cells adhering to white and grey chalk were more active in TBP degradation than cells in suspension. In column experiments, significant TBP degradation was retained up to 30 days after a single injection of TBPZ cells. Thereafter, activity was fully recovered by amendment of yeast extract. Chalk surfaces that were incubated in situ in contaminated groundwater for 20 days still allowed the adhesion and activity of TBPZ cells. CONCLUSIONS: Taken together, our results show that bacteria adhere efficiently to specific sites on the chalk surfaces, and that sustained bacterial activity of the attached cells can be achieved by adding a carbon source such as yeast extract which also overcome toxic constituents that may occur in some chalk types. SIGNIFICANCE AND IMPACT OF THE STUDY: Bioremediation of TBP-contaminated chalk aquifers is made possible by the injection of bacterial cultures.

• Sol-gel applications in environmental biotechnology.

  Authors: R Armon, C Dosoretz, J Starosvetsky, F Orshansky, I Saadi

  Journal of biotechnology. 12/1996; 51(3):279-85.

  Sol gel process was applied for three different applications in environmental biotechnology: (1) thin, fluorescein diacetate-doped sol-gel film made possible epifluorescent microscopic examination ofSol gel process was applied for three different applications in environmental biotechnology: (1) thin, fluorescein diacetate-doped sol-gel film made possible epifluorescent microscopic examination of adsorbed Escherichia coli CN13 cells without additional staining: (2) Thiobacillus thiooxidans cell-free extract entrapped into sol-gel matrix displayed oxidative activity on H2S in liquid medium; and (3) two media (E. coli (EC) and sulfate-reducing bacteria (SRB)) were doped into sol-gel and used to enumerate environmental samples for E. coli and sulfate-reducing bacteria, by the most probable number (MPN) method. The comparison of the modified method with the standard enumeration method revealed very good correlation. The sol-gel MPN method is sensitive, saves times, and the substrate can be prepared and stored long-term at room temperature (up to 1 year).