Browsing by Author "Jackson, Vanessa A. (Vanessa Angela)"

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    Microbial response to oxidising biocides
    (Stellenbosch : Stellenbosch University, 2003-03) Jackson, Vanessa A. (Vanessa Angela); Wolfaardt, Gideon M.; Bessarabov, D. G.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Biofouling of water systems is a problem extensively experienced in industry. Although this subject is the focus of many studies, the ability of microorganisms to survive exposure to biocides is still poorly understood. This study aimed to assess the biocidal effect of ozone on planktonic cells and biofilm communities, to evaluate different ozone generation techniques, and to follow population shifts within the biofilm community. Specific objectives included determining the effect of different ozone concentrations, the effect of different exposure times, and an assessment of microbial responses after exposure to sub-lethal ozone concentrations. Typically, 300 ml of an ovemight bacterial culture was exposed to ozone that was generated by anodic oxidation (0.3% wt or 18- 20% wt, respectively) or silent electric discharge (3.5% wt 03). The ozone was purged into the culture for 5-, 7-, 10- and 15 min., respectively. Enumeration of cells following ~10 min. exposure to 18-20% wt ozone showed a significant reduction in viable cell numbers. In contrast, when exposed to the two lower 03 concentrations, there was little change in the viable cell numbers even after prolonged exposure (30- and 60 min.). To evaluate biofilms, ozone was bubbled into the irrigation that was pumped through replicate flow cell channels. Response to ozone exposure was evaluated after staining the biofilms with the Baclight Viability probe, observation with fluorescence microscopy, and image analysis. The higher ozone concentration (18-20% wt 03) more effectively disrupted the biofilm structure of denser biofilms than the lower concentration, especially after 90 min. exposure. When compared to the controls, the 90 min. exposure resulted in a notable reduction in viable cells from 69% to 38% and a corresponding increase in nonviable cells from 29% to 62%. The lower concentration ozone (3.5% wt 03) was effective against the less dense, thinner biofilms evaluated, but not effective against the thicker biofilm. An analysis of the differences between continuous culture biofilms and batch culture biofilms showed that the biofilms in the batch system were less rigid. To evaluate microbial response to biocides, techniques such as Biolog whole-community metabolic profiles and terminal restriction fragment length polymorphisms (T-RFLP) were used. Biolog analysis of planktonic cells revealed changes following exposure to sub-lethal biocide concentrations, however carbon utilisation profiles resembled that of the controls after 24-48 hours. For biofilm communities, no carbon utilization differences could be detected under these conditions. There was, however differences in T-RFLP patterns between treated and untreated biofilm communities.