Microbial response to oxidising biocides

[摘要] ENGLISH ABSTRACT:Biofouling of water systems is a problem extensively experienced in industry. Althoughthis subject is the focus of many studies, the ability of microorganisms to surviveexposure to biocides is still poorly understood. This study aimed to assess the biocidaleffect of ozone on planktonic cells and biofilm communities, to evaluate different ozonegeneration techniques, and to follow population shifts within the biofilm community.Specific objectives included determining the effect of different ozone concentrations, theeffect of different exposure times, and an assessment of microbial responses afterexposure to sub-lethal ozone concentrations. Typically, 300 ml of an ovemight bacterialculture 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 purgedinto 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 cellnumbers. In contrast, when exposed to the two lower 03 concentrations, there was littlechange in the viable cell numbers even after prolonged exposure (30- and 60 min.). Toevaluate biofilms, ozone was bubbled into the irrigation that was pumped throughreplicate flow cell channels. Response to ozone exposure was evaluated after staining thebiofilms with the Baclight Viability probe, observation with fluorescence microscopy,and image analysis. The higher ozone concentration (18-20% wt 03) more effectivelydisrupted the biofilm structure of denser biofilms than the lower concentration, especiallyafter 90 min. exposure. When compared to the controls, the 90 min. exposure resulted ina notable reduction in viable cells from 69% to 38% and a corresponding increase in nonviablecells from 29% to 62%. The lower concentration ozone (3.5% wt 03) waseffective against the less dense, thinner biofilms evaluated, but not effective against thethicker biofilm. An analysis of the differences between continuous culture biofilms andbatch culture biofilms showed that the biofilms in the batch system were less rigid. Toevaluate microbial response to biocides, techniques such as Biolog whole-communitymetabolic profiles and terminal restriction fragment length polymorphisms (T-RFLP)were used. Biolog analysis of planktonic cells revealed changes following exposure tosub-lethal biocide concentrations, however carbon utilisation profiles resembled that ofthe controls after 24-48 hours. For biofilm communities, no carbon utilization differences could be detected under these conditions. There was, however differences inT-RFLP patterns between treated and untreated biofilm communities.

[发布机构] Stellenbosch University