Thesis (MSc)--University of Stellenbosch, 2003. / 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. / AFRIKAANSE OPSOMMING: Biobevuiling van watersisteme is 'n probleem wat algemeen in industriëe ervaar word.
Alhoewel hierdie onderwerp die fokus van vele studies is, word die vermoëns van
mikroorganismes om blootstelling aan biosiede te weerstaan steeds swak verstaan. Die
doel van hierdie studie was om die biosidiese effek van osoon op planktoniese selle en
biofilm gemeenskappe waar te neem, om die verskillende osoon generasie tegnieke te
evalueer, asook om verskuiwings in die samestelling van die biofilm gemeenskap waar te
neem. Spesifieke doelwitte sluit in die bepaling van die effek van verskillende osoon
konsentrasies, die blootstellingtye, en 'n waarneming van mikrobiese reaksies na
blootstelling aan sub-dodings osoon konsentrasies. Drie honderd ml van 'n oornag
bakteriese kultuur was aan osoon, wat deur anodiese oksidasie (0.3% wt of 18% - 20%
wt) of geluidlose elektriese ontlading (3.5% wt), gegenereer is, blootgestel. Tye van
blootstelling was 5-, 7-, 10-, of 15 min., onderskeidelik. Bepaling van selgetalle na :2:10
min. blootstelling aan 18 - 20% wt osoon, het 'n betekenisvolle verlaging in die getal
lewensvatbare mikrobeselle getoon. In teenstelling hiermee, het blootstelling aan twee
laer osoon konsentrasies min verskil in die lewensvatbare selgetalle, selfs na verlengde
blootstellingstye (30- en 60 min.), getoon. Om biofilms te evalueer is osoon in die
medium geborrel wat deur replikaat vloeisel kanale gepomp is. Na osoon blootstelling,
was die vloeisel onderwerp aan beeld analise deur gebruik te maak van die Baclight
lewensvatbare peiler en fluoressensie mikroskopie. Die hoër osoon konsentrasie (18 -
20% wt 03) het die struktuur van dikker biofilms meer effektiefuiteengeskeur as die laer
konsentrasie, veral na 90 min. blootstelling. In vergelyking met die onderskeie kontroles,
het die getalle van lewensvatbare selle na 90 min. blootstelling drasties verlaag vanaf
69% tot 38% en 'n ooreenstemmende toename in die nie-lewensvatbare selgetalle vanaf
29% tot 62%. Die laer osoon konsentrasie (3.5% wt 03) was meer effektief teenoor die
minder digte en dunner biofilms wat ge-evalueer was, maar nie so effektief teenoor die
dikker biofilms nie. 'n Analise van die verskille tussen kontinue-kultuur biofilms en lotkultuur
biofilms het getoon dat die lot-kultuur biofilms minder rigied is. Vir die
evaluering van mikrobiese reaksies na biosied blootstelling, is tegnieke soos Biolog
gemeenskap metaboliese profiele en eind-restriksie-fragment-lengte polimorfisme (TRFLP)
gebruik. Biolog analise van planktoniese selle het verskille getoon na blootstelling aan sub-dodelike biosied konsentrasies. Koolstof benutting het wel na 24 -
48 ure met dit van die kontrole ooreengestem. Vir biofilm gemeenskappe was daar geen
noemenswaardige verskille in koolstof benutting nie. Daar was wel verskille in T-RFLP
patrone tussen die onbehandelde en biosied-behandelde biofilm gemeenskappe.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53499 |
| Date | 03 1900 |
| Creators | Jackson, Vanessa A. (Vanessa Angela) |
| Contributors | Wolfaardt, G. M., Bessarabov, D. G., Stellenbosch University. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xi, 74 p. : ill. |
| Rights | Stellenbosch University |
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