| Summary: | Thesis (MSc)--Stellenbosch University, 2003. === ENGLISH ABSTRACT: Microorganisms play an important role in the stability and maintenance of the
ecosystem and in the condition of the soil. However, in their natural environment,
microorganisms often experience changing and hostile conditions. They therefore
need to be able to adapt physiologically and modify their micro-environment. Biofilm
formation is one mechanism to establish favorable micro-environments. The
extracellular polymeric substances (EPS) that are typically associated with biofilm
formation may also have an impact on soil structure. The aim of this project was to
evaluate the potential of microbial manipulation on EPS production and the possible
impact thereof on soil structure in order to improve water retention.
Specific objectives of this study included the screening of natural environments for
EPS-producers, developing techniques to observe EPS production and accumulation
in the pores between soil particles, measuring the effect of EPS production on soil
water hydraulic gradient, as well as determining the fate and impact of EPS-producers
when introduced to naturally-occurring soil microbial communities. Several
environmental samples have been screened for EPS-producing microorganisms. Soil
columns were then inoculated with these EPS-producers and the passage of 20 mlaliquots
water through the columns measured at 3 or 4-day intervals. Microbes
isolated from soil, through their EPS production capability proved to retain water
more effectively than was the case for water-borne EPS-forming microbes. This
phenomenon was further studied using flow cells, filled with soil and inoculated with
the EPS-producers isolated from either soil or water. Fluorescence microscopy
showed that the soil microbes produced EPS that clogged pores between sand
particles more effectively. This clogging resulted in lowering the soil water hydraulic
gradient. To evaluate the effect of EPS-producers on existing soil microbial
communities, cell counts, Biolog™whole-community carbon utilization studies and
T-RFLP (terminal-restriction fragment length polymorphism) analyses were
performed. Shifts in the soil microbial community could not be readily seen by
observing microbial numbers and T-RFLP-analysis, but was noticeable in carbon
utilization patterns. === AFRIKAANSE OPSOMMING: Mikroorganismes speel 'n belangrike rol in die stabiliteit en instandhouding van die
ekosisteem en in die kondisie van die grond. In hul natuurlike omgewing ervaar
mikroorganismes dikwels veranderlike en ongunstige toestande. Mikroorganismes
het dus nodig om hulself fisiologies aan te pas en verander hul mikro-omgewing
daarvolgens. Biofilm-vorming is een meganisme om gunstige mikro-omgewings te
skep. Die ekstrasellulêre polimeriese produkte (EPP) wat tydens biofilm-vorming
gevorm word, mag ook 'n impak hê op die grondstruktuur. Die doel van hierdie
projek was om die potensiaal van mikrobiese manipulasie op EPP-vorming te
evalueer asook die moontlike impak daarvan op grondstruktuur wat sodoende
waterretensie kon bevorder.
Die spesifieke doelwitte van hierdie studie het ingesluit die isolasie van EPPproduseerders
vanuit natuurlike omgewings, die ontwikkeling van verskeie tegnieke
waarvolgens EPP-produksie en die akkumulasie daarvan in die porieë tussen
gronddeeltjies bestudeer kon word, die effek van EPP-produksie op hidrouliese
gradiënt van grondwater en om die lot en impak wat EPP-produseerders op natuurlike
grondmikrobiese populasies te bepaal. Verskeie grond- en watermonsters was getoets
vir die voorkoms van EPP-produserende mikroorganismes. Grondkolomme is
geïnokuleer met EPP-produseerders en die vloei van 20 ml-volumes water deur die
kolomme is gemeet met 3 of 4-dag intervalle. Grond-geïsoleerde mikrobes het beter
waterretensie tot gevolg gehad as water- geïsoleerde mikrobes. Hierdie verskynsel
was verder bestudeer deur die gebruik van vloeiselle, gevul met grond of sand en
geïnokuleer met EPP-produseerders geïsoleer vanuit grond of water. Fluoressensie
mikroskopie het aangetoon dat grondmikrobes EPP produseer wat die porieë tussen
gronddeeltjies meer effektief verstop. Dié verstopping het gelei tot die verlaging van
die grondwater se hidrouliese gradiënt wat bepaal is deur die gebruik van die
konstante-vlak bepalingsmetode. Om die effek van EPP-produseerders op bestaande
mikrobiese populasies te bepaal, is seltellings, Biolog™ heel-gemeenskap koolstofverbruik
studies en T-RFLP (terminale-restriksie fragment-lengte polimorfisme)
analises uitgevoer. Veranderinge in die mikrobiese populasie kon nie geredelik bloot
deur die bepaling van mikrobiese getalle en T-RFLP-analise waargeneem word nie,
maar wel met die koolstofverbruikspatrone.
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