| Summary: | 碩士 === 國立中興大學 === 環境工程學系 === 93 === The role of biofilms in the deterioration of metals and their alloys in both freah water and marine environments has been of considerable interest to industry worldwide. Problems associated with microbially influenced corrosion（MIC）due to the formation of biofilms are widespread and have serious economic and safety implications. Most MIC takes place in the presence of microbial consortion in which many different physiological types of bacteria interact in complex ways within the structure of biofilms. The aim of this study, is to investigate the iron-oxidizing bacteria biofilm formation on the wall of cooling water system by in situ flourescent hybridization（FISH）and confocal laser scanning microscopy（CLSM）.
Leptothrix sp.（TPH-2）, Denitrifying Fe-oxidizing Bacteria（TPH-7）, Nocardia farcinica（TPH-13-3）were inoculated for biofilm formation. The biofilms were stained with calcofluor white for extracellular polymeric substances（EPS）and to observe by CLSM. Batch experiments indicated that the biofilm depth increased with the EPS concentration. Weight loss was measured in batch experiments. The experimental results show that the formation of biofilm can decrease the corrosion rate of mild steel because the formation of a biofilm was crucial, as oxygen depletion under the biofilm was responsible for the corrosion protection. The community structure of biofilm on the wall of cooling water system was determined by in situ hybridization using fluorescently labelled 16S rRNA-targeted oligonucleotide probes LEP445-Cy3, which is specific for the iron-oxidizing bacteria（TPH-2 and TPH-7）. In these experiments the iron-oxidizing bacteria accounted on average for 51.4% of the total CFU. Phylogenetic analysis of a bacterial 16S rDNA clone library from the biofilm on the wall of cooling water system showed that major phylogenetic three groups are Actinobacteria, Alphaproteobacteria, and Betaproteobacteria. Clone 1, 10, 15, and 21 belonged to Mycobacterium sp.（similarity 98%）；Clone 12 Sphingomonas subterranean（similarity 100%）； Clone 13 Denitrifying Fe-oxidizing bacteria（similarity 98%）.
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