Masters Theses

Date of Award

12-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Microbiology

Major Professor

David C. White

Committee Members

Gary Sayler, David Bemis, Dewey Bunting

Abstract

This research intended to study the role of the Sulfate Reducing Bacteria (SRB) in the corrosion of two different metal surfaces, 1010 mild steel (MS) and 304 stainless steel (SS) surfaces, and their influence on the microbial community that developed within the biofilm and corrosion products attached to the metal surfaces. A total of twelve metal surfaces of each type were exposed for a period of 56 days at three different aquatic sites, Douglas Dam Lake and two of its tributaries. The scrapped biofilm and corrosion products collected from the top side metal surface were evaluated by acridine orange direct counts, most probable number and 16s rRNA oligonucleotide probes, targeting the eubacteria and SRB community. The non-scrapped sides were suspended in a modified Bligh and Dyer solution from which the organic phase was collected and further processed. Of the organic phase, only the phospholipid fatty acid fraction was further separated and each component identified for a total of 54 samples. The metal sample corrosion rates were evaluated by the weight loss method and pit density. The inflow waters were evaluated in the laboratory by polarization resistance. The biological results recovered by the above techniques indicated no significant differences for the total biomass, lipid biosynthesis and tran/cis ratio. However, the molecular and biochemical techniques indicated that SRB favored the colonization of the MS surfaces versus the SS surfaces under oxic conditions. The phospholipid ester-linked fatty acid fractions (PELFA) recovered from both surfaces exposed at three aquatic sites indicated that the microbial communities formed on the SS metal surfaces contained significantly higher concentration of polyunsaturated fatty acids (PUFA) than the MS metal surfaces. However, the monoenoic and iso and anteiso branched saturated fatty acids were recovered in significantly higher concentration on the MS surfaces than on the SS surfaces. Statistical analysis of the PELFA fraction separated the communities formed on the metals exposed at the three sites based on the influence exerted by the presence of biomarkers characteristics of eukaryotes and eubacteria. The MS surfaces exposed to the sites experienced significantly higher corrosion rates under oxic conditions than the SS surfaces. Electrochemical evaluation of the MS surfaces did not result in significant corrosion rates between the collected water. However, the SS surfaces did not show significant differences in pit density regardless of the exposed site. Overall, these in situ results indicate that microbial community structure is influenced by the type of metal substratum, while the MS corrosion rates are influenced by the presence of bacteria (i,e., SRB).

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