PhD, University of Cincinnati, 2010, Engineering and Applied Science: Environmental Engineering

Identification and quantification of phylogenetically defined bacterial populations in the environment are often performed using molecular tools targeting 16S rRNA. Fluorescence in situ hybridization has been used to monitor the expression and processing of pre16S rRNA. To expand this approach, reverse transcription of total RNA using primer S-D-Bact-0338-a-A-18 was optimized and detected by denaturing high performance liquid chromatography (DHPLC). The relative abundance of the precursor (pre) compared to the abundance of mature 16S rRNA was shown to be a sensitive indicator of the physiologic state of pure cultures. The assay was also used to differentiate among pre 16S rRNA levels with mixed pure cultures, as well as to examine the response of a mixed activated sludge culture exposed to fresh growth medium and the antibiotic chloramphenicol. It was further optimized to study soil bacterial population. Several soil enrichment media and incubation times were tested to increase the pre16S rRNA levels. The results demonstrated that this was a sensitive and reliable method with a detection limit of 10 ng of single-stranded DNA or 0.75 grams of soil samples. Signature bacterial population including Actinobacteria and Bacillus by pre16S rRNA libraries was identified while Proteobatceria was absent under pyrene and Cr (VI) contamination. Comparison of pre16S rRNA and mature 16S rRNA clone libraries showed ribosome genesis was a sensitive indicator for pyrene and chromium contamination. Pre16S rRNA levels were significantly decreased compared with mature 16S rRNA levels in LTU soil samples with varying degrees of contaminate. These results demonstrated that active bacterial species can be assessed by pre16S rRNA levels. A negative correlation between active bacterial diversity and contamination levels has also been found. This method was the first demonstration of monitor the diversity of the metabolically – active fraction of the soil bacterial community in soil systems. (open full item for complete abstract)

Committee: Daniel Oerther PhD (Committee Chair); Paul Bishop PhD (Committee Member); Katherine Banks PHD (Committee Member); Jodi Shann PhD (Committee Member); Brian Kinkle PhD (Committee Member) Subjects: Environmental Engineering

Doctor of Philosophy, The Ohio State University, 2008, Food Agricultural and Biological Engineering

In microbial fuel cells (MFCs), bacteria generate electricity by mediating the oxidation of organic compounds and transferring the resulting electrons to an anode electrode. The objectives of this study were to: 1) test the possibility of generating electricity in an MFC with rumen microorganisms as biocatalysts and cellulose as the electron donor, 2) analyze the composition of bacterial communities enriched in cellulose-fed MFCs, 3) determine the effect of various external resistances on power output and coulombic efficiency of cellulose-fed MFCs, 4) evaluate bacterial diversity and cellulose metabolism under different circuit loads, 5) assess the influence of methane formation on the performance of cellulose-fed MFCs under long-term operation, and 6) characterize the diversity of methanogens in cellulose-fed MFCs. The results demonstrate that electricity can be generated from cellulose by exploiting rumen microorganisms as biocatalysts. Cloning and analysis of 16S rRNA gene sequences indicated that the most predominant bacteria in the anode-attached consortia were related to Clostridium spp., while Comamonas spp. abounded in the suspended consortia. Results suggest that oxidation of metabolites with the anode as an electron sink was a rate limiting step in the conversion of cellulose to electricity in MFCs. This study also shows that the size of external resistance significantly affects the bacterial diversity and power output of MFCs. A maximum power density of 66 mW/m2 was achieved by the 20-ohm MFCs, while MFCs with 249, 480 and1000 ohms external resistances produced 57.5, 53 and 47 mW/m2, respectively. Thus the external resistance may be a useful tool to control microbial communities and consequently enhance performance of MFCs. Furthermore, this study demonstrates that methanogenesis competes with electricity generation at the early stages of MFC operation but operating conditions suppress methanogenic activity over time. The suppression of methanoge (open full item for complete abstract)

Committee: Ann Christy PhD (Advisor); Burk Dehority PhD (Committee Member); Olli Tuovinen PhD (Committee Member); Alfred Soboyejo PhD (Committee Member); Zhongtang Yu PhD (Committee Member) Subjects: Agricultural Engineering; Chemical Engineering; Energy; Environmental Engineering; Environmental Science; Microbiology