Undergraduate Honors Theses

Thesis Defended

Spring 2019

Document Type


Type of Thesis

Departmental Honors


Geological Sciences

First Advisor

Boswell Wing

Second Advisor

Christy McCain

Third Advisor

Brian Hynek


The distribution of sulfur isotopes in geologic materials reveals information about Earth history and biogeochemical processes, and largely attributed to microbial processes in the sediment, specifically by sulfate-reducing bacteria (SRB). The interplay between growth conditions, microbial growth, and isotopic fractionation have been investigated in vitro and modeled in silico, but only in homogenous, suspended cultures, (planktonic state), rather than in environments more representative of contemporary environments, where SRB are sediment-associated (particle-associated state). In this study, we investigate the growth characteristics and sulfur isotopic fractionation by the sulfate-reducing bacterium, Desulfovibrio vulgaris strain Hildenborough (DvH) in planktonic and particle-associated states. Assessment on the growth characteristics of DvH showed that the cell-specific sulfate-reduction rate (csSRR) in the planktonic state (PLK-PLK) = 228 fmol SO42-/cell/day, and the particle-associated component the particle-associated state (PA-PA) = 0.037 fmol SO42-/cell/day and 0.164 fmol SO42-/cell/day, based on Assumption 1 and 2, respectively, were different. As for the planktonic component of the particle-associated state (PLK-PA), this value is undetermined since we do not have actual value of sulfate consumed for each component in PA cultures. These differences between PLK-PLK and PA-PA cultures showed SRB metabolized differently as the environment changes. The results of our research indicate that current experiments designed to study the sulfate-reducing bacteria, especially DvH, are appropriate to be performed without considering the actual physical environment representative of the one in which SRB are actually reducing sulfate. Future research should be done on the same conditions, with different strains to see more variations in the growth characteristics.