This document summarizes a study on testing two bodies of water, McKellar Lake and Brinkley Bayou, for the presence of sulphate reducing bacteria (SRBs). SRBs produce hydrogen sulfide, which is toxic and causes corrosion. The study aims to determine if McKellar Lake, near potential polluters, has problematic SRB levels compared to the control site of Brinkley Bayou in a state park. Soil samples were taken from both sites and tested using standard microbial techniques to quantify and compare SRB presence.

1. Aaron Banks and Andrew Tutor
Department of Chemistry, Rhodes College, Memphis, TN 38112
Microbial Assay of McKellar Lake and Brinkley Bayou
Sampling Method
Sulphate reducing bacteria (SRBs) are an important part of the natural sulfur
cycle. As obligate anaerobes, they grow only in anaerobic environments, such as
marine soils. SRBs use sulphate as their terminal electron acceptor, producing
hydrogen sulfide (H2S) in the process2.
Sulphate Reducing Bacteria
Sampling Locations
1. Lamers, P.M. Frontiers in Plant Science. 2013.
2. Postgate, J.R, The Sulphate Reducing Bacteria, 1984.
3. Beuchamp, R.O. CRC Critical Reviews in Toxicology, 2010, 13, 25-97.
4. Ma et al. Corrosion Science, 2000, 42, 1669-1683.
5. Ren et al. Materials Chemistry and Physics, 2005, 93, 305-309.
6. Azevedo. Engineering Failure Analysis, 2007, 14, 978-994.
7. Postgate. Bacteriological Reviews, 1965, 29 (4), 425-441.
8. Benka-Coker et al. Bioresource Technology, 1995, 54, 151-154.
9. Altshuller, Environmental Science and Technology, 1973, 7 (8), 709-712.
10.Staub et al. Bioscience, 1970, 20 (16), 905-912.
11.Smith. International Oil Spill Conference Proceedings, March 1973
12.Cochran, Biometrics, 1950, 6 (2), 105-116.
Conclusions
The Sulfur Cycle
Growth and Quantification
References
• The presence of sulphate reducing bacteria can cause or indicate problematic
levels of pollution
• They can cause such levels by the production of hydrogen sulfide, which is
both toxic and corrosive
• They can indicate high levels of aquatic sewage and oil and atmospheric
sulfur dioxide
• McKellar Lake is an ideal location to test for the presence of SRBs
Figure 1: Diagram illustrating the process by which sulfur moves through the environment. For
our research, we have focused on the anthropogenic production of sulfur dioxide, its
spontaneous change to sulphate in the atmosphere, and the reduction of sulphate in marine
soils1.
Motivation
The hydrogen sulfide produced by sulphate reducing bacteria is toxic to
humans, along with many other organisms. It induces toxicity stress by
inhibiting cytochrome C, thereby blocking energy production3. Toxicity is
perhaps most prevalent in aquatic systems, where it has been reported to kill
large numbers of fish and marine plants1.
The concentration of H2S has also been proven to be directly related to the
corrosion of both iron4 and steel5, and, specifically, has been shown to cause
multiple oil pipeline failures6. This presents a significant economic hazard, as
McKellar lake contains multiple oil pipelines, and is home to a number of
steel-hulled barges.
SRBs can also serve as an indicator of environmental pollution, as they have
been shown to be indigenous to both sewage7 and oil8, two potential
contaminants of McKellar Lake. Their growth is also dependent on the
Figure 2: A map detailing McKellar Lake, as well as several potential environmental polluters on its
banks (outlined in red). To the north is an industrial park on President’s Island, which contains over a
dozen different chemical plants. To the south is TVA Allen Coal Plant and to the east is a Valero oil
refinery. There are also two major parks on its banks (outlined in green), TO Fuller State Park to the
south and Martin Luther King Jr. Riverside Park to the east. The lake is also upriver of multiple
municipal water sources10 and has been the site of previous chemical spills11.
Figure 3: Map showing the location of Brinkley Bayou, a stream located in Meeman-Shelby Forest State
Park. Located in Shelby Forest, pollution, especially from sewage and oil, should be minimal; therefore,
it serves as our negative control.
Samples were taken according to the methods laid out by J.R. Postgate in The
Sulphate Reducing Bacteria2. An amount of soil was taken ~6 inches deep and
placed in media within 24 hours of collection to limit exposure to an aerobic
environment. Six sites around each body of water were chosen, and eight
samples will be taken over the course of two months.
We ground one gram of each soil sample with a sterile pestle and mortar,
then added 9 mL of 2% saline solution to create the first dilution. For each
sample, three tubes at each dilution level (1:10, 1:100 and 1:1,000) were
made. The growth media used was Postgate’s Media E2 and were allowed to
incubate for two weeks.
The media used contained FeSO4, which is reduced to FeS as a result of SRB
metabolism. FeS then forms a black precipitate in the tubes, allowing us to
tell visually whether colonies have formed. The most probable number
technique with three dilutions was then employed to provide an estimate of
SRB prevalence in the original sample12.