Mark Merkley and Professor Russell Rader, Integrative Biology
Bioassessment is the practice of using organisms to detect environmental health and integrity. Ecosystem health and integrity depend on the interaction between living organism and ecosystem function. All organisms or groups of organisms do not respond the same to environmental stress. Depending on various disturbance characteristics, each group may respond at different rates and provide different information (Rader, 2001). Besides the usual macrophytes, macroinvertebrates, or algae, bacteria have the capability of being strong bioindicators. Because of their extremely small size, bacteria have the highest surface-to volume ratios of any living organisms. Thus, bacteria should be the most environmentally aware organisms, and as such, excellent early warning signals (Rader, 2001).
The ability of bacteria to utilize a wide range of carbon sources (including the ability to break down some toxic chemicals) makes them important “sentinel species” in any wetland. This study focuses on wetlands in the Bonneville Basin of Utah. Disturbance in this area refers to impacts made by cattle grazing. We sought to determine whether bacterial communities associated with reference and disturbance sites were more similar within rather than between sites. To accomplish this, we screened environmental samples using physiological test strips and molecular biological techniques. Three samples were taken from a total of 20 sites (10 disturbed, 10 reference). These samples were inoculated on Biolog’s Ecolog microtitre plates.
The objective of this was to determine if the Ecolog plate is a fast and efficient method of describing the microbial community of a wetland. In addition, eubacterial DNA was extracted from all the samples, amplified by PCR, and run on a Denaturing Gradient Gel Electrophoresis (DGGE) for separation of species based on differences in the 16s rDNA gene. DGGE is a relatively fast method to compare community composition among samples. Out data indicates that differences in microbial communities are detectable by Ecolog, and supported by DGGE analysis.
Preliminary analysis results in some interesting patterns. On a denaturing gradient gel, the DNA from the bacteria separates according to differences in specie. Thus, each band on a gel represents a different specie of bacteria. Microbial diversity was found to be higher in samples that came from grazed wetlands. On average, each sample from a disturbed wetland was found to have 10.3 bands or species. In comparison, samples from pristine wetlands had an average of 9 bands per sample.
The claim that diversity is greater in the disturbed wetlands comes from a comparison in similarity. The Jacard’s Similarity index was used to compare the similarity within and between sites. In this index, a 1 represents complete similarity of species between two sites, while a 0 represents complete dissimilarity. When the pristine sites are compared, their similarity index averaged .84. Disturbed sites averaged .4 when compared to each other. When disturbed and pristine sites were compared to each other, the index rested at an average of .32. This is important to the question of diversity. Not only did the disturbed sites average a greater number of species per sample, but the similarity of those species between samples varied greatly. Pristine sites had a lesser number of species per sample, and the similarity index indicates that those same species are conserved between samples, thus lower diversity.
The samples from the Ecolog experiment also indicate that there is a detectable difference in the microbial communities of disturbed and pristine wetlands. It appears however, that it is only able to discriminate between sites that are in close geographic proximity to one another. Further research is being pursued at this time to try and understand the reason for this.
References
- Rader R., D.P. Batzer, S.A. Wissinger. 2001, Bioassessment and Management of North American Freshwater Wetlands, John Wiley & Sons, New York, NY, 4-5, 249.