Browsing by Subject "Microbial communities"
Item Effects of long-term metal contamination on the structure and function of microbial communities in soils.(Texas Tech University, 2007-08) Humphries, Jennifer A.; Cox, Stephen B.; Zak, John; Hooper, Michael J.; Anderson, ToddMicrobial communities are critical components of soils and are known to be important for a wide range of ecosystem-level processes. However, due in part to methodological limitations, much of the basic structure and activity of microbial communities in both pristine and anthropogenically disturbed soils remains unknown. One hundred years of mining and smelting activity at the Anaconda Smelter Site in Anaconda, Montana has caused high concentrations of metals to be deposited in surrounding areas, leading to significant degradation of the soils, loss of above-ground vegetation and toxicological effects on humans and wildlife. Different phytoremediation strategies were tested in situ within the 1.5 acre Dragstrip demonstration area, to assess the efficacy of different soil amendments (fertilizer formulations, organic matter, liming materials, and depth of soil plowing) for supporting plant growth. The success of plant-based remediation techniques is largely dependent on the health and stability of the soil, of which soil microbial communities play essential roles. While high concentrations of metals are known to negatively affect microbial activity, biomass, and enzyme function, amendment of soils during the remediation process may further modify microbial community structure and function in soils. Little is known about the effects of soil amendments on the structural and functional diversity of microbial communities in heavy metal contaminated soils. Additionally, a better understanding is needed of the effects of metals on microbial community structure and function following long-term in sutu exposure, and following contamination with increasing concentrations of metals. The following research attempts to characterize the effects of anthropogenic disturbance (i.e., soil metal contamination and/or different soil amendment strategies) on the structure and function of microbial communities in soils surrounding the Anaconda Smelter as follows: 1) Microbial communities within the six remediated Dragstrip demonstration plots and adjacent unremediated control plot were characterized using a combination of culture-based (Biolog) and non-culture based (DGGE) techniques to characterize the combined effects of soil metal contamination and amendment strategy on microbial community structural (community DGGE banding profiles) and functional diversity (community carbon substrate utilization profiles (SUPs)). 2) Microbial communities native to six smelter-impacted sites (representing a gradient of soil metal concentrations) and a non-impacted site (representing background levels of metals) were compared to determine the long-term effects of metal contamination on microbial community dynamics (microbial activity, biomass, structural diversity and functional diversity). 3) Soil native to two smelter-impacted sites and a non-impacted site (previously exposed to high, low or background concentrations of aerially-deposited metals, in situ, respectively) were artificially-amended with metal-salts in the laboratory to characterize the dose-response effects of increasing concentrations of metals on microbial community dynamics. Additionally, this research tested the hypothesis that soil metal contamination, acting as an extreme environmental stressor, will catalyze a shift in species diversity and abundance, causing initially unique communities to converge on a community with similar structure and function. Results from these studies show that several physiochemical soil characteristics (percent organic matter, soil pH, cation exchange capacity) significantly influence the bioavailability of metals in soils, and metal bioavailability in turn influenced the toxicity of metals to soil microbes. Not only did soil metals significantly decrease microbial activity and biomass, but they also caused significant shifts in community structure, indicating the potential for metal stress to shift species diversity and abundance. The effects of soil metal contamination on community SUPs was less pronounced, which may give evidence of functional redundancy within the enriched portion of the communities. Soil physiochemical profiles were influenced by soil remediation amendment strategies, and several physiochemical parameters (K, NH4organic matter, and cation exchange capacity) were correlated with shifts in microbial community structure, indicating that amendment strategy has the potential to modify microbial communities over time. Finally, while microbial communities were not observed to converge on a common community as a result metal stress, these studies have documented the potential for metal contamination to shape the structural and functional diversity of microbial communities in soils. Microbial community endpoints are increasingly being marketed as potentially good indicators of soil ecosystem health and stability. These studies have shown that microbial community activity, biomass, community structure, and community function are sensitive endpoints for monitoring microbial responses to metal stress. However, additional studies are necessary to truly understand the complexity of microbial community responses to long-term metal contamination.Item Microbial responses to CO₂ during carbon sequestration : insights into an unexplored extreme environment(2014-05) Santillan, Eugenio Felipe Unson; Bennett, Philip C. (Philip Charles), 1959-; Cardenas, Bayani; Shanahan, Timothy M; Omelon, Christopher R; Altman, Susan JWhen CO₂ is sequestered into deep saline aquifers, significant changes to the biogeochemistry of the system are inevitable and will affect native microbial populations both directly and indirectly. These communities are important as they catalyze many geochemical reactions in these reservoirs. We present evidence that the injection of CO₂ will cause a large scale disturbance to subsurface microbial populations which will ultimately affect the solution and mineral trapping of CO₂ as well as the movement of CO₂ charged water through the subsurface. Representative subsurface microorganisms including a Gram negative bacterium (G⁻), two Gram positive bacteria (G⁺), and an archaeon were tested for CO₂ survival at pressures up to 50 bar and exposure times up to 24 hours. CO₂ tolerance varied but shows effects on microbes is more complex than just decreasing pH and is not significantly dependent on cell wall structure. Imaging reveals that CO₂ disrupts the cytoplasm possibly from changes to intracellular pH. The geochemical effect of CO₂ stress is a decrease in metabolic activity such as Fe reduction and methanogenesis. Subsurface microbial populations interact with the surrounding reservoir minerals which likely influence their ability to survive under CO₂ stress. When the G⁻ organism was grown in the presence of a mineral substrate, survival depended on the mineral type. Quartz sandstone provided a good substrate for survival while kaolinite provided a poor substrate for survival. Biofilms on quartz sandstone were rich in extracellular polymeric substances (EPS) that likely act as a barrier to slow the penetration of CO₂ into the cell. The release of toxic metals from mineral dissolution at high PCO₂ enhanced cell death. To understand the long term effects of CO₂ on microbial communities, water samples were taken from CO₂ springs in the western United States and compared to unaffected springs. Community 16S rRNA sequence data suggests that CO₂ exposed environments exhibit lower microbial diversity, suggesting environmentally stressed communities. However, differences among diversity in the springs surveyed also indicates other environmental factors that affect diversity beyond CO₂. Furthermore, the isolation of a novel fermentative Lactobacillus strain from a CO₂ spring, indicates viable microbial communities can exist at high PCO₂.