Yellowstone Acid Pools

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Description of Niche

Introduction

Yellowstone National Park located in the states of Wyoming, Montana, and Idaho is known for its great wildlife diversity as well as it unique geothermal features. One of the most prominent and interesting sites within the park are the acid pools. Their high acid levels and their great bacteria and microorganism diversity characterize these pools. Recently, the study of microorganisms within these pools have come into interest due to their unique biochemistry of coping with harsh conditions. These extremophiles have many useful applications to society and are especially important to other microorganisms inhabiting the same environment. Undoubtedly, the acid pools in Yellowstone National Park have become excellent tourist attractions not only due to their bright and vivid colors, but also for the great diversity of microorganisms that inhabit this extreme environment.

Location

Most of these highly acidic geothermal pools can be found in areas near Norris Geyser Basin, including the superheated metal-rich Amphitheater Springs and Roaring Mountain Springs, as well as in the Mud Volcano and sulfur cauldron areas. Similar niches can also be found in the pyrite-rich (iron sulfides) acid mine drainages around the world, with one notable example located in the Iron Mountain Mine, California.

Physical Conditions

This thermoacidophilic niche is typically located in aquatic environments with high moisture content, including various geothermal hot springs and volcanic mud pools. The niche is adapted to highly acidic environments, generally with a pH of less than 3. Due to active volcanic activities in the area, the springs and pools in which the acidophilic niche is found are typically of fairly high temperature, usually ranging from 65 to 90 degrees Celsius. The niche is typically immersed in pools with high sulfur contents, either as hydrogen sulfide (H2S(g)) emitted as a volcanic gas, or as elemental sulfur crystals. Some niches are also found in pools rich with other metals, typically iron (1).

Influence by Adjacent Communities (if any)

Is your niche close to another niche or influenced by another community of organisms?

The Mud Volcano area is responsible for the low pH of many acid pools, such as the Cinder Pool. It is probably the largest vapor-dominated area in Yellowstone. The vapor consists of hot gases that are released into the hot, acidic pool water. Solfataras, or sulfur streams, are common among gases released in active volcanic regions. Because microbes oxidize many ions, such as iron and arsenic, in a hot environment, microbes are in charged for oxidizing the elemental sulfur received from the nearby volcano into sulfuric acid. The acid pool also receives hydrogen sulfide, H2S, and the microbes living in the spring oxidizes it to form sulfuric acid, which contribute to the main source of acid waters in this area.

Conditions under which the environment changes

Do any of the physical conditions change? Are there chemicals, other organisms, nutrients, etc. that might change the community of your niche.

Since most of the sulfuric acid is formed on the surface of the acid pool, it becomes part of the circulating water that permeates back into the aquifer and mixes with ascending pool water. This recurring process makes the water more acidic over time.

Who lives there?

Presence of Microbes

Acidophiles

The term Acidophiles derives from the Greek roots words of "acido" and "phile" which basically means acid-loving. This refers to all organism that survive in a highly acidic environment usually less than pH 3.

Highly thermophilic. Crenarchaeota This group of archea is the most thermophilic of the acidophiles.

Moderately thermophilic Curyarchaeota This group of archea along with mostly positive gram-positive bacteria are the moderate thermoacidophiles. Galdieria Sulphuraria, formally known as Cyanidium caldarium, is a moderately thermophilic acidophile that has been found in Yellowstone.

Low thermophilic Most of the low thermophilic acidophiles are known as mesophilic acidophiles. Most of these lower temperature and acidic environments are populated by gram-negative bacteria.

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Presence of Non-microbes

Due to the high acidity of the pools at Yellowstone, very few non-microbes can survive using the methods of more simpler microbes. Although some insects can be found at some extreme environments, usually any environment with pH 4 or lower will support very few or none non-microbes. But there are a few non-microbes surviving in these environments possibly having a strong hydrogen pump or a low hydrogen permeable membrane. Acontium cylatium, Cephalosporium sp., and Trichosporon cerebriae, are three fungi that live near pH level of 0. Also, the characteristic colors of acid pools of red and green are from Cyanidium caldariu and Dunaliella acidophila which are also acidophiles that can live below pH 1. (12)

Plants? Animals? Fungi? etc.

Microbial Interaction

Describe any negative (competition) or positive (symbiosis) behavior

A facultative intercellar gram-negative bacteria of the Legionella species, a known agent that causes a sometimes fatal type of pneumonia called Legionnarrie's disease , has been found at the acidic geothermal streams and pools which is uncommon. This bacteria has a parasitic relationship with phagocytic Amoebae such as Naegleria, Acanthamoeba, and Hartmanella. These Amoebae ingest the gram-negative bacteria while grazing. The Legionella survive the acidic conditions of the pools due to the protective environment of the host amoebae cells. The Legionella avoid the amoebae defense systems while multiplying within the vacuoles of the host cell. They eventually kill the host cell and return to the environment. But, in microbial biofilm communities, Legionella can survive as free-living organisms. (11)

Another microbial interaction between lysogenic viruses and bacteria is found from a bacteria species called Sulfolobus. This species is unique due to its ability to reduce sulfur and use it for energy and tolerate highly acidic environment. The lysogenic viruses infect and are able to survive the extreme environments using the protective bacteria. The natural ability of surviving in high acidic conditions of Sulfolobus makes it the perfect host for lysogenic viruses. (X)

Do the microbes change their environment?

Do they alter pH, attach to surfaces, secrete anything, etc. etc.

Due to the unique formation of Yellowstone Park, elemental sulfur is abundant. Heterotrophic microorganisms take advantage of this elemental sulfur and as a result the oxidation of sulfur generates sulfuric acid. This is the primary mechanism that dramatically lowers the pH level in microsites or on the macro level which generates acid pools. (8) Also, the pools and springs are often converted into "mud" gradually due to the sulfur-oxidizing capability of the niche's microorganism: as hydrogen sulfide gas and atmospheric oxygen are oxidizied, the resulted sulfuric acid is incorporated into the spring water, and the highly acidic water, in addition to contributing to the low pH of the niche's environment, is capable of dissolving nearby rocks into mud. (X)

Metabolism Useful to the Environment

Do they ferment sugars to produce acid, break down large molecules, fix nitrogen, etc. etc.

Most extremely acidic pools contain relatively low concentrations of organic compounds and high concentrations of reduced inorganic compounds, such as hydrogen, sulfur, elemental sulfur, thiosulfate, or ferrous iron. The high inorganic compound content is essential as iron and sulfur oxidation are the primary energy source for chemlitotrophic microorganisms comprising this niche (8). Metabolism via oxidation or organic materials coupled with presence of sulfur results in optimum growth for many microbes, such as the sulfur-reducing Crenarchaea residing in the Dragon Springs of Yellowstone National Park. The ability of such bacteria to utilize sulfur is important for other microorganism cohabiting in the same environment. The reduced forms of sulfur from aqueous hydrogen sulfide provide essential electron donors and acceptors for the other microorganisms in their biosynthesis. In this sense, the byproducts of these sulfur-reducing bacteria provide important intermediates for the biochemistry of other microorganism that inhabit the same environment. (3)

Another interesting metabolic mechanism found is the use of arsenite-oxizidizing Hydrogenbaculum isolated in the Norris Geyser Basin of Yellowstone Park. This unique redox reaction changes the Aresenite levels in geothermic scource waters. The levels of Arsenite (both As(III) and As(V)) change frequently when waters are mixed with each other. This Hydrogenbaculum also influence this change of Aresenite levels with differing results. As(V) redox has been frequently observed when As(V) has been utilized as an electron acceptor for anaerobic or microaerobic respiration or as a part of a detoxification strategy. Another type of As(III) oxidation occurs which uses As(III) as a detoxification mechanism or as a source of energy to support growth. This type of detoxification mechanism is not yet fully understood. Another unique aspect was that the redox reactions were inhibited by H2S.(9)

Current Research

Enter summaries of the most recent research. You may find it more appropriate to include this as a subsection under several of your other sections rather than separately here at the end. You should include at least FOUR topics of research and summarize each in terms of the question being asked, the results so far, and the topics for future study. (more will be expected from larger groups than from smaller groups)

Viral Phage as Mobile Genetic Material

The diversity of Sulfolobus spindled-shaped viruses (SSVs) and Sulfolobus islandicus rod-shaped viruses (SIRVs), which are virus types that are genus-specific for Yellowstone-dwelling Sulfolobus species, was monitored over a 2-year period of time. Comparison of amplified viral DNA sequences indicated that viral movement and immigration, rather than mutation, contributes to the high local population diversity even though the viral host sulfolobus is confined within specific geographic barriers (different thermoacidic pools). This result is significant as SSVs and SIRVs exhibit physical structures similar to that of bacteriophages and human viral pathogens. Researching of this rapid viral movement can provide significant information regarding virus circulation as well as the potential use of the viruses as mobile genetic material (4).

Role of Viruses in Microbe Populations

The acid pools located in Yellowstone National Park are noted and distinctive due to their geothermal features. In specific, their high acidity and temperature give rise to a diverse and varied microbe population who possess unique capabilities. Recently, scientists have hypothesized that the virus population in these acid pools are actually responsible for controlling the microbe population. Most viruses would perish under the extreme environmental conditions that these acid pools present, however they find refuge within common bacteria such as Sulfolobus who are able to withstand the high acidity and temperature. By living within these host bacteria, viruses are able to continue to replicate and thrive under the harshest conditions. Furthermore, scientists have discovered that while microbe populations stay relatively constant between different acid pools, the population of viruses fluctuates tremendously. This observation suggest that the viruses somehow control the population of certain microbes within these acid pools. The next question scientists inquired concerned about how these viruses are able to relocate and migrate to different acid pools, which sometimes covered long distances. It has been recently proposed that the viruses travel through the steam that these pools produce as a result of extremely high temperatures. Right now, scientists have been committed to obtaining and unlocking the genomes of the many microorganisms that live within the acid pools in hopes of uncovering and understanding how they all interact with each other. (5)

Sulfur Levels Used to Predict Volcanic Activity

The Cinder Pool located in Yellowstone National Park is an acid-sulfate-chloride boiling spring in the Norris Geyser Basin. The Cinder Pool is unique in that it contains a molten layer of sulfur on the bottom of the pool. In addition, it has been discovered that the highest concentrations of thiosulfate and polythionate are found in the Cinder Pool compared to the other acid pools located in Yellowstone National Park. Moreover, scientists and researches are currently evaluating changes in the depth of the acid pool as well as the presence and significance of sulfur spherules. Researches have employed techniques including ion chromatography and colorimetric techniques in order to measure and observe the levels of sulfur spherules. Furthermore, researchers are investigating the use of sulfur and role of sulfur spherules such as polythionate and thiosulfate in the pathways of sulfur redox reactions. Studying these unique sulfur spherules are of great importance in helping monitor volcanic activity. More importantly, measuring the variation of polythionate can predict volcanic activity thus potentially helping warn residents who live near active volcanic sites. The different and variation of polythionate concentrations in the Cinder Pool may be applied to other acid crater lakes as well. (6)

Insights into extreme thermoacidophily based on genome analysis of Picrophilus torridue and other thermoacidophilic archaea

Thermoacidophilic microorganisms, members of the Kingdom Archaea, have the extraordinary ability to survive and replicate at hot, acidic conditions. Researchers are pondering upon the mechanism utilize by these organisms to tolerate an extreme lifestyle. The experiment was based upon comparing known sequences of thermoacidophilic genera Picrophilus, Thermoplasma and Sulfolobus. After a series of comparison of genome sequences encoding for transport proteins, energy metabolism, and genetic input via lateral gene transfer. The results revealed a high frequency of shared genes among thermoacidophiles, suggesting a high rate of lateral gene transfer. This further demonstrates that microorganisms that live in close proximity often exchange genes at a higher frequency, which allow for the overall acidophilic survival capabilities of these microbes. More importantly, with the genome sequence of P. torridus known, more comparative and functional genome studies can be performed to help further understand the features that allow these organism to withstand very acidic conditions (7).