Yellowstone Acid Pools

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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 attraction and of scientific interest 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 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

Norris Geyser Basin

Norris Geyser Basin comprises of three main areas: Porcelain Basin, Black Basin, and One Hundred Springs Plain. It is one of the most dynamic places in Yellowstone National Park because some of the pools here are some of the oldest, hottest and most acidic around. 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 4. 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).

Echinus Geyser

Echinus Geyser, unlike most geyser that tends to be alkaline in nature, is the largest, active acid geyser known in the world. Its waters have a pH ranging from 3.3-3.6, nearly as acidic as lemon juice. The temperature of its water has been recorded as being as high as 85 degrees Celsius. The red-orange that characterizes this geyser is caused by iron oxide.

Cinder Pool

Cinder Pool is an acid-sulfate pool that locates in Norris Geyser Basin at Yellowstone National Park. The pH of the pool water is approximately 4, which is close to the pH of acid rain. Such acidity provides an excellent environment for “acid-loving” microorganisms that thrive in surroundings with the pH values range of 1 to 5. The pool maintains a temperature around 196-198 degrees Celsius while the vent temperature is 0 degrees Celsius. It is an oval pool with a diameter of 30 feet and a depth of 38 feet, respectively. The pool is rich in sulfate and chloride giving rise to its grayish color. Around the edges of the Cinder Pool are small, black and hollow beads, which are extremely fragile. These black beads, whose size does not exceed that of a pea, are composed of sulfur, quartz, feldspar and obsidian rhyolite.

Image 1: Cinder Pool at Yellowstone National Park. The picture is provided by the National Park Service (Spatial Analysis Center) on RCN website

Roaring Mountain

North of Norris Geyser Basin, Roaring Mountain is a large acidic hydrothermal area with many fumaroles, or steam vents. It has an elevation of 2260 meters or 740 feet. With magma closest (1.6 to 2.2 km below surface) to the surface in this part of the park, it is the hottest part of Yellowstone National Park. The pH is typically below 2 and the temperature is around 40 degrees Celsius.

Mud Volcano

The Mud Volcano area is responsible for the low pH of many acid pools, such as the Cinder Pool in the Norris Geyser Basin. It is probably the largest vapor-dominated area in Yellowstone. Within the mud volcano area of Yellowstone National Park, many highly acidic and high temperature springs and geysers reside. Their extremely high temperatures and low pH characterize the geysers and springs that are located in the Mud Volcano area. Some of the geothermal pools here such as Black Dragon Cauldron reach temperatures up to and even exceeding 192 degrees Fahrenheit! Among the most acidic places in the park include Dragon’s Mouth Spring, Black Dragon Cauldron, and Sulfur Cauldron. In fact, in the Sulfur Cauldron, the pH has been measured to be almost 1.2, which is nearly identical to citric acid. The springs and geyser present in this fascinating area contain both sulfur-oxidizing and iron-oxidizing bacteria, which help create distinct colors of certain springs. Otherwise, the presence of iron sulfides within the pools and springs create the typical gray and black color of most of the pools. The vapors that are emitted consists of hot gases that are released from 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 charge of 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 acidity in this area. 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 even more acidic over time.

Adjacent Communities

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

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.

Who lives there?

Presence of Microbes

Thermoacidophiles

Thermoacidophiles are unique group of bacteria that are a combination of acidophiles and thermophiles. They belong to the kingdom of Archaebacteria and some of their features even resemble that of eukaryotes. Some notable thermoacidophiles include Sulfolobus and Acidithiobacillales Ferrooxidans. Thermoacidophiles are characterized by their exclusive ability to live in both highly acidic environments and also high temperatures. The typical conditions these thermoacidophiles live under include pH at around 2 with temperatures ranging from 80 to 90 degrees Celsius. Most notably, these fascinating bacteria tend to live in some of the most extreme environments and they provide distinctive metabolism that is beneficial to both their own species and other microorganisms. Typically, thermoacidophiles tend to be anaerobic and chemolithotrophs. However, some of these extremophiles are aerobic and can obtain energy from organic sources. The combination of their unique metabolism such as sulfur oxidation coupled with their resistance to extreme conditions make thermoacidophiles a fascinating area of study in Yellowstone National Park.

Norris Geyser Basin

Mycobacterium parascrofulaceum

This particular mycobacterium is found in the Norris Geyser Basin of Yellowstone Park. Temperatures within this environment range from 48 to 40 degrees Celsius. In addition, the pH levels (pH = 3.0) indicate that this environment is extremely acidic. The combination of both extreme temperatures and pH levels suggest that this particular mycobacterium is unique in their structure and adaptations. Normal mycobacterium can be fairly neutral and normal environments such as in drinking water and other water ecosystems. However, it long known that mycobacterium are able to survive in dire starvation leading to the notion that can adapt and flourish in extreme conditions and environments. Furthermore, tests have proved that mycobacterium parascrofulaceum possesses temperature resistance, as it was able to grow normally at temperatures reaching upward toward 56 degrees Celsius. Like other bacteria who reside in acidic and high temperature environments, mycobacterium parascrofulaceum can be classified as a thermoacidophile. (17)

Arsenite-Oxidizing Hydrogenobaculum

In the Norris Geyser Basin of Yellowstone National Park, an arsenite-oxidizing Hydrogenobaculum was isolated. This specific bacterium is categorized as a chemolithoautotroph meaning it uses inorganic material to synthesize essential reducing equivalents for biosynthesis. Indeed, the hydrogenobaculum uses hydrogen gas as its sole energy source. Furthermore, the environment that this bacterium lives in can be categorized as both extreme temperature (55 to 60 degrees Celsius) and pH (pH = 3.0). It is interesting to note that the primary function for the arsenite oxidation capability of this bacterium is not fully understood yet. The ability to oxidize arsenic could be a detoxification mechanism that the bacterium employs or a mechanism for harvesting energy. An interesting result upon studying this particular bacterium reveals that addition of aqueous sulfide inhibits its ability to oxidize arsenite. This should be noted considering that Hydrogenobaculum live in a very acidic environment that contains aqueous sulfide. Another interesting metabolic mechanism found is the use of arsenite-oxizidizing Hydrogenbaculum. 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 arsenite 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)

Green Dragon Spring

This highly acidic geothermal region is home to two novel chemoorganotrophic and anaerobic Crenarchaeal species: Caldisphaera draaconis, which thrives at 70 – 72 degrees Celcius and pH 2.5 – 3.0, and Acidilobus sulfurireducen, which thrives at 81 degrees Celcius and pH 3.0. Both species utilize complex peptide-containing carbon fermentation and elemental sulfur reduction as energy sources. The presence of sulfur enhances the growth rate of these microbes significantly.

Roaring Mountain

The extremely hot temperature and acidic conditions make this area a favorable environment for Sulfolobus acidocaldarius, a chemotropic archaea. It is considered a hyperthermophile because it likes temperatures as high as 90 degrees Celsius. These are colorless and spherical microorganisms with sulfur reducing capabilites(16). Since 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 chemotrophic microorganisms comprising this niche. Metabolism via oxidation of organic materials coupled with presence of sulfur results in optimum growth for many microbes. 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 (8).

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.

You may refer to organisms by genus or by genus and species, depending upon how detailed the your information might be. If there is already a microbewiki page describing that organism, make a link to it.

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.

Sulfur Reducing Bacteria

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 of 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)

Arsenite Oxidizing

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 Arsenite 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)

Acid Mine Drainages

Acid mine drains located in various parts of the world are another environment that have come into interest in recent years. Acid mine drains can be found in many parts of the world including France, China, and North America. Primarily, scientists are concerned with the microbial diversity within these areas and their role in bioremediation and bioleaching. Acid mines are formed when abandoned mines, metal and coalmines in particular, are flooded with water creating a pool that becomes rich with minerals and metals. Upon the outflow from these the mines, the waters have become greatly acidic. As a result, many microorganisms and acidophiles, in specific, are attracted by the low pH of these waters and make their homes within these drains. Furthermore, the low concentration of oxygen within the mines lends to the proliferation of bacteria that are capable of surviving in anaerobic environments and also possessing the ability to oxidize metals such as iron. One particular important bacterium involved in bioleaching within acid mine drains is Acidithiobacillus ferrooxidans. Found in Carnoulès of southeastern France, this unique acidophile is been used as way of removing arsenic from the mine drains through bioleaching. Bioleaching is a novel and often-effective way of removing metals from the mines via bacteria. It is often used in acid mine drains as a way of removing certain metals from the area thus removing contaminants from the highly acidic water. However, in the process, the bacteria may produce toxic chemicals as a byproduct. Acidithiobacillus ferrooxidans utilizes iron oxidation as it’s primary source of energy and metabolism. Upon growing it on ferrous iron within the mine, Acidithiobacillus ferrooxidans is able to coprecipitate out arsenite from the mines. This significant ability now allows scientists and researchers to safely and easily removes arsenic from the acid water within the drains. Coupled with the ability to recycle bacteria easily, Acidithiobacillus ferrooxidans has become a microbe of great interest and importance. (15)

Current Research

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 between 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).

A ubiquitous obligate thermoacidophilic archaeon from deep-sea hydrothermal vents

The evolution of life that may exist on other planets can be best understood by examining how life evolves and survives in harsh environments. In the past, microbes found in hydrothermal vents lived in pH-neutral environments, but the findings have found that these microbes can also be tolerable to acidic conditions. Their findings confirmed that acidophile can flourish rapidly in the acidic condition, such as in hot springs and acid pools in Yellowstone National Park. The microbes discovered are named aciduliprofundum boonei, which belongs to a special group of microbes called Archaea. They grow at a pH range of 3.3 to 5.8 and at temperatures of 55-75°C. These strains of microbes may be useful into many fields other than science. For example, in bio-mining, these microbes may help to extract metals from mine tailings. However, many uses of these microbes still await being studied (14).