Acidianus brierleyi

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1. Classification

a. Higher order taxa

Archaea; Thermoproteota;Thermoprotei; Sulfolobales; Sulfolobaceae

b. Species

NCBI: [1]

"Acidianus brierleyi" (1)

2. Description and significance

Acidianus brierleyi is a species of Archaea in the family Sulfolobaceae that lives at extreme temperature and acidity, found in volcanoes and acidic hot springs (2). A. brierleyi metabolizes metals within these habitats, making it potentially valuable for biomining, bioleaching, and bioremediation (3). Other members of the Sulfolobaceae family do not utilize sulfur as an electron donor despite the large amounts of sulfur in their environment, from which they received their namesake (2). Progress has been made in sequencing the genome and studying metabolic pathways in A. brierleyi although aspects of its functional capabilities and ecological roles remain unresolved.

3. Genome structure

Acidianus brierleyi possesses a circular chromosome, with no plasmids. The complete genome comprises 2,947,156 base pairs and contains 2,871 protein-coding genes. The GC content is approximately 31% (2). Compared to other genera such as Sulfolobus or Metallosphaera, A. brierleyi has a relatively lower GC content. The genome contains genes associated with acidophilic adaptation and heavy metal resistance, like CorA family divalent cation transporter and Fox complex (12). Additionally, as a member of the Sulfolobaceae family, A. brierleyi encodes sulfur metabolism pathways involved in sulfur oxidation and mobilization, such as sulfurtransferase and sulfur oxygenase/reductase (12). Conversely, its relatively large genome size is postulated to encode genes that provide broader metabolic capacity and increased environmental adaptability by possessing expanded sets of lithotrophic and stress-response genes. These genes include sulfur-processing genes such as sulfide:quinone oxidoreductase paralogs, components of the metal-oxidation Fox gene cluster, and acidophily-associated proteins such as OsmC-family peroxiredoxins (12).

4. Cell structure

Acidianus brierleyi has a irregularly shaped cells between cocci and bacilli, called coccoid, which aids in its ability to adapt to high temperature and high pH conditions (5). The cell envelope of A. brierleyi consists of a cytoplasmic membrane surrounded by a surface layer (S-layer), composed of proteinaceous subunits forming a crystalline lattice, that maintains cell integrity under acidic conditions (2). The membrane lipids of A. brierleyi are composed predominantly of tetraether lipids (3) that confer stability and impermeability in acidic conditions (3). Further structural adaptations include the presence of metal-binding proteins and complexes, facilitating heavy metal resistance and metal oxidation (5). Additionally, arsenic speciation studies show that Arsenite oxidase and multiheme c-type cytochromes in conjunction with quinones may transform arsenic and iron, respectively, through oxidation reactions (4). A. brierleyi can also mobilize metals such as nickel, molybdenum, and lead from industrial waste by acidifying the surrounding environment (4).

5. Metabolic processes

A. brierleyi is a facultative anaerobe and a chemolithoautotroph capable of heterotrophic growth, using organic compounds as a carbon source (4). A. brierleyi is strictly chemolithotrophic, unable to grow without sulfur and oxidizing organic compounds as a source of energy (5). Acidianus brierleyi oxidizes or reduces sulfur compounds and metals such as ferrous iron and arsenic, using these electron sources under acidic conditions to enable carbon fixation, depending on oxygen availability. The ability to oxidize or reduce sulfur makes this archaeon a facultative anaerobe, capable of growth in both oxygen-rich surfaces or deeper areas containing volcanic gases (5). A. brierleyi can oxidize arsenite (AsIII) under high levels of arsenic and iron (4). The capacity for A. brierleyi to biooxidize heavy metals is of interest for bioremediation of arsenic-contaminated wastewater. Additionally, the A. brierleyi can selectively mobilize copper while precipitating arsenic as arsenate (4).

6. Ecology

Acidianus Brierleyi thrives in extremely acidic (pH of 1.5 ~ 3) and high temperature (70 ~ 80 °C) solfataras and hydrothermal volcanic systems. Acidianus Brierleyi exhibits facultative anaerobic metabolism, enabling it to oxidize sulfur compounds both aerobically and anaerobically, which allows it to live in fluctuating oxygen levels common in its native habitats (2). Ecologically, A. brierleyi cycles sulfur and metals, particularly heavy metals, including iron, copper, and arsenic (3). Arsenic speciation studies demonstrate that A. brierleyi oxidizes arsenite in both its cells and the surrounding environment, which reduces its reactivity and membrane permeability, aids in metal detoxification, and facilitate environmental arsenic cycling (4). Using its flagella, A. brierleyi can form biofilms, which increases competition for nutrients but also allows microbes that are less tolerant of arsenite to grow (8).

A. brierleyi can also oxidize trace gases, such as sulfide, at suboptimal temperatures, below 70 °C (6). Additionally, the presence of S-layer proteins and proton pumps enables Acidianus Brierleyi to survive at extremely low pH. The organism’s ability to bioleach, or extract metals by oxidizing sulfide minerals, at high temperatures, has made A. brierleyi a target of research for its potential to improve metal extraction efficiency and decrease environmental toxicity (3).

7. Current Research

Recent research shows that Acidianus brierleyi can bioleach electronic waste, such as printed circuit boards and lithium-ion batteries. Operating optimally at 65–75°C, A. brierleyi achieves a faster rate of dissolution, due to higher reaction rates and because elevated temperatures help prevent corrosion on metal surfaces, leading to more efficient recovery of cobalt, lithium, nickel, and copper (9). A. brierley ioxidizes both ferrous iron and reduced inorganic sulfur compounds, and uses cheap, readily available elemental sulfur as an energy source to drive the bioleaching process. Studies on pyrite have shown that A. brierleyi interacts minimally with the mineral surface, which can enhance bioleaching and its capability to extract metal within the first few days to a few weeks (8). This, combined with its high tolerance to metal toxins such as cobalt and nickel that typically inhibit other microorganisms, allows it to survive and maintain high-quality leaching performance in the metal-rich conditions (7). Another study explored the oxidation of arsenite by A. brierleyi and its utility in reducing environmental pollution. A. brierleyi uses iron as an electron donor, which in turn acts as a chemical oxidant and turns arsenite into its less toxic form, arsenate. In aquatic environments, arsenic can accumulate in fish tissues, particularly in the liver and kidneys, leading to health issues such as immune system suppression, cell death, lesions, and reduced fertility (10). This suggests A. brierleyi’s potential utility in bioremediation and detoxification in contaminated ecosystems.

References

1. Schoch, C. L., Ciufo, S., Domrachev, M., Hotton, C. L., Kannan, S., Khovanskaya, R., Leipe, D., Mcveigh, R., O’Neill, K., Robbertse, B., Sharma, S., Soussov, V., Sullivan, J. P., Sun, L., Turner, S., & Karsch-Mizrachi, I. (2020). NCBI taxonomy: A comprehensive update on curation, resources and Tools. Database, 2020. https://doi.org/10.1093/database/baaa062

2. Counts, James A., Nicholas P. Vitko, and Robert M. Kelly. 2018. Complete Genome Sequences of Extremely Thermoacidophilic Metal-Mobilizing Type Strain Members of the Archaeal Family Sulfolobaceae, Acidianus Brierleyi DSM-1651, Acidianus Sulfidivorans DSM-18786, and Metallosphaera Hakonensis DSM-7519. Microbiology Resource Announcements 7, no. 2. https://doi.org/10.1128/mra.00831-18.

3. Wheaton, Garrett, James Counts, Arpan Mukherjee, Jessica Kruh, and Robert Kelly. 2015. The Confluence of Heavy Metal Biooxidation and Heavy Metal Resistance: Implications for Bioleaching by Extreme Thermoacidophiles. Minerals 5, no. 3: 397–451. https://doi.org/10.3390/min5030397.

4. Higashidani, Naoki, Takashi Kaneta, Nobuyuki Takeyasu, Shoji Motomizu, Naoko Okibe, and Keiko Sasaki. 2014. Speciation of Arsenic in a Thermoacidophilic Iron-Oxidizing Archaeon, Acidianus Brierleyi, and Its Culture Medium by Inductively Coupled Plasma–Optical Emission Spectroscopy Combined with Flow Injection Pretreatment Using an Anion-Exchange Mini-Column. Talanta 122: 240–45. https://doi.org/10.1016/j.talanta.2014.01.057.

5. Segerer, A., Neuner, A., Kristjansson, J. K., & Stetter, K. O. 1986. Acidianus Infernus gen. Nov., sp. nov., and acidianus brierleyi comb. nov.: Facultatively aerobic, extremely acidophilic thermophilic sulfur-metabolizing archaebacteria. International Journal of Systematic Bacteriology, 36(4), 559–564. https://doi.org/10.1099/00207713-36-4-559.

6. Leung, P.M., Grinter, R., Tudor-Matthew, E. et al. 2024. Trace gas oxidation sustains energy needs of a thermophilic archaeon at suboptimal temperatures. Nat Commun 15, 3219. https://doi.org/10.1038/s41467-024-47324-2.

7. Zhang, X., Shi, H., Tan, N. et al. Advances in bioleaching of waste lithium batteries under metal ion stress. 2023. Bioresour. Bioprocess. 10, 19. https://doi.org/10.1186/s40643-023-00636-5.

8. Camila Castro, Ruiyong Zhang, Jing Liu, Sören Bellenberg, Thomas R. Neu, Edgardo Donati, Wolfgang Sand, Mario Vera. 2016. Biofilm formation and interspecies interactions in mixed cultures of thermo-acidophilic archaea Acidianus spp. and Sulfolobus metallicus. Research in Microbiology, Volume 167, Issue 7, Pages 604-612, ISSN 0923-2508. https://doi.org/10.1016/j.resmic.2016.06.005.

9. Aguilar-López R, Medina-Moreno SA, Sharma A, Tec-Caamal EN. 2022. Synergistic Effect of As(III)/Fe(II) Oxidation by Acidianus brierleyi and the Exopolysaccharide Matrix for As(V) Removal and Bioscorodite Crystallization: A Data-Driven Modeling Insight. Processes.10(11):2363. https://doi.org/10.3390/pr10112363.

10. Pei J., Zuo, J., Wang, X., Yin, J., Liu, L., Fan, W. 2019. The Bioaccumulation and Tissue Distribution of Arsenic Species in Tilapia, Int J Environ Res Public Health, 16(5):757, doi: 10.3390/ijerph16050757. https://doi.org/10.3390/ijerph1605075.

11. Dinkla, I. J. T., Gericke, M., Geurkink, B. K., & Hallberg, K. B. (2009). Acidianus brierleyi is the dominant thermoacidophile in a bioleaching community processing chalcopyrite containing concentrates at 70°C. Advanced Materials Research, 71–73, 67–70. https://doi.org/10.4028/www.scientific.net/amr.71-73.67

12. Counts, J. A., Willard, D. J., & Kelly, R. M. (2021). Life in hot acid: a genome-based reassessment of the archaeal order Sulfolobales. Environmental microbiology, 23(7), 3568–3584. https://doi.org/10.1111/1462-2920.15189

13. Zhang, R., Neu, T. R., Li, Q., Blanchard, V., Zhang, Y., Schippers, A., & Sand, W. (2019). Insight Into Interactions of Thermoacidophilic Archaea With Elemental Sulfur: Biofilm Dynamics and EPS Analysis. Frontiers in microbiology, 10, 896. https://doi.org/10.3389/fmicb.2019.00896

Edited by Rachel Huang, SJ Park, Savannah Parke, and Caden Witt, students of Jennifer Bhatnagar for [http://www.bu.edu/academics/cas/courses/cas-bi-311/BI 311 General Microbiology,2025,Boston University.