Thermoanaerobacter kivui

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Classification

CLASSIFICATION

Kingdom: Bacteria

Phylum: Firmicutes

Class: Clostridia

Order: Thermoanaerobacterales

Family: Thermoanaerobacteraceae

Genus: Thermoanerobacter

Species: T. kivui (⁵)

T. kivui is also known as Acetogenium kivui(⁶).

Species

NCBI: Taxonomy

Thermoanaerobacter kivui

Description and Significance

Thermoanaerobacter kivui, formerly known as Acetogenium kivui, is a thermophilic obligate anaerobe which was isolated from sediments of Lake Kivu in Africa. It oxidizes hydrogen and reduces carbon dioxide, released from volcanic activity under the lake, into acetic acid(¹). It is a non-motile, non-spore forming, non-flagellated rod with no outer membrane(¹). The optimum growth temperature for T. kivui is 66oC with a pH of 6.41, but has a temperature range of 50-72 oC and a pH range of 5.3-7.51. T. kivui is a part of the microbial nutrient cycling that makes Lake Kivu one of the largest known stores of methane in the world. The acetate it produces from the abundance of carbon dioxide derived from volcanic activity is utilized by methanogens which led to this large accumulation of methane.

Genome Structure

The structure of the T. kivui genome has not fully been sequenced; therefore, information regarding the genome is relatively unknown. Of the known sequences contained in the T. kivui genome the G+C base composition is 38% and the G+C content of the rDNA sequences are 54% per mole(⁹). This composition probably implies there is higher G+C composition located in parts of the unknown sequences. This is T. kivui is a thermophile and to keep the genome intact at such high temperatures G+C content must be relatively high(⁸). Most of the known genes in T. kivui are involved in developing S-layer proteins that are used to coat the outer surface of the bacteria(⁸). It is also known that the genome is linear. Additionally, T. kivui has a genome similar to the organisms T. ethanolicus, T. brockii, T. firmii, T. ethanolicus, T. acetoethylicus, T. thermohydrosulfuricus, and C. thermocopriae. This is inferred from the fact that the rDNA sequences of these organisms compared with T. kivui share 95 to 98% similarity(⁹).

Metabolism

‘‘T. kivui’’ is a hydrogen-oxidizing chemotrophic organism that can use organic or inorganic forms of carbon to produce acetic acid(⁷). ‘‘T. kivui’’ cannot form spores nor does it have a flagella ; therefore, the nutrients for growth must be provided in the immediate environment for ‘‘T. kivui’’ to survive(⁷). Additionally, ‘‘T. kivui’’ is a Gram-negative bacteria that has a S-layer coating the bacteria (⁸).

Energy

‘‘T. kivui’’ is an obligate anaerobe making oxygen an enviable option as a final electron acceptor in oxidizing H2(⁷). Therefore, ‘‘T. kivui’’ needs to use a reducing agent as the final electron acceptor. This reducing agent is cysteine-sulfide(⁷). ‘‘T. kivui’’ uses both autotrophic and heterotrophic means of producing energy. These two different ways of obtaining carbon result in differing pathways of conserving energy. For heterotrophic ‘‘T. kivui’’ cells, ‘‘T. kivui’’ growth relies on sodium enrichment, whereas in autotrophic ‘’T. kivui’’ cells, growth does not rely on sodium enrichment in the environment(⁷).

Carbon

‘‘T. kivui’’ can use both organic and inorganic forms of carbon for growth; therefore, there are several carbon sources ‘‘T. kivui’’ can use(⁷). The main carbon sources used by ‘‘T. kivui’’ to produce acetic acid are glucose, fructose, mannose, pyruvate and carbon dioxide(¹¹). When a carbon source that is not a sugar is used in ‘‘T. kivui’’ growth is strictly dependent upon the amount of sodium that is in the surrounding environment using a Na+/H+ antiport to receive Na+ in the internal environment(¹¹).

Nickel

‘‘T. kivui’’ is not a mobile bacteria(⁷). Therefore when energy sources are not present in the environment, ‘‘T. kivui’’ cannot survive well. In situations of minimal growth requirements in the environment, ‘‘T. kivui’’ transports nickel into the internal environment and uses this nickel as a hydrogenase to oxidize hydrogen and produce energy(¹⁰).

Ecology

Lake Kivu is a freshwater African Great Lake which experiences limnetic eruptions, also called exploding lakes. It is oligotrophic the dominant organism in the lake are diatoms(⁴). The lake bed lies on top of a rift valley which is slowly separating, causing volcanic activity and saturation of the lake with carbon dioxide. T. kivui is one of the acetogenic bacteria in Lake Kivu which reduces that carbon dioxide into acetate, which is then oxidized by methanogens to yield methane. This is one of the causes of an accumulation of methane in the water that is nearly saturated with carbon dioxide(²). The limnetic eruptions occur by various means, one of which is methane ignition by volcanic activity which causes the lake to overturn(²). When this happens, a massive amount of carbon dioxide gas is released which settles along the landscape, suffocating any aerobic organisms within its radius. This could be catastrophic at Lake Kivu due to the approximately 2 million people that live in the lake basin(²). Due to these explosions, the fish fauna in Lake Kivu is relatively poor, only harboring about 28 species(³).

References

[1] J. A. Leigh, F. Mayer, R. S. Wolfe. Acetogenium kivui, a new thermophilic hydrogen-oxidizing acetogenic bacterium. Archives of Microbiology, 1981, Volume 129, Number 4, Page 275

[2] Anjali Nayar . Earth science: A lakeful of trouble. Published online 15 July 2009 | Nature 460, 321-323 (2009) | doi:10.1038/460321a

[3] Snoeks, J; De Vos, L., Thys van den Audenaerde, D. (1997). "The ichthyogeography of lake Kivu". South African Journal of Science 93: 579–584.

[4] Sarmento, H. (2006). Phytoplankton ecology of Lake Kivu (Eastern Africa). Belgium: University of Namur. ISBN 978-2-87037-532-7.

[5] "Acetogenium kivui." Acetogenium kivui. N.p., n.d. Web. 19 Apr. 2014.

[6] "European Nucleotide Archive." EMBL European Bioinformatics Institute. N.p., n.d. Web. 20 Apr. 2014.

[7] Leigh, J. A., F. Mayer, and R. S. Wolfe. "Acetogenium kivui, a New Thermophilic Hydrogen-oxidizing Acetogenic Bacterium." Archives of Microbiology 129.4 (1981): 275-80. Print.

[8] Lupas, A., Engelhardt, H., Peters, J., Santarius, U., Volker, S. and Baumeister, W. (1994) Domain structure of the Acetogenium kivui surface layer revealed by electron crystallography and sequence analysis. J Bacteriol, 176, 1224-1233. [PubMed: 8113161]

[9] Rainey, F. A., N. L. Ward, H. W. Morgan, R. Toalster, and E. Stackebrandt. "Phylogenetic Analysis of Anaerobic Thermophilic Bacteria: Aid for Their Reclassification." Journal of Bacteriology (1993): 4772-779. Web. 20 Apr. 2014.

[10] YANG, HSIUCHIN, STEVEN L. DANIEL, TSUNGDA HSU, and HAROLD L. Drake. APPLIED AND ENVIRONMENTAL MICROBIOLOGY 55.5 (1989): 1078-081. Web.

[11] Yang, HC, and Drake HL. "Differential Effects of Sodium on Hydrogen- and Glucose-dependent Growth of the Acetogenic Bacterium Acetogenium Kivui." APPLIED AND ENVIRONMENTAL MICROBIOLOGY 56.1 (1990): 81-86. Web. 23 Apr. 2014.

Author

Page authored by Navi Sahi and Phil Colgan, students of Prof. Jay Lennon at IndianaUniversity.