Methanosarcina acetivorans

A Microbial Biorealm page on the genus Methanosarcina acetivorans

Classification

Higher order taxa

Archaea; Euryarchaeota; Methanomicrobia; Methanosarcinales; Methanosarcinaceae; Methanosarcina

Species

NCBI: Taxonomy

Methanosarcina acetivorans

Description and significance

Describe the appearance, habitat, etc. of the organism, and why it is important enough to have its genome sequenced. Describe how and where it was isolated. Include a picture or two (with sources) if you can find them.

Methanosarcina acetivorans is a recently discovered "acetotrophic marine methane-producing bacterium that was isolated from methane-evolving sediments" (1). Early samples of these marine sediments were obtained from the Sumner branch of Scripps Canyon located near La Jolla, CA. It is also important to note that this species has optimal growth at 35 to 40 degrees celcius and an optimal pH range of 6.5 to 7.0. Additionally, NaCl and Mg2+ are required for its growth (1). After Methanosarcina acetivorans was enriched and isolated, the colonies were found to be blue-green when examined under UV fluorescence microscopy. the colonies that were incubated in roll tubes were pale yellow and found in colonies that were 0.5 mm in diameter (after 14 days), smooth, and circular (1).

Methanosarcina acetivorans was sequenced due to the availability of genetic tools (such as shuttle vectors and shotgun sequencing) that allow for it to be used as a model species for methanogens(3). The C2A strain was isolated from acetate-grown cultures and is the primary strain that is studied for Methanosarcina acetivorans (1). Methanosarcina acetivorans is a unique methanogen because it uses acetate as a source of carbon and as a source of energy. It does so by breaking down acetate to produce carbon dioxide and methane. This property makes it a possible key player in global warming.

Genome structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?

The genome of Methanosarcina acetivorans is one of the largest known archaeon genomes and and is comparatively larger than many sequenced prokaryote genomes. It consists of 5,751,492 nucleotides and 4528 protein coding genes (1). Of the protein coding genes, 49% have an assigned putative function, 20% are conserved hypothetical proteins, and 31% are predicted to be proteins with unknown functions (1). This makes it "over three times as large as the two previously sequenced methanogens, Methanobacterium thermoautotrophicum and Methanococcus jannaschii" (2). It is also significant to note that Methanosarcina acetivorans has a linear genome.

The plasmid pC2A was isolated from Methanosarcina acetivorans and thoroughly studied, but the exact function of plasmid pC2A remains unknown. The pC2A plasmid appears to be stable because it was isolated from strains that were maintained in laboratory settings for a long period of time (4). Due to the recent discovery of this plasmid, limited information of plasmid pC2A is available.

Cell structure and metabolism

Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.

Methanosarcina acetivorans has a great number and diversity of surface layer protens in comparison to other archaea species (1). Although Methanosarcina acetivorans is Gram-negative, there were thin sections that revealed a monolayer cell wall 10nm thick that is characteristice of marine methanogenic bacteria with a protein cell wall (2). Motility has not been observed in any Methanosarcina species, but one flagellin (fla) and two complete chemotaxis (che) gene clusters were found which may suggest that motility could be possible under certain situations (2).

Methanosarcina acetivorans is also capable of methanogenesis (a form of anaerobic respiration) which classifies it as a methanogen (capable of producing methane). Acetic acid is the terminal electron acceptor in this pathway by which methane and carbon dioxide are evolved from acetic acid. Additionally, some species of Methanosarcina acetivorans are capable of growing by using carbon monoxide (CO) as a methanogenic substrate (5).

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Methanosarcina acetivorans interacts with other organisms and affects the environment primarily through its production of methane (2). Methane is a potent greenhouse gas that reflects heat better than carbon dioxide. Due to this ability of Methanosarcina acetivorans, it is capable of not only affecting organisms that it is in direct contact with, but all organsims that are affected by greenhouse gases (such as humans). Methane is also a potential alternative energy source. Aside from its ecological influences, not much is known about the interaction of Methanosarcina acetivorans with other microorganisms.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Methanosarcina acetivorans is not known to cause any diseases. Refer to ecology section for information on how this microbe affects humans.

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

The biotechnological implications of Methanosarcina acetivorans are limited because a precise understanding of the enzymatic processes involved in methanogenesis are still a mystery. A single-subunit enzyme (CO dehydrogenase) that is used by Rhodospirillum rubrum was found to be present on the genome of Methanosarcina acetivorans which allows certain strains to grow on carbon monoxide (2). Methanosarcina acetivorans is a methanogen which means that it is capable of producing methane. Methane is not utilized by other organisms and is only a byproduct of methanogenesis.

Current Research

Enter summaries of the most recent research here--at least three required

Current research conducted by the Broad Institute of MIT seeks to understand the role of Methanosarcina acetivorans in the global carbon cycle especially because it is the only known species to posess all three known pathways for methanogenesis (3). Additionally, research of methanogenesis on the genetic level would allow for more detailed analysis of the process; however, the large size of the Methanosarcina acetivorans makes this quite difficult (4).

Additoinally, the exact mechanism for methanogensis in Methanosarcina acetivorans is still being researched, but could have implications for controlling the amount of methane that is released into the atmosphere.

References

(1) Sowers, K.R., Baron, S.F., and Ferry, J.G. 1984. Methanosarcina acetivorans sp. nov., an acetotrophic methane-producing bacerium isolated from marine sediments. Appl. Environ. Microbiol. 47: 971-978

(2) Galagan, J.E., et al. "The Genome of M. acetivorans Reveals Extensive Metabolic and Physiological Diversity" Genome Res., Apr 2002, 12: 532 - 542.

(3) Metcalf, W.W., Zhang, J.K., Apolinario, E., Sowers, K.R., and Wolfe, R.S., "A genetic system for Archaea of the genus Methanosarcina: Liposome-mediated transformation and construction of shuttle vectors" Proc Natl Acad Sci U S A. 1997 March 18; 94(6): 2626–2631.

(4) Sowers, K.R., Gunsalus, R.P., "Plasmid DNA from the acetotrophic methanogen Methanosarcina acetivorans." J Bacteriol. 1988 October; 170(10): 4979–4982.

(5) Lessner, D.J., Li, L., Li, Q., Rejtar, T., Andreev, V.P, et al. "An unconventional pathway for reduction of CO2 to methane in CO-grown Methanosarcina acetivorans revealed by proteomics." Proc Natl Acad Sci U S A. 2006 November 21; 103(47): 17921–17926.

Edited by Paul Molina, student of Rachel Larsen and Kit Pogliano