A Microbial Biorealm page on the genus Methanococcoides alaskense
Archaea; Euryarchaeota; Methanomicrobia; Methanosarcinales; methanosarcinaceae; methanococcoides; alaskense
Description and significance
Currently, Methanococcoides alaskense has only been isolated from sediments of Skan Bay, Alaska. Its impacts, if any, on humans or other organisms remain unknown. Similarly, its effects on the environment are also poorly studied. However, it has been suggested that global warming is more pronounced at high latitudes, such as the Arctics. Some research has shown an association between the degredation of the Arctic permafrost and the intensitifed release of methane, which may represent a potential hazard. Since this species is one of many that produce methane, it could potentially contribute to global warming in the Arctics. (3)
The exact size of the genome is still unknown, and general knowledge of content is limited. The 16s rRNA gene sequences of 2 strains, AK-5 and AK-9 were determined to be identical, and both strains were 99.8% similar to Methanococcoides burtonii. Strain AK-5 had a DNA G+C content of 41.9 mol%, and strain AK-9 has a DNA G+C content of 39.5 mol%. DNA-DNA hybridization techniques showed a 55% DNA-DNA relatedness value between strain AK-5 and Methanococcoides burtonii, its closest relative. There was an 88% DNA-DNA relatedness value between strain AK-5 and AK-9, indicating that they are both the same species. (1)
Cell structure, metabolism & life cycle
This species forms colonies that are approximately 1 milimeter in diameter or less, yellow to white in color, circular, and concave. Individual cells are single irregular coccoids that range from 1-2 micrometers in diameter. The cells stain gram negative and are autoflourescent with proeinaceous cell walls. Pili cover the cell surface, but they do not have a flagellum and are non-motile. One strain does, however, have two appendages per cell that appear to be flagella, yet the cells are still non-motile. Some cells contain long rod-like strutures with tubular subunits that are similar to structures that are believed to be the origin of the flagella in Pyrococcus furiosus. Electron-dense regions were also found in many cells, yet the nature of these structures is not known. (1)
They can grow in a temperature range of -2.3-30.6 degrees Celcius, but grow best at 23.6 degrees Celcius. They require a salinity concentration of 0.1M-0.7M and a pH of 6.3-7.5. (1)
Ecology (including pathogenesis)
Methanococcoides alaskense was isolated from sediment samples from Skan Bay, Alaska. They were collected in sediment 65 meters deep that has a year-round temperature of 1-6 degrees Celcius. The sediment is permanently anoxic below the top centimeter and rich in organic matter from diatoms and kelp. Sulfate is depleted around 45 centimeters below the sediment. The cells use trimethylamine as the only organic catabolic substrate and produce methane. (1)
Methanosarcinales are typically described as organisms that can reduce methylamines and acetate as well as carbon dioxide and formate with hydrogen gas. (2). Although Methanococcoides alaskense is placed in this category, it cannot use methanol, formate, dimethysusulfide, formate or hydrogen as catabolic substrates. (1) It uses trimethylamine as its sole organic substrate. Thus, this was the first resport of methyltrophic methanogens that could not grow on methanol. (1) This highlights our limited knowledge of methenogens in general, and of species like Methanococcoides alaskense specifically.
(1) Singh, N., Kendall, M. M., Liu, Y., and Boone, D. R. "Isolation and Characterization of methylotrophic methanogens from anoxic marine sediments in Skan Bay, Alaska: description of Methanococcoides alaskense sp. nov., and emended description of Methanosarcina baltica". International Journal of Systematic and Evolutionary Microbiology. 2005. Volume 55. p. 2531-2538.
(2) Slonczewski, J. L., and Foster, J. W. "Archaeal Diversity." Microbiology: An Evolving Science. 2011. p. 715-751.