| Methanohalophilus mahii | |
|---|---|
 | |
| Scanning electron microscope image ofMhp. mahii SLP | |
Scientific classification | |
| Domain: | Archaea |
| Kingdom: | Methanobacteriati |
| Phylum: | Methanobacteriota |
| Class: | "Methanomicrobia" |
| Order: | Methanosarcinales |
| Family: | Methanosarcinaceae |
| Genus: | Methanohalophilus |
| Species: | M. mahii |
| Binomial name | |
| Methanohalophilus mahii Paterek and Smith (1988) | |
Methanohalophilus mahii (also known asMhp. mahii) is an obligatelyanaerobic,[1]methylotrophic,[2]methanogenic[1]cocci-shaped[2]archaeon of thegenusMethanohalophilus[2] that can be found in highsalinityaquatic environments.[1] The nameMethanohalophilus is said to be derived frommethanum meaning "methane" inLatin;halo meaning "salt" inGreek; andmahii meaning "of Mah" in Latin, after R.A. Mah, who did substantial amounts of research onaerobic andmethanogenicmicrobes.[2] The proper word in ancient Greek for "salt" is howeverhals (ἅλς).[3] The specificstrain type was designated SLP (= ATCC 35705) and is currently the only identified strain of this species.[2]
There are a total of fourspecies in thegenusMethanohalophilus includingMethanohalophilus mahii,Methanohalophilus halophilus,Methanohalophilus portucalensis, andMethanohalophilus euhalobius.[1] The closest relative,Methanohalophilus portucalensis, has a 99.8% similarity in sequence across the whole genome toMethanohalophilus mahii.[1] The otherMethanohalophilus species have less than a 94.7% similarity toMethanohalophilus mahii.[1] All species in the genus arehalophilicmethanogens that contribute tomarine ecosystemmineral cycling.[1]
In 1988, Robert Paterek and Paul Smith were searching formethanogenicbacteria in theGreat Salt Lake inUtah when they first discovered thearchaeonMethanohalophilus mahii in its anoxicsediments.[2] Sediment samples were collected and stored inplexiglas tubes, and sub-core samples taken with abrass cork borer and transferred to fifty milliliter serum bottles.[4] All samples were processed within forty-eight hours of collection.[4] The media used forisolation ofMethanohalophilus mahiicolonies was prepared using the Hungate technique for proper isolation of anaerobic microbes.[4]Serial dilutions were prepared in a 1:10 ratio,[4] andagar roll tubes wereinoculated andincubated at 30 °C for eight weeks.[4] Isolated methanogenic colonies were chosen by identifying those with afoamy texture, denotinggas release,[1] and repeatedly diluted and inoculated on agar roll tubes until only one type of colonymorphology remained.[4] These colonies appeared ascream to paleyellow-coloredcircular-shaped colonies with an overallfoamy texture due to gas release.[2]
Several analyses were done to determinecell characteristics.[4]Methanohalophilus mahii is classified as a moderatehalophile, or an organism that can grow in highsalinity environments, since it can grow anywhere from a 0.5 to 3.5 MNaCl (about 30-200 g/L) range,[1] with an optimal growthconcentration at 2.0 M (about 115-120 g/L) NaCl,[1] but with a 1.2 M NaCl (about 70 g/L) concentration yielding the highest culture density.[1] It can also grow in varyingpH levels ranging from 6.5 to 8.2,[1] with an optimum pH of 7.5.[1]Methanohalophilus mahii is amesophile, or an organism that thrives at moderate temperatures, and grows best at a temperature of 37 °C.[2]
Methanohalophilus mahii cellsstainGram negative,[1] and are non-motile,[2] irregularcocci[2] approximately 0.8 to 1.8 micrometers in diameter.[2] Additionally, the cellsfluoresce under 420nanometer light.[2]Membranephospholipids are composed of β-hydroxyarchaeol cores,glucoseglycolipids, andethanolamine,glycerol, andmyo-inositol polar head groups.[1]
Methanohalophilus mahii is an obligately anaerobic[1]methylotrophic[2] andmethanogenicchemoheterotroph, able toreduce single-carbon compounds and multi-carbon compounds given that there are no carbon-carbondouble bonds present.[1] Trace amounts ofMg2+,K+,Ca2+, andFe2+ions are required for methanogenic growth.[1]Methanol can be used independently as a carbon source, and theEmbden-Meyerhof-Parnas (EMP)glycolytic pathway can be utilized forcatabolic processes.[1] Possibleelectron donors includemethanol,methylamines,dimethylamines, andtrimethylamines.[1]Methanohalophilus mahii is capable of utilizing severalmetabolic pathways to either reduce oroxidizemethyl groups, creating eithermethane orcarbon dioxide in the process.[1] In the reductive methylotrophic methanogenic pathway,Methanohalophilus mahii can eventually reduce a methyl group to a methane, which is released.[1] In the oxidative methylotrophic pathway, the methyl group is instead oxidized tocarbon dioxide and released.[1] This process directly contributes to carbonmineralization in marine ecosystems.[1]
Methanohalophilus mahii's genome was sequenced throughshotgun sequencing using a 6.8kilobaseSanger DNA library.[1] The complete genome size was determined to be 2,012,424base pairs long, with 2,906 totalgenes, and 2,032 actualprotein-coding genes.[1] Thesequence had a 42.6%GC content, and forty-fivepseudogenes were located.[1]
Methanohalophilus mahii has a uniquesuppressor tRNA with a modifiedpyrrolysine, anamino acid that is most commonly found inprokaryotes, that can recognize and bind to theamber STOP codon (UAG) which is also coded for by the genes used formethylaminemethyltransferases.[1] This species was also the first member to have itsgenome completely sequenced in the genusMethanohalophilus[1], which comprises mildlyhalophilic,methylotrophicmethanogens.[1] These archaea in general are known to greatly contribute to the carbonmineralization process in marine ecosystems.[1] Specifically, theoxidativemethylotrophic pathwayMethanohalophilus mahii utilizes allows the species to oxidizemethane tocarbon dioxide, which, in turn, is used by otherplants andorganisms.[1] Thismineral cycling process allows for more growth anddiversity in theocean.[1]
