Mariprofundus ferrooxydans
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''Mariprofundus ferrooxydans'' is a
neutrophilic Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying in ...
, chemolithotrophic,
Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...
bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
which can grow by oxidising
ferrous In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to " ferric" or iron(III), meaning iron in its +3 oxidation state, suc ...
to
ferric In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to sp ...
iron. It is one of the few members of the class
Zetaproteobacteria The class Zetaproteobacteria is the sixth and most recently described class of the Pseudomonadota. Zetaproteobacteria can also refer to the group of organisms assigned to this class. The Zetaproteobacteria were originally represented by a singl ...
in the phylum Pseudomonadota. It is typically found in iron-rich deep sea environments, particularly at hydrothermal vents. ''M. ferrooxydans'' characteristically produces stalks of solid iron oxyhydroxides that form into iron mats. Genes that have been proposed to catalyze Fe(II) oxidation in ''M. ferrooxydans'' are similar to those involved in known metal redox pathways, and thus it serves as a good candidate for a model iron oxidizing organism.


Discovery

The bacterium was isolated from iron-rich
microbial mats A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts. ...
associated with hydrothermal vents at a submarine volcano,
Kamaʻehuakanaloa Seamount Kamaʻehuakanaloa Seamount (previously known as Lōʻihi) is an active submarine volcano about off the southeast coast of the island of Hawaii. The top of the seamount is about below sea level. This seamount is on the flank of Mauna Loa, the la ...
(formerly Lōʻihi), near
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
, and has only 85.3% 16S similarity to its nearest cultivated species '' Methylophaga marina''. It has a doubling time at 23 °C of 12 hours and a curved rod (about 0.5×2–5 µm) morphology.


Etymology

Despite being validly published, the etymology of the generic epithet is grammatically incorrect, being a concatenation of the Latin neutral ''mare -is'' (the sea) with the Latin masculine adjective ''profundus'' (deep) intended to mean a deep-sea organism (the neuter of ''profundus'' is ''profundum''). The specific epithet is ''ferrum'' (Latin noun), iron and ''oxus'' (Greek adjective), acid or sour, and in combined words indicating oxygen. (N.L. v. ''oxydare'', to make acid, to oxidize; N.L. part. adj. ''ferrooxydans'', iron-oxidizing.)


Physiology

''M. ferrooxydans'' lives in microoxic conditions and uses Fe(II) as an electron donor and oxidizes it to Fe(III) as its main energy acquiring pathway, using oxygen as the electron acceptor and CO2 as its carbon source. It is a chemolithotroph that requires marine salts and has not been shown to grow heterotrophically. Biotic iron oxidation is in competition with abiotic iron oxidation, so ''M. ferrooxydans'' thrives in environments with high concentrations of Fe(II) but low concentrations of oxygen, where biotic oxidation of iron is able to compete with abiotic oxidation. Having high concentrations of Fe(II) in the environment is critical since iron oxidation is a low energy-yielding process, and high amounts of iron must be oxidized to yield an adequate amount of energy. The proposed model of iron oxidation in ''M. ferrooxydans'' involves oxidation of Fe(II) by an outer membrane iron oxidase, funneling the electron through an electron transport chain made up of cytochromes; oxygen is used as the terminal electron acceptor and then reverse electron transport is used to make NADH.


Lifestyle

''M. ferrooxydans'' cells are Gram-negative curved rods that cycle through two life stages: they have a free-living stage where they are motile, and a second stage where they are oxidizing iron and forming solid iron oxides. The fibrous twisted stalks of iron oxyhydroxides extruded by ''M. ferrooxydans'' are found in iron mats and are predicted to consist of an organic matrix which allows the iron oxide structure to form in a manner characteristic of ''M. ferrooxydans''. This organism is also motile and chemotactic, which enables it to move towards appropriate concentrations of oxygen even in the heterogeneous and rapidly changing environment of hydrothermal vents; the organism can rapidly detect and respond to changing oxygen concentrations to allow aerotaxis towards appropriate levels of oxygen. Motility allows ''M. ferrooxydans'' to remain in microoxic conditions despite the amount of mixing occurring in its environment, and remain where it can out-compete abiotic iron oxidation to acquire enough energy to survive.


Genome

''M. ferrooxydans'' is capable of fixing CO2 using RuBisCo genes encoded in its genome; it has multiple different RuBisCo genes which suggests that the organism has adapted to fix CO2 across a broader spectrum of concentrations of oxygen and carbon dioxide. This organism has never been observed to grow heterotrophically, yet its genome encodes for a sugar phosphotransferase system, typically used as a carbohydrate transporter, which is specific for fructose and mannose. Carbohydrate transport is thus encoded in its genome, but it is unknown if they can be used as a carbon source or if they are used for forming the carbohydrate scaffolding matrix of the twisted stalks formed by the organism.


Role in corrosion

''M. ferrooxydans'', along with other FeOB, have been implicated in the corrosion of Q235 steel; they are able to form a biofilm on the surface of the steel and cause pitting in the surface of the steel. The main products of Q235 steel corrosion caused by ''M. ferrooxydans'' are iron oxides such as FeOOH and Fe2O3, and this organism also causes acidification of the environment around the attachment site, which allows the pitting to occur.


See also

* Pseudomonadota phylogeny for more on placement


References


External links


Type strain of ''Mariprofundus ferrooxydans'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q10957092 Zetaproteobacteria Bacteria described in 2010