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Nitrogen metabolism in haloarchaea.

Bonete MJ, Martínez-Espinosa RM, Pire C, Zafrilla B, Richardson DJ - Saline Syst. (2008)

Bottom Line: It was described as a denitrifier and it is also able to grow using NO3(-), NO2(-) or NH4(+) as inorganic nitrogen sources.This review summarizes the advances that have been made in understanding the N-cycle in halophilic archaea using Hfx mediterranei as a haloarchaeal model.The results obtained show that this microorganism could be very attractive for bioremediation applications in those areas where high salt, nitrate and nitrite concentrations are found in ground waters and soils.

View Article: PubMed Central - HTML - PubMed

Affiliation: División de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain. mjbonete@ua.es

ABSTRACT
The nitrogen cycle (N-cycle), principally supported by prokaryotes, involves different redox reactions mainly focused on assimilatory purposes or respiratory processes for energy conservation. As the N-cycle has important environmental implications, this biogeochemical cycle has become a major research topic during the last few years. However, although N-cycle metabolic pathways have been studied extensively in Bacteria or Eukarya, relatively little is known in the Archaea. Halophilic Archaea are the predominant microorganisms in hot and hypersaline environments such as salted lakes, hot springs or salted ponds. Consequently, the denitrifying haloarchaea that sustain the nitrogen cycle under these conditions have emerged as an important target for research aimed at understanding microbial life in these extreme environments.The haloarchaeon Haloferax mediterranei was isolated 20 years ago from Santa Pola salted ponds (Alicante, Spain). It was described as a denitrifier and it is also able to grow using NO3(-), NO2(-) or NH4(+) as inorganic nitrogen sources. This review summarizes the advances that have been made in understanding the N-cycle in halophilic archaea using Hfx mediterranei as a haloarchaeal model. The results obtained show that this microorganism could be very attractive for bioremediation applications in those areas where high salt, nitrate and nitrite concentrations are found in ground waters and soils.

No MeSH data available.


Related in: MedlinePlus

N-cycle scheme. NO3- is used as nitrogen source for growth under aerobic conditions using an assimilatory NO3- reductase, while it acts as an electron acceptor to eliminate excess of reductant power through dissimilatory NO3- reduction. Dissimilatory NO3- reduction, NO3- respiration or denitrification are often used equivalently in the literature. However, dissimilatory pathway makes reference to non-assimilatory reactions that are not directly coupled to generation of proton-motive force. In some Enterobacteriaceae, NO2- is reduced to NH4+ which is then excreted; this process is known as NO3-/NO2- ammonification. Specialised organisms are able to oxidize either NH4+ or NO2- by using a pathway called nitrification, while other organisms such as some planctomycetes oxidize NH4+ and utilize NO2- as respiratory electron acceptor in a pathway named anammox. Finally, (di)nitrogen fixation allows several bacteria and archaea to reduce N2 to NH4+ to provide N-requirements.
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Figure 1: N-cycle scheme. NO3- is used as nitrogen source for growth under aerobic conditions using an assimilatory NO3- reductase, while it acts as an electron acceptor to eliminate excess of reductant power through dissimilatory NO3- reduction. Dissimilatory NO3- reduction, NO3- respiration or denitrification are often used equivalently in the literature. However, dissimilatory pathway makes reference to non-assimilatory reactions that are not directly coupled to generation of proton-motive force. In some Enterobacteriaceae, NO2- is reduced to NH4+ which is then excreted; this process is known as NO3-/NO2- ammonification. Specialised organisms are able to oxidize either NH4+ or NO2- by using a pathway called nitrification, while other organisms such as some planctomycetes oxidize NH4+ and utilize NO2- as respiratory electron acceptor in a pathway named anammox. Finally, (di)nitrogen fixation allows several bacteria and archaea to reduce N2 to NH4+ to provide N-requirements.

Mentions: Nitrogen (N) is a major element in all organisms. It accounts for approximately 6% of their dry mass on average and thus in nature its assimilation is a key process of the N-cycle carried out by higher plants [1], algae [2], yeast [3], and bacteria [4]. In the environment, N can be found in different redox states from +5 (as nitrate) to -3 (as ammonia), but in biological compounds it is almost exclusively present in the most reduced form as a component of the two pre-eminent biological macromolecules: proteins and nucleic acids [5]. The reactions of the global biogeochemical N-cycle makes possible the interconvertions of nitrogen compounds and it includes both reductive and oxidative processes, in which prokaryotes play a predominant role (Fig. 1).


Nitrogen metabolism in haloarchaea.

Bonete MJ, Martínez-Espinosa RM, Pire C, Zafrilla B, Richardson DJ - Saline Syst. (2008)

N-cycle scheme. NO3- is used as nitrogen source for growth under aerobic conditions using an assimilatory NO3- reductase, while it acts as an electron acceptor to eliminate excess of reductant power through dissimilatory NO3- reduction. Dissimilatory NO3- reduction, NO3- respiration or denitrification are often used equivalently in the literature. However, dissimilatory pathway makes reference to non-assimilatory reactions that are not directly coupled to generation of proton-motive force. In some Enterobacteriaceae, NO2- is reduced to NH4+ which is then excreted; this process is known as NO3-/NO2- ammonification. Specialised organisms are able to oxidize either NH4+ or NO2- by using a pathway called nitrification, while other organisms such as some planctomycetes oxidize NH4+ and utilize NO2- as respiratory electron acceptor in a pathway named anammox. Finally, (di)nitrogen fixation allows several bacteria and archaea to reduce N2 to NH4+ to provide N-requirements.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2483277&req=5

Figure 1: N-cycle scheme. NO3- is used as nitrogen source for growth under aerobic conditions using an assimilatory NO3- reductase, while it acts as an electron acceptor to eliminate excess of reductant power through dissimilatory NO3- reduction. Dissimilatory NO3- reduction, NO3- respiration or denitrification are often used equivalently in the literature. However, dissimilatory pathway makes reference to non-assimilatory reactions that are not directly coupled to generation of proton-motive force. In some Enterobacteriaceae, NO2- is reduced to NH4+ which is then excreted; this process is known as NO3-/NO2- ammonification. Specialised organisms are able to oxidize either NH4+ or NO2- by using a pathway called nitrification, while other organisms such as some planctomycetes oxidize NH4+ and utilize NO2- as respiratory electron acceptor in a pathway named anammox. Finally, (di)nitrogen fixation allows several bacteria and archaea to reduce N2 to NH4+ to provide N-requirements.
Mentions: Nitrogen (N) is a major element in all organisms. It accounts for approximately 6% of their dry mass on average and thus in nature its assimilation is a key process of the N-cycle carried out by higher plants [1], algae [2], yeast [3], and bacteria [4]. In the environment, N can be found in different redox states from +5 (as nitrate) to -3 (as ammonia), but in biological compounds it is almost exclusively present in the most reduced form as a component of the two pre-eminent biological macromolecules: proteins and nucleic acids [5]. The reactions of the global biogeochemical N-cycle makes possible the interconvertions of nitrogen compounds and it includes both reductive and oxidative processes, in which prokaryotes play a predominant role (Fig. 1).

Bottom Line: It was described as a denitrifier and it is also able to grow using NO3(-), NO2(-) or NH4(+) as inorganic nitrogen sources.This review summarizes the advances that have been made in understanding the N-cycle in halophilic archaea using Hfx mediterranei as a haloarchaeal model.The results obtained show that this microorganism could be very attractive for bioremediation applications in those areas where high salt, nitrate and nitrite concentrations are found in ground waters and soils.

View Article: PubMed Central - HTML - PubMed

Affiliation: División de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain. mjbonete@ua.es

ABSTRACT
The nitrogen cycle (N-cycle), principally supported by prokaryotes, involves different redox reactions mainly focused on assimilatory purposes or respiratory processes for energy conservation. As the N-cycle has important environmental implications, this biogeochemical cycle has become a major research topic during the last few years. However, although N-cycle metabolic pathways have been studied extensively in Bacteria or Eukarya, relatively little is known in the Archaea. Halophilic Archaea are the predominant microorganisms in hot and hypersaline environments such as salted lakes, hot springs or salted ponds. Consequently, the denitrifying haloarchaea that sustain the nitrogen cycle under these conditions have emerged as an important target for research aimed at understanding microbial life in these extreme environments.The haloarchaeon Haloferax mediterranei was isolated 20 years ago from Santa Pola salted ponds (Alicante, Spain). It was described as a denitrifier and it is also able to grow using NO3(-), NO2(-) or NH4(+) as inorganic nitrogen sources. This review summarizes the advances that have been made in understanding the N-cycle in halophilic archaea using Hfx mediterranei as a haloarchaeal model. The results obtained show that this microorganism could be very attractive for bioremediation applications in those areas where high salt, nitrate and nitrite concentrations are found in ground waters and soils.

No MeSH data available.


Related in: MedlinePlus