Nitrogen metabolism in haloarchaea

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 NO 3 -, NO 2 -or NH 4 + 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.

Anaerobic Metabolism in Haloferax Genus

“…In general terms, Haloferax growth under those microaerobic or even strict anaerobic conditions is possible because oxygen is replaced by other final electron acceptors such us nitrate, nitrite (Lledó, Martinez-Espinosa, Marhuenda-Egea & Bonete, 2004;Bonete et al, 2008;Nájera-Fernández, Zafrilla, Bonete & Martinez-Espinosa, 2012;Esclapez, Zafrilla, Martinez-Espinosa & Bonete, 2013) (per)chlorate (Oren, Elevi-Bardavid & Mana, 2014; Martínez-Espinosa, Richardson & Bonete, 2015), sulphur or sulphide (Elshahed et al, 2004), arsenate (Rascovan, Maldonado, Vazquez & Eugenia Farias, 2015), dimethyl sulfoxide (DMSO), trimethylamine N-oxide (TMAO) and fumarate (Oren & Trüper, 1990;Oren, 1991;Oren, 1999;Müller & DasSarma, 2005).…”

“…mediterranei are complete denitrifiers (Bonete et al, 2008), other such as Hfx. volcanii are incomplete and in some cases (Hfx.…”

Elemental sulfur and acetate can support life of a novel strictly anaerobic haloarchaeon

“…According to physiological and genomic studies, cultivated haloarchaea are predominantly aerobic heterotrophs (Andrei et al, 2012). There are only a few known examples of facultative anaerobic haloarchaea species capable of growth by either fermentation, or anaerobic respiration using nitrate, fumarate, dimethyl sulfoxide or trimethylamine N-oxide as terminal electron acceptors (Oren and Trüper, 1990;Oren, 1991;Antunes et al, 2008;Bonete et al, 2008;Werner et al, 2014). As these electron acceptors are present in hypersaline anoxic habitats at very low concentrations (Oren, 2011), it might appear that these facultative anaerobes cannot play a significant role in anaerobic environments.…”

Archaeal Diversity and Their Biotechnological Potential

“…The increase of salinity and nitrate/nitrite concentrations in soils and ground waters in the last few decades has focused much attention on the physiological and molecular mechanisms involved in salt-stress tolerance and nitrate metabolism by microorganisms. Physiological studies carried out with Haloferax mediterranei have revealed that it is resistant to very high nitrate (up to 2 M) and nitrite (up to 50 mM) concentrations (Bonete et al, 2008). Microorganisms are in general sensitive to low nitrate and nitrite concentrations.…”

“…Microorganisms are in general sensitive to low nitrate and nitrite concentrations. The inhibitory effect of these nitrogen compounds is due to the extreme toxicity of nitrite and nitric oxide produced upon nitrate reduction (Bonete et al, 2008).…”