In this paper we describe denitrification at extremely high salt and pH in sediments from hypersaline alkaline soda lakes and soda soils. Experiments with sediment slurries demonstrated the presence of acetate-utilizing denitrifying populations active at in situ conditions. Anaerobic enrichment cultures at pH 10 and 4 M total Na+ with acetate as electron donor and nitrate, nitrite and N2O as electron acceptors resulted in the dominance of Gammaproteobacteria belonging to the genus Halomonas. Both mixed and pure culture studies identified nitrite and N2O reduction as rate-limiting steps in the denitrification process at extremely haloalkaline conditions.
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"In this case, no accumulation of nitrites was measured. This suggests that the optimum pH of the nitrite reductase of Hd is located around 11 in the chemical conditions of the experiment, similarly to the findings of Shapovalova et al. (2008) for Halomonas strain AGD3. The absence of nitrate and/or nitrite in the outlet of the bioreactor prevents further growth of Hd in the exposure chamber and explains why acetate concentration did not change after the passage through the exposure chamber. "
[Show abstract][Hide abstract]ABSTRACT: This study investigates the reactivity of nitrates in abiotic and biotic conditions at alkaline pH in the
context of a repository for long-lived inter-mediate-level radioactive waste. The work, carried out under
environmental conditions comparable to those prevailing in the repository: alkaline pH, no oxygen, solid
materials (cementitious material, steel), aims to identify the by-products of the nitrate reduction and to
evaluate reaction kinetics of these reactions with and without the presence of denitrifying microorganisms.
This paper demonstrates that, even at the high pH characteristic of nuclear waste repositories,
nitrate reduction may be a likely scenario, with biotic catalysis in the presence of microorganisms and
surface catalysis in the presence of steel and/or corrosion products.
"It is unfortunate that all these reported halophilic species only grew and actively denitrified under aerobic conditions. Because of the low concentrations of dissolved oxygen in industrial wastewaters, these reported aerobic halophilic species were not suitable for application in treatment of industrial wastewater (Shapovalova et al., 2008). The objective of this research was to isolate and characterize new halophilic denitrifying bacteria with better potential for saline industrial wastewater treatment . "
[Show abstract][Hide abstract]ABSTRACT: The isolation and characterization of a novel halophilic denitrifying marine bacterium is described. The halophilic bacterium, designated as NY-4, was isolated from soil in Yancheng City, China, and identified as Marinobacter hydrocarbonoclasticus by 16S rRNA gene sequence phylogenetic analysis. This organism can grow in NaCl concentrations ranging from 20 to 120 g/L. Optimum growth occurs at 80 g/L NaCl and pH 8.0. The organism can grow on a broad range of carbon sources and demonstrated efficient denitrifying ability (94.2% of nitrate removal and 80.9% of total nitrogen removal in 48 h). During denitrification by NY-4, no NO2--N was accumulated, N2 was the only gaseous product and no harmful N2O was produced. Because of its rapid denitrification ability, broad carbon use range and ability to grow under high salinity and pH conditions, NY-4 holds promise for the treatment of saline waste waters.
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The online version of this article (doi:10.1186/2193-1801-2-346) contains supplementary material, which is available to authorized users.
"Chemoheterotophic aerobes thriving in soda lakes are well represented by archaea, as well as Gram-negative and Gram-positive bacteria. Haloalkaliphilic members of the family Halomonadaceae (e.g., Halomonas magadiensis , H. kenyensis , H. mongoliensis ) have been isolated from soda lakes around the world, being an important part of the easily culturable aerobic chemoheterotrophic communities thriving in these ecosystems (Duckworth et al., 1996Duckworth et al., , 2000 Boltyanskaya et al., 2007 ; Shapovalova et al., 2008 ) . Other haloalkalitolerant and haloalkaliphilic Halomonas spp. "
[Show abstract][Hide abstract]ABSTRACT: Haloalkaliphiles differ from natronophiles by their requirement for chloride ions in addition to high alkalinity. Natronophilic bacteria grow optimally in soda medium buffered at alkaline pH by a combination of NaHCO3 and Na2CO3. The majority of known haloalkaliphilic and natronophilic prokaryotes are isolated from saline–alkaline ecosystems such as soda lakes and saline–alkaline soils. A great taxonomic and metabolic biodiversity is found in soda systems, enabling the functioning of all the cycles of the essential elements. In spite of the increasing number of haloalkaliphilic and natronophilic isolates, scarce biochemical and functional information on simultaneous adaptation at high salinity and alkalinity is reported. Most of the available data on haloalkaline adaptation can be inferred from the functional characterization of alkaliphilic and halophilic bacterial models as well as from a few haloalkaliphilic and natronophilic genome sequences deposited in databases. At the level of cell envelopes (cell wall and cytoplasmic membrane), the salt and alkaline adaptation strategies are different and relatively conserved between Gram-positive and Gram-negative bacteria. The cell wall of the former group is characterized by the excessive presence of acidic polymers, while cell membranes abound in phospholipids with branched fatty acids. Cell membranes of salt- and alkaline-adapted Gram-negatives contain a large variety of fatty acids as well as significant amounts of nonpolar lipids. Osmotic adaptation mostly depends on the accumulation of organic compatible solutes either by active solute uptake or by combined strategies of importing osmolytes or osmolyte precursors and de novo synthesis of organic compatible solutes. Aerobic and anaerobic haloalkaliphiles are distinguished from each other by very different bioenergetics. Energy conservation in aerobic alkaliphiles and haloalkaliphiles is mainly based on functioning of H+-driven F-type ATP synthase. In spite of the low transmembrane electrochemical proton gradient (equivalent to proton-motive force, pmf) encountered in the alkali-exposed membrane, the energy metabolism remains highly efficient, supporting high growth rate and yield in many aerobic alkaliphiles and haloalkaliphiles. The energetics of haloalkaliphilic anaerobes is less understood, but it seems to involve a greater deal of Na dependency than in their aerobic counterpart. Na+-dependent ATPase activity is reported in a few anaerobic haloalkaliphiles and its role probably deals with active Na+ ejection from the cytoplasm. In haloalkaliphiles and natronophiles, the sodium-motive force (smf) is mainly driving the flagellar movement and sodium/solute symport. Cytoplasmic pH and ion homeostasis in haloalkaliphiles and natronophiles are most probably achieved by a concerted activity of a constellation of alkaline-activated ion transporters, among which Na+/H+ and Mrp-like antiporters have a major contribution.