Role of the denitrifying Haloarchaea in the treatment of nitrite-brines

Haloferax mediterranei is a denitrifying halophilic archaeon able to reduce nitrate and nitrite under oxic and anoxic conditions. In the presence of oxygen, nitrate and nitrite are used as nitrogen sources for growth. Under oxygen scarcity, this haloarchaeon uses both ions as electron acceptors via a denitrification pathway. In the present work, the maximal nitrite concentration tolerated by this organism was determined by studying the growth of H. mediterranei in minimal medium containing 30, 40 and 50 mM nitrite as sole nitrogen source and under initial oxic conditions at 42 °C. The results showed the ability of H. mediterranei to withstand nitrite concentrations up to 50 mM. At the beginning of the incubation, nitrate was detected in the medium, probably due to the spontaneous oxidation of nitrite under the initial oxic conditions. The complete removal of nitrite and nitrate was accomplished in most of the tested conditions, except in culture medium containing 50 mM nitrite, suggesting that this concentration compromised the denitrification capacity of the cells. Nitrite and nitrate reductases activities were analyzed at different growth stages of H. mediterranei. In all cases, the activities of the respiratory enzymes were higher than their assimilative counterparts; this was especially the case for NirK. The denitrifying and possibly detoxifying role of this enzyme might explain the high nitrite tolerance of H. mediterranei. This archaeon was also able to remove 60 % of the nitrate and 75 % of the nitrite initially present in brine samples collected from a wastewater treatment facility. These results suggest that H. mediterranei, and probably other halophilic denitrifying Archaea, are suitable candidates for the bioremediation of brines with high nitrite and nitrate concentrations (AU)

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Perdida cerebral de sal: medio siglo de un síndrome no bien definido / Cerebral salt wasting: half a century of a largely undefined syndrome

Peters made the original description of the cerebral salt wasting syndrome (CSWS) in 1950 in three patients with hyponatremia that he assumed to be secondary to natriuresis of cerebral mechanism. Few years later, Schwartz describe the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in two patients with bronchial carcinoma, with characteristics similar to CSWS. Wijdicks gave clinical entity to CSWS when referring that it is the prevalent cause of hyponatremia in patients with subarachnoid hemorrhage, and stressed the risk of secondary cerebral infarction if restrictive plans of water and salt were used as a consequence of a miss diagnosis. However, CSWS has been recently questioned because of its atypical characteristics, not shared by other saline wasting syndromes. The volume status of patients with hyponatremia and natriuresis determines whether the cause of this disorder is SIADH or CSWS. Nevertheless the evidence are contradictory, the vasopressin level can be recognized only in relation to the tonicity of body fluids, and the natriuresis is a common final pathway for both syndromes. In this literature review, some issues of CSWS that are associated or opposed with SIADH and other saline wasting syndrome are discussed. We conclude that the reports that sustain CSWS are insufficient in their methodology and interpretation of the results. The absence of strict metabolic studies has been negatively replaced by the original information casually quoted, and the strength of tradition. Thereafter, the paradigm generates unfounded ethical dilemmas which render difficult any further investigations with appropriate controls. (Au)