Living with salt: metabolic and phylogenetic diversity of archaea inhabiting saline ecosystems

Abstract

Archaea that live at high salt concentrations are a phylogenetically diverse group of microorganisms. They include the heterotrophic haloarchaea (class Halobacteria) and some methanogenic Archaea, and they inhabit both oxic and anoxic environments. In spite of their common hypersaline environment, halophilic archaea are surprisingly diverse in their nutritional demands, range of carbon sources degraded (including hydrocarbons and aromatic compounds) and metabolic pathways. The recent discovery of a new group of extremely halophilic Euryarchaeota, the yet uncultured Nanohaloarchaea, shows that the archaeal diversity and metabolic variability in hypersaline environments is higher than hitherto estimated.

Diversity of extremely halophilic cultivable prokaryotes in Mediterranean, Atlantic and Pacific solar salterns: Evidence that unexplored sites constitute sources of cultivable novelty

“…This observation was reinforced by previous reports indicating that single clusters in the MALDI-TOF/MS dendrogram (OTUs) can be regarded as individual species [34]. The diversity observed was in accordance with haloarchaea shown to be the principal prokaryotic component of hypersaline habitats [2], and the fact that bacteria (despite having been underestimated for decades) could constitute up to 20% of their total diversity [5]. Our isolates were distributed among 35 distinct archaeal and 6 bacterial OPUs or species.…”

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

“…The two main factors that determine whether a microorganism can live anaerobically at extreme salinity (4250 g l − 1 ) are (i) the amount of energy it can generate through dissimilatory metabolism and (ii) the mode of maintaining osmotically balanced functional cytoplasm (haloadaptation) (Oren, 2011;2013;Andrei et al, 2012). Haloadaptation has high energetic costs, thus limiting the number of prokaryotes that can thrive in these environments.…”

“…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).…”

Seasonal fluctuations in ionic concentrations drive microbial succession in a hypersaline lake community

“…Paradoxically, the dominant microorganisms in these habitats are aerobic, heterotrophic Archaea, along with bacteria from the genus Salinibacter. Although most cultivated microbial strains isolated from extreme hypersaline environments are capable of facultative anaerobic fermentation, they grow optimally in the laboratory under aerobic conditions (Dyall-Smith, 2009;Andrei et al, 2012). The surprising abundance of oxygen-loving organisms in environments with such low oxygen solubility may be explained by the occurrence of nonequilibrium conditions at the air-water interface, providing locally higher oxygen availability.…”