Osmoadaptive Strategies of the ArchaeonHalococcus hamelinensisIsolated from a Hypersaline Stromatolite Environment

Abstract

Biogenic stromatolites are sources of significant information on the evolution of microbial life. Despite their evolutionary significance, little is known about the mechanisms of osmoadaptation by microorganisms that comprise living stromatolites thriving in hypersaline environments. Osmoadaptive strategies for Halococcus hamelinensis, a novel halophilic archaeon recently isolated from living stromatolites in the hypersaline reaches of Shark Bay, were thus a particular interest in this study. To investigate the possibility of "salt-in-cytoplasm"-associated osmoadaptation for this archaeon, flame photometry studies were performed. From the results, it was evident that this halophilic archaeon did not accumulate intracellular K(+) ions when cells were exposed to either osmotic shock or conditions with gradual increments in salinity. These results were further supported by polymerase chain reaction (PCR) analyses where there was no evidence for the existence of homologous genes to an ATP-driven, high-affinity potassium uptake system in Halococcus hamelinensis. To identify an alternative salt adaptation mechanism associated with accumulation of compatible solutes for this archaeon, (1)H nuclear magnetic resonance (NMR) spectroscopy experiments were carried out. Results indicate that glycine betaine, trehalose, and glutamate are solutes likely to be involved in osmoregulation in this archeaon. Subsequent (1)H NMR analysis of cell extracts from this microorganism grown under various NaCl concentrations revealed that intracellular levels of glycine betaine increased with increasing concentrations of NaCl. This behavior of increasing glycine betaine concentration with increasing external NaCl is consistent with its identity as an osmolyte. In contrast, intracellular levels of trehalose were decreased in high concentrations of NaCl. This provides evidence that compatible solute accumulation appears to be the preferential salt regulation mechanism for this haloarchaeon, in contrast to the salt-in-cytoplasm strategy employed by many other halophilic archaea.

Patterns and Determinants of Halophilic Archaea (Class Halobacteria) Diversity in Tunisian Endorheic Salt Lakes and Sebkhet Systems

“…Further, a pathway for the dependence on the H ϩ /K ϩ symporter of the Trk family for potassium uptake has recently been proposed on the basis of an extensive genomic survey of 80 different Halobacteria genomes (63). In addition to the salting-in strategy, recent studies have led to an increasing appreciation of the role played by another osmoadaptive mechanism, compatible solute accumulation, as a supplemental strategy in species of numerous taxa within the Halobacteria (37,(64)(65)(66). We have recently demonstrated that the biosynthesis and accumulation of molar levels of trehalose (or 2-sulfotrehalose) occur in multiple genera within the Halobacteria and that the genes mediating the process (the otsAB operon) are present in 61/80 examined genomes (37).…”

Insights into the metabolism, lifestyle and putative evolutionary history of the novel archaeal phylum ‘Diapherotrites’

“…Historically, Archaea were regarded as a collection of extremophiles that could only thrive in extreme habitats, for example, high temperature (Huber et al, 1991;Jannasch et al, 1992;Antoine et al, 1995;Whitaker et al, 2003), high salinity (Oren et al, 1990;Cui et al, 2010;Goh et al, 2011;Inoue et al, 2011), low pH (Edwards et al, 2000;Dopson et al, 2004), strict anaerobic conditions (Mikucki et al, 2003;Sakai et al, 2007) or combinations thereof (Huber et al, 1989;Itoh et al, 1999;Minegishi et al, 2008Minegishi et al, , 2013.…”

Trehalose/2-sulfotrehalose biosynthesis and glycine-betaine uptake are widely spread mechanisms for osmoadaptation in the Halobacteriales

“…Here, we decided to investigate the potential for alternative mechanisms of osmoadaptation in multiple Halobacteriales genera, with special emphasis on Haladaptatus paucihalophilus, known for its capability to grow in low and fluctuating salinities and survive extended incubations in distilled water (Savage et al, 2007). While few prior studies on the production (Nicolaus et al, 1988;Desmarais et al, 1997;Goh et al, 2011) and uptake (Kokoeva et al, 2002) of compatible solutes in the Halobacteriales have been published, detailed understanding of the extent of distribution, genetic basis and ecological significance of the process is lacking. We demonstrate that multiple Halobacteriales genera are capable of trehalose or 2-sulfotrehalose production, and that the uptake of glycine betaine is a widely utilized process for osmoadaptation in the Halobacteriales.…”