How can halophiles survive

One mechanism halophiles use to survive in high concentrations of salt is the synthesis of osmoprotectants, which are also known as compatible solutes. These work by balancing the internal osmotic pressure with the external osmotic pressure, making the two solutions isotonic, or close to it. Compatible solutes are small-molecular weight molecules. A second, less common mechanism of defense against salt is through controlling potassium levels. To deal with the increased solute level, and to increase the solubility of the proteins within the cytoplasm, many proteins have evolved to become more acidic.

A large number of research projects have been focused on finding and classifying novel halophiles. A paper by Ndwigah in isolated a halophilic fungus, determining its optimal growth conditions and its metabolites. This paper also provided a novel species description of Haloferax namakaokahaiae. This bacterium was isolated from a brine lake in Iran. Because of the unique conditions to which the proteins of halophiles are subjected, their proteins are heavily studied, especially for their use in industry.

Varun in looked at the possibility of using a specific halophile to generate electricity. This species under its normal growth conditions fermented glycerol to ethanol, and produced electricity through iron reduction. The ubiquity of viruses does not stop when the environment gets salty.

Viral infection in hypersaline environments is also being actively investigated. Atanasova in investigated how haloviruses and their hosts interact on an ecology level, and gave general lifestyle descriptions of numerous haloviruses. Amoozegar, M. Bagheri, A. Makhdoumi, M. Nikou, S. A S Fazeli, P. Schumann, C. Each experiment was carried out in triplicate. Errors bars represent standard errors. The viability of stressed Hbt.

Mainly used for eukaryote and bacterial analysis, the extreme physico-chemical conditions around Hbt. Aspects of different cell populations are shown in scanning and transmission electron micrographs in Fig. After moderate salt stress 2. However, for cells incubated in NaCl 0. A possible explanation for these results is that most cells are lysed under these extreme conditions, and the signal is dominated by a small fraction of surviving cells.

To monitor reactivation, low salt 0. The tendency is confirmed in CRh, in which only one population is observed with undamaged DNA and intact membranes. Taken together, these results indicated that a significant sub-population of Hbt. The cells were incubated in 4.

In an exploration of Hbt. Stressed cells 0. Interestingly, rod-shaped cell formation did not follow classical binary fission, used by most Archaea for cell division. Cell division rather initiated from flat sacculi that eventually acquired conventional rod morphology. The rod-shape cells then elongated and split into two daughter cells.

The cycle was repeated as long as cells were cultured under favorable conditions, consistent with growth rates presented in Fig. Time-lapse light microscopy. The effect of low salt exposure on respiration is shown in Fig. We observed that the respiratory sensitivity of Haloarchaea is NaCl concentration and time-dependent. As illustrated in Fig. The longer the shock, the higher the minimum value of salt concentration for which respiration rate reached zero.

The O 2 -uptake rate of stressed cells decreased notably for cells exposed to below 1. The progressive loss of respiration, under these conditions, parallels slow or stopped Hbt. Figure 5 also shows the respiration activity of low salt stressed Hbt. It shows that the respiratory activity increases rapidly after transfer to 4. In all cases, respiration increases instantaneously including for the longest shock 7 days at the lowest salt concentration 0.

This cannot be the result of undesired contaminations, as demonstrated by control measurements of the recovery medium alone data not shown.

The observations suggested that a significant part of the cell population is still able to produce energy even during a brutal salt shock or when exposed to prolonged periods of stress at moderately low salt concentrations.

Respiration rate of Hbt. Respiration activity RA, light grey of cells in low-salt shock 2. The experiment starts with basal respiration of unstressed cells HS 4. Harvested cells were then exposed to various low-salt concentrations A 2. Finally, oxygen consumption of recovered cells was measured immediately after incubation of stressed cells in 4. Results are mean values for three independent experiments. Time on the x-axis corresponds to the low-salt incubation time.

Note that different scales were used in figure D. As discussed previously, the molecular dynamic state of the cellular proteome represents a robust indicator of cellular fitness 14 , 15 , Macromolecular denaturation through unfolding leads to lower effective force constants indicating less rigid structures. According to in vitro experiments on a model halophilic protein and to our previous work on Hbt. Here, we performed in vivo neutron scattering experiments to characterize the molecular dynamics parameters of the Hbt.

Sample preparation for the neutron experiments is described in Materials and Methods. A centrifugation step prior to sample load in the measurement cell eliminated most of cell debris and lysed material.

We considered, therefore, that the measured signal was dominated by the fraction of intact cells in the low salt stress samples to provide relevant information on their functional state. The experiments displayed in Fig. The scattering vector modulus Q range of IN13 extends from 0.

The analysis was limited to the low Q end, where the time-length window is appropriate for MSD of macromolecular internal motions as well as the larger fluctuation amplitudes involved in unfolding processes Fig. Unfolded proteins have been measured by neutron scattering to display lower resilience than folded states 34 so that the effective force constants in the low salt samples in Fig.

Even if the unfolded structures tended to aggregate, it is not unlikely on the time scale of internal motions that such aggregates would be less resilient than the compact cores of native states We subsequently measured the effective average force constants of Hbt. The 2. The white column is the control sample at physiological salt molarity.

The reactivated samples CR, solid grey blocks are compared to the corresponding value under stress dashed patterns and the control white column. Low salt concentrations, in vitro , were found to be strongly destabilizing for model halophilic proteins 8 , Previous neutron scattering experiments established this was also the case in the cytosol of Hbt.

In this work, we extended the neutron scattering observations to extreme low salt shock. And, as expected, a more substantial dynamic perturbation of the proteome was observed. Furthermore, we characterized cellular and physiological modifications resulting from low salt stress and shock. Most cells adopt a spherical shape; an increasing fraction of dead cells and cells with damaged membranes is detected together with a dramatic decrease in residual respiratory activity.

Strikingly, even for the sample exposed to 0. The evolution of cell architecture suggested that cell division property is recovered after several hours incubation in 4.

This cycle was repeated, consistent with the growth rate measurements. The observations indicated that despite the harsh low salt shock exposure, which significantly affected the molecular dynamics of the proteome and consequently cell metabolism, a fraction of cells maintained their capacity to recover. Different non-exclusive hypotheses could explain the observation: 1 large intracellular molecular assemblies, like chaperonins, proteasomes, peptidases, that were shown to be more resistant to low salt conditions in vitro 17 , 18 , 35 trigger the recovery; 2 low salt conditions induce the accumulation of protective stress response molecules, such as chaperones or compatible solutes; 3 The formation of persisters, dormant stress-tolerant phenotypic variants first identified while investigating antibiotic resistance in bacteria Even though the latter hypothesis is supported by the biphasic time-kill curves, further investigation will be required to establish whether or not H.

The neutron scattering results showed that the presence of cells that could be reactivated in low salt stress populations 2. This implies that a modified molecular dynamics landscape, reduced metabolic activity and morphological changes in the case of the 2. The rapid recovery, after incubation in physiological salt, of proteome molecular dynamics and respiration indicates that the perturbation is reversible. Note that other cellular functions may be much slower to appear as suggested by the later onset of cell division.

In this work, we highlighted the capacity of specific Hbt. The observation contributes to the understanding of how halophilic Archaea, exposed to important salt fluctuations occurring in their natural environments, can survive and disseminate in low salt conditions, such as in soils, human or plant microbiomes and in the stratosphere, where they have been shown to occur 25 , 26 , 27 , 28 , The characterization of in cellular molecular dynamics of stressed and reactivated cells illustrated the physico-chemical aspects of the survival process.

The determination of the cell biology mechanisms involved in the selection and reactivation of resistant cells is a major challenge to be tackled in the future, in particular by combining single cell metabolomics and proteomics. Halobacterium salinarum R1 DSM is the hyperhalophilic archaea strain used for the study. The impact of the remaining salt concentration in the cellular paste on the final NaCl concentration of the medium used to stress the cells is negligible, as the pellet was resuspended at least in volumes of low-salt buffer.

One way halophilic archaea avoid this fate is by bathing their molecular machinery in a similarly salty intracellular environment that would cause ordinary proteins to lose their shape. How do the proteins inside these cells survive? At least part of the answer seems to relate to an abundance of certain amino acid residues on the protein surface.

Salt-tolerant proteins tend to have lots of aspartic acid, glutamic acid, and other non-hydrophobic residues on their surfaces. They also tend to have fewer lysines than similar proteins from non-halophilic counterparts, their places often being taken by bulkier arginine instead.

What traits of these residues make them salt-friendly? One school of thought suggests it's the charge they carry. In archaea, this adaptation is restricted to the the extremely halophilic family Haloarchaea often known as Halobacteriaceae. To use this method, the entire intracellular machinery — including enzymes, structural proteins, and charged amino acids that allow the retention of water molecules on their surfaces — must be adapted to high salt levels.

In the compatible solute adaptation, little or no adjustment is required of intracellular macromolecules — in fact, the compatible solutes often act as general stress protectants as well as osmoprotectants. These are the primary inhabitants of salt lakes, inland seas, and evaporating ponds of seawater.

The red color of deep salterns is due to the carotenoids organic pigment in these archaea.