Saltern Crystallizer Ponds Research Articles

Characterization of the halophilic archaeal community in saltern crystallizer ponds by means of polar lipid analysis

Saltern crystallizer ponds are coloured red due to the presence of dense communities of red halophilic archaea (family Halobacteriaceae). Little quantitative information exists on the species distribution within the archaeal community in such ponds. As the different genera of the Halobacteriaceae differ in polar lipid content, and especially in the types of glycolipids, lipid analysis can be used to obtain information on the nature of the organisms present. Analysis of the polar lipids extracted from the biomass collected from the saltern crystallizer ponds in Eilat, Israel, showed one major glycolipid to be present, co-chromatographing with the sulfated diglycosyl diether lipid characteristic of the genusHaloferax. No indications were found for the presence of significant amounts of those glycolipids that would indicate the presence of large numbers of other archaea such asHalobacterium species (H. cutirubrum andH. salinarium, characterized by sulfated triglycosyl and tetraglycosyl diethers), orHaloarcula species (possessing a triglycosyl diether). Phosphatidyl glycerosulfate, a polar lipid absent inHaloferax species, was present in the lipid extract from the crystallizer ponds, suggesting that the dominant microorganism present may be related to strains which are presently classified in the genusHalobacterium but are awaiting a taxonomic reappraisal (H. sodomense, H. saccharovorum, andH. trapanicum). Organisms of the latter group are characterized by sulfated diglycosyl diethers, and the presence of phosphatidyl glycerosulfate. Attempts to isolate the dominant type of bacterium on agar plates yielded relatively low counts (1–2 orders of magnitude lower than the numbers observed microscopically) of bacteria, and most of the isolates had a polar lipid composition characteristic of theH. salinarium group or theH. sodomense-H. saccharovorum-H. trapanicum group.

On the red coloration of saltern crystallizer ponds. II. Additional evidence for the contribution of halobacterial pigments

In a previous paper we attempted to assess the contribution of red bacteria of theHalobacterium — Haloferax — Haloarcula group and of the β-carotene-rich green algaDunaliella salina to the red colour of saltern crystallizer ponds. By means of light absorption measurements, we showed that bacterioruberin contained in the bacteria was mainly responsible for the colour of the brines, in spite of the fact that β-carotene derived fromDunaliella was the pigment present in the greatest amount. This apparent discrepancy was explained by the very smallin vivo optical cross-section of β-carotene, which is densely packed in globules inside theD. salina cells. We recently observed that the centrifugation technique used in the previous study to collect biomass from the ponds was unsuitable for this type of measurements, as a substantial part of theDunaliella cells present did not sediment upon centrifugation due to the low specific gravity caused by the high β-carotene content. Therefore similar measurements were performed with biomass collected by filtration. Again,in vivo absorption spectra were dominated by the absorption peaks of bacterioruberin. The results reported here show that, in spite of the methodological problem associated with the earlier study, all views and conclusions expressed in our earlier paper retain their validity.

Availability, uptake and turnover of glycerol in hypersaline environments

A sensitive assay for glycerol and other polyols was developed, based on periodate oxidation to formaldehyde, followed by a colorimetric assay with 3-methyl-2-benzothiazolone hydrazone. Apparent glycerol concentrations thus measured in saltern crystallizer ponds were around 20–36 μM, while in the Dead Sea, during a Dunaliella bloom, values were up to 27 μM. However, these values probably overestimate the glycerol concentrations present, as shown by labeled glycerol uptake experiments. Values of [K + Sn] (natural concentration + affinity constant) in saltern ponds were as low as 0.76–1.4 μM, with Vmax values of 193–303 nmol 1−1h−1, and turnover times between 2.6–7.2 h at 35°C. Similar measurements in the Dead Sea were: [K + Sn] 0.07–1.41 μM, Vmax values 160–426 nmol 1−1h−1, and turnover times in the range of 0.45–3.3 h.

On the red coloration of saltern crystallizer ponds

To assess, respectively, the contribution of red bacteria of theHalobacterium-Haloferax-Haloarcula group and of the β-carotene-rich green algaDunaliella salina to the red colour of saltern crystallizer ponds, we studied the optical properties of the brines of NaCl-saturated saltern ponds in Eilat, Israel, and quantified the pigments present in their biota. The absorption spectrum of the brines, as measured using the opal glass method to reduce the interference by scattering, or using an integrating sphere, nearly corresponded to thein vivo absorption spectrum of bacterioruberin-containing red archaeobacteria. However, extracts of the microbial community in organic solvents were dominated by β-carotene, a pigment occurring in high concentrations in theDunaliella cells present, and bacterioruberin contributed only between 13 and 28 per cent of the total visible light absorption by the extracts. The apparent discrepancy between these results can be explained by the very small in vivo optical cross-section of β-carotene, which is densely packed in globules inside theD. salina cells.

A method for the differential microscopic enumeration of Halobacterium cells

When hypersaline brines are treated with low concentrations of bile salts, such as sodium deoxycholate or sodium taurocholate, Halobacterium and related halophilic archaebacteria lyse while both halophilic eubacteria and halococci remain intact. Microscopic enumeration of bacteria before and after treatment with bile salts, thus, enables the estimation of Halobacterium population sizes in natural samples. Sodium deoxycholate was found to be superior to sodium taurocholate as at least one strain ( Haloferax volcanii) resists lysis by taurocholate. Treatment with 0.003% sodium deoxycholate caused lyusis of ≈ 42% of the bacteria present in a solar saltern crystallizer pond; using the same method, it was shown that no significant population of halobacteria was present in the Dead Sea in 1988.