File:Hypersaline environments and extremely halophilic microbes.jpg

English: Hypersaline environments and extremely halophilic microbes

A. Satellite view of the salterns in Bhavnagar, India, showing vivid red, orange and green ponds in which seawater evaporates leaving behind salt (field of view is ~ 10 km2). The colours are due to the pigments of the halophilic microbes in the brines of different salinity. The red/orange pigments of haloarchaea and Dunaliella salina (see D) encourage the absorption of solar radiation leading to increased rates of evaporation, resulting in more rapid salt production.

B. A teacher and her class wade into Great Salt Lake (Utah, USA) to collect samples to study under field microscopes.

C. A student investigates the biofilms that form stromatolite-like structures in Great Salt Lake, impressive calcium carbonate deposits precipitated by the actions of cyanobacteria.

D. Microscopic image from the hypersaline Lake Tyrrell, Australia (salinity> 20% w/v), in which we can tentatively identify the eukaryotic chlorophyte, Dunaliella salina (grown commercially for the carotenoid, β-carotene, which is widely used as a natural food colorant as well as a precursor to vitamin A), living alongside the haloarchaeon, Haloquadratum walsbyi, which has flat square-shaped cells with gas vesicles that allow flotation to the surface, most likely to acquire oxygen (scale bar is 5 μm).

E. Gypsum crust from the bottom of a shallow saltern pond (~20% w/v salinity) in Eilat, Israel, showing layered microbial communities of phototrophic microbes. The orange-brown upper layer is most likely dominated by unicellular cyanobacteria; the green layer by filamentous cyanobacteria; and the purple layer by anoxygenic purple sulfur bacteria. These microbes use light as a source of energy, and their layering is explained by differential tolerance to ultraviolet light and oxygen, and their capacity to use light of different wavelengths in photosynthesis. The anoxygenic purple sulfur bacteria are adapted to use light at the far-red end of the spectrum, which is less attenuated than visible light in sediments, and they benefit by living in close proximity to anaerobic sulfate-reducing bacteria (grey layer directly beneath the purple layer), which produce hydrogen sulfide. This compound is split to form oxidized sulfur in a similar way to which the oxygenic phototrophs, like cyanobacteria, produce oxygen from water. Such layering of microbial communities can trigger discussions about chemistry (the electron donors and products), physics (diffusion of oxygen and hydrogen sulfide, and the electromagnetic spectrum), geology (microbial fossils in gypsum) and ecological concepts (interspecies interactions and niche partitioning).

F. A laboratory-made salt (halite) crystal coloured red due to the presence of haloarchaea trapped inside small pockets of brine within the crystal (the central crystal is about 0.5 by 0.5 cm). This is a survival strategy used by haloarchaea to avoid desiccation. They remain viable inside the halite, and evidence suggests that some haloarchaea can survive over geological time inside buried halite. Some haloarchaea play a major role in hydrolysing biopolymers in salty environments, such as those used in the production of fish sauces. When we consume the sauces or sea salt, we consume haloarchaea!

G. During an excursion, students can collect samples from which they can inoculate media (in this case to grow extreme halophiles) after returning to the classroom, bringing the field-collected microorganisms into the laboratory and further connecting students to their environment.