Extremophiles

Microbes SEM

Scanning electron microscope image of thermophilic bacterium Chthonomonoas calidirosea. Photo Credit: Kevin Lee.

Microorganisms are present in almost every environment on earth, including in the heated water-bodies and soils of geothermal environments. As a general definition, microorganisms are any life form that cannot be seen without magnification. Examples of microorganisms can be found in all three kingdoms of life including Eukaryotes (for example protozoa, algae and some fungi), Bacteria and Archaea.

Some microorganisms, primarily bacterial and archaeal species, are the only life forms that survive such harsh conditions. Temperatures can be up to 122°C, the pH can range from highly acidic to strongly alkaline, and there can be elevated concentrations of salts and/or heavy metals. These unique forms of microorganisms are appropriately termed ‘extremophiles’.

Extremes of temperature

Extremes of Temperature

Microbial Community Members

Extremes of pH

Extremes of pH

Microorganisms derive energy either via photosynthesis or via the chemical oxidation of organic or inorganic compounds. Photosynthetic microorganisms including algae, cyanobacteria and a small number of other bacterial species are capable of living in geothermal environments, but are limited to temperatures less than 65°C. Conversely, microorganisms generating energy from chemical oxidation processes use gases (e.g. methane or hydrogen), metals (e.g. iron) or organic compounds (e.g. sugars, fats or protein) as energy sources. They can be found at temperatures up to 100°C in New Zealand’s terrestrial environments.

Where are they?

While the individuals are invisible to the naked eye, these micro-communities can be “seen” in some characteristic features of a geothermal ecosystem. A distinctive characteristic of algae and cyanobacteria is their ability to form microbial mats and films. Some mats change colour with the season and sunshine hours, being dark green in winter and orange in summer.

In some areas, the silica structures are shaped the way they are due to interaction with the microbial communities. For example, when silica precipitation and microbial mats occur together, the mats are encased in silica forming a spectacular structure. Many of the pink, yellow and orange colours seen on silica terraces and structures are due to pigmented microorganisms.