Extremophilic microorganisms

What are extremophilic microorganisms? Let’s start by looking closer at microorganisms.

All the organisms we know about on Earth are either cellular (by far the majority) or non-cellular (viruses).

Cellular organisms fall into one of three domains: bacteria, archaea and eukaryotes.

Bacteria and archaea are often called microorganisms or microbes. These terms are used to describe organisms based on their size and also include some eukaryotes such as proteans, fungi and algae. Microorganisms, in particular bacteria and archaea, are found in almost every location on Earth.

A microorganism is any biological organism that you can’t see with your naked eye – things that are so small that you need to use a microscope to see them.

Dr Adele Williamson

Some microorganisms live as single-celled organisms, and some grow in colonies like the mould on bread – what we see as mould is actually a group of fungal cells growing together in a colony.

Bacteria (including blue-green algae) and archaea are prokaryotes. These are single-celled organisms that don’t have a cellular nucleus. Their nucleic acids (RNA and DNA) aren’t separated from the rest of the cell and are exposed to all cellular processes.

The term ‘archaea’ is derived from the Greek word ‘archaios’, which means primitive or ancient. Archaea are mostly anaerobic and live in low-oxygen environments. Most archaea cannot be cultured in laboratories and are identified through culture-independent techniques such as PCR and other genetic tools and processes.

Bacteria and archaea look very similar, and until 30–40 years ago, they were considered to be one group of organisms. They both live as single-celled organisms and share many features. It wasn’t until the development of sophisticated genetic and biochemical technologies that their differences were discovered. The main differences are at the molecular level in their genes and the proteins they produce, including the enzymes controlling their biochemical pathways.

Eukaryotes are much more complex and have a cellular nucleus. The genetic material is protected from the rest of the cell by the nuclear membrane. Plants and animals including humans are eukaryotic.

The very first organisms on Earth were prokaryotes. Eukaryotes didn’t evolve until a billion years or so later!

These are some of the major similarities and differences between the organisms in the three domains of life:

Extreme environments

The biochemistry of each species is uniquely adapted for living in a particular environment. Some bacteria and archaea are adapted to live where other organisms can’t survive. These environments include deep-sea volcanic vents, geothermal landscapes, Arctic and Antarctic conditions, extreme saltiness and even deep below petroleum deposits.

These extreme environments are inhospitable for most living things, and we call the organisms living there extremophiles. In New Zealand, the easiest place to see extremophiles in nature is in the geothermal areas around Taupō and Rotorua.

Extremophilic microorganisms

We now understand that a lot of what we had once called extremophilic bacteria are actually archaea. Some bacteria are extremophiles, and almost all archaea are.

Extremophiles are able to live in extreme environments by using whatever energy and carbon sources are available to them. Many are able to get energy and the carbon they need to build their cells from chemicals in their environment that aren’t able to be utilised by other organisms, such as methane, sulfur and iron. In order to do this, they have distinct and unique metabolic pathways as well as genes that code for the proteins involved in the life processes necessary for their survival in an extreme environment. For example, halophilic (salt-living) archaea have a unique set of genes that limit the extent of osmosis, facilitating their survival in an environment so salty that other cells would be unable to retain water.

These unique adaptations to extreme environments make extremophiles very interesting for biotechnological research. The genes that code for their proteins, the enzymes involved in their unique cellular processes and the products of these processes have various potential applications in medicine and industry.