What is a microbe?

  • Microbes are the most numerous and diverse organs on earth
  • Microbes are living things too small to be seen with the naked eye
  • There are 10 orders of magnitude more microbial cells than stars in the universe
  • The majority of the earth’s biomass is microbial

All living things consist of:

  1. Bacteria – simple (single celled), no nucleus, no DNA in nucleus
  2. Archaea – simple (single celled), no nucleus, no DNA in nucleus
  3. Eukaryotes – more complex and have a nucleus with DNA
  4. Viruses – the border of what we consider living and made up of DNA and RNA. Viruses are inactive until in contact with a host and then inject genetic material.

Bacteria have three shapes bacilli (rods), cocci (balls) and spirals. Some are solitary and some are in groups (colonies or films). They move with scillia or flagella.

Archaea are similar to bacteria and also use scillia or flagella to move. They have a different function to bacteria. Many live in extreme environments. They can use sulphur for food, can live deep in the digestive tracts of many mammals and produce methane. For instance Halophiles live in a salty environment and Thermophiles live in a high temperature environment. Psychrophiles live in the cold and are also found in soil.

Bacteria and Archaea dominate the human gut

Eukaryotes (for instance fungi, yeast etc.) decompose organic material by secreting enzymes to break it down and then absorb nutrients. They can produce beneficial enzymes for humans such as riboflavin or detergent or negative such as aflatoxin (found on peanuts). Fungal cells are static and cannot move like bacteria. They produce spores or stems.

Other eukaryotes include protozoa, algae, amoebas and slime moulds.

Viruses are much smaller than bacteria and archaea. They need to infect a cell to reproduce (unlike the previous 3 organisms which can reproduce on their own). Different viruses have different hosts but they can evolve.

Microbes can produce vitamins and enzymes used in the health industry. They also have a number of environmental functions i.e. replacing the nutrients in the environment. They have an important role in the carbon cycle, for instance by decomposing dead leaves. Microbes can clean waste water and can even eat oil and clear oil spills.

Microbes are the only being that can take nitrogen in the air and convert it to nitrogen in the soil – therefore fertilizer should not be necessary if the soil is microbe-rich. There is only a need for fertilizer because we have grown the same crop on the same soil too long and depleted the microbes.

Microbes can survive in varying environments:

Anaerobes are bacteria that do not survive in an oxygenated environment.

Facultative Anaerobes are bacteria that can survive with or without oxygen

Obligate Anaerobes cannot survive without oxygen

The gastro-intestinal tract of humans contains no oxygen.


Jack Gilbert: Earth Microbiome Project

The Earth Microbiome Project started in 2010 and compares samples from different environments such as air, earth, animals etc. to see the difference in the microbe communities and to gain perspective on the microbial life on the planet.

We can see what bacteria live where, for example in deserts where there is an absence of plants. Plants photosynthesize sunlight, make carbon, synthesize this into sugars and pump them into the soil for the microbes. As there are very few plants in the desert environment, microbes fight each other and produce antibiotics.

Under 7 km of ocean there are bacteria living in rocks. These are barely alive and produce one energetic reaction every 10,000 years.

They are the longest living organisms on earth and potentially could survive and populate new worlds. We could terraform new planets with these microbes. If we wanted to create life on another planet, we would turn to organisms that created life for us. Without them we could not exist.

There was no oxygen on earth to begin with. Bacteria took energy from the sun and used it to fix carbon dioxide in the earth. Then they expired oxygen. This made it an oxygenated atmosphere and changed the type of iron on the planet. It started to rust. All iron on earth rusted. These two things changed the life on the planet.

The relationship between us and the environment is predicated entirely on bacterial life. Microbes are the number one thing that will affect how we intersect with life. We need to understand them to prolong our lives on this planet. Without doing this, we will struggle.

Microbes can be pathogenic or non-pathogenic (symbiotic); living in or on animals. We are starting to find that they have a lot more functions for the health of the host than we knew previously.

Amphibians are in trouble. There is a huge decline due to fungal skin bacterial communal pathogens which infect the skin.  The skin bacterial community can inhibit this and we are studying probiotic treatment. The Vertebrate Microbiome Project looks at what role the microbiome play in a host being able to evolve novel traits i.e. colour of feathers, behaviour etc. For instance, flying animals have to have a lower body weight therefore what role does the microbiome play in weight, density of bones etc.? Microbes that live with a host animal are very different from those that live in the environment i.e. on earth or in the soil.



The Human Microbiome Course

What is a Microbe?

The Human Microbiome

How we study the Microbiome Part 1

How we study the Microbiome Part 2

Impacts on the Microbiome

Microbiome and Obesity

The gut microbiota, autoimmune diseases and allergies

Human Microbiota and Gut Disease

Interactions between the Gut Microbiota and Immune System

The Gut-Brain Axis

Useful website articles and links

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