Cyanobacteria

Cyanobacteria are believed to be one of the first ever life forms on Earth and the predecessor of all plants and many other photosynthetic organisms. They have survived billions of years and can be found in almost every environment on Earth, from oceans to deserts and the polar regions of the Arctic and Antarctica.

Also known as the blue-green algae, cyanobacteria are a hugely important organisms on a global scale. One, for their role as primary producers and two, because of their ability to turn nitrogen gas from the atmosphere into compounds that can be used to make proteins.

Cyanobacteria are single-celled organisms with prokaryotic cells but will often form colonies with individual cells working together, often arranged into long stringy filaments. Certain cyanobacteria cells, known as heterocytes, have the ability to fix nitrogen and work in unison with other cells. The heterocytes produce excess nitrates which are shared with neighboring cells. In exchange for nitrates, the neighboring cells provide the heterocytes with carbohydrates and other compounds.

 

Heterocytes

A special feature of the cyanobacteria which increases their global importance are heterocyte cyanobacteria cells. Heterocytes are a special type of cell that is able to take nitrogen from the atmosphere and convert it into usable nitrogen compounds that can be used to make vital proteins. The heterocytes allow cyanobacteria colonies to survive in areas where limited nitrogen would otherwise prevent them from living.

 

Reproduction

Cyanobacteria are able to reproduce in a number of ways. For the most part they reproduce simply by duplicating their DNA and splitting into two cells. Some species are able to reproduce by splitting into a number of fragments called ‘homogonia’ and which then regenerate into whole cells. Other species have special cells known as ‘akinetes’ which can survive through tough conditions and then germinate when conditions become more favorable.

 

Akinetes

Akinetes are a special type of cyanobacteria cell which is able store food and survive for tremendously long periods of time. When a colony of cyanobacteria cells find themselves in a stressful environment, species that have the capability to produce akinetes will do so in order to survive long enough until the conditions in the environment change back to suit the cyanobacteria and it the akinete will then reproduce normal cyanobacteria cells.

 

Taxonomy

The cyanobacteria are a division within the Kingdom Bacteria, a kingdom of microscopic organisms with prokaryotic cells. Within the Cyanobacteria there are four orders, each with different structures and forms.

Chroococcales – can be species of unicellular or colonial cyanobacteria.

Nostocales – are filamentous cyanobacteria with sheath and heterocytes.

Oscilatories – filamentous cyanobacteria without heterocytes.

Stigonematales – filamentous cyanobacteria with sheath, heterocytes and branching.

 

Nitrogen Fixing

Some species of cyanobacteria are able to take nitrogen from the atmosphere and turn it into usable forms to produce proteins. Nitrogen gas, N2, has a triple nitrogen-nitrogen bond which is difficult to break and is done by a special enzyme called nitrogenase. The enzyme is inhibited by oxygen so for the nitrogenase to work it must be separated from other cellular processes. For this reason many species have heterocytes which physically separate the process of nitrogen-fixing from the external environment and other cellular processes where oxygen is involved such as respiration and photosynthesis. Heterocytes will also often have thick cell walls to prevent oxygen diffusing into the cell.

Species that have nitrogen-fixing capabilities are better adapted to surviving in nitrogen limited environments. Nitrogen is an essential element for producing proteins which are the building blocks of cells and therefore life. By being able to utilise atmospheric nitrogen, cyanobacteria have an advantage over other bacteria in circumstances when a lack of nitrogen compounds (NO, NH) reduces their ability to grow, reproduce and survive. An interesting discovery about cyanobacteria colonies is that you can witness their response to environmental changes by seeing the changing proportions of nitrogen-fixing cells to normal cyanobacteria cells depending on the amount of nitrogen available.

 

Cyanobacteria Blooms

When conditions are right, colonies of cyanobacteria can grow and accumulate into giant algal blooms. Floating cyanobacteria blooms can completely cover the surface of lakes and coastal seas and makes swimming in such waters dangerous. Often these blooms can be toxic due to the chemicals produced by some species of cyanobacteria and they have been the cause of many cases of human illness and sometimes death.

 

Cyanotoxins

Many species of cyanobacteria produce toxins to help prevent them being eaten by animals. Cyanotoxins is the collective name for the different types of toxins produced by cyanobacteria they can be separated into three broad categories; each of which consists of a range of different toxic compounds. The hepatotoxins are toxins that cause damage to the liver and are the most common class of cyanotoxin. Neurotoxins attack the nervous system and can cause a victim to lose muscle control, mental abilities or become paralyzed. The third class of cyanotoxin are dermatotoxins which have various effects on the skin.

Last edited: 25 May 2015

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