Cyanobacteria Or Blue Green Algae Biology Essay


Rajish Bhrath.

ID. # 110004521

Friday, February 15, 2012


Cyanobacteria or blue-green algae are single-celled organisms (prokaryotes) whose existence dates back nearly four billion years, placing it among the earth oldest and most primitive forms of life. Cyanobacteria thrive in almost every environment like hot springs, salt marshes, moist soils etc. They are found most frequently in freshwater lakes and rivers throughout the world, but variants exist almost anywhere where there is water, including inside of other organisms such as lichen, plants and protists. They have thick cell walls to protect them from the outside and preserve homeostasis. Cyanobacteria usually exist in low concentrations, and are not visible without the use of a microscope. However the organism can grow rapidly, in favorable conditions, such as calm nutrient-rich fresh or marine waters in warm climates or during the late summer months in cooler parts of the world. Rapid bacterial growth results in the formation of cyanobacteria blooms or mats which can accumulate to form surface scum in shallow inlets and bays, and along the shoreline of lakes and rivers. This surface scum can block sunlight and decrease oxygen in the water below, which can lead to plant and animal death.

Cyganobacteria blooms may occur as a result of high quantities of nutrients in the water. Nutrients may concentrate in natural bodies of water due to: Inadequate water flow or exchange of water when tides changes, nutrients such as nitrogen and phosphorus from  fertilizers used in agricultural process and in lawn and landscape work, sewage waste, industrial waste, etc. being drained into waterways, changes in rivers and their surroundings due to urbanization , farming practices, construction and housing.

Cyanobacteria have been classified into five groups: chroococcales, pleurocapsales, oscillatoriales, nostocales and stigonematales. They are photosynthetic organisms like green plants that consume carbon dioxide and produce oxygen. Scientists believe that cyanobacteria were among the first photosynthetic organism to occur on the earth’s surface and the oxygen produced by cyanobacteria enriched the earth’s atmosphere and converted it to its modern form. Cyanobacteria also has the ability to fix nitrogen, therefore, the bacteria plays a significant role in the nitrogen cycle as well as in the cycles of oxygen and carbon.

Cyanobacteria contain chlorophyll a as a major pigment for harvesting light and conducting photosynthesis. They also contain other pigments such as the phycobiliproteins which include allophycocyanin (blue), phycocyanin (blue) and sometimes phycoerythrine (red). These pigments harvest light in the green, yellow and orange part of the spectrum which is hardly used by other phytoplankton species. The phycobiliproteins, together with chlorophyll enable cyanobacteria to harvest light energy efficiently and to live in an environment with only green light.  Photosynthesis in cyanobacteria generally uses water as an electron donor and produces oxygen as a by-product, though some may also use hydrogen sulfide a process which occurs among other photosynthetic bacteria. Carbon dioxide is reduced to form carbohydrates via the Calvin cycle. 

Dinitrogen fixation is a fundamental metabolic process of cyanobacteria, giving them the simplest nutritional requirements of all living organisms. By using the enzyme nitrogenase they convert N2 directly into ammonium (NH4) and by using solar energy to drive their metabolic and biosynthetic machinery, only N2, CO2, water and mineral elements are needed for growth in the light. Nitrogen-fixing cyanobacteria are widespread among the filamentous, heterocyst forming genera (e.g. Anabaena, Nostoc). However, there are also several well documented examples of nitrogen fixing among cyanobacteria not forming heterocysts (e.g. Trichodesmium). Under predominantly nitrogen limited conditions, but when other nutrients are available, nitrogen fixing cyanobacteria may be favoured and gain growth and reproductive success.

The structure and organization of cyanobacteria are studied using light and electron microscopes. The basic morphology comprises unicellular, colonial and multi cellular filamentous forms. The only means of reproduction in cyanobacteria is asexual. Filamentous forms reproduce by trichome fragmentation, or by formation of special hormogonia. Hormogonia are distinct reproductive segments of the trichomes. They exhibit active gliding motion upon their liberation and gradually develop into new trichomes.

Many species of cyanobacteria possess gas vesicles. These are cytoplasmic inclusions that enable buoyancy regulation and are gas-filled, cylindrical structures. Their function is to allow the bacteria to adjust their vertical position in the water column, to optimize their position, and thus to find a suitable niche for survival and growth, cyanobacteria use different environmental stimuli (e.g. photic, gravitational, chemical, thermal) as clues. Gas vesicles become more abundant when light is reduced and the growth rate slows down. Increases in the turgor pressure of cells, as a result of the accumulation of photosynthate, cause a decrease in existing gas vesicles and therefore a reduction in buoyancy. Cyanobacteria can, by such buoyancy regulation, poise themselves within vertical gradients of physical and chemical factors. Other ecologically significant mechanisms of movement shown by some cyanobacteria are photo-movement by slime secretion or surface undulations of cells.

Some strains of cyanobacteria are known to produce toxins that affect humans and animals. These toxins affect different parts of the body, from the skin and upper respiratory system to the neurons. Some of the toxins can affect the liver, causing hemorrhaging, vomiting, cancer, and even death. Swimming or drinking from contaminated water source is the most common cause of poisoning.

Cyanobacterial toxins are classified by how they affect the human body. Hepatotoxin affects the liver and is produced by strains of the cyanobacteria Microcystis, Anabaena, Oscillatoria, Nodularia, Nostoc, Cylindrospermopsis and Umezakia. Neurotoxin affects the nervous system and is produced by strains of Aphanizomenon and Oscilatoria. Cyanobacteria from the species Cylindroapermopsis raciborski may also produce toxic alkaloids, causing gastrointestinal symptoms or kidney disease in humans.

Detoxification of contaminated water sources is a complex process and the best option is to institute measure to prevent or suppress bacterial growth by reducing or eliminating the food source and allow the bacteria to die slowly, this is usually a lengthy process and can take years. Some toxin breaks down naturally in lakes, and conventional water treatment facilities can remove cells by adding chemicals that bind them together. As the cells clump together, they become heavier and fall to the bottom of the reservoir or tank, where they can be easily filtered out. While this method will remove cells, it will not remove potentially harmful cyanobacterial toxins. These can be removed using certain oxidation procedures or activated charcoal. The World Health Organization (WHO) says that 100,000 cells/mL is a moderate human health risk.

Researchers are conducting studies into cyanobacteria as a source for producing renewable biofuels and chemicals due to their ability to capture solar energy and CO2, and their relatively simple genetic background for genetic manipulation. Scientist has successfully modified cyanobacteria for various biotechnological applications.