Introduction

The first thought which comes to mind when people hear the word “bacteria” is germs - a micro-organism, especially one that produces diseases in animals and plants. In fact, these “bacteria”, such as cyanobacteria , make it possible for Earth to sustain life.

Cyanobacteria, also known as blue-green algae or pond scum, lives in aquatic environments and are photosynthetic; manufacturing their own food. Without struggle, cyanobacteria existed since 3.5 billion years ago, distinguished as being one of the oldest known fossils. Surviving as one of Earth’s important group of bacteria, cyanobacteria contribute a lot to the survival of organisms. 

Other common types of cyanobacteria include spirulina, oscillatoria, anabaena, and nostoc.

Structure & Function

The structure of the cyanobacterium (above) is composed of the following functions:

I) Lipid droplet -spherical droplets composed of lipids and proteins that are used as a way of storing lipids

II) Nucleoid (circular DNA) – similar to a nucleus, keeping genetic information

III) Protein Granule – grains of protein providing protein throughout the cell

IV) Ribosome – synthesizes protein chains from amino acid molecules

V) Photosynthetic Lamellae -  a thin layer, plate, or membrane for  a stronger structure

VI) Phycobilisomes (cyanosomes) – responsible for a result of 95% efficient energy transfer

VII) Plasma membrane – surrounds the bacteria, controlling the movement of substances into and out of the cell

VIII) Cell wall - a structural support and protection, in addition to acting as a filtering mechanism

IX) Gelatinous coat – an exterior fibrin gel protecting the cell from injuries

Habitat / Adaptation

In the past, cyanobacteria were known to be present in fresh water and terrestrial areas and were thought to be unimportant in the oceans. Still present in fresh water and earthbound environments, cyanobacteria are now considered to be important for being present in our oceans. Inside our modern oceans, within the cyanobacterium group, Synechococcus and Prochlorococcus were discovered to adapt as one of the ocean’s bases of the food chain. As the bases of the food chain, they are responsible for converting air, light, and water into available food for their predators.

Since the Pre-Cambrian era, cyanobacteria have contributed to produce oxygen and remove carbon dioxide from the air through a photosynthetic procedure, similar to that of plants. This ability to perform oxygenic photosynthesis was thought to have crucially changed the Earth’s selection of biodiversity and lead to a close extinction of organisms which are oxygen intolerant. In whole, from the processes of the past, Earth has now become an environment available to support life.

Movement / Dispersal

The way in which cyanobacteria moves is not through the usage of a flagella, cilia, or through pseudopodia, but moving through surfaces called gliding motility. Gliding motility is a well know trait upon other bacteria, yet the mechanism, the propeller movement of the cell, is still unknown.

Nutrition

Cyanobacteria contain other photosynthetic pigment other than chlorophyll, such as Phycobilins. Phycobilins are efficient because they are able to efficiently absorb red, orange, yellow, and green light, the light wavelengths which are not well absorbed by chlorophyll. There are three types of Phycobilins, which are phycocyanin (blue), phycourobilin (orange), and phycoerythrin (red). Different combinations of each phycobiliproteins can be found to approve different and specific spectroscopic properties.

Life cycle(s) and Reproduction

Within the cyanobacterium life cycle, cyanobactera undergo cell division approximately once per day under the influence of moderate constant light and through intensifying the light, the cells start dividing more frequently as more energy is available. It takes about 19 hours for the cyanobacteria to rest before it can process cell division once more. 

Cyanobacteria reproduce by either through asexual or vegetative methods and no sexual methods are in existence because there are no meiosis and gamete formations.

The asexual reproductive method involves the creation of thick walled cells named akinetes, which are able to store food, and some form endogenous or exogenous spores. Transformation, transduction, and recombination have been known to occur, but conjugation has yet to be seen observed by cyanobacteria.

Vegetative reproduction arises from fission, fragmentation, or by the formation of the hormogonia. The unicellular form of the cyanobacteria display fission and the multicellular form display fragmentation. 

Types of reproduction

Few examples of cyanobacterium reproduction:

Binary Fission: an individual bacterial cell divides into two equal parts and each will grow back to its original form. This process is repetitive and is one of the most common procedure of asexual reproduction.

Hormogonia Formation: at regular intervals, cyanobacteria form pieces of filaments containing from5 to 15 cells called hormogonia. They show motion of gliding motility and evolve into new filaments.

Hormocysts: hormocysts are produced from some cyanobacteria, a multicelluar structure containing a big sheath. It may germinate from either end, or both, to give formation to new filaments.

Fragmentation: an asexual process division where multiple fragments are grown into new organisms from the division of the parent cell.

Spores: another common asexual reproductive method, sporulation, is when an organism’s cell creates one or more reproductive cells within its cell wall. Spores are produced often in a great number for a rapid increase in population.

Relationship with humans

Not only can cyanobacteria be consumed by aquatic organism, but can be also offered as food for humans too, such as spirulina. Spirulina is provided with rich protein in food, therefore can be used in other circumstances, such as manure or fodder. They can be used in agricultural fields because these bacteria contain special cells called heterocyst, which fix and preserve nitrogen in the fields, and spirulina can also reclaim used soil.

Other than the positive effects of cyanobacteria, there are also the negative effects of it. Some cyanobacteria species contain toxins that harm humans and animals, which can be exposed from drinking or bathing in contaminated water. The toxins affect humans with symptoms such as skin irritation, stomach cramps, vomiting, nausea, diarrhoea, fever, sore throat, headache, muscle and joint pain, blister of the mouth, and liver damage. Instant exposure to cyanobacteria toxins may cause asthma, eye irritation, rashes, and blisters around the face.