Symbiosis: The Art of Living Together

Context

1. Symbiosis 
    1.1 Mutualism
    1.2 Commensalism
    1.3 Parasitism
    1.4 Predation and Herbivory
2. Endosymbiosis and Endosymbiotic theory
    2.1 Evidence 
    2.2 Examples 
    2.3 Simple History Hypothesis 
3. Mixotrophs and Kleptoplasty

1. Symbiosis 

Symbiosis is a phenomenon in which two different organisms live in close physical proximity to one another and interact in a way that benefits at least one of the organisms. There are several different types of symbiosis, including mutualism, commensalism, and parasitism.

1.1 Mutualism

In mutualism, both organisms benefit from the relationship. An example of mutualism is the relationship between nitrogen-fixing bacteria and leguminous plants. The bacteria fix nitrogen gas from the air and convert it into a form that the plants can use as a nutrient, while the plants provide the bacteria with a place to live and grow. 

Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with the roots of legumes and other flowering plants.

1.2 Commensalism

In commensalism, one organism benefits from the relationship while the other is neither harmed nor helped. An example of commensalism is the relationship between barnacles and whales. The barnacles attach themselves to the whales and feed on small particles in the water that the whales stir up as they swim, but the whales are not affected by the barnacles. 

The simplest example of commensalism is a bird making a nest in a tree. The tree provides shelter and protection to the bird without getting significantly harmed or affected by the bird. Another typical example is the cattle egrets (birds) that feed upon the insects stirred up by the feeding cattle

1.3 Parasitism

In parasitism, one organism (the parasite) benefits at the expense of the other (the host). All parasitic organisms can be considered parasites. An example of parasitism is the relationship between ticks and humans. Ticks feed on the blood of humans, which can transmit diseases to humans, but the ticks do not benefit humans in any way.

1.4 Predation and Herbivory

Predation is a symbiotic relationship in which one organism, the predator, hunts and eats another organism, the prey. This relationship can have a significant impact on the population sizes and behaviors of both the predator and prey species. Some examples of predator-prey relationships include:

• Lions and gazelles
• Wolves and elk
• Sharks and fish

Herbivory is a symbiotic relationship in which one organism, the herbivore, feeds on plants or other photosynthetic organisms. This relationship can also have a significant impact on the population sizes and behaviors of both the herbivore and the plant species. Some examples of herbivore-plant relationships include:

• Deer and grass
• Elephants and trees
• Koalas and eucalyptus leaves

Both predation and herbivory are important components of many ecosystems and play a role in maintaining the balance of nature.

2.  Endosymbiosis and Endosymbiotic theory

Endosymbiosis is a type of symbiosis in which one organism lives inside the body or cells of another organism. The endosymbiotic theory is a scientific theory that explains how certain organelles within eukaryotic cells, such as mitochondria and chloroplasts, came to be.

According to the endosymbiotic theory, these organelles were once free-living prokaryotes that entered into a symbiotic relationship with other cells, eventually becoming integrated into the host cells and taking on specialized functions. This theory is supported by the fact that mitochondria and chloroplasts have their own DNA and are similar in many ways to prokaryotes, suggesting that they have a separate evolutionary history.

The endosymbiotic theory helps to explain how complex cells with specialized organelles, such as those found in plants and animals, could have evolved from simpler cells. It suggests that these complex cells arose through a process of gradual incorporation of other cells into their own bodies, rather than arising all at once through a sudden mutation. This theory has been widely accepted by the scientific community and has had a significant impact on our understanding of the evolution of life on Earth.

Endosymbiosis or The endosymbiont Theory was articulated in 1905 and 1910 by the Russian botanist Konstantin Mereschkowski, and advanced and substantiated with microbiological evidence by Lynn Margulis in 1967.

2.1 Evidence 

There are several pieces of evidence that support the endosymbiotic theory, including:

1. Mitochondria and chloroplasts have their own DNA and are similar in many ways to prokaryotes. This suggests that they have a separate evolutionary history from the eukaryotic cells in which they reside.
2. Mitochondria and chloroplasts have a double membrane, with the inner membrane being similar to the cell membrane of prokaryotes. This is thought to be a remnant of the original prokaryotic cell membrane.
3. Mitochondria and chloroplasts reproduce independently of the host cell, similar to how prokaryotes reproduce.
4. The size and shape of mitochondria and chloroplasts are similar to those of prokaryotes.
5. Mitochondria and chloroplasts contain ribosomes, which are similar in size and structure to prokaryotic ribosomes.
6. The genetic code used by mitochondria and chloroplasts is similar to that used by prokaryotes, further supporting the idea that they have a separate evolutionary histories.

2.2 Examples 

1. Endosymbiotic nitrogen-fixing bacteria: Certain bacteria are able to fix nitrogen from the air into a form that plants can use as a nutrient. These nitrogen-fixing bacteria can live inside the cells of plants, forming a mutually beneficial relationship in which the bacteria provide the plant with a vital nutrient and the plant provides the bacteria with a protected environment.
   
   
2. Symbiotic fungi: Many plants have a mutually beneficial relationship with fungi, in which the fungi live inside the plant's cells and help the plant absorb water and nutrients from the soil. In return, the plant provides the fungi with a source of sugars and other organic compounds.
   
   
3. Symbiotic protists: Some protists, such as the slime mold Dictyostelium discoideum, live inside the cells of other organisms and help to break down and recycle organic matter. In return, the host organism provides the protists with a protected environment and a source of nutrients.
   
   
4. Hydra is an example of endosymbiosis. Hydra is a small, freshwater invertebrate that belongs to the phylum Cnidaria. Hydra are known to harbor a diverse community of symbiotic microorganisms, including bacteria, archaea, and algae. These microorganisms live inside the cells of the Hydra and play important roles in the host's physiology and survival. For example, some of the bacteria found in Hydra are involved in nitrogen metabolism and help the host to obtain nutrients from its environment. Other bacteria produce toxins that protect the Hydra from predators. Algae, which are photosynthetic, can also be found inside the cells of Hydra and provide the host with additional energy through photosynthesis. Overall, the endosymbiotic microorganisms found in Hydra help to provide the host with a variety of benefits, including increased nutrient acquisition and protection from predators.
   
   
5. Some species of Paramecium have a symbiotic relationship with endosymbiotic bacteria called holospora. Holospora are rod-shaped bacteria that live inside the cells of Paramecium and are thought to play a role in the host's immune system. Specifically, it is believed that holospora help Paramecium to defend against other types of bacteria that may be harmful to the host. In return, Paramecium provides holospora with a protected environment and a source of nutrients
   
   
6. Entamoeba histolytica, a species of amoeba that causes a type of illness called amoebiasis. This amoeba has a symbiotic relationship with bacteria called Endolimax nana, which live inside the amoeba's cytoplasm (the material inside the cell). The bacteria provide the amoeba with nutrients, and in return, the amoeba provides the bacteria with a protected environment. Another example is Paulinella chromatophora, a species of amoeba that has a symbiotic relationship with photosynthetic algae. The algae live inside the amoeba's cytoplasm and provide the amoeba with energy in the form of glucose. In return, the amoeba provides the algae with a protected environment and access to light.
   
   
7. Paulinella chromatophora: This is a species of amoeba that has a symbiotic relationship with photosynthetic algae. The algae live inside the amoeba's cytoplasm and provide the amoeba with energy in the form of glucose, while the amoeba provides the algae with a protected environment and access to light.
   
   
8. Coral: Coral is a type of marine animal that has a symbiotic relationship with photosynthetic algae called zooxanthellae. The algae live inside the coral's tissues and provide the coral with energy in the form of glucose, while the coral provides the algae with a protected environment and access to sunlight.
   
   
9. Termites: Termites are insects that have a symbiotic relationship with bacteria and protozoa that live in their gut. These microorganisms help the termites digest cellulose, which is a major component of plant material. In return, the termites provide the microorganisms with a protected environment and a constant supply of food.
   
   
10. Lichens: Lichens are composite organisms that are made up of a fungus and an algae or cyanobacterium. The fungus provides the algae or cyanobacterium with a protected environment and access to nutrients, while the algae or cyanobacterium provides the fungus with energy in the form of glucose.

2.3 Simple History Hypothesis 

In easy language.

Around 2 billion years ago, when the Oxygen levels started rising on earth.1 fine day a prokaryotic organism engulfed 2 organisms. Still, it didn't digest it, the prokaryotic cell found out that 1 cell was able to use solar energy to perform photosynthesis and make sugar molecules. The other cell used oxygen gas to break down materials like sugar and release its energy into a form useful for life activities. Humans came and named 1 cell chloroplast and the other mitochondria. 

3. Mixotrophs and Kleptoplasty

Mixotrophs are organisms that can utilize both autotrophic and heterotrophic modes of nutrition. This means they can produce their own food through photosynthesis or chemosynthesis, as well as consume other organisms as a source of energy and nutrients.

For example, some mixotrophic algae are found in symbiotic relationships with certain marine animals, such as coral and sea anemones. The algae provide the host with nutrients through photosynthesis, while the host provides the algae with a protected environment and access to sunlight. This is known as mutualism, as both species benefit from the relationship.

Another example is the relationship between mixotrophic bacteria and certain protozoa. The bacteria can produce their own food through photosynthesis, but they also have the ability to consume organic matter. The protozoa can consume the bacteria, but they also have the ability to consume organic matter. In this case, the mixotrophic bacteria and protozoa are able to benefit from each other's different modes of nutrition, leading to a mutually beneficial relationship known as commensalism.

Kleptoplasty is a type of symbiotic relationship in which one organism (the kleptoplast) steals and incorporates the chloroplasts (the organelles responsible for photosynthesis) from another organism (the donor) into its own cells. The kleptoplast then uses these chloroplasts to produce its own energy through photosynthesis.

One example of kleptoplasty is the relationship between the sacoglossan sea slug, Elysia chlorotica, and various species of algae. The sea slug consumes the algae and then incorporates the algae's chloroplasts into its own cells, using them to produce energy through photosynthesis. This allows the sea slug to survive in environments where food may be scarce, as it can supplement its diet with energy produced through photosynthesis.

Another example is the relationship between the sea cucumber and certain species of dinoflagellates. The sea cucumber consumes the dinoflagellates and incorporates their chloroplasts into its own cells, using them to produce energy through photosynthesis. This allows the sea cucumber to survive in environments where food may be scarce, as it can supplement its diet with energy produced through photosynthesis.