Symbiotic Relationship

 

A symbiotic relationship between two organisms of various species wherein one accomplice derives a benefit and the opposite suffers no damage.

From: Encyclopedia of Microbiology (Third Edition), 2009

Related phrases:

David P. Clark, ... Michelle R. McGehee, in Molecular Biology (Third Edition), 2019

8.2 Primary and Secondary Endosymbiosis

A symbiotic affiliation in which one organism lives in the other is known as endosymbiosis. Primary endosymbiosis refers back to the unique internalization of prokaryotes by means of an ancestral eukaryotic cell, resulting within the formation of the mitochondria and chloroplasts. Two membranes surround mitochondria and chloroplasts. The internal one is derived from the bacterial ancestor and the outer “mitochondrial” or “chloroplast” membrane is really derived from the host-cell membrane. However, numerous lineages of protozoans appear to have engulfed other single-celled eukaryotes, particularly algae. Several agencies of algae therefore have chloroplasts acquired at 2nd-hand with the aid of what is termed secondary endosymbiosis.

Secondary endosymbiosis takes place whilst a eukaryotic cell is engulfed by means of every other eukaryote. The resulting cell for that reason receives organelles from  lineages.

In comparison to the typical  membranes of number one organelles, 4 membranes surround chloroplasts received by way of secondary endosymbiosis. In most instances, the nucleus of the engulfed eukaryotic alga has disappeared without trace. Occasionally, the remains of this nucleus are nonetheless to be located mendacity among the two pairs of membranes (Fig. 29.26). This structure is named a nucleomorph and can be seen in cryptomonad algae in which it represents the remains of the nucleus of a crimson alga that become swallowed via an amoeba-like ancestor. The nucleomorph incorporates three vestigial linear chromosomes totaling 550 kb of DNA. These carry genes for rRNA that is integrated into some eukaryotic kind ribosomes which might be additionally positioned in the space between the two pairs of membranes.

Cells attributable to secondary endosymbiosis are composites of four or 5 authentic genomes. These include the primary ancestral eukaryote nucleus and its mitochondrion, plus the nucleus, mitochondrion, and chloroplast from the secondary endosymbiont. Many genes from the subordinate genomes were lost at some stage in evolution and no hint has ever been located of the secondary mitochondrion. Some genes from the secondary endosymbiont nucleus had been transferred to the number one eukaryotic nucleus. The protein merchandise of approximately 30 of those are made on ribosomes belonging to the primary nucleus and shipped from the primary eukaryotic cytoplasm back into the nucleomorph compartment. In turn, the nucleomorph contains genes for proteins that are made at the 80S ribosomes inside the nucleomorph compartment and transported throughout the inner two membranes into the chloroplast. Finally, there are proteins now encoded by means of the number one nucleus that need to be translocated across each sets of double membranes from the number one cytoplasm into the chloroplast! An particularly thrilling case is that of malaria, which later lost the potential to photosynthesize and have become a parasite (Box 29.02).

Is Malaria Really a Plant?

Malaria is a disease that influences many hundreds of thousands of people worldwide and is chargeable for two or 3 million deaths every year, mostly in Africa. Malaria is as a result of the single-celled eukaryote Plasmodium. The malaria parasite and different associated unmarried-celled eukaryotes are individuals of the phylum Apicomplexa. Although those parasites stay internal people and mosquitoes, some distance from the sunlight, they possess plastids in addition to mitochondria. These plastids are degenerate, nonphotosynthetic chloroplasts with a circular genome. In Plasmodium the plastid DNA is 35 kb and encodes rRNA, tRNA, and a few proteins, normally concerned in translation (Fig. 29.27).

The malarial plastid or “apicoplast” is notion to derive from secondary endosymbiosis. The ancestor of the Apicomplexa seems to have swallowed a single-celled eukaryotic alga that possessed a chloroplast. The algal nucleus has been completely misplaced, but the plastid turned into stored and is surrounded by using 4 membranes. Sequence comparisons endorse the malarial apicoplast is most closely associated with the chloroplast of red algae.

Although it does not convert mild into electricity, the apicoplast is critical for the survival of Plasmodium. The apicoplast performs a important function in lipid metabolism. Several enzymes of fatty-acid synthesis are encoded within the nucleus but translocated into the apicoplast wherein fatty-acid synthesis happens. As a end result, positive herbicides that prevent fatty-acid synthesis within the chloroplasts of inexperienced flowers are effective in opposition to Plasmodium and different pathogenic apicomplexans including Toxoplasma and Cryptosporidium. For example, clodinafop objectives the acetyl-CoA carboxylase and triclosan inhibits the enoyl ACP reductase of vegetation and bacteria. These herbicides have no effect on fatty-acid synthesis in animals or fungi. In addition, the herbicide fosmidomycin inhibits the isoprenoid pathway of plants and micro organism, which differs from that of animals. Fosmidomycin inhibits boom of Plasmodium and cures malaria-infected mice. Plasmodium and its loved ones are also inhibited by way of chloramphenicol, rifamycin, macrolides, and quinolones, all of which are antibacterial antibiotics. These also are thought to behave via the apicoplast.

Jan Šobotník, Cecilia A.L. Dahlsjö, in Reference Module in Life Sciences, 2017

Gut Microbiota and Fungi

The symbiotic dating between termites and microorganisms is obligatory as it permits termites to break down natural count number. This symbiotic dating has also been proven to benefit the microbial communities, that are covered from doubtlessly adversarial environments with a constant supply of assets.

Termite guts are inhabited with the aid of a high range of microbial taxa, although, many are unculturable and can be detected with the aid of sequencing simplest. While the technological development in excessive-throughput sequencing has furnished better mapping of symbiotic taxa it has also found out the presence of microorganisms that play a mere function in the termite gut. While some “true” symbionts attain excessive abundances in termite guts, there are numerous which can be exceptionally rare. Some microorganisms had been proven to no longer provide any offerings to the host and some are suspected to take part in commensalism or moderate parasitism (e.G., some micro organism or Apicomplexa: Gregarinasina). Symbiotic associations need to consequently be studied throughout geographical and seasonal scales that allows you to better recognize the useful role of the one-of-a-kind microbial strains.

The current understanding of the function of gut symbionts in termites are (1) dissimilatory metabolism of sugar polymers (cellulose, hemicelloloses) and their cleavage into short chains to be used by termites or other symbionts, (2) removal of oxygen so that you can keep an anoxic surroundings that lets in for fermentation to take area in the intestine, (3) nitrogen metabolism either by way of solving atmospheric nitrogen or recycling nitrogen waste, (4) hydrogen elimination via reduction acetogenesis, (five) degradation of aromatic compounds originated from lignin units (demethylation, deacetylation, decarboxylation, and to a limited quantity smash-down of fragrant cores), and (6) humification of complex natural matters and carbon mineralization from protein additives of humus in soil-feeders.