(no subject)
The temperate regions on Earth act as a center for the 4,400 kinds of aphids that are known to exist. With the exception of 20 to 30 very particular kinds of aphids, the rest have in them a symbiotic bacterium called Buchnera. Buchnera is concentrated in the 20 to 30 big cells called bacterium cells in the fatty tissue of an aphid. It is a well-known fact that Apogamia, blastogenesis without fertilization is common among aphids. When an aphid begins blastogenesis, a part of Buchnera in the bacterium cell of the mother aphid goes into the embryo in the early stage of development, thereby passing Buchnera into the aphid of the next generation. If a mother aphid is injected with a small portion of a certain kind of antibiotic, the aphid of the next generation won't have Buchnera, and at the same time, will grow to be underdeveloped, having no reproductive function. Buchnera, on the other hand, can't reproduce itself outside a bacterium cell. Therefore, the inter-relationship of aphids and Buchnera is vital.
A great deal of evidence supports the current consensus that the history of symbiosis between aphids and Buchnera is 200 million years. During some kind of event, an ancestor of the aphid took an ancestor of Buchnera into its cell, and since that time for 200 million years, Buchnera has lived in the cells of aphids for several 100 million generations. In the meantime, the host aphid has differentiated into more than 4,000 kinds, and probably, Buchnera has differentiated into an amount that is now equal to the differentiation of the host.
Through genetic analysis, Buchnera family bacterium was found to be closely related to Escherichia coli (E. coli). The genetic difference between the currently existing Buchnera and E. coli shows the difference of living environments between them, in other words, it shows the difference between a symbiont living in a cell and a free living thing. A significant difference is genome size. Genome of Buchnera has 640,000 base pairs, which represent about one seventh of those in E. coli's genome (E. coli genome has 4,640,000 base pairs). Among genomes which have already been analyzed, the genome of Buchnera is the smallest next to a cyto-parasitic bacterium, mycoplasma (580,000 base pairs). Most genes of Buchnera that were lost were not necessary for working in an environment rich in materials and stable in a cell, but interestingly, some genes which are not related to a living environment, but are considered essential for maintaining cell identity, have been lost. An example is the phospholipid synthetic gene, which is associated with the synthesis of the main component of the bio-membrane.
Also, among the genes associated with energy production, some genes have remained and some have been lost. I want to know just how Buchnera makes up for the function that should have been lost with the loss of the genes. This must be the key of this close symbiotic relationship (Specifically, the genes of electron transfer system and ATP synthesis system remain, but only one gene of the citric acid cycle remains.)
On the other hand, the remaining genes in the genome of Buchnera show a strong bonding of symbiosis. Cyto-parasitic bacteria such as Richettsia, Chlamydia, and Mycoplasma have lost most genes associated with the amino acid synthesis, and these bacteria take amino acid from their hosts. Although Buchnera depend on its host for many things, the number of their genes is about half as many as those of E. coli for amino acid synthesis. In reality, the remaining genes of Buchnera are associated with the production of amino acid, which aphids can't synthesize. Just like E. coli, an ancestor of Buchnera could synthesize all kinds of amino acid, but since they started a symbiotic relationship with aphids, they must have started depending on the host for what it can synthesize. A symbiotic relationship is now established between Buchnera and aphids, in which Buchnera provides its host with amino acid its host can't produce, and the host provides Buchnera with amino acid Buchnera can't produce. This relationship can be explained by the nutrition physiological study, too. Plant sieve tube fluid, which is the only nutritional source for aphids doesn't include most of the amino acid, which aphids can't produce. However, aphids are probably not able to possess the best propagation among all creatures without Buchnera which provides it with amino acid.
By the way, there is a time when aphids sacrifice these important amino-acid providers. That is, when aphids have to break up their colony. When a colony of aphids becomes too crowded, alate aphids (aphids with wings) appear and fly away to form new colonies. Alate aphids must develop fly-muscle very quickly as soon as they become imagos. While they develop fly-muscle, they temporarily sacrifice Buchnera. After molting into an imago, bacterial cells in alate aphids rapidly become small, and on the contrary, fly-muscle grows. When aphids, after scattering, begin eating in a new place, bacterial cells with Buchnera grow back to their original size as the fly-muscle deteriorates. Symbiotic phenomenon occurs at various levels, and a clever relationship of symbiosis in a cell from an aphid was investigated considerably as a symbiotic example. And yet, many unknown mysteries of aphids remain to be solved.
A great deal of evidence supports the current consensus that the history of symbiosis between aphids and Buchnera is 200 million years. During some kind of event, an ancestor of the aphid took an ancestor of Buchnera into its cell, and since that time for 200 million years, Buchnera has lived in the cells of aphids for several 100 million generations. In the meantime, the host aphid has differentiated into more than 4,000 kinds, and probably, Buchnera has differentiated into an amount that is now equal to the differentiation of the host.
Through genetic analysis, Buchnera family bacterium was found to be closely related to Escherichia coli (E. coli). The genetic difference between the currently existing Buchnera and E. coli shows the difference of living environments between them, in other words, it shows the difference between a symbiont living in a cell and a free living thing. A significant difference is genome size. Genome of Buchnera has 640,000 base pairs, which represent about one seventh of those in E. coli's genome (E. coli genome has 4,640,000 base pairs). Among genomes which have already been analyzed, the genome of Buchnera is the smallest next to a cyto-parasitic bacterium, mycoplasma (580,000 base pairs). Most genes of Buchnera that were lost were not necessary for working in an environment rich in materials and stable in a cell, but interestingly, some genes which are not related to a living environment, but are considered essential for maintaining cell identity, have been lost. An example is the phospholipid synthetic gene, which is associated with the synthesis of the main component of the bio-membrane.
Also, among the genes associated with energy production, some genes have remained and some have been lost. I want to know just how Buchnera makes up for the function that should have been lost with the loss of the genes. This must be the key of this close symbiotic relationship (Specifically, the genes of electron transfer system and ATP synthesis system remain, but only one gene of the citric acid cycle remains.)
On the other hand, the remaining genes in the genome of Buchnera show a strong bonding of symbiosis. Cyto-parasitic bacteria such as Richettsia, Chlamydia, and Mycoplasma have lost most genes associated with the amino acid synthesis, and these bacteria take amino acid from their hosts. Although Buchnera depend on its host for many things, the number of their genes is about half as many as those of E. coli for amino acid synthesis. In reality, the remaining genes of Buchnera are associated with the production of amino acid, which aphids can't synthesize. Just like E. coli, an ancestor of Buchnera could synthesize all kinds of amino acid, but since they started a symbiotic relationship with aphids, they must have started depending on the host for what it can synthesize. A symbiotic relationship is now established between Buchnera and aphids, in which Buchnera provides its host with amino acid its host can't produce, and the host provides Buchnera with amino acid Buchnera can't produce. This relationship can be explained by the nutrition physiological study, too. Plant sieve tube fluid, which is the only nutritional source for aphids doesn't include most of the amino acid, which aphids can't produce. However, aphids are probably not able to possess the best propagation among all creatures without Buchnera which provides it with amino acid.
By the way, there is a time when aphids sacrifice these important amino-acid providers. That is, when aphids have to break up their colony. When a colony of aphids becomes too crowded, alate aphids (aphids with wings) appear and fly away to form new colonies. Alate aphids must develop fly-muscle very quickly as soon as they become imagos. While they develop fly-muscle, they temporarily sacrifice Buchnera. After molting into an imago, bacterial cells in alate aphids rapidly become small, and on the contrary, fly-muscle grows. When aphids, after scattering, begin eating in a new place, bacterial cells with Buchnera grow back to their original size as the fly-muscle deteriorates. Symbiotic phenomenon occurs at various levels, and a clever relationship of symbiosis in a cell from an aphid was investigated considerably as a symbiotic example. And yet, many unknown mysteries of aphids remain to be solved.