Ultra-tiny bacteria (Introduction)

by David Turell , Friday, October 20, 2017, 18:57 (2379 days ago) @ David Turell

Found in symbiotic relationship within other bacteria:

https://www.quantamagazine.org/tiny-genomes-may-offer-clues-to-first-plants-and-animals...

"With just 121 protein-coding genes, the diminutive Tremblaya princeps, a symbiotic bacterium that lives inside specialized cells of the sap-eating mealybug, has the smallest known genome of any cellular organism on the planet. Tremblaya helps to supply the mealybug with essential amino acids and likely receives nutrients and other life-sustaining molecules in return. And even as it tests the lower limits of genome size, the Tremblaya genome may still be shedding genes.

"Even more surprisingly, scientists discovered in 2011 that Tremblaya plays host to its own bacterial guest. Called Moranella endobia, the bacterium is smaller in physical size than its host but has more than three times as many genes. Together the three organisms form a complex, co-dependent web; the nested bacteria complement each other and their insect host, creating a genetic patchwork of enzymes needed to produce amino acids lacking in the mealybugs’ sap diet.

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"Indeed, scientists now know that some organelles evolved from endosymbiont bacteria, raising hopes that studying tiny endosymbionts like Tremblaya could shed light on the evolution of those organelles. “There is no bright line between endosymbionts and organelles,” McCutcheon said. “We might be looking at something pretty darn similar to the endosymbiont-to-organelle transition.”

"In a paper published today in the journal Cell, McCutcheon and collaborators reveal a striking new level of interdependency among the Tremblaya troika. The mealybug genome appears to include genes from other varieties of bacteria distinct from Tremblaya and Moranella, and the two endosymbiont bacteria may use the protein products of these genes to manufacture nutrients and to make their membranes.

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"The collection of bacteria with tiny genomes is surprisingly diverse, having emerged from an array of bacterial ancestries, and having retained and shed a variety of genes. Thanks to the protected environment of the host cell, these organisms tend to evolve rapidly, with the smallest mutating the fastest. Tremblaya and its counterparts have shed many of the genes involved in DNA repair, further accelerating their rates of evolution. They have also lost genes required to make the protective membranes that enclose them and instead are thought to rely on membrane components from the host cell. The genes these organisms retain tend to be involved in producing nutrients for the host, as well as carrying out so-called information repair, which includes DNA replication and the translation of genes into proteins. (Beneficial endosymbionts, such as Tremblaya, are fairly common in invertebrates, but are rare in humans and other vertebrates.)

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"The findings provide a more detailed understanding of the symbionts’ differences and similarities to organelles. Tremblaya hasn’t transferred genes to its host, a defining property of organelles. But, like mitochondria, McCutcheon’s findings suggest, Tremblaya coopts some host-derived proteins that originally came from other types of bacteria. “This is a murky gray area; the host encodes genes the symbiont needs to survive, which suggests the hosts target proteins to the organism,” said Patrick Keeling, a biologist at the University of British Columbia, who was not involved in the Cell study. “That’s something organelles do but not usually endosymbionts.”

"Not everyone agrees that understanding Tremblaya may help illuminate the evolution of organelles. William Martin, a biologist at the University of Düsseldorf in Germany, wrote in an email that Tremblaya is instead “a beautiful contrast to organelles.” He noted, for example, that organelles import the vast majority of proteins from the host. Tremblaya also seems to import some proteins, but “it’s a far cry from the protein import apparatus of chloroplasts and mitochondria,” he wrote.

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"The intracellular parasites that Keeling studies, which also have reduced genomes and are unable to produce their own source of energy or survive without their hosts, are typically thought of as organisms. “But no one refers to mitochondria as an organism because it’s so integrated with its host,” he said.

"The difference is that Keeling’s parasites steal energy, in the form of a molecule called adenosine triphosphate or ATP, from their hosts, but they possess the necessary genes to replicate DNA. An organelle, on the other hand, relies on proteins provided by the host to replicate its DNA. “We have arbitrarily decided that stealing ATP from a host constitutes an organism and stealing proteins does not,” said Keeling. “It’s truly just a matter of degrees.'”

Comment: These findings indirectly support Margulies theory about mitochondria. This is a strange branch of the tree of life, but these organisms are not fully independent organisms, but do represent the experimentation that goes on within evolution. I am unsure about God's role here. Does God allow these guys to play together on their own or does He take control? I don't think this advances evolution but it does support balance of nature. The arrangement of mitochondria is only tangentially related, and I suspect He controlled that advancement in complexity.