Article from The Hitchhiker's Guide to the Quantum World

last update: Sept. 14 '17

Ixodes ricinus, Tick

The Ixodes tick (on the left)
lives in a symbiotic relationship with MIDICHLORIA,
a type of bacteria. We, as humans, live in a symbiotic relationship with mitochondria, which has it's own DNA.

Midichloria is the ancestor of mitochondria,
the powerhouse that fuels every living cell in the known universe,
including you and me.

Seriously. :-)

Midichloria is a Gram-negative, non spore-forming bacteria,
with bacillus shape around 0.45 Ám in diameter and 1.2 Ám in length.

First described in 2004, Midichloria species are symbionts of the hard tick Ixodes ricinus.
Midichloria live in the cells of the ovary of the females of this tick species.

These bacteria have been observed in the mitochondria of the host cells,
a trait that has never been described in any other symbiont of animals.

Midichloria bacteria seem to consume the mitochondria they parasitize,
possibly using them as a source of energy and/or molecules to multiply.

The interaction of these symbionts with their host is currently unknown,
though the 100% prevalence in the females of the host tick seems to suggest a mutualistic association.

The name of this bacterial genus, Midichloria, is derived from the midi-chlorians,
a symbiotic, microscopic life form first described in the fictional Star Wars universe.

Midichloria is evolutionarily close to mitochondria that means that it is not only a symbiont of mitochondria,
but also a 'close relative' of these organelles.

MitochondrionMITOCHONDRIA are exclusively inherited from the mother in humans.

The mitochondrion is a double membrane-bound organelle
found in all eukaryotic organisms.

Some cells in some multicellular organisms
may however lack them (for example, mature red blood cells).

Mitochondria generate most of the cell's supply of adenosine triphosphate (ATP),
used as a source of chemical energy! ATP is found in all forms of life,
often referred to as the "molecular unit of currency"
of intracellular energy transfer.

Mitochondria exist in every living cell on Earth.

In addition to supplying cellular energy,
mitochondria are involved in other tasks,
such as signaling, cellular differentiation, and cell death,
as well as maintaining control of the cell cycle and cell growth.

Defective mitochondria have been implicated in several human diseases,
including cardiac dysfunction, heart failure and autism.

that shows substantial similarity to bacterial genomes.

Mitochondrium_electron_microscopyThere are two hypotheses about the origin of mitochondria:
endosymbiotic and autogenous.

The endosymbiotic hypothesis suggests that mitochondria
were originally prokaryotic cells,
capable of implementing oxidative mechanisms
that were not possible for eukaryotic cells;
they became endosymbionts living inside the eukaryote.

In the autogenous hypothesis, mitochondria were born by splitting off a portion of DNA from the nucleus of the eukaryotic cell at the time of divergence with the prokaryotes; this DNA portion would have been enclosed by membranes, which could not be crossed by proteins.

However, since mitochondria have many features in common with bacteria,
the endosymbiotic hypothesis is more widely accepted.

The Rickettsiales are widely regarded as being the closest relatives to mitochondria.
Based on the fact that the Midichloria genes for the flagellum and for the cbb3 cytochrome oxidase were proven to be ancestral, it was inferred that they were present in the bacterium that established the symbiosis with the ancestor of the eukaryotic cell to become the mitochondrion.

The sequencing of the genome of Midichloria mitochondrii thus allowed an updated reconstruction of the free-living mitochondrial ancestor.

The conclusions of the study allow depicting a novel reconstruction of the free-living ancestor of mitochondria:
it was a flagellated bacterium that thrived even under low levels of oxygen (microaerophilic).

Both these characteristics may have played an important role in the beginning of the symbiosis between the eukaryotic cell and the mitochondrion.



A study by an international team involving the Universities of Milano, Valencia, Pavia and Sydney, presents new insights into the origin of cells: http://www.uv.es/uvweb/college/en/news-release/a-study-an-international-team-involving-universities-milano-valencia-pavia-sydney-presents-new-insights-origin-cells-1285846070123/Noticia.html?id=1285848765428

Image: https://flic.kr/p/55Lvde Electron microscopy of the tick Ixodes ricinus by Andreas Weck-Heimann