Monocercomonoides
One of the problems creationism suffers from, apart from not having any supporting evidence, is that it relies almost entirely on counter-factual dogma. One such dogma, for example, is that scientists believe evolution is all about life progressing from the simple to the complex and that somehow all evolutionary change must involve an increase in complexity.
Yes, I know this is nonsensical and at odds with the facts, but that's the point of dogma; it means evidence doesn't need to be bothered with because the truth is 'known' by fiat. The dogma says so...
What this dogma is for, and probably the reason it's clung to with such tenacity, is so creationists can cite yet another dogma - that new information can't arise because of the Second Law of Thermodynamic (sic) so increasing complexity, which so it is assumed, involves new information, is impossible. Two pieces of dogma with no supporting evidence and which run counter to the actual evidence. But this enables creationist frauds to construct what looks to the scientifically illiterate people they are duping like a logical, scientific argument, even involving real science like the Second Law, albeit misrepresented and misapplied.
But, what about parasites, particularly endoparasites where evolution almost always leads to a loss of complexity - Parasitic worms, for example, which have lost their digestive tracts and simply absorb nutrients directly through their skins from their host?
Now here we have an example which may be the first example of a complex (eukaryote) cell losing what were thought to be an essential organelle for a eukaryote cell - their mitochondria. Mitochondria are the powerhouses of a complex cell, building ATP from ADP and phosphate. They also have another function. They produce small clusters of iron and sulphur which form prosthetic groups for some proteins.
Mitochondria are the descendants of bacteria which formed a symbiotic relationship with other prokaryote cells to form the eukaryote cells from which all multicellular organisms are made. They have retained at least some of their own DNA and replicate independently within the cell, so forming their own evolutionary tree. Some organisms are known to have transferred some mitochondrial DNA into the cell nucleus. However, this organism, known to science as as member of the Monocercomonoides genus seems to have lost its mitochondria altogether. Some close relatives have very much reduced mitochondria but this is the first which seems to have dispensed with them altogether.
This particular species inhabits a highly specialised environment, being found only in the gut of the chinchilla. The team from Charles University in Prague, led by Anna Karnkowska, sequenced the genome of this Monocercomonoides and found no trace of mitochondrial DNA.
HighlightsGraphical abstract
- Monocercomonoides sp. is a eukaryotic microorganism with no mitochondria
- The complete absence of mitochondria is a secondary loss, not an ancestral feature
- The essential mitochondrial ISC pathway was replaced by a bacterial SUF system
Summary
The presence of mitochondria and related organelles in every studied eukaryote supports the view that mitochondria are essential cellular components. Here, we report the genome sequence of a microbial eukaryote, the oxymonad Monocercomonoides sp., which revealed that this organism lacks all hallmark mitochondrial proteins. Crucially, the mitochondrial iron-sulfur cluster assembly pathway, thought to be conserved in virtually all eukaryotic cells, has been replaced by a cytosolic sulfur mobilization system (SUF) acquired by lateral gene transfer from bacteria. In the context of eukaryotic phylogeny, our data suggest that Monocercomonoides is not primitively amitochondrial but has lost the mitochondrion secondarily. This is the first example of a eukaryote lacking any form of a mitochondrion, demonstrating that this organelle is not absolutely essential for the viability of a eukaryotic cell.
Introduction
Mitochondria are organelles that arose through the endosymbiotic integration of an α-proteobacterial endosymbiont into the proto-eukaryote host cell. During the course of eukaryotic evolution, the genome and proteome of the mitochondrial compartment have been significantly modified, and many functions have been gained, lost, or relocated [1]. In extreme cases, the derivatives of mitochondria in anaerobic protists had become so modified that they had been overlooked [2] or not recognized as homologous to the mitochondrion [3]. Indeed, in the 1980s, the Archezoa hypothesis [4] proposed that some microbial eukaryotes primitively lacked mitochondria, peroxisomes, stacked Golgi apparatus, spliceosomal introns, and sexual reproduction. However, over the following decade, double-membraned organelles were identified in all investigated putative Archezoa. The final nail in the coffin of the Archezoa hypothesis was the demonstration that these organelles all contain some mitochondrial marker proteins, such as those involved in the iron-sulfur cluster (ISC) Fe-S clusters biogenesis system, translocases, maturases, and/or molecular chaperones known to facilitate the import of proteins into mitochondria. It is now widely accepted that mitochondria or mitochondrion-related organelles (MROs) are essential compartments in all contemporary eukaryotes and that mitochondrial endosymbiosis took place before radiation of all extant eukaryotes [5].
Metamonada, originally part of the Archezoa, are now classified as one of the main clades of the eukaryotic “super-group” Excavata [6] and are comprised of microaerophilic or anaerobic unicellular eukaryotes that are often specialized parasites or symbionts. Detailed cell and molecular biological studies, including genome sequencing, have been undertaken only for three parasitic species from two metamonad lineages—Giardia intestinalis [7] and Spironucleus salmonicida [8] (Fornicata) and Trichomonas vaginalis [9] (Parabasalia), which have provided important information regarding the functions of their MROs. The third lineage of metamonads, Preaxostyla, contains the basal paraphyletic free-living trimastigids and the derived endobiotic oxymonads [10]. The presence of mitochondrial homologs has been convincingly demonstrated in Paratrimastix (formerly Trimastix) pyriformis, although the biochemical functions of these organelles are largely unknown [11]. Endobiotic oxymonads belong to the least-studied former Archezoa. Here, we describe the first complete genome sequence analysis of an oxymonad, Monocercomonoides sp. PA203. We find that although this organism is a standard eukaryotic cell in other respects, it completely lacks any traces of a mitochondrion.
Karnkowska, Anna et al.
A Eukaryote without a Mitochondrial Organelle
Current Biology , Volume 0 , Issue 0 DOI: http://dx.doi.org/10.1016/j.cub.2016.03.053
Copyright: © 2024 The authors.
Published by Cell Press. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
The organism seems to have replaced the normal mitochondrial energy production function and now uses enzymes in the cell cytoplasm to release energy from nutrients, possible because although the chinchilla gut is high in nutrients, it is low in the oxygen normally needed for mitochondrial function.
In another interesting twist, the iron and sulphur cluster production seems to have been replaced by acquired bacterial genes.
So, here we have an example of evolution in a highly specialised environment resulting in a radical reduction in complexity amounting to the loss of an entire cell organelle together with its entire genome. This is an interesting but fully explainable discovery for biology; it is a massive refutation of one of creationism central dogmas. Evolution has occurred by a loss of complexity and a loss of information.
Would a creationist like to explain this and say how creationism will be revising its dogma, or will it continue to be based on necessity not facts?
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