Rotifers - A link to horizontal gene transfer in eukaryotes?

Rotifers - A link to horizontal gene transfer in eukaryotes?
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2019-11-07T18:30:00Z

In today’s causerie which was presented by @saida we discussed about the basics of pagalopos i.e what is pagalopos - manholes present on gutter lids, why do we use pagalopos and how do we find rotifers from pagalopos and culture them.

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After this, we discussed what is rotifers, how do we isolate rotifers from pagalopos and why is rotifer an important organism for studying Horizontal gene transfer(HGT) . But before diving into HGT we tried to clear the basics to know how gene transfer takes in bacteria in the first place…
Gene transfer in bacteria takes place through the following process :

transformation : a bacterium takes up a piece of DNA floating in its environment.

transduction : DNA is accidentally moved from one bacterium to another by a virus.

conjugation : DNA(in the form of plasmid) is transferred between bacteria through a tube(pilus)between cells.

Transposable elements : are chunks of DNA that “jump” from one place to another. They can move bacterial genes that give bacteria antibiotic resistance or make them disease-causing.

In bacteria, reproduction can be very fast, with a generation taking little more than a few minutes for some species. This short generation time, together with random mutations and the mechanisms of genetic recombination, allow bacteria (and other prokaryotes) to evolve very quickly.

Is that a good thing? It depends on your perspective. Rapid evolution means that bacteria can adapt to environmental changes, such as the introduction of an antibiotic, very quickly. That’s good for them—but bad for us, when we are the ones with the infection!

Horizontal gene transfer (HGT), the movement of genes from one organism to another by means other than direct descent (vertical inheritance), has been documented in prokaryotes and in some parasitic unicellular eukaryotes.
The rotifers are a phylum of tiny animals which are common in freshwater environments, such as ponds and puddles (pagalopos in our case) . About 2200 species of rotifers have been described. Fossils of the species Habrotrocha angusticollis have been found in 6000 year old Pleistocene peat deposits. The oldest known fossil rotifers have been found in Eocene Dominican amber.
The rotifers are of significance because gene transfer takes place in bacteria (prokaryotes) but rotifers is the only eukaryote which shows the presence of bacterial genes and therefore it is proposed that HGT takes place in rotifers through the bacteria which it eats!
Reference : (PDF) Massive Horizontal Gene Transfer in Bdelloid Rotifers

The difference between rotifers and bacteria were pointed out, how do antibiotics affect bacteria and which part of bacteria do they affect - the cell wall.

A lot of questions were asked such as

  1. If rotifers had genes similar to bacteria, couldn’t it be possible that rotifers and bacteria share a common ancestor?
  2. Humans have 147 genes common to bacteria
    Reference : https://www.sciencemag.org/news/2015/03/humans-may-harbor-more-100-genes-other-organisms
    So has HGT taken place in us humans as well? :scream:
  3. How is a single plasmid passed on from one bacteria to another? What is the size of plasmid? Is it circular or linear? Does bacteria contain one or many plasmids?

After this we had a heated🔥 debate and continued a little on yesterday’s causerie and me, @⁨Harshita Bhanushali⁩ @⁨RitikBaviskar⁩ @⁨HarshadSir @⁨Zahra⁩ @⁨Saida @⁨GauraV⁩ were discussing the exact process of mitosis and meiosis and why does 2n(46) number of chromosomes result to the formation of 4 single n(23) number of gametes (n, n, n, n) in meiosis and how does recombination (a process by which pieces of DNA are broken and recombined to produce new combinations of alleles ) takes place during meiosis and how the gametes are different from parent DNA i.e how does the offspring can have different combinations of genes than their parents.

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@saida786110 @khushdeep @Ameya
Introduce us to your Research question, objectives…

As the rotifers reproduce by asexual reproduction or parthenogenetically, does crossing over occur here?

You could provide more literature regarding the Mitosis and Meiosis…

These are all basic topics which would lead us to introduction to a whole new Cascade of Mechanisms ultimately linking us to Horizontal Gene Transfer (HGT).

Can we clarify how these " allow" bacteria " to evolve quickly"? @Ameya

Are we sure other Eukaryotes do not have residues of bacterial genome? @Ameya

You must be meaning Ampicillin group of Antibiotics …!!!

So, what is the conclusion on 9 Nov., Saturday at the Causerie on the difference in the process of cell division Mitosis and Meiosis

Yes, @drishtantmkawale what is the research question in Rotifers? That was missed out by @Ameya

In apomictic parthenogenesis only one
maturation division takes place in the egg, and this is an ordinary mitosis. As no bivalents are formed and there is no reduction
division, the zygoid chromosome number
and the whole genome is maintained unchanged in apomicts
Reference : https://www.google.com/url?sa=t&source=web&rct=j&url=https://academic.oup.com/icb/article-pdf/19/3/739/274011/19-3-739.pdf&ved=2ahUKEwjU4uC5rOXlAhXKfH0KHd2gAUgQFjAMegQIBBAB&usg=AOvVaw0shKjPbzmorq505MmHeXLS

Both Daphnia and Monogononta rotifers are cyclic parthenogens and reproduce asexually via. apomictic parthenogenesis. So the crossing over stage does not happen in case of sexually reproducing rotifers (Monogononta)

Bacterial species evolve quickly both because their huge populations offer many opportunities for mutations, and because they readily exchange genetic information, even between species.
No drug has perfect effectiveness, killing every bacterial cell. Instead, the most drug-sensitive cells are killed, leaving the most resistant to survive, reproduce and pass on their drug resistance to their progeny. Over many rapid generations of bacterial cells, this selection process drives the population’s evolution toward increasing drug resistance.
Reference : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3981165/

I was not sure, that’s why I verified it and found out this!
On average, eukaryotic genes are 56% bacterial in origin.
The majority drops to 53% in eukaryotes that never possessed plastids, and increases to 61% in
photosynthetic eukaryotic lineages, where the cyanobacterial ancestor of plastids contributed
additional genes to the eukaryotic genome, reaching 67% in higher plants
Reference : https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.biorxiv.org/content/biorxiv/early/2019/09/23/779579.full.pdf&ved=2ahUKEwiRw5n_sOXlAhVbXSsKHcZZCFEQFjANegQICBAB&usg=AOvVaw2xV8G-LJT40HKHG5h04cgg

Yes!the Beta lactam antibiotics

We concluded that :
Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same genetic component as the parent cell. Chromosomes are divided in such a way as to ensure that each daughter cell receives a copy of every chromosome.The number of chromosomes in each daughter cell remains the same

Meiosis is the form of eukaryotic cell division that produces haploid sex cells or gametes (which contain a single copy of each chromosome) from diploid cells (which contain two copies of each chromosome). The process takes the form of one DNA replication followed by two successive nuclear and cellular divisions (Meiosis I and Meiosis II). As in mitosis, meiosis is preceded by a process of DNA replication that converts each chromosome into two sister chromatids. Crossing over occurs during prophase I of meiosis I to produce recombination in chromosomes which contributes to variations along with two daughter cells which contain these recombinant chromosomes. These recombinant chromosomes are split up in meiosis II along with the daughter cells produced in meiosis I to form 4 gametes

Class Bdelloidea (diploid) reproduces exclusively by ameiotic parthenogenesis.

Reference -Rotifers: Exquisite Metazoans1 | Integrative and Comparative Biology | Oxford Academic

Ameiotic Parthenogenesis: In some Crustaceans and Molluscs the first meiotic division. which is a reduction division is completely suppressed and only a mitotic division resulting in diploid eggs which develop into new individuals without fertilization. It is also known as apomeiotic parhthenogenesis.
Reference- doc_368.pdf (72.4 KB)