AP Biology class blog for discussing current research in Biology

Author: foodvacuolola

Did ants originate from zombies? This fungus will give you the answers.

There is a certain fungus that turns ants into zombies, but afterward, they explode. When ants are just walking by minding their own business they step on fungal spores. It attaches to the ant’s body and the fungal cell goes inside of the ant. The fungus feeds from within and increasingly multiples cells and it is called, Ophiocordyceps,   mainly living in the tropics. The danger about this fungus is that the ant is unaware of this whole process, it goes about its daily life, searching for food and bringing back to its nest. However, the fungus takes up half of an ant’s body mass. It undergoes a parasitic relationship where the fungus benefits, while the ant is harmed.

Once the fungus is done feeding, the ant will feel a needle-like sensation. What is happening here is that the fungus is pushing on the ant’s muscle cells. And the cell signals also get sent to the ant’s brain, then the ant will climb upwards above its nest. Ophiocordyceps does something very weird where it allows the ants to move upwards to a leaf above ground and then the ant bites down, where it locks its jaw. Then it sends out “sticky threads that glue the corpse to the leaf.” The ant’s head then bursts open, called a “fruiting body”, where it looks like horns projecting from the ant’s heads and the horns disperse more of these fungal spores onto its nest below it leaving behind a trail of spores. 

Hornlike antlers that come out of the ant’s head

There is still so much that is unknown about Ophiocordyceps because scientists don’t even know what kind of chemical gets into the ant’s brain causing it to climb. There are ants that age back to 48 million years old gripped onto leaves.  Scientists thought there was one species that zombified ants but it turns out there are at least 28 different fungal species that attack other insects as well. Dr. Araújo drew out a family tree to see what was infected by Ophiocordyceps. It became known that all Ophiocordyceps species come from a common ancestor, first infecting beetles larvae, not hemipteran.

The beetles that are affected by the larvae live in eroding logs.

“They’re mostly solitary creatures, with a very different life history,” compared to ants, she said.

It can now be inferred that possibly millions of years ago when this was happening to beetles, ants picked up the fungus if they were living in the same logs. Thus a constant cycle and more spreading of fungal spores. Even though natural selection favored keeping the ant’s host healthy and away from parasites, Ophiocordyceps had to find a way to make the ant leave the nest, not far enough from its environment, but just in the right place to send out the spore to infect whatever other ants were living around it. 

Because this behavior is so unordinary it is not possible that only one gene is responsible for all of this. They keep finding new species. Dr. Hughes and Dr. Araújo are still researching to find that there are hundreds of other species of Ophiocordyceps that are yet to be discovered.

How the “unknown” of the human gut microbiome gets in the way of metagenomic studies…

Did you know that the greatest concentration of bacteria lives in your gut? At two or three years old we have a balanced microbiome. While we know a lot about the human gut microbiome, there is a lot that is unknown about it. There has been a lot of improvement in finding an “unknown microbiome” for example, shotgun metagenomics enables researchers to take a sample of all genes in all organisms and allows them to find an abundance of microbes in many different environments.

What we know: 25 Phyla, ~2,000 Genera, ~5,000 Species, ~80% Metagenome mappability, and 316 million genes

What is unknown?: Undetected unknowns, hidden taxa and strain-level diversity (~20% sequences not matching microbial genomes), functional unknowns (~40% genes without a match in functional databases)

For example, one study where researchers studied a stool sample from 2 lean African men and a stool sample from 1 obese European. In the stool, they found 174 new species never seen in the human gut before and 31 new genome species (which can help in later studies). Found within these new species was, Microvirga Massiliensis which has the largest bacterial genome acquired from a human, along with Senegalvirus which is the largest virus in the human gut. We definitely know a lot more about the human gut microbiome than we did, even though there is a long way to go.

However, organizing large numbers of draft genomes from uncharacterized taxa is challenging, and while performing well for bacteria, assembly-based metagenomic tools are less effective when targeting new eukaryotic microbes and viruses.

The human gut microbiome intestines in an obese person vs. a lean person

To make improvements in uncovering “hidden strain-level diversity” it is vital to alter sample-specific associations from the metagenomes and to additionally incorporate as many genomes for each species in reference databases. Most species are “open”, meaning they don’t have an upper bound on the size of accessory genomes and it may seem impossible to reclaim all strain-level diversity; however, preserving “the effort of cataloguing strain variants remains crucial for an in-depth understanding of the functional potential of a microbiome.”

The difficulty is that the microbiome contains viruses. The “functional unknown” of the human gut microbiome is the broadest and most challenging to delve and study further into because there is little known about understanding its pathways and genes. There is one creation though, that helped try and find out what was “unknown” about the microbiome, called the Integrated Gene Catalogue. The Integrated Gene Catalogue of the human gut microbiome which consists of 10 million genes. It groups genes into thresholds, thus the genes then fall into sub-units of gene-families. Locating these genes is only a small part of finding out what they actually do. For example, out of 60.4% of the genes that were annotated, 15-20% of the genes have been discovered, but are stilled labelled “function unknown.” These results show how little is known about genes, their functions, and what is current in microbial communities. There is not enough investment in microbiome research. It is difficult because there could be viruses that can be discovered; however, not enough time is being put into finding it.

Lastly, there is a lot of research going into the human gut microbiome. For example, Fecal microbiome transplantation is where stool from a healthy donor gets placed into the other patients intestine, this transplant usually occurs when more bad bacteria take over the good bacteria in the intestine. However, it could cause more disease which is why further investigation in the human gut can solidify that transplantation could overall prevent a bad bacteria take over. The microbiome field is open to all technologies. Understanding the function of the microbiome still remains the largest challenge researchers face, along with the biggest challenge that “targeting specific genes are irreplaceable”, technology should be able to provide solutions (including microbial transcriptome, metabolome, and proteome, and the automation of cultivation-based assays to scale-up the screening of multiple taxa and genes for phenotypes of interest.)


How did butterflies evolve to eat poison?!

A recent article confirms that scientists have researched that caterpillars are now eating milkweed (which is supposed to kill them). How is this happening? “Scientists have unraveled the sequence of gene mutations that enabled the monarch butterfly to thrive on toxic milkweed.” We learn at a young age that caterpillars turn into beautiful butterflies, so something must be happening before metamorphosis. There are three gene changing mutation amino acid sites including, 111, 119, and 122. Mutation 122 had the biggest boost in resistance. Another article states that ‘monarch flies’ continue to have small amounts of cardiac glycosides through metamorphosis, which is a trait that has been developed in monarch butterflies to restrain predators.

Monarch butterfly eating milkweed

Monarch butterflies can eat milkweed due to a peculiarity in a crucial protein in their bodies, which is a sodium pump, that the cardenolide(steroid) toxins intervene with. How the pumps work? They move positively charged sodium atoms out of the cell resulting in the inside of the cell is negatively charged. In order for a heart to beat, the sodium pump has to build up enough electric charge and then nerves use the pumps to send signals to the brain.

Potassium pump diagram where the pump moves the sodium and potassium ions through the membrane

What does milkweed have to do with this? In the study, they first addressed how milkweed is toxic to almost all insects, but caterpillars depend on milkweed. Females use milkweed to lay eggs and caterpillars eat as much as they can before chrysalis. In the article, they are referred to as “flying poison” because the milkweed toxin gets send from their gut to their wings and anything that tries to eat it immediately vomits it up.  After these mutations, they now NEED milkweed to live and it altered the sodium pumps, so cardiac glycosides in the monarchs cells don’t affect them.

This mutation allowed butterflies to have their own food supply since milkweed is poisonous to other insects. Noah Whiteman, a biologist at the University of California, Berkely used CRISPR to try the mutations on fruit flies. The fruit fly experiment resulted in the findings that mutation 122 has bad side effects and is only useful if followed by another mutation. Other researchers say the order that mutations are done can make a big difference as well.


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