Are amoebae safe harbors for plague?

New research shows that plague bacteria not only survive, but thrive and replicate once ingested by an amoeba

Date:  January 16, 2018

Source:  Colorado State University

Summary:

Amoebae, single-celled organisms common in soil, water and grade-school science classrooms, may play a key role in the survival and spread of deadly plague bacteria. New research shows that plague bacteria, Yersinia pestis, not only survive, but thrive and replicate once ingested by an amoeba. The discovery could help scientists understand why plague outbreaks can smolder, stay dormant for years, and re-emerge with a vengeance.

Continued  

Tiny vampires

May 26, 2016 by Julie Cohen

Vampires are real, and they've been around for millions of years. At least, the amoebae variety has. So suggests new research from UC Santa Barbara paleobiologist Susannah Porter.

Using a scanning electron microscope to examine minute fossils, Porter found perfectly circular drill holes that may have been formed by an ancient relation of Vampyrellidae amoebae. These single-celled creatures perforate the walls of their prey and reach inside to consume its cell contents. Porter's findings appear in the Proceedings of the Royal Society B.

"To my knowledge these holes are the earliest direct evidence of predation on eukaryotes," said Porter, an associate professor in UCSB's Department of Earth Science. Eukaryotes are organisms whose cells contain a nucleus and other organelles such as mitochondria.

"We have a great record of predation on animals going back 550 million years," she continued, "starting with the very first mineralized shells, which show evidence of drillholes. We had nothing like that for early life—for the time before animals appear. These holes potentially provide a way of looking at predator-prey interactions in very deep time in ancient microbial ecosystems."

Porter examined fossils from the Chuar Group in the Grand Canyon—once an ancient seabed—that are between 782 and 742 million years old. The holes are about one micrometer (one thousandth of a millimeter) in diameter and occur in seven of the species she identified. The holes are not common in any single one species; in fact, they appear in not more than 10 percent of the specimens.

"I also found evidence of specificity in hole sizes, so different species show different characteristic hole sizes, which is consistent with what we know about modern vampire amoebae and their food preferences," Porter said. "Different species of amoebae make differently sized holes. The Vampyrellid amoebae make a great modern analog, but because vampirelike feeding behavior is known in a number of different unrelated amoebae, it makes it difficult to pin down exactly who the predator was."

Read more at: 

Scientists solve mystery of the giant armor-clad amoebas (via Chad Arment)

Ancient armored amoebas called fusulinids grew so large that they were clearly visible to the naked eye.

Imagine a world that swarmed with armor-clad single-celled organisms so large and monstrous that you could see them with the naked eye, and even pick them up and feel them wriggling in your hand.

It might sound like an alien world, but 300 million years ago giant amoebas fitting this description swam the seas right here on Earth.

 

Scientists have long been unable to prove how these ancient protozoa, called fusulinids, were able to grow to lengths as long as 10 centimeters-- a massive size for a single-celled creature. But now a research team headed by Jonathan Payne, a paleobiologist at Stanford University, has collected new evidence that may finally put the mystery to rest, according to ScienceNews.org.

One reason that single-celled organisms don't grow to such epic sizes today is because they are limited by how far oxygen can penetrate into them. But 300 million years ago, during the Paleozoic Era, the atmosphere was much different; Oxygen levels were so high that the air could almost spontaneously combust.

Payne and his colleagues thus looked for hints that heightened levels of oxygen might explain the amoebas' size. He enlisted undergraduates and high school students to compare how the armor-like shells that once adorned these ancient microorganisms changed over geological time. Sure enough, they found that the amoebas tended to grow larger during periods when atmospheric oxygen rose. After oxygen peaked at levels 66 percent higher than today and began to fall, the amoebas shrank accordingly.

The way the amoebas grew over time also revealed the influence of oxygen on their size. Instead of ballooning like beach balls, the amoebas elongated. While they grew to lengths of up to 10 centimeters, they rarely measured more than about two millimeters across. These "stringy" shapes would have been much more efficient than round ones at allowing oxygen to penetrate throughout the cell.

Payne and his team also studied how oxygen levels can influence the size of modern amoebas. They found that species which live close to the surface, where oxygen levels are higher, are typically bigger than those living in deeper waters.

All of this evidence taken together points clearly to oxygen being the spinach that allowed Paleozoic amoebas to grow so large.

Luckily, the odds of ever encountering one of these giant armor-clad amoebas today are pretty slim. Current oxygen levels make such large sizes impossible to achieve. But who knows, someday the Earth may again blossom into an oxygen-rich enclave, and the giant amoebas will live again.

Bryan Nelson
http://www.mnn.com/earth-matters/wilderness-resources/stories/scientists-solve-mystery-of-the-giant-armor-clad-amoebas

Texas-sized tract of single-celled clones

Biologists find world-record colony of amoebae in Houston cow pasture

HOUSTON -- (March 11, 2009) -- A Rice University study of microbes from a Houston-area cow pasture has confirmed once again that everything is bigger in Texas, even the single-celled stuff. The tests revealed the first-ever report of a large, natural colony of amoebae clones -- a Texas-sized expanse measuring at least 12 meters across.

The research is available online and featured on cover of the March issue of Molecular Ecology.

This is the Houston pasture where the amoeba colony was found.
Credit: O. Gilbert/Rice University
Some large organisms like aspen trees and sea anemones are well-known for growing in large clonal colonies. For example, one colony of aspen clones in Utah contains more than 40,000 trees that share a massive root system.

In contrast, the short-lived patch of amoeba clones contained millions of genetically identical individuals of the species Dictyostelium discoideum. Though they typically live as loners, hunting and eating bacteria, D. discoideum are known to cooperate when food gets scarce and even to sacrifice their lives altruistically. Biologists say the discovery of the clonal colony could yield important clues about the evolution of such cooperative behavior.

"This discovery is important for our understanding of microbial social evolution because the processes of selection, cooperation and competition play out differently when populations are geographically mixed as opposed to being isolated in patches," said study co-author Joan Strassmann, the Harry C. and Olga K. Wiess Professor in Natural Sciences and chair of Rice's Department of Ecology and Evolutionary Biology.

Studies of clonal colonies in other species show that the colonies often appear at the edge of a species' natural range.

D. discoideum cooperate to form stalks topped with "fruiting bodies."
Credit: O. Gilbert/Rice University
"People had seen this in studies of sea anemone and other species," said study co-author Owen Gilbert, a Rice graduate student in ecology and evolutionary biology. "There are thought to be two ways that these colonies can form at the edge of a species' natural range: either just one clone finds its way there, or perhaps a few make it there but they compete with each other and just one wins out."

Based on these studies, Strassmann, Gilbert and co-author and evolutionary biologist David Queller, Rice's Harry C. and Olga K. Wiess Professor of Ecology and Evolutionary Biology, surmised that clonal patches could form on the edge of a microbial species' range, and they looked for a suitable location to test the idea in D. discoideum.

"D. discoideum tends to thrive at higher altitudes and in densely wooded areas where the soil stays moist," Gilbert said. "A Texas cattle pasture is simply the wrong type of habitat. But D. discoideum thrives on the dung of various animals, which suggests that given a good amount of rain, a cattle pasture could be the perfect place for a population explosion."

Strassmann, Gilbert and a team of Rice undergraduate researchers took samples from 18 local pastures. In each, they plotted a grid and collected soil and dung samples. Back at the lab, they put the samples on clear plates and examined them daily to see whether they produced any feeding amoebae. When amoebae were found, they were analyzed genetically to see whether they were the same species, and if so, whether they were genetic clones.

In one of the fields, they found that all the D. discoideum samples were genetic clones. Subsequent tests in the lab showed that the strain didn't have a distinct competitive advantage over three other strains found in nearby pastures. Exactly how and why the large clonal patch appeared in that particular field isn't clear, but the fact that it was there raises some intriguing questions.

For example, Strassmann and Queller's prior work with D. discoideum has turned up more than 100 genes that help the organism regulate its cooperative behavior. They also know that mutations to these genes can allow individual amoebae to "cheat" and take advantage of nonmutants' willingness to sacrifice themselves. How species like D. discoideum manage to keep cheaters from out-producing and eliminating cooperative strains is one focus of their work.

"The existence of clonal patches in microbial species presents very interesting possibilities for the appearance and regulation of cheating behaviors," Queller said. "It is likely that additional natural studies of social microbes will continue to complement the genetic and evolutionary laboratory studies of these organisms."

###

The research was supported by a grant from the National Science Foundation, a Wray-Todd Graduate Fellowship and a Houston Livestock Show and Rodeo Scholarship.

http://www.eurekalert.org/pub_releases/2009-03/ru-tto031109.php