Amoebae diversified at least 750 million years ago, far earlier than expected

Publicado em 28 fevereiro 2019

Brazilian scientists have reconstructed amoeba's evolutionary history and demonstrated that at the end of the preshambrian period, at least 750 million years ago, life on earth was much more versatile than was suggested by classical theory.

The study, supported by the São Paulo Research Foundation – FAPESP, revealed eight new tribal births of Thecamoebae, the largest group in Amoebozoa. The camoebians are known as testers because of their hard outer carpace or shell.

Interpretations of the evolution of the Earth's atmosphere and climate change are also affected by the discovery that amoeba is more versatile than previously thought.

In this study, published in the journalCurrent Biologyresearchers who joined the University of the São Paulo Bioscience Institute (IB-USP) in Brazil, in collaboration with colleagues at the Mississippi State University in the United States, used innovative techniques to reconstruct the phylogenetic (evolutionary) tree of Thecamoeba, belonging to the order Arcellinida.

The new phylogenetic tree was created with the help of mathematical algorithms and the transcriptomes of 1

9 arcellinides found in nature today. The researchers also set up the morphology and composition of the hypothetical ancestors of this group of amoeba and compared them to the fossil record.

The results showed that the ancestors of the camoebians were already developing at least 750 million years ago. This result suggests that the late pre-Cambian was more versatile than before.

"We reached our conclusions using a combination of two major scientific fields – paleontology and phylogenetic systematics, the field of biology that reconstructs evolutionary history and studies patterns of relationships between organisms. In this way, we could remove one of the knots of the evolutionary The theory of life on the planet, says Daniel Lahr, professor at IB-USP and senior author of the article.

Reclassification of Amoebozoa

The researchers completely discontinued the previous classification of thecamoebians. robust structure and discovered for the first time eight deep lines [from 750 million years ago] of arcelinides on which nothing was known, "Lahr says.

The old tecamoebic classification was based on the shell composition." They were divided into agglutinate and organic. But from our molecular reconstruction, we discovered that the classification is actually determined by scallop rather than composition, "said Lahr.

The old classification, he added, had questioned several years, but more evidence is needed to demolish it. Previous genetic research has shown the classification was unsustainable, but there was not enough data to justify a new classification.

"The scientific community suspected that the arcelinidae testate mounds had arisen and developed enough to diversify about 750 million years ago.

Earlier and future

According to Lahr, the study presents another view of how microorganisms developed on the planet. The late pre-chambers were considered a period of low biotic diversity, with only a few bacteria and some protists.

"It was during this period 800 million years since the oceans became oxygen-shaped. For a long time, oxygen formation was believed to have led to the diversification of eukaryotes, unicellular and multicellular organisms where the nucleus of the cell is isolated by a membrane culminating in the diversification of macroorganisms millions of years. later in Kambrian, Lahr said.

The study published in Current Biology, he added, focuses on a detail of this issue. "We show that diversification seems to have existed already in the precambrian and that it probably occurred while oceanic steering. Also, geophysicists find that the process was slow and may have been 100 million years or so, "he said. 19659003] However, scientists do not know what pressure triggers this oxygen formation." Whatever the cause, oxygen uptake led to more niches, the Eucharites diversified and there was more competition for niches. One way to solve the competition was that some lines would become larger and consequently multicellular, "Lahr said.

The study has also contributed to a better understanding of today's climate change." We began to understand more deeply how this microbial life affected the Earth in several way, "Lahr said." The climate changed fundamentally during the period, which saw the presence of the Sturtian glacier about 717 million years ago. It was one of the greatest icebreaking events ever. "

According to Lahr, these changes may have had biological origin." By increasing the resolution of how life evolved in the very distant past, we can understand a little better how life affects the planet's climate and also its geology. It helps us understand the climate changes we are currently experiencing, he says.

In stone

In addition to the discovery of greater diversity in the pre-Cambrian, the study also innovates by reconstructing the morphology of the ancestors of thecamoebians to determine that the vascular microfossils (VSM) found in various parts of the world already existed in the pre-Cambrian and also during the great ice age that arose during this time.

VSMs are believed to be fossils of tested amoeba. They are unicellular and eukaryotic and have an external skeleton. Significant diversity of VSM has been documented for the Neoproterozoic Era, which ranged between 1 billion and 541 million years ago, and was the precambrian's terminal era.

"The study is a completely different view of how microorganisms developed on the planet. Although the fossils do not contain genetic information, it is possible to obtain morphological and compound information and to check whether they are organic or silica-based. form and chemical composition, which in this case is particularly well-preserved, with the current thecamoebians who are reconstituted by large data, "said Luana Morais, a postdoctoral scholar with FAPESP scholarship and co-author of the article.

Innovative Techniques

In addition to the lack of DNA-containing fossils, the researchers encountered another obstacle in reconstructing the phylogenetic tree: thecamoebians cannot be grown in the laboratory and the gene Ethical sequencing by conventional means is therefore excluded.

The solution to this problem was to use the single cell transcriptoma technique to analyze phylogenetics (rather than gene expression, its normal application). "We sequenced the entire transcriptomes of arcellinid amoeba using live samples," Lahr explained. "This gave several thousand genes and about 100,000 amino acids, or 100,000 data points that gave us the phylogenetic tree that had never seen before."

The researchers used transcriptome-based methodology to capture all messenger RNAs from each individual cell and convert them into a sequentially complementary DNA library.

"Our research was based on single cell transcriptomics, where our lab is one of the world's pioneers," Lahr said. "It is a revolutionary technology in this field because it allows us to find a single [unicellular] amoeba, isolate and clean it, and perform all laboratory procedures to sequence the entire transcriptome."

In this study, the researchers chose 250 genes to construct the phylogenetic tree. "It's not good to look at only one cell when studying gene expression, because the solution will be insufficient," Lahr said. "However, in an evolutionary study, it does not matter. You need to get the sequence, not how many times a gene is expressed. So it is possible to use this technique that was originally developed for tumor cells and adapt it, with the advantage that an amoeba cell is much larger than A tumor cell. "

Before the technology was developed, only organisms grown in the laboratory could be sequenced. "It expands the range of my research in this area by getting genetic information from organisms that I've only found once. It is estimated that only 1% or less of all biodiversity is cultivable," Lahr said.