Researchers uncover key processes in the evolution of marine microbes

Изследователите разкриват ключови процеси в еволюцията на морските микроби

This tree corresponds to the best maximum likelihood tree inferred using an alignment with 7160 sites and the GTRCAT model in RAxML99. The tree contains 16,821 OTUs generated from PacBio sequencing of 21 environmental samples (no reference sequences included). Ring #1 around the tree shows the taxonomy of ecological sequences, with all major eukaryotic lineages considered in this study labeled. Ring #2 depicts percent similarity to PR2 database references calculated using BLAST and set at a minimum of 70% with the two black lines in the middle indicating 85% and 100% similarity levels. Ring #3 depicts the habitat origin of each OTU. b, Hierarchical clustering of the four habitats based on a phylogenetic distance matrix generated using the unweighted UniFrac method (n = 7, n = 5, n = 4, and n = 5 samples for soil, freshwater, marine euphotic, and marine, respectively aphotic). All communities were found to be significantly different from each other using Monte Carlo simulations (Bonferroni-corrected P

A study recently published in Natural ecology and evolution revealed some of the key processes in the evolution of marine microbes. According to the study, led by the University of Uppsala (Sweden) and with the participation of the Institut de Ciències del Mar (ICM-CSIC) in Barcelona, ​​this is the large number of habitat transitions – from sea to land and back – that have occurred in the last millions years, which explains the great present diversity.

According to the authors, “crossing the salinity barrier is not easy for organisms, and when it happens, the resulting transitions are key evolutionary events that can trigger explosions of diversity.” Until now, however, it was not known how frequent these transitions were in the eukaryotic tree of life, which includes animals, plants, and a wide variety of eukaryotic microorganisms.

Small but very versatile

Specifically, the now published work shows that microbial eukaryotes have made hundreds of great leaps from sea to land and also to freshwater habitats, and vice versa, during their evolution. This, in turn, made it possible to infer where the ancestors of each of the microbes were eukaryotic groups were found.

“Thanks to the fact that we have good phylogenetic trees and samples from different environmentswe were able to analyze habitat transitions in different groups of eukaryotes that have occurred hundreds of times during millions of years of eukaryotic evolution, which is more than we thought,” explains Ramon Massana, ICM-CSIC researcher and one of the authors of the study.

To develop it, the scientific team used the latest technologies to sequence the DNA of microbes living in samples collected in boreal lakes, forest soils, the Indian Ocean and the Mariana Trench, among many other environments. Specifically, ICM-CSIC provided marine samples obtained during the Malaspina expedition in different oceans and water column depths.

Thanks to this, it was possible to construct large evolutionary trees of the organisms found in these environments, and even to observe a series of patterns in the evolution of habitat preferences.

“We found that organisms in the eukaryotic tree of life are generally grouped according to whether they live in oceans or in non-marine habitats,” explains Mahvash Jamie, a researcher at Uppsala University and lead author of this study. In this regard, Jamie adds that “this finding confirms that adapting to different salinities – or crossing the salt barrier – is difficult, even for microbes.”

Nevertheless, the study demonstrates that microbial eukaryotes have successfully established themselves in new habitats several hundred times throughout their evolution. Thus, the authors suggest that it is precisely these elusive transitions that would have allowed colonizing organisms to occupy vacant ecological niches, giving rise to the great diversity of eukaryotes today.

More clues about the first eukaryotes

On the other hand, evolutionary trees built from DNA sequences have also allowed researchers to peer into the deep past and infer what the ancestral habitats of each microbial group were.

“Probably two of the largest groups of eukaryotes, SARS and Obozoa, each larger than, for example, animals or plants, arose in completely different habitats,” says Fabien Bourqui, also a researcher at Uppsala University and one of the lead authors of the study.

According to Burkey, the SAR lineage, which includes groups such as diatoms, ciliates, dinoflagellates, radiolaria, etc., would have appeared first in the Precambrian oceans, while the ancestor of the Obazoa group, which diversified into fungi, animals, choanoflagellates, and amoebae – could live in non-marine habitats.”

This once again shows that crossing the salinity barrier played an important role in eukaryotic shaping evolution. For this reason, for future research, experts will turn to genomics to discover what genetic mechanisms underlie these key evolutionary events.

Chromatin has been found to originate from ancient microbes one to two billion years ago

More info:
Mahwash Jamy et al, Global patterns and rates of habitat transitions across the eukaryotic tree of life, Natural ecology and evolution (2022). DOI: 10.1038/s41559-022-01838-4

Provided by the Institut de Ciències del Mar

Quote: Researchers Unveil Key Processes in Marine Microbial Evolution (2022, August 5), Retrieved August 6, 2022, from .html

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