Hexbyte Glen Cove Bacterial bloom as the Earth thawed thumbnail

Hexbyte Glen Cove Bacterial bloom as the Earth thawed

Hexbyte Glen Cove

Changes in Earth’s environment and lifeforms during the Snowball Earth and its aftermath 650-630 million years ago. Black arrows show changes. The appearance of a supercontinent caused a decrease in ocean volcanism, which resulted in a decrease in atmospheric CO2 and the Snowball Earth. Red words show new findings in this paper. Credit: Kunio Kaiho

Around 650 million years ago, the Earth entered into the Marinoan glaciation that saw the entire planet freeze. The “Snowball Earth” impeded the evolution of life. But as it warmed, biotic life began to flourish. A research team from Tohoku University has analyzed rock samples from China to tell us more about this transition.

Some researchers hypothesize that ice sheets enveloped the earth during the Marinoan glaciation (650–535 million years ago) in what is dubbed the “Snowball Earth.” The glaciation also impacted the climate and chemical compositions of the oceans, restraining the evolution of early life. Yet, as the earth warmed, and the Ediacaran period dawned, biotic life began to evolve.

A research team from Tohoku University has unveiled more about the evolutionary process of the Marinoan-Ediacaran transition. Using biomarker evidence, they revealed possible photosynthetic activity during the Marinoan glaciation. This was followed by photosynthetic organisms and bacteria entering a period of low productivity. However, as eukaryotes expanded during the early Ediacaran period, they blossomed.

Dr. Kunio Kaiho, who co-authored a paper with Atena Shizuya, said, “Our findings help clarify the evolution of primitive to complex animals in the aftermath of the Snowball Earth.” Their paper online was published in the journal Global and Planetary Change on August 8, 2021.

The late Neoproterozoic era (650–530 million years ago) witnessed one of the most severe ice ages in the Earth’s 4.6-billion-year history. Researchers believe that ice sheets covered the entire since glaciogenic units, such as ice-rafted debris, are distributed globally. Overlaying these glaciogenic formations are cap carbonates. These precipitate under warm conditions and therefore suggest that the glacial environment changed rapidly into a greenhouse environment.

The Snowball Earth hypothesis purports the atmospheric carbon dioxide concentration controlled the change from a frozen state to an ice-free state. Ice sheet-covered oceans prevented the dissolution of carbon dioxide into seawater during the Marinoan ice age, meaning greenhouse gas concentration, emitted by volcanic activity, increased gradually. Once the extreme greenhouse effect kicked in, glaciers melted and excess carbon dioxide precipitated on glaciogenic sediments as cap carbonates.

Whilst the Snowball Earth theory explains the wide distributions of glacial formations, it fails to shed light on the survival of living organisms. To counteract this, some researchers argue that sedimentary organic molecules, a molecular clock, and fossils from the late Neoproterozoic era are evidence that primitive eukaryotes such as sponges survived this severe ice age. Alternative models also propose that an ice-free open sea existed during the glaciation and acted as an oasis for marine life.

But what is understood is that the Marinoan glaciation and the succeeding extreme climatic transition likely had a marked impact on the biosphere. Shortly after the ice age, the Lantian biota, the earliest-known complex macroscopic multicellular eukaryotes, emerged. The Lantian biota includes macrofossils that are phylogenetically uncertain but morphologically and taxonomically diverse. Meanwhile, pre-Marinoan species have simple body plans with limited taxonomic variety.

Bacteria and eukaryote biomarkers demonstrate that bacteria dominated before the glaciation, whereas steranes/hopanes ratios illustrate that eukaryotes dominated just before it. However, the relationship between the biosphere changes and the Marinoan glaciation is unclear.

In 2011, Kaiho and his team traveled to Three Gorges, China under the guidance of China University of Science’s Dr. Jinnan Tong to take sedimentary rock samples from the deeper outcrops of marine sedimentary rocks. From 2015 onwards, Shizuya and Kaiho analyzed the biomarkers of algae, photosynthetic activity, bacteria, and eukaryotes from the rock samples.

They found photosynthetic activity based on n-C17 + n-C19 alkanes for algae and pristane + phytane during the Marinoan . Hopanes within the early and late carbonate deposition showed and other bacteria entering a state of low productivity before recovering. And steranes from carbonates and mudstones after the cap carbonate deposition from the early Ediacaran period indicated the expansion of eukaryotes. The expansion of eukaryotes corresponded to the Lantian biota being morphologically diverse when compared to pre-Marinoan species.

Kaiho believes we are one step closer to understanding the evolutionary process that occurred before and after Snowball Earth. “The environmental stress of closed ocean environments for the atmosphere followed by high temperatures around 60°C may have produced more complex animals in the aftermath.” Their findings show that bacterial recovery preceded eukaryotes’ domination.

Kaiho’s team is doing further studies to clarify the relationship between climate change and the biosphere in other locations. They are also studying the relationship between atmospheric oxygen increases and animal evolution from the late Cryogenian to early Cambrian (650 to 500 million years ago).

More information:
Atena Shizuya et al, Marine biomass changes during and after the Neoproterozoic Marinoan global glaciation, Global and Planetary Change (2021). DOI: 10.1016/j.gloplacha.2021.103610

Bacterial bloom as t

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Hexbyte Glen Cove The incredible bacterial 'homing missiles' that scientists want to harness thumbnail

Hexbyte Glen Cove The incredible bacterial ‘homing missiles’ that scientists want to harness

Hexbyte Glen Cove

An illustration of tailocins, and their altruistic action painted by author Vivek Mutalik’s daughter, Antara. Credit: Antara Mutalik

Imagine there are arrows that are lethal when fired on your enemies yet harmless if they fall on your friends. It’s easy to see how these would be an amazing advantage in warfare, if they were real. However, something just like these arrows does indeed exist, and they are used in warfare … just on a different scale.

These weapons are called tailocins, and the reality is almost stranger than fiction.

“Tailocins are extremely strong protein nanomachines made by ,” explained Vivek Mutalik, a research scientist at Lawrence Berkeley National Laboratory (Berkeley Lab) who studies tailocins and phages, the bacteria-infecting viruses that tailocins appear to be remnants of. “They look like phages but they don’t have the capsid, which is the ‘head’ of the phage that contains the viral DNA and replication machinery. So, they’re like a spring-powered needle that goes and sits on the , then appears to poke all the way through the making a hole to the cytoplasm, so the cell loses its ions and contents and collapses.”

A wide variety of bacteria are capable of producing tailocins, and seem to do so under stress conditions. Because the tailocins are only lethal to specific strains—so specific, in fact, that they have earned the nickname “bacterial homing missiles”—tailocins appear to be a tool used by bacteria to compete with their rivals. Due to their similarity with phages, scientists believe that the tailocins are produced by DNA that was originally inserted into during viral infections (viruses give their hosts instructions to make more of themselves), and over evolutionary time, the bacteria discarded the parts of the phage DNA that weren’t beneficial but kept the parts that could be co-opted for their own benefit.

But, unlike most abilities that are selected through evolution, tailocins do not save the individual. According to Mutalik, bacteria are killed if they produce tailocins, just as they would be if they were infected by true phage virus, because the pointed nanomachines erupt through the membrane to exit the producing cell much like replicated viral particles. But once released, the tailocins only target certain strains, sparing the other cells of the host lineage.

“They benefit kin but the individual is sacrificed, which is a type of altruistic behavior. But we don’t yet understand how this phenomenon happens in nature,” said Mutalik. Scientists also don’t know precisely how the stabbing needle plunger of the tailocin functions.

These topics, and tailocins as a whole, are an area of hot research due to the many possible applications. Mutalik and his colleagues in Berkeley Lab’s Biosciences Area along with collaborators at UC Berkeley are interested in harnessing tailocins to better study microbiomes. Other groups are keen to use tailocins as an alternative to traditional antibiotics -which indiscriminately wipe out beneficial strains alongside the bad and are increasingly ineffective due to the evolution of drug-resistance traits.

In their most recent paper, the collaborative Berkeley team explored the and physical mechanisms governing how tailocins attack specific strains, and looked at genetic similarities and differences between tailocin producers and their target strains.

After examining 12 strains of soil bacteria known to use tailocins, the biologists found evidence that differences in the lipopolysaccharides—fat- and sugar-based molecules—attached to the outer membranes could determine whether or not a strain is targeted by a particular tailocin.

“The bacteria we studied live in a challenging, resource-poor environment, so we’re interested to see how they might be using tailocins to fight for survival,” said Adam Arkin, co-lead author and a senior faculty scientist in the Biosciences Area and technical co-manager of the Ecosystems and Networks Integrated with Genes and Molecular Assemblies (ENIGMA) Scientific Focus Area. Arkin noted that although scientists can easily induce bacteria to produce tailocins in the lab (and can easily insert the genes into culturable strains for mass production, which will be handy if we want to make tailocins into medicines) there are still a lot of unanswered questions about how bacteria deploy tailocins in their natural environment, as well as how—and why—particular strains are targeted with an assassin’s precision.

“Once we understand the targeting mechanisms, we can start using these tailocins ourselves,” Arkin added. “The potential for medicine is obviously huge, but it would also be incredible for the kind of science we do, which is studying how environmental microbes interact and the roles of these interactions in important ecological processes, like carbon sequestration and nitrogen processing.”

Currently, it’s very difficult to figure out what each microbe in a community is doing, as scientists can’t easily add and subtract and observe the outcome. With properly harnessed tailocins, these experiments could be done easily.

Mutalik, Arkin, and their colleagues are also conducting follow-up studies aiming to reveal tailocins’ mechanisms of action. They plan to use the advanced imaging facilities at Berkeley Lab to take atomic-level snapshots of the entire process, from the moment the tailocin binds to the target cell all the way to cell deflation. Essentially, they’ll be filming frames of a microscopic slasher movie.

More information:
Sean Carim et al, Systematic discovery of pseudomonad genetic factors involved in sensitivity to tailocins, The ISME Journal (2021). DOI: 10.1038/s41396-021-00921-1


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