Tel Aviv University researchers have discovered that sponges called Theonella swinhoei living in the Red Sea and the Indo-Pacific Ocean have the curious ability to encapsulate and neutralize the toxin arsenic from the environment.
Arsenic is the leading freshwater contaminant in the world, affecting millions of people worldwide and causing an untold number of deaths every year.
Removing arsenic from groundwater and freshwater is a major challenge facing scientists and policymakers.
Prof. Micha Ilan of TAU’s zoology department, who led the study, has just published the team’s unique biological model of arsenic detoxification in the journal Nature Communications.
The researchers found that the Entotheonella bacterium that inhabits the sponge is one of the only known cases of a bacterium protecting its host from metal poisoning. It safeguards these sponges against the dangers of arsenic as well as another common toxin, barium.
“This particular sponge species, which is among the most ancient animals inhabiting the earth today, is home to a very diverse, very crowded number of microorganisms,” said Ilan. “These sedentary animals evolved to contain an in-house arsenal of chemicals and associated microbiota to deal with predators and pathologies.”
While studying the biology of the sponge, Ilan and his colleague Dr. Boaz Mayzel discovered and published in 2014 the curious ability of these sponges to accumulate and concentrate a million times more arsenic than that found in seawater.
Dr. Ray Keren, also of TAU’s zoology department and co-author of the new research with Mayzel, suspected a bacterium was involved in the detoxification. After extensive testing, a single bacterial species was found to drive the accumulation of both arsenic and barium.
“We have discovered not only that a single bacterial species was the accumulator of both arsenic and barium. We have also found that this bacterium mineralizes the toxic elements, transforming them into inert products within its cells in a controlled manner,” said Keren.
“Sponges are eaten by turtles and worms, and even though they are exploding with arsenic, the bacteria renders them non-toxic. They become biologically inert. It is a very unique biological model.”
The TAU scientists, in collaboration with Prof. Boaz Pokroy of the Technion Institute of Science and Dr. Sirine Fakra of the Advanced Light Source in the Lawrence Berkeley National Lab, harnessed cutting-edge technology to validate their initial findings, which were procured using the backscatter mode of a scanning electron microscope.
“Pokroy took a sample of the sponge to the European Synchrotron Radiation Facility within a week of seeing that first image,” Keren recalled. “There, he saw that barium is mineralized as barite and arsenic formed smaller peaks of an unknown mineral.”
Subsequent diffraction analysis revealed that the mineral, crystalline arsenic, was, in fact, calcium arsenate. Fakra then validated the presence of these minerals under subfreezing cryogenic conditions.
“To render this unique detox method applicable to other situations, we need to somehow get rid of the sponge,” said Ilan. “In other words, there is a lot more work to be done before we, human beings, can capitalize on this.”
HOW HYDRAS KNOW WHERE TO REGROW BODY PARTS
Few animals can match the humble hydra’s resilience.
The small, tentacled freshwater animals can be literally shredded into pieces and regrow into healthy animals. A study published recently in Cell Reports suggests that pieces of hydras have structural memory that helps them shape their new body plan according to the pattern inherited by the animal’s “skeleton.” Previously, scientists thought that only chemical signals told a hydra where its heads and/or feet should form.
Regenerating hydras use a network of tough, stringy protein fibers, called the cytoskeleton, to align their cells.
When pieces are cut or torn from them, the cytoskeletal pattern survives and becomes part of the new animal. The pattern generates a small but potent amount of mechanical force that shows cells where to line up. This mechanical force can serve as a form of “memory” that stores information about the layout of animal bodies.
“You have to think of it as part of the process of defining the pattern and not just an outcome,” explained senior author and biophysicist Kinneret Keren of the Technion- Israel Institute of Technology in Haifa.
When pieces of hydra begin the regeneration process, the scraps of hydra fold into little balls, and the cytoskeleton has to find a balance between maintaining its old shape and adapting to the new conditions.
“If you take a strip or a square fragment and turn it into a sphere, the fibers have to change or stretch a lot to do that,” said Keren. But some portions retain their pattern. As the little hydra tissue ball stretches into a tube and grows a tentacle-ringed mouth, the new body parts follow the template set by the cytoskeleton in fragments from the original hydra.
The main cytoskeletal structure in adult hydra is an array of aligned fibers that span the entire organism. Tampering with the cytoskeleton is enough to disrupt the formation of new hydras, the researchers found. In many ways, the cytoskeleton is like a system of taut wires that helps the hydra keep its shape and function.
In one experiment, the researchers cut the original hydra into rings that folded into balls that contained multiple domains of aligned fibers. Those ring-shaped pieces grew into two-headed hydras. However, anchoring the hydra rings to stiff wires resulted in healthy one-headed hydras, suggesting that mechanical feedbacks promote order in the developing animal.
Hydras are much simpler than most of their cousins in the animal kingdom, but the basic pattern of aligned cytoskeletal fibers is common in many organs, including human muscles, heart and guts. Studying hydra regeneration may lead to a better understanding of how mechanics integrate with biochemical signals to shape tissues and organs in other species.
“The actomyosin cytoskeleton are the main force generator across the animal kingdom,” says Keren. “This is very universal.”
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