Most seafloor invertebrate marine animals, such as sponges, corals, worms, and oysters, produce tiny larvae that swim through the ocean before attaching to the seabed and developing into juveniles. A new study published in the Proceedings of the National Academy of Sciences (PNAS) and led by the University of Hawai’i (UH) at Mānoa, researchers have revealed that a large, complex molecule, called lipopolysaccharide, produced by bacteria is responsible for inducing larval marine tubeworms, hydroid elegans, to settle on the seabed and begin the complex processes of metamorphosis.
“This is a major step in understanding the factors that determine where bottom-dwelling invertebrate larvae settle and metamorphose,” said Michael Hadfield, lead author of the paper and professor emeritus at the ‘UH Manoa School of Ocean and Earth Science and Technology. “This is the key to understanding how benthic communities establish and maintain themselves on all surfaces under salt water, i.e. on 71% of the Earth’s surface.”
Most invertebrate larvae are able to stay in the larval stage for long periods of time until they find a good spot. In the study, led by Marnie Freckelton, a postdoctoral researcher at the Kewalo Marine Lab, a unit of SOEST’s Pacific Biosciences Research Center (PBRC), the research team asked the question: how do the “right places” indicate the larvae to settle and metamorphose?
Metamorphosis is a profound change in the shape of the animal – from a small swimming larva to an animal with a very different anatomy anchored to the seabed. Although researchers know that biofilms, thin layers composed of bacteria, diatoms and small algae that cover submerged surfaces, induce the metamorphosis of a wide range of marine invertebrate larvae, the induction mechanism remains unclear. understood.
In laboratory experiments with tubeworm larvae, the team discovered that they would not settle on clean surfaces. They needed a signal from a surface biofilm.
“The team isolated a single bacterial species, lytic cellulophage, which could, once formed into a surface biofilm, induce the worm larvae to settle, and then we asked: what is it about this particular bacterium that causes the larvae to settle and metamorphose? “, said Freckelton.
Through a series of enzymatic experiments, the researchers eliminated bacterial protein-based compounds as potential inducers of compaction. From there, they studied, one by one, various lipid-containing compounds and identified the trigger – lipopolysaccharide, which forms the outer layer of most marine bacteria.
They studied biofilm-bacterial communities from many different habitats to learn which bacterial species were present and how they compared between communities. They found that although thousands of bacterial species make up the biofilm of a given marine habitat, they vary greatly from place to place.
“In fact, we have different strains of the same bacterial species obtained from Kaneʻohe Bay and Pearl Harbor, and the Hydroids the larvae settle only in response to the Pearl Harbor one,” said Hadfield, who has been a Kewalo Marine Lab researcher at PBRC since 1968. Pocillopora damicornis, which is abundant in Kaneʻohe Bay, will only settle in response to the strain of the Kaneʻohe Bay bacteria. This is a breakthrough because it tells us about the specificity of certain bacteria that guide and maintain a community of animals where they occur. »
The recent discovery may help address a number of immediate issues, such as restoring coral reefs; mariculture of clams, oysters, mussels and possibly shrimps and crabs; and biofouling, the buildup of animals and algae on ship hulls that costs global navies and the shipping industry billions of dollars a year.
“I hope we can help these efforts by discovering the bacterial molecules – likely lipopolysaccharides – that guide the settlement of lab-reared corals in vulnerable reef areas or oyster larvae in places like Pearl Harbor to use their filtering abilities to clean waters, as has already been done in the Chesapeake Bay,” Hadfield said. “In addition, our research can directly contribute to the development of ship hull coatings that resist biofouling .”
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Material provided by University of Hawaii at Manoa. Original written by Marcie Grabowski. Note: Content may be edited for style and length.