New research has found that shipworms digest wood using symbiotic microbes in their guts, a discovery that overturns previous insights and has significant implications for biotechnology and environmental modeling. A cross-section of Belfast dock pilings, riddled with shipwormholes. Credit: Barry Goodell
Unlocking the secrets of the world’s most fascinating and destructive mollusk could impact everything from climate change to public health.
They confused the ancient Greek navy, helped shipwreck Christopher Columbus, helped sink the Spanish Armada and caused the San Francisco Bay wharves to collapse into the sea, but so far scientists have been unable to to determine exactly how shipworms – a family of molluscs – can cause such damage. A team of researchers, led jointly by the University of Massachusetts Amherst and the University of Plymouth, along with collaborators from the University of Maine and UMass Chan Medical School, has discovered that a population of symbiotic microbes living in an overlooked suborgan of the intestines called ‘typhlosole’ have the ability to secrete the enzymes needed to digest lignin – the heaviest part of wood.
“Shipworms are such important animals,” says Reuben Shipway, co-corresponding author of the study recently published in International biodegradation and biodegradation and who initiated this work as part of his postdoctoral fellowship at UMass Amherst. “They are found in the world’s oceans and have not only changed history, they are also ecosystem engineers and play a fundamental role in the carbon cycle in aquatic environments. It’s incredible that we don’t yet fully understand how they do this.”
Wood digestion by shipworms
Wood is a wonderful substance: flexible and tough, its fibrous but nutritious cellulose can make a great meal, but only for living things that can digest it and also penetrate the layer of lignin, a tough, armor-like substance that surrounds the body. cellulose-like “wrap rage”-inducing packaging around your favorite treat. Microbiologists have long known that animals that can digest lignin-like termites harbor specialized, symbiotic colonies of microbes in their guts that do the work of breaking down the lignin for them. “But,” says lead author Barry Goodell, recently retired professor of microbiology at UMass Amherst and professor emeritus at the University of Maine, “the shipworm’s digestive tract has long been thought to be virtually sterile.”
The shipworm is actually a mollusk found all over the world. Credit: Reuben Shipway
So how do shipworms do what they do?
Goodell and Shipway have spent the better part of the last decade trying to answer this question, testing a variety of innovative hypotheses, none of which have given away the secret of shipworms.
“We decided to look very carefully at the shipworm’s gut again,” Goodell says, “just in case the researchers of the last hundred years have missed something.”
That indeed appears to be the case.
It turns out that shipworms have a curious sub-organ called a typhlosole – “it looks like Salvador Dali’s mustache turned upside down,” says Shipway – that is embedded in the mollusk’s digestive tract. Previous researchers had thought it served as a mixture structure, but when Goodell and Shipway did careful breeding work, they then enlisted the help of the Argonne National Lab’s facilities for metagenomic analysis and the advanced genetic probe microscopy technique at the UMass Amherst Institute for Applied Life Sciences, they discovered what generations of researchers had overlooked: hidden clusters of bacterial symbionts with the ability to produce lignin-digesting enzymes.
Barry Goodell (UMass Amherst) inspects wood riddled with shipwormholes. Credit: Barry Goodell
Potential applications and impact on the environment
Not only does this research help solve a long-standing mystery, but the findings could also have important practical applications. Biotech companies are looking for new enzymes that can digest recalcitrant substrates more efficiently than current bioindustrial processes allow, and new sources of enzymes that can open the structure of biomass residues are very important in cultivation in this field. Furthermore, previous shipworm symbionts have proven to be a treasure trove of natural products – such as new antiparasitic antibiotics – that could have significant impacts on human health.
In the field of climate change, research like this can help refine models that predict how CO2 and other greenhouse gases are released into the environment, especially given that large amounts of wood waste on land end up in the ocean, where much of it passes through the shipworm’s gut.
Finally another animal kind, including other mollusks, the common earthworm, and even the tadpole stages of frogs, also possess a typhlozole that has not previously been thoroughly studied. If symbionts similar to those in shipworms were found in these animals, it could change our understanding of how these animals also navigate the world. “It’s very satisfying,” Goodell says of the research. “We have been trying to unravel this mystery for years and we have finally discovered the shipworm’s hidden bacterial symbiont secret.”
Reference: “First report of microbial symbionts in the digestive tract of shipworms; wood-boring molluscs” by Barry Goodell, James Chambers, Doyle V. Ward, Cecelia Murphy, Eileen Black, Lucca Bonjy Kikuti Mancilio, Gabriel Perez-Gonzalez and J. Reuben Shipway, June 5, 2024, International biodegradation and biodegradation.
DOI: 10.1016/j.ibod.2024.105816