Seeking SciNote, Biology: Shipworms
How do shipworms bore through wood?
For clarification, the scientific name for the shipworm that I focus on here is Bankia setacea. Before I get to what I find really fascinating about this species, it is useful to view its basic anatomy. The first visual is from an article on "Bivalvia: Teredinidae" (2). Teredindae is the family in which shipworms belong to in the biological tree of life.
It should first be noted that shipworms are not worms at all; rather, they are really clams that look like worms, belonging thus to bivalvia (the class of animals that contains clams, oysters, scallops, and similar molluscs) (2). The key to understanding this anatomical diagram of this clam is shown to the right of the image.
aa, anterior adductor muscle;
pa, posterior adductor muscle;
Please draw your attention to the lengthy gill (g), and then look at the second picture from a more recent 2014 paper (1). This is a photo of a shipworm removed from its burrow. As before, the labeling key is shown to the right.
O'Connor et al, 2014 (1).
Again, I ask you to look at the clam's gill (gi). This because their gills contain a gland unique to the Teredinidae, called the gland of Deshayes. Within this gland are specialized cells that store symbiotic bacteria that make the enzymes that break down wood, called cellulolytic enzymes. This means that these enzymes break down cellulose, the main structural component of the cell walls of trees and other plants.
"Because it requires few enzymes, and these enzymes are neatly translocated to the gut", the first paper describes, "the shipworm provides a simple model system in which to explore minimum enzymatic requirements and efficient enzyme mixtures for lignocellulose decomposition" (1). Another function of this brown, irregular mass of tissue is producing amino acids.
Here is a fantastic article on the new discovery of this digestive strategy-- with nearly 1,000 genes in the gills creating cellulolytic enzymes. These enzymes are especially interesting to researchers like Dan Distel because they convert plant biomass, or cellulose, into sugar, which can be used to make biofuels like ethanol (4).
Their capacity to degrade woody plant materials gives shipworms potential as a source of novel enzymes for industry. This is, in my view, the most important discovery that can be taken away from my answer. If you're wondering how biofuel is made from cellulose, take a look at this infogram describing cellulosic ethanol production (5).
Thank you for asking, we're grateful for all your questions!
Answered by John M, Expert Supervisor.
Edited by Margaret G, Editor.
Roberta M. O’Connor, Jennifer M. Fung, Koty H. Sharp, et al. Gill bacteria enable a novel digestive strategy in a wood-feeding mollusk. Proceedings of the National Academy of Sciences, Vol. 111, No. 47. (25 November 2014), pp. E5096-E5104,doi:10.1073/pnas.1413110111
Betcher MA, Fung JM, Han AW, O’Connor R, Seronay R, et al. (2012) Microbial Distribution and Abundance in the Digestive System of Five Shipworm Species (Bivalvia: Teredinidae). PLoS ONE 7(9): e45309. doi: 10.1371/journal.pone.0045309
Sherif I. Elshahawi, Amaro E. Trindade-Silva, Amro Hanora, et al. Boronated tartrolon antibiotic produced by symbiotic cellulose-degrading bacteria in shipworm gills. Proceedings of the National Academy of Sciences, Vol. 110, No. 4. (22 January 2013), pp. E295-E304, doi: 10.1073/pnas.1213892110
St. Martin, Greg. Researchers discover new digestive strategy in shipworms. November 10, 2014. News @ Northeastern: Campus & Community, Science & Technology.
Image: European Biofuels Technology Platform (EBTP). 2007-2014, EBTP-SABS