The byssal thread of Mytilus califorianus, or the California Mussel as with other mussel species is used to hold the mussels onto rocks after they settle.As mentioned elsewhere, mussels to help move if they need to can also use the threads.For the M. califorianus, the threads are about 200micrometers in diameter and can be up to several centimeters long.These threads have four different sections; the stem, which attaches the thread to the mussel tissues, the plaque, at the other end is an adhesive that attaches the thread to substratum.The thread itself is divided into two more portions the distal and proximal ends.The proximal end is closer to the body of the mussel and has low initial stiffness with a corrugated appearance.The distal side is closer to the plaque, and has a much higher initial stiffness, but softens greatly after just 15% strain.
The process of settling and attaching with bryssus on average, takes 2-5 minutes.The mussel first touches down and then begins secreting soluble precursors down the ventral groove of the foot.In the foot, contractions happen that fold the precursors into threads.The main protein of the threads if preCol also known as byssal collagen.It makes up approximately 96% of the distal portion and 66% of the proximal portion.
The California Mussel in particular has the most mechanically superior byssal threads compared to Mytilus edulis and Mytilus galloprovincialis.This means that it performs better under stress as well as recovers faster to its initial stiffness.
At first, it was thought that this was due to a unique histidine-rich domain sequence because it was thought that the histidine metal-coordinations are the first bonds sacrificed during stress yield.But after compiling data for all three species, these domain sequences were highly conserved.And it appears that instead, it is superior because of a greater abundance of silk-like polyamine tracts.
Due to the high initial stiffness followed by a high amount of softness, these threads have been studied for their application into biotechnologies.The goal is to imitate these properties in forming new compounds that are harder to break.
