Adhesive Structure of the Freshwater Zebra Mussel, Dreissena polymorpha
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Adhesive Structure of the Freshwater Zebra Mussel, Dreissena polymorpha Nikrooz Farsad1, Trevor W. Gilbert2 and Eli D. Sone1,2,3 1 Department of Materials Science & Engineering, University of Toronto, Toronto, Canada 2 Institute of Biomaterials & Biomedical Engineering, University of Toronto, Toronto, Canada 3 Faculty of Dentistry, University of Toronto, Toronto, Canada ABSTRACT The freshwater Zebra Mussel, Dreissena polymorpha, was accidently released into the Great Lakes approximately 20 years ago. Since then it has spread rapidly, thanks in part to its ability to adhere to hard substrates, resulting in serious environmental and economic consequences. Like the marine mussels, attachment of the Zebra Mussel is achieved by means of its byssus, a series of proteinaceous threads that connect the animal to surfaces via secreted adhesive plaques. While the byssus of the Zebra Mussel is superficially similar to those of its marine counterparts, significant structural and compositional differences suggest that further investigation of the adhesion mechanisms in this freshwater species is warranted. Here we examine for the first time the detailed distribution of DOPA (3,4-dihydroxyphenylalanine)containing proteins in the Zebra Mussel plaque and threads, as well as the enzyme responsible for their cross-linking. We show that the plaque-substrate interface retains the greatest amount of DOPA after aging, consistent with an adhesive role, while in the threads and bulk of plaque DOPA is presumably cross-linked for cohesive strength. We report also on a remarkably uniform layer ~10 nm thick on the underside of the plaque, which is most likely responsible for adhesion. INTRODUCTION The freshwater Zebra Mussel is notorious in the Great Lakes region for its ability to attach to surfaces such as boat hulls and water intake pipes under conditions that are, from an engineering perspective, quite impressive: it is able to rapidly adhere underwater, at ambient temperature, to hard substrates with varied surface chemistry, and with considerable strength. The impressive adhesive capacity of Zebra Mussels is also an important factor in the rapid spread of this invasive species since its accidental release into the Great Lakes in 1985 [1]. There is no doubt that several native mussel species have been virtually wiped out by the invasion, and a number of fish populations have been seriously jeopardized [2]. For industries in the Great Lakes, prevention of biofouling of water intake pipes alone is expected to cost ~$3 billion over the next decade [3]. Moreover, current adhesion controls involve non-specific agents that often have adverse effects on non-target species [4]. The attachment mechanism of Zebra Mussels is at least superficially similar to that of their better understood marine counterparts, in that the adhesion is mediated by a proteinaceous structure called the byssus, consisting of adhesive plaques that are secreted onto the substrate and connected to the mussel via a series of threads (Fig. 1a) [5,6]. In the commo
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