Exploring the Interface Between Macroorganisms and Microorganisms: Biochemical, Ecological, and Evolutionary Contexts

Abstract

<p>The focus of this dissertation is the extension of the innate immune response in wound healing and non-wound healing contexts. I am interested in interactions at the interface between macroorganisms and microorganisms from marine/aqueous environments. This dissertation explored two aspects of the interactions: 1) the presence and function of macroorganism secretions and 2) the role of secretions in managing microfouling on macroorganism surfaces. Particularly of interest are how barriers are biochemically reinforced to mitigate microfouling and the potential consequences of a breach in those barriers. The innate immune response, an evolutionary conserved system in vertebrates and invertebrates, provides an evolutionary context for developing the hypotheses. </p><p>In this dissertation the biochemical composition and uses of crustacean secretions are explored for barnacles, fiddler crabs and blue crabs. Fluids of interest were secretions released during barnacle settlement and metamorphosis and those collected from living adult barnacles, fluids on fiddler crab sensory appendages including dactyl washings and buccal secretions, and fluids from blue crab egg masses. The biochemical composition was determined using a combination of fluorescent probes and confocal microscopy, proteomics, and enzyme-specific substrates with a spectrophotometer. </p><p>I demonstrated that self-wounding is inherent to the critical period of settlement and metamorphosis, in barnacles. Wounding occurs during cuticle expansion and organization and generates proteinaceous secretions, which function as a secondary mode of attachment that facilitates the transition to a sessile juvenile. I showed extensive proteomic evidence for components of all categories of the innate immune response, especially coagulation and pathogen defense during attachment and metamorphosis. This work provides insight into wound healing mechanisms that facilitate coagulation of proteinaceous material and expands the knowledge of potential glue curing mechanisms in barnacles. </p><p>In order to test macroorganism secretions in a non-wound healing context, I examined fluids sampled from body parts that macroorganisms must keep free of microorganisms. I showed that two types of decapod crustaceans can physically manage microorganisms on most parts of their body, but certain parts are particularly sensitive or difficult to clean mechanically. I examined sensory regions on the fiddler crab, including dactyls that are important for chemoreception and the buccal cavity that is used to remove microorganisms from sand particles, and blue crab egg mass fluids that protect egg masses from fouling through embryo development. </p><p>This dissertation explores organismal interactions across scales in size, space, and time. The findings from the barnacle work inform mechanisms of attachment and glue curing, both central to understanding bioadhesion. The work on fiddler crabs and blue crabs contributes to our understanding of chemoreception of feeding and reproductive behaviors.</p><p>The work presented here highlights how biological secretions from macroorganisms serve multifaceted roles. In cases of physical breaches of barriers, or wounding, secretions coagulate to obstruct loss of hemolymph and have antimicrobial capabilities to prevent infection by microorganisms. In non-wounding cases, secretions remove microorganisms from surfaces, whether that is on the body of the macroorganism or in the immediate environment.</p>