Abstract
Horseshoe crabs are a group of marine chelicerates that contain only four extant species, some of which are endangered. Their hemolymph has been widely used in medical applications for endotoxin detection. Nevertheless, there is limited information on the profiles of their hemolymph proteins and their gut microbial diversity. In this study, we performed the first detailed investigation of the hemolymph proteomics and gut microbiota of two Asian horseshoe crabs Tachypleus tridentatus and Carcinoscorpius rotundicauda. Among the identified proteins being cataloged in the juvenile and adult hemolymph, unexpectedly, sesquiterpenoid signaling pathway proteins including Heat shock protein 83 (HSP83), Chd64, and a juvenile hormone binding protein (JHBP) were revealed. This provides evidence for the presence of functional sesquiterpenoid hormonal systems in these marine chelicerates. consumption of certain horseshoe crab species often leads to tetrodotoxin poisoning and the horseshoe crab is thought to possess a tetrodotoxin resistance mechanism. As such, sodium channels were analyzed and found to have critical amino acid residues that are similar to the toxin resistant pufferfish sodium channels. The source of the toxin is unknown so we investigated the gut microbiota, and found that Clostridium and Vibrio were the most dominant bacteria in T. tridentatus and C. rotundicauda, respectively. Together, this study provides a framework for further understanding of sesquiterpenoids and gut microbiota of these marine chelicerates.
Highlights
The Chelicerata is the second largest subphylum in the Arthropoda after the Insecta, comprising more than 77,000 described living species
The Limulus amebocyte lysate (LAL) test is an in vitro test that is commonly used for the detection of gram-negative bacteria since the 1970s based on the fact that a coagulative protein in the Limulus amebocyte was found to be highly sensitive to bacterial endotoxins (Levin and Bang, 1964, 1968)
The molecular weight distribution of C. rotundicauda and T. tridentatus hemolymph proteins was both observed with ∼80% within 80 kDa (Figure 1A)
Summary
The Chelicerata is the second largest subphylum in the Arthropoda after the Insecta, comprising more than 77,000 described living species. Hemolymph Proteomics and Gut Microbiota rotundicauda, Tachypleus gigas, and Tachypleus tridentatus distributed in Asia (Vestbo et al, 2018) These animals generally live in shallow water regions with soft sandy or muddy bottoms, mainly the estuaries. Coagulation proteins released from crab amebocytes detect endotoxin, a type of pyrogen that presents on the surface of the outer membrane of gram-negative bacteria, that could be life-threatening when introduced intravenously (Maloney et al, 2018). The Limulus amebocyte lysate (LAL) test is an in vitro test that is commonly used for the detection of gram-negative bacteria since the 1970s based on the fact that a coagulative protein in the Limulus amebocyte was found to be highly sensitive to bacterial endotoxins (Levin and Bang, 1964, 1968). It had been suggested that the LAL test could be more ethical and sustainable than the traditional rabbit pyrogen test (Mehmood, 2019)
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