Abstract
The amphipod Hirondellea gigas inhabits the deepest regions of the oceans in extreme high-pressure conditions. However, the mechanisms by which this amphipod adapts to its high-pressure environment remain unknown. In this study, we investigated the elemental content of the exoskeleton of H. gigas specimens captured from the deepest points of the Mariana Trench. The H. gigas exoskeleton contained aluminum, as well as a major amount of calcium carbonate. Unlike other (accumulated) metals, aluminum was distributed on the surface of the exoskeleton. To investigate how H. gigas obtains aluminum, we conducted a metabolome analysis and found that gluconic acid/gluconolactone was capable of extracting metals from the sediment under the habitat conditions of H. gigas. The extracted aluminum ions are transformed into the gel state of aluminum hydroxide in alkaline seawater, and this gel covers the body to protect the amphipod. This aluminum gel is a good material for adaptation to such high-pressure environments.
Highlights
The deepest bottom of the ocean is an extreme environment characterized by extra-high pressures, low temperatures, and oligotrophy, and few animals can adapt to such extreme environments [1,2,3]
H. gigas inhabits the bottom of the deepest trench by obtaining glucose, a resource of gluconolactone/ gluconic acid, from plant debris buried in sediment and digesting the glucose with its own cellulase and hemicellulose hydrolases [5,6,7]
Aluminum hydroxide gel is constructed by the chemical behavior of aluminum ion in response to pH
Summary
The deepest bottom of the ocean is an extreme environment characterized by extra-high pressures, low temperatures, and oligotrophy, and few animals can adapt to such extreme environments [1,2,3]. The amphipod Hirondellea gigas is a resident of the deepest points of the Mariana Trench (Challenger Deep), the Philippine Trench, the Izu-Ogasawara Trench, and the Japan Trench, where it inhabits depths greater than 8,000 m [4,5,6,7,8]. We attempted to widely capture marine creatures using baited traps along deep-sea points, but these amphipods were the only catch [5, 6]. The extra-high pressure in the deep sea affects the various chemical components of organisms. Calcium carbonate is an important component of crustacean exoskeletons; this component dissolves in seawater deeper than approximately 4,000–5,000 m (carbonate compensation depth, CCD) [9]; crustaceans cannot migrate on the deep-sea
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