Aug 16, 2012
Senior Scientist Hideki Kobayashi and research team members from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC: Asahiko Taira, President) Institute of Biogeosciences have been investigating the ecology of an amphipod (Hirondellea gigas) living in the Challenger Deep of the Marianas Trench (10,900 m depth).
The amphipod Hirondellea gigas is an amazing creature living in the deepest part of the Mariana Trench. The H. gigas thrives at low temperatures, extreme pressures, and very nutrient-poor environments at the bottom of deepest sea. The existence of the deepest sea lives was known from 1960s, however, their lifestyle as well as their foods was still unknown. What are they eating? We caught 185 amphipods using bait traps on the "ASHURA" (an 11,000-m class free-fall sediment sampler with a camera system), and analyzed the activities of digestive enzymes in H. gigas. As the result, we found that H. gigas survives, in part, by digesting plant materials that have sunk into the hadal sea. They accomplish this by producing enzymes of amylase, cellulase, mannanase, and xylanase (Fig. 1). The H. gigas contained much glucose, maltose, and cellobiose, which were products of their digestive enzymes in their body. We succeed in purifying H. gigas cellulase (HGcel) from 10 amphipods, and analyzed its enzymatic property. HGcel produced glucose and cellobiose from carboxymethyl cellulose at a molar ratio of 2:1 (Fig. 2). We found that HGcel can digest even sawdust, which is one of the possible substrates for bio-ethanol production. Furthermore, HGcel reacted on plain paper, and produced glucose at room temperature without water (Fig. 3). HGcel was a novel cellulase, and showed very different property from known cellulases of other organisms. This makes it an excellent candidate for industrial production of ethanol, an important biofuel.
The deepest sea was the extra high pressure, low temperature, and nutrient-poor environment, whose sediments contained organic carbon less than 6 ppm/g (dry-weight). H. gigas adapted to the deepest nutrient-poor environments by eating sunk plants. HGcel helps its getting nourishment by one-step production of glucose from cellulose.