Abstract
Shallow-water hydrothermal vents off Kueishan Island (northeastern Taiwan) provide a unique, sulfur-rich, highly acidic (pH 1.75–4.6) and variable-temperature environment. In this species-poor habitat, the crab Xenograpsus testudinatus is dominant, as it mainly feeds on zooplankton killed by sulfurous plumes. In this study, 16S ribosomal RNA gene amplicon pyrosequencing was used to investigate diversity and composition of bacteria residing in digestive gland, gill, stomach, heart, and mid-gut of X. testudinatus, as well as in surrounding seawater. Dominant bacteria were Gamma- and Epsilonproteobacteria that might be capable of autotrophic growth by oxidizing reduced sulfur compounds and are usually resident in deep-sea hydrothermal systems. Dominant bacterial OTUs in X. testudinatus had both host and potential organ specificities, consistent with a potential trophic symbiotic relationship (nutrient transfer between host and bacteria). We inferred that versatile ways to obtain nutrients may provide an adaptive advantage for X. testudinatus in this demanding environment. To our knowledge, this is the first study of bacterial communities in various organs/tissues of a crustacean in a shallow-water hydrothermal system, and as such, may be a convenient animal model for studying these systems.
Highlights
A deep-sea hydrothermal vent is one of the most extreme environments on earth, due to its poorly oxygenated, oligotrophic and toxic ecosystem [1]
OTU1, which was predominant in X. testudinatus, was closely related to Epsilonproteobacterum ectosymbiont of deep sea hydrothermal vent shrimp Rimicaris exoculata (i.e., 99% in sequence identity); OTU6, closely related to genus Sulfurovum sp., was only dominant in seawater
Chemoautotrophic Gamma- and Epsilonproteobacteria were recovered from several crabs around hydrothermal vents and cold seep habitats
Summary
A deep-sea hydrothermal vent is one of the most extreme environments on earth, due to its poorly oxygenated, oligotrophic and toxic ecosystem [1]. In such ecosystems, chemolithotrophic bacteria are common residents [2]. Bacteria associated with host animals (e.g., Crustacea), are believed to support their hosts and enable them to adapt to their extreme environment, including high toxicity and limited nutrients [3,4]. Some chemolithotrophic bacteria have been identified and characterized in deep-sea hydrothermal vent shrimp Rimicaris exoculata [5,6,7] and in crabs, including Kiwa spp. Some Crustacea-associated bacteria in hydrothermal vents have host specificity, and site specificity within the host’s gut or gill chamber [5,6,7], consistent with important roles in nutrient supply [11] and detoxification [6] for their hosts, which live in oligotrophic and toxic hydrothermal vent environments [5,12]
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