Abstract
BackgroundIn some sedimentary environments, such as coastal intertidal and subtidal mudflats, sulfide levels can reach millimolar concentrations (2–5 mM) and can be toxic to marine species. Interestingly, some organisms have evolved biochemical strategies to overcome and tolerate high sulfide conditions, such as the echiuran worm, Urechis unicinctus. Mitochondrial sulfide oxidation is important for detoxification, in which sulfur dioxygenase (SDO) plays an indispensable role. Meanwhile, the body wall of the surface of the worm is in direct contact with sulfide. In our study, we chose the body wall to explore the SDO response to sulfide.MethodsTwo sulfide treatment groups (50 µM and 150 µM) and a control group (natural seawater) were used. The worms, U. unicinctus, were collected from the intertidal flat of Yantai, China, and temporarily reared in aerated seawater for three days without feeding. Finally, sixty worms with similar length and mass were evenly assigned to the three groups. The worms were sampled at 0, 6, 24, 48 and 72 h after initiation of sulfide exposure. The body walls were excised, frozen in liquid nitrogen and stored at −80 °C for RNA and protein extraction. Real-time quantitative RT-PCR, enzyme-linked immunosorbent assay and specific activity detection were used to explore the SDO response to sulfide in the body wall.ResultsThe body wall of U. unicinctus consists of a rugal epidermis, connective tissue, outer circular muscle and middle longitudinal muscle. SDO protein is mainly located in the epidermis. When exposed to 50 µM sulfide, SDO mRNA and protein contents almost remained stable, but SDO activity increased significantly after 6 h (P < 0.05). However, in the 150 µM sulfide treatment group, SDO mRNA and protein contents and activity all increased with sulfide exposure time; significant increases all began to occur at 48 h (P < 0.05).DiscussionAll the results indicated that SDO activity can be enhanced by sulfide in two regulation mechanisms: allosteric regulation, for low concentrations, and transcription regulation, which is activated with an increase in sulfide concentration.
Highlights
Hydrogen sulfide (H2S) at low concentrations can act as a biological signaling molecule in many physiological processes, including regulation of vascular tone, cellular stress response, apoptosis, and inflammation (Li, Rose & Moore, 2011; Módis, Wolanska & Vozdek, 2013; Kabil & Banerjee, 2014), H2S is inherently toxic at high concentrations by reducing complex IV activity, lowering the electrochemical potential across the inner mitochondrial membrane, reducing ATP generation and inducing apoptosis (Beauchamp et al, 1984; Jiang et al, 2016)
In the 50 μM sulfide treatment group (Fig. 2), no significant changes were observed during different sulfide exposure times
In the 150 μM sulfide treatment group (Fig. 2), the expression level of sulfur dioxygenase (SDO) mRNA was upregulated at 48 h (1.885-fold, P < 0.05) and 72 h (2.183-fold, P < 0.05)
Summary
Hydrogen sulfide (H2S) at low concentrations can act as a biological signaling molecule in many physiological processes, including regulation of vascular tone, cellular stress response, apoptosis, and inflammation (Li, Rose & Moore, 2011; Módis, Wolanska & Vozdek, 2013; Kabil & Banerjee, 2014), H2S is inherently toxic at high concentrations by reducing complex IV activity, lowering the electrochemical potential across the inner mitochondrial membrane, reducing ATP generation and inducing apoptosis (Beauchamp et al, 1984; Jiang et al, 2016). In some sedimentary environments, such as coastal intertidal and subtidal mudflats, sulfide levels can reach millimolar concentrations (Arp, Hansen & Julian, 1992), in which animals living there have a variety of adaptations to avoid the toxicity of sulfide. In some sedimentary environments, such as coastal intertidal and subtidal mudflats, sulfide levels can reach millimolar concentrations (2–5 mM) and can be toxic to marine species. We chose the body wall to explore the SDO response to sulfide. Real-time quantitative RTPCR, enzyme-linked immunosorbent assay and specific activity detection were used to explore the SDO response to sulfide in the body wall. In the 150 μM sulfide treatment group, SDO mRNA and protein contents and activity all increased with sulfide exposure time; significant increases all began to occur at 48 h (P < 0.05). All the results indicated that SDO activity can be enhanced by sulfide in two regulation mechanisms: allosteric regulation, for low concentrations, and transcription regulation, which is activated with an increase in sulfide concentration
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