Reduced
oxygen levels and increased
sulfide concentrations have become a concern for marine animals. This study examines respiratory and energetic adaption to acute (0-96 h)
hypoxia (0.5 mg/L dissolved
oxygen) with or without
sulfide (0.2 mM, 1 mM, 3 mM) in the
hypoxia-resistant and
sulfide-tolerant ark shell, Anadara broughtonii. The different states of aerobic respiration, energy-balance, and activity of the mitochondrial
sulfide oxidation chain (MSOC) under these conditions were evaluated. The results indicated that the anaerobic pathway was activated by
hypoxia at 24 h without
sulfide, but was activated in the presence of
sulfide at only 2 h. Exposure to
sulfide resulted in significant accumulation of
ATP, probably due to the activated MSOC and lowered metabolism via suppression of Na+-K+
ATPase activity and
protein synthesis. During
hypoxia, both
enzyme activity and
mRNA levels of
alternative oxidase (AOX) increased while the key
enzymes in MSOC,
sulfide: quinone oxidoreductase (SQR) and
sulfur dioxygenase (SDO), were not altered. With additional
sulfide, the
enzyme activity and
mRNA levels of AOX, SQR, SDO significantly increased. Classical aerobic respiration was significantly inhibited, and induction of alternative respiration was detected. The corresponding alternative electron transport chain (AETC) accepted the electrons originating from both the tricarboxylic acid cycle and MSOC during the challenge, indicating that the capacity of aerobic respiration and
sulfide-oxidation under a reduction state might greatly depend on AETC. The synergistically induced alternative chains (AETC and MSOC) and anaerobic pathway suggested energy-balance between respiration and
sulfide-oxidation, which might contribute to the endurance of ark shells to acute
sulfide exposure.