Possible Roles of Sulfur-Containing Amino Acids in a Chemoautotrophic Bacterium-Mollusc Symbiosis

Abstract

Invertebrate hosts of chemoautotrophic symbionts face the unique challenge of supplying their symbionts with hydrogen sulfide while avoiding its toxic effects. The sulfur-containing free amino acids taurine and thiotaurine may function in sulfide detoxification by serving as sulfur storage compounds or as transport compounds between symbiont and host. After sulfide exposure, both taurine and thiotaurine levels increased in the gill tissues of the symbiotic coastal bivalve Solemya velum. Inhibition of prokaryotic metabolism with chloramphenicol, inhibition of eukaryotic metabolism with cycloheximide, and inhibition of ammonia assimilation with methionine sulfoximine reduced levels of sulfur-containing amino acids. Chloramphenicol treatment inhibited the removal of sulfide from the medium. In the absence of metabolic inhibitors, estimated rates of sulfide incorporation into taurine and thiotaurine accounted for nearly half of the sulfide removed from the medium. In contrast, amino acid levels in the nonsymbiotic, sulfide-tolerant molluscs Geukensia demissa and Yoldia limatula did not change after sulfide exposure. These findings suggest that sulfur-containing amino acids function in sulfide detoxification in symbiotic invertebrates, and that this process depends upon ammonia assimilation and symbiont metabolic capabilities.

Effects of acclimation temperature and cadmium exposure on cellular energy budgets in the marine molluskCrassostrea virginica: linking cellular and mitochondrial responses

“…Cycloheximide is widely used as an inhibitor of cytoplasmic protein synthesis in ectotherms including marine mollusks (Giuditta et al, 1968;Alkon et al, 1987;Fuery et al, 1998;Joyner and Peyer, 2003). In our preliminary studies, we tested different cycloheximide concentrations and found that concentrations between 75 and 750·mol·l -1 showed a similar and consistent degree of inhibition of cellular M O 2 (by 10-15%).…”

Sulfide intrusion in seagrasses assessed by stable sulfur isotopes—a synthesis of current results

“…In contrast all sulfur compounds in the leaves originated of a mixture of reoxidised sulfide and bulk pore water sulfate (Hasler-Sheetal, 2014). Also S-containing amino acids, such as taurine and thiotaurine, have been suggested as storage compounds of toxic sulfide in chemoautotrophic bacteria experiencing high sulfide concentrations (Joyner et al, 2003), a similar mechanism is possible in the seagrasses, but further studies are needed.…”

Hypotaurine and sulfhydryl-containing antioxidants reduce H2S toxicity in erythrocytes from a marine invertebrate

“…However, HT can also react with sulfide directly, forming thiotaurine (ThT) in vitro (Cavallini et al, 1963). If this reaction occurs in vivo, it would scavenge free sulfide and might, therefore, reduce sulfide toxicity by acting as a sulfide 'buffer' (Alberic and Boulegue, 1990;Brand et al, 2007;Joyner et al, 2003;Pruski and Fiala-Medioni, 2003;Rosenberg et al, 2006). In sulfide-exposed animals that lack sulfide-oxidizing endosymbionts, the resulting ThT may be enzymatically recycled back to HT, thereby releasing sulfide at a rate that allows detoxification through other mechanisms (Rosenberg et al, 2006).…”