. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SULFUR AMINO ACIDS IN SOLEMYA VELUM 337 Environment NH3 HS Host -*• Glutamate Cysteine. Taurine Thiotanrine Figure 3. Proposed model of taurine and thiotaurine biosynthesis in Solfin\;i vfliiin. The clams extract ammonia and sulfides from the burrow einitonmcm. Ammonia is assimilated into glutamate. which is probably utilized by the xymbionts in cysteine synthesis. Cysteine is translocated to the host and utili/cd in the synthesis of taurine and thiotaurine. amino acid cysteine from gram-negative symbionts to host may occur
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SULFUR AMINO ACIDS IN SOLEMYA VELUM 337 Environment NH3 HS Host -*• Glutamate Cysteine. Taurine Thiotanrine Figure 3. Proposed model of taurine and thiotaurine biosynthesis in Solfin\;i vfliiin. The clams extract ammonia and sulfides from the burrow einitonmcm. Ammonia is assimilated into glutamate. which is probably utilized by the xymbionts in cysteine synthesis. Cysteine is translocated to the host and utili/cd in the synthesis of taurine and thiotaurine. amino acid cysteine from gram-negative symbionts to host may occur in 5. velum gill tissue as modeled in Figure 3. Such translocations have been demonstrated in bacteria- aphid and algal-cnidarian associations (Wang and Douglas. 1999: Douglas etui, 2001). The results of this study suggest that S. velum relies upon its symbionts as a source of taurine precursors, as modeled in Figure 3. The inhibition of symbiont metabolism with chloramphenicol, therefore, may equate to a loss of cysteine metabolism, thus decreasing sulfide consumption and tau- rine and thiotaurine synthesis by the host. Ammonia limi- tation, either by MSX treatment or reduced exogenous am- monia resources, may limit glutamate availability in S. velum tissues, thereby limiting cysteine production in the symbionts (Fig. 3). This could result in the lower taurine levels seen in the solemyid clams in this study and in previous work (Lee et al., 1997). Thus, taurine and thiotau- rine may be a link between nitrogen and sulfur cycling in chemoautotrophic symbioses and serve as nontoxic sulfide storage and transport compounds. The absence of similar patterns in nonsymbiotic sulfide-tolerant molluscs (Geuken- sia demissa and YolJin limatula) suggests these functions of sulfur-containing free amino acids may be limited to sym- biotic molluscs. Acknowledgments We thank Gerhard Munske of Washington State Univer- sity for his aid in conducting the amino acid analyses. We also thank David
Size: 1979px × 1262px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
