criteria may show aberrant values in particular symbioses due to 

 biological, environmental or methodological variability. But 

 when a range of carefully selected criteria are used, a pattern 

 usually stands out indicating the nutritional basis of the 

 symbionts . 



It is particularly interesting to note that on the Louisiana 

 slope, although one species has methanotrophic symbionts, the 

 others appear to use sulfide as their energy source even though 

 methane appears to be available to at least some of them 

 (Childress 1986). The apparent rarity of methane based symbioses 

 is somewhat puzzling at this time. However, it may simply 

 indicate that there are relatively few habitats which have a 

 sufficient abundance of methane to support symbionts located 

 within the tissues of an animal. In contrast, the hosts of 

 sulfur oxidizing bacteria have a variety of mechanisms for 

 concentrating sulfide from their environments allowing them to 

 live at very low sulfide concentrations in some cases (Childress 

 1987) . 



While the nature of the symbionts is coming into focus in 

 these symbioses, the nature of the functional relationship 

 between the symbionts and their hosts has proven much more 

 elusive. There is little direct evidence concerning the benefits 

 which the hosts derive from these symbioses. The seep animals 

 have proven particularly useful for such studies because since 

 they live at only modest depths they can be kept alive without 

 pressure systems. This opens the possibility of making rapid 

 progress in understanding these symbioses. In the case of the 

 seep mussel for example we are able to keep individuals alive for 

 more than a year in the laboratory. This has allowed us to 

 undertake studies on the growth of this species with methane as 

 the sole energy and carbon source as well as studies to determine 

 this species ability to ingest and use particulate food. 



ACKNOWLEDGMENTS 



These studies were supported by NSF grants OCE83-11256 and 

 OCE86-10514, as well as Johnson Sea Link dives funded by the 

 National Undersea Research Program of NOAA. 



LITERATURE CITED 



Anthony, C. 1982. The Biochemistry of Methylotrophs . London, 

 England, Academic Press. 431 pp. 



Anthony, C. and L. J. Zatman. 1965. The microbial oxidation of 

 methanol. The alcohol dehydrogenase of Pseudomonas sp. M27. 

 Biochem. J. , Vol. 96, pp. 808-812. 



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