FATTY-ACIDS OF HYDROTHERMAL VENT RIDGEIA-PISCESAE AND INSHORE BIVALVES CONTAINING SYMBIOTIC BACTERIA

Ridgeia piscesae from a hydrothermal vent and lucinid and thyasirid bi valves from inshore Canadian and UK waters, known to contain sulphur-o xidizing symbiotic bacteria, had lipids rich in 16:0, 16:1(n-7) and 18 :1(n-7) fatty acids in both bacteria-rich trophosome or gill tissue an d in tissues without symbiotic bacteria. The results are consistent wi th the animals deriving these fatty acids from their sulphur-oxidizing symbionts. Ridgeia piscesae, Lucinoma annulata, Parvilucina tenuiscul pta, Lucinoma borealis and Myrtea spinifera also contained substantial amounts of the non-methylene-interrupted dienoic fatty acids 20:2 Del ta 5,13 and 22:2 Delta 7,15. It is proposed that these fatty acids are produced by chain elongation and Delta 5 desaturation in animal tissu es of 18:1(n-7) produced by the bacterial symbionts. Thyasira flexuosa did not contain 20:2 Delta 5,13 or 22:2 Delta 7,15 but instead contai ned 18:1(n-11) and 20:1(n-13) which were nor present in the other spec ies analysed. It is proposed that 18:1(n-11) and 20:1(n-13) arise from the Delta 9 desaturation of 20:0 and 22:0, respectively, followed by chain shortening of the mono-unsaturated fatty acid products of Delta 9 desaturation. It is considered that 20:2 Delta 5,13 and 22:2 Delta 7 ,15 are formed in the animals in response to a relative excess of 16:0 , 16:1(n-7) and 18:1(n-7), accompanied by a relative deficiency of (n- 3) and (n-6) polyunsaturated fatty acids. The results are discussed in relation to the lipid nutrition of marine invertebrates containing ba cterial symbionts.