Surface alkanes and fatty acids from the thalli of the lichen Xanthoria parietina, its photobiont Trebouxia sp., and its mycobiont were analysed by GC-MS. The green alga Trebouxia sp. synthesized mainly unsaturated fatty acids such as (Z,Z,Z)-9,12,15-18 : 3 (Z,Z)-9,12-18 : 2 and (Z)-9-18 : 1, and light alkanes C 8 -C 15 (up to 83% of total n-alkanes). However, the mycobiont contained mainly saturated fatty acids such as hexadecanoic (16 : 0) and octadecanoic acid (18 : 0), and also very long-chain n-alkanes C 22 -C 34 . Dehydroabietic acid was found in both lichen and mycobiont. The occurrence of different amounts of n-alkanes and fatty acids in the photobionts and mycobionts of X. parietina was shown for the first time. Lichens collected from different locations in the Jerusalem hills contained n-alkanes ranging in concentration from 187 to 211 mgAE(g dry wt) )1 ; n-alkane concentrations in the photobiont and mycobiont were 17-24 and 215-262 mgAE(g dry wt) )1 , respectively.Keywords: alkanes; lichen; mycobiont; photobiont Trebouxia; Xanthoria.Lichens have been described as Ôdual organismsÕ because they are symbiotic associations between two (or sometimes more) entirely different types of micro-organism: a fungus (termed the mycobiont) and a green alga or a cyanobacterium (termed the photobiont). These organisms have both algal and fungal properties [1,2] and produce n-alkane, unusual betaine ether glycerolipids [3,4], and saturated, unsaturated, branched, and halogenated fatty acids [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Many different bioactive secondary metabolites have also been isolated from lichen species [21,22], which have been used in pharmaceutical sciences [23]. One of main questions in lichen biology and chemistry is which compounds are synthesized by which symbiotic lichen partner? As fungi are often rich in secondary products [24,25,26], it is not surprising that many typical lichen substances are synthesized by the mycobiont. Culberson et al. [27] showed that experimentally produced combinations of a mycobiont with foreign photobionts generate the same lichen products as the mycobiont in a natural thallus with its usual partner. Fox & Huneck [28] showed that mycobionts could synthesize long-chain aliphatic acids, but they did not indicate which fatty acids were synthesized by the photobiont.In this study, we attempt to show which aliphatic hydrocarbons and fatty acids are produced by the photobiont and which by the mycobiont isolated from the lichen Xanthoria parietina.
Materials and methods
Lichen samplesSamples of X. parietina lichens were collected from the bark of trees in the Givat Ram Campus, Hebrew University, Abu Ghosh Village, Gilo Aleph and Ein Kerem (all on the outskirts of Jerusalem) during June to August 1998. X. parietina is widespread in Israel and also around the Jerusalem hills [29,30].
Isolation and cultivation of photobiontsPhotobiont was isolated by the micropipette method of Ahmadjian [31] and grown as described by Friedl [32]. The photobiont was examined...