International Journal of Biological Macromolecules 41 (2007) 193–197 First report on polysaccharides of Asterochloris and their potential role in the lichen symbiosis Lucimara M.C. Cordeiro, Guilherme L. Sassaki, Marcello Iacomini ∗ Departamento de Bioqu´ ımica e Biologia Molecular, Universidade Federal do Paran´ a, CP 19.046, CEP 81.531-990, Curitiba, PR, Brazil Received 18 October 2006; received in revised form 1 February 2007; accepted 8 February 2007 Available online 16 February 2007 Abstract A structural study of the carbohydrates from the aposymbiotically cultured Asterochloris sp., the algal symbiont of the lichen Cladina confusa was carried out for the first time. A xylorhamnogalactofuranan was purified and was predominated by (1 → 3)-linked galactofuranosyl units with sidechains in position 6 on approximately 6.4% of the units. The sidechains have galactofuranosyl units 5-O and 6-O-substituted, as well rhamnopyranosyl units 2-O, 3-O and 2,3-di-O-substituted. Xylose was detected only as nonreducing end units, together with galactofuranosyl units. Amylose and a -(1 → 4)-xylan were also present. These polysaccharides have not been found in the symbiotic thallus of C. confusa, which contained only glucans, galactomannoglucan and galactoglucomannan. A potential role of these carbohydrates in lichen recognition proccess is also discussed. © 2007 Elsevier B.V. All rights reserved. Keywords: Photobiont; Lichen; Asterochloris; Cladina confusa; Xylorhamnogalactofuranan; Xylan 1. Introduction Lichen thalli, the symbiotic phenotype of lichen-forming fungi in association with their photobiont, are known to contain considerable amounts of polysaccharides. If these polysaccha- rides are produced by the mycobiont or photobiont alone or by both in symbiosis has been an open question along many years. The preliminary investigation of Takahashi et al. [1] showed that aqueous extracts obtained from cultivated myco- and photobiont had different monosaccharide composition and physical properties. They found that while the extracts of the mycobiont had a similar composition to that of the parent intact lichen, the photobiont fractions are different from those of the symbiotic thalli and its mycobiont. Detailed structural analysis performed by Cordeiro et al. [2] agreed with Takahashi’s study, and showed that the nigeran, laminaran and the galactomannan, found previously in the symbiotic thalli of Ramalina peruviana [3] were also produced by the aposymbiotically cultured fungal partner. ∗ Corresponding author. Tel.: +55 41 33611655; fax: +55 41 32662042. E-mail address: iacomini@ufpr.br (M. Iacomini). Despite many genera of algae have been recorded from lichens, the carbohydrates produced by these photobiont cells have still been scarcely studied, probably due, in most cases, to the need of culturing as a prerequisite. Recently, extracts of the algal partner Trebouxia sp. of the lichen Ramalina gracilis provided a fungus-type -galacto- furanan, which contained a (1 → 5)-linked -galactofuranosyl backbone, substituted in a small proportion at O-6 by -Galf units. The storage polysaccharide amylose was also found [4]. In the present study we determine the fine chemical structure of polysaccharides produced by the aposymbiotically grown tre- bouxioid photobiont (Asterochloris sp.) of Cladina confusa, as well compare them with those produced by the symbiotic thallus in order to amplify the knowledge on carbohydrate production in lichen symbiosis. 2. Material and methods 2.1. Photobiont isolation and culture conditions Thalli of C. confusa were obtained from lichens growing on sandy soil, sea level, Ilha do Mel (25 ◦ 32 ′ 05 ′′ S/48 ◦ 20 ′ 30 ′′ W), Pontal do Paran´ a, PR, Brazil, during August/2001 and were 0141-8130/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ijbiomac.2007.02.006