title: Differences in the cell walls and extracellular polymers of the two Trebouxia microalgae coexisting in the lichen Ramalina farinacea are consistent with their distinct capacity to immobilize extracellular Pb.
abstract: Trebouxia TR1 and T. TR9 are the two microalgae that coexist within Ramalina farinacea thalli. In the presence of Pb, TR9 formed extracellular aggregates, while TR1 showed a lower wall lead retention capability. Herein, we studied the cell walls and extracellular polymers (EPS) of TR1 and TR9, and their possible implication in the different Pb retention capacity of these microalgae. The proportion of cell walls on the overall cell biomass was 2.6 times higher in TR9 than in TR1. Glycosyl linkage analysis indicated the presence of hot-water soluble β-galactofuranan(s) in both cell walls, distinct from that previously described in Asterochloris, with increased rhamnose content in TR9 and a higher substitution by side chains in TR1. In the EPS of both microalgae, monosaccharide composition resembled their cell walls; however, TR9 produced two times more EPS than TR1. EPS also contained proteins, displaying distinct polypeptide patterns, modulated by Pb in TR9. Uronic acid content in EPS was higher in TR9, and increased in this phycobiont after the addition of Pb. Our findings suggest that the differential extracellular Pb retention capabilities of TR1 and TR9 microalgae can be related to differences in the main features of their cell walls and EPS.
authors.affiliation: Department of Life Sciences, University of Alcalá, 28805 Alcalá de Henares (Madrid), Spain. Electronic address: leonardo.casano@uah.es.
authors.forename: Leonardo M
authors.initials: LM
authors.lastname: Casano
authors.affiliation: Department of Plant Physiology and Biochemistry, Institute of Botany, 04305-012 São Paulo, SP, Brazil.
authors.forename: Marcia R
authors.initials: MR
authors.lastname: Braga
authors.affiliation: Department of Life Sciences, University of Alcalá, 28805 Alcalá de Henares (Madrid), Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Álvarez
authors.affiliation: Department of Life Sciences, University of Alcalá, 28805 Alcalá de Henares (Madrid), Spain.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Del Campo
authors.affiliation: Department of Botany-ICBIBE, University of Valencia, 46100 Burjassot (Valencia), Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Barreno
mesh_terms: D001203:Ascomycota / Q000502:physiology*; D002473:Cell Wall / Q000378:metabolism; D000460:Chlorophyta / Q000502:physiology*; D004785:Environmental Pollutants / Q000378:metabolism*; D007854:Lead / Q000378:metabolism*; D008011:Lichens / Q000502:physiology*; D058086:Microalgae / Q000502:physiology; D011108:Polymers / Q000378:metabolism; D013045:Species Specificity; D013559:Symbiosis
chemical_list: D004785:Environmental Pollutants; D011108:Polymers; D007854:Lead
keywords: Cell wall; Extracellular polymers; Heavy metal; Lichen; Microalgae; Trebouxia