title: The interaction of boron with glycolipids is required to increase tolerance to stresses in Anabaena PCC 7120.
abstract: Boron (B) is an essential nutrient for heterocystous cyanobacteria growing under diazotrophic conditions. Under B-deficient conditions, the heterocyst envelope is highly disorganized, and the glycolipid layer is predominantly lost. Therefore, we examined whether B is implicated in the regulation of synthesis or processing and/or stability of glycolipids in Anabaena PCC 7120. RT-PCR analysis indicated that the expression of hglE was not significantly changed under B deficiency, suggesting that the synthesis of glycolipids during heterocyst formation was not compromised. In contrast, the overexpression of devB and hepA, encoding a glycolipid and a carbohydrate transporter, respectively, results in the instability of the envelope under B-deficient conditions. The capacity of borate to bind and stabilize molecules is considered the basis of any B biological function. Using a borate-binding-specific resin and thin layer chromatography, we detected the glycolipids that interact with B. Several heterocyst-specific glycolipids were detected as putative B ligands, suggesting a role for B in stabilizing the heterocyst envelope. Moreover, the glycolipids of Anabaena growing in non-diazotrophic conditions were also detected as putative B ligands. Although B is not essential for Anabaena under non-N2-fixing conditions, the presence of this micronutrient increased the tolerance of Anabaena to detergent treatment, salinity and hyperosmotic conditions. Taken together, the results of the present experiment suggest a beneficial role for B in environmental adaptation. Furthermore, we discuss the nutrient requirement for living organisms growing in nature and not under laboratory conditions.
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Univesidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: Isidro
authors.initials: I
authors.lastname: Abreu
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Univesidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Orús
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Univesidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain. Electronic address: luis.bolarios@uam.es.
authors.forename: Luis
authors.initials: L
authors.lastname: Bolaños
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Univesidad Autónoma de Madrid, Darwin 2, 28049 Madrid, Spain.
authors.forename: Ildefonso
authors.initials: I
authors.lastname: Bonilla
mesh_terms: D000222:Adaptation, Physiological; D017033:Anabaena / Q000737:chemistry / Q000502:physiology*; D001895:Boron / Q000737:chemistry*; D002462:Cell Membrane / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006017:Glycolipids / Q000737:chemistry*; D013312:Stress, Physiological
chemical_list: D006017:Glycolipids; D001895:Boron
keywords: Boron-ligands; Cell membrane stability; Detergent resistance; Environmental adaptation; Heterocyst envelope architecture; Hyperosmotic stress tolerance; Salt-stress tolerance