title: Rhizosphere bacteria of Costularia spp. from ultramafic soils in New Caledonia: diversity, tolerance to extreme edaphic conditions, and role in plant growth and mineral nutrition.
abstract: Rhizosphere bacteria were isolated from Costularia spp., pioneer sedges from ultramafic soils in New Caledonia, which is a hotspot of biodiversity in the South Pacific. Genus identification, ability to tolerate edaphic constraints, and plant-growth-promoting (PGP) properties were analysed. We found that 10(5) colony-forming units per gram of root were dominated by Proteobacteria (69%) and comprised 21 genera, including Burkholderia (28%), Curtobacterium (15%), Bradyrhizobium (9%), Sphingomonas (8%), Rhizobium (7%), and Bacillus (5%). High proportions of bacteria tolerated many elements of the extreme edaphic conditions: 82% tolerated 100 μmol·L(-1) chromium, 70% 1 mmol·L(-1) nickel, 63% 10 mmol·L(-1) manganese, 24% 1 mmol·L(-1) cobalt, and 42% an unbalanced calcium/magnesium ratio (1/16). These strains also exhibited multiple PGP properties, including the ability to produce ammonia (65%), indole-3-acetic acid (60%), siderophores (52%), and 1-aminocyclopropane-1-carboxylate (ACC) deaminase (39%); as well as the capacity to solubilize phosphates (19%). The best-performing strains were inoculated with Sorghum sp. grown on ultramafic substrate. Three strains significantly enhanced the shoot biomass by up to 33%. The most successful strains influenced plant nutrition through the mobilization of metals in roots and a reduction of metal transfer to shoots. These results suggest a key role of these bacteria in plant growth, nutrition, and adaptation to the ultramafic constraints.
authors.affiliation: Institut de recherche pour le développement (IRD), Laboratoire des symbioses tropicales et Méditerranéennes (LSTM UR040), B.P. A5, 98848 Nouméa, Nouvelle-Calédonie.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Gonin
authors.forename: Simon
authors.initials: S
authors.lastname: Gensous
authors.forename: Alexandre
authors.initials: A
authors.lastname: Lagrange
authors.forename: Marc
authors.initials: M
authors.lastname: Ducousso
authors.forename: Hamid
authors.initials: H
authors.lastname: Amir
authors.forename: Philippe
authors.initials: P
authors.lastname: Jourand
mesh_terms: D001419:Bacteria / Q000235:genetics / Q000254:growth & development* / Q000302:isolation & purification / Q000378:metabolism; D001483:Base Sequence; D044822:Biodiversity; D018533:Biomass; D019755:Carbon-Carbon Lyases / Q000378:metabolism; D029785:Cyperaceae / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology*; D007210:Indoleacetic Acids / Q000378:metabolism; D019216:Metals, Heavy / Q000378:metabolism*; D008903:Minerals / Q000378:metabolism*; D008969:Molecular Sequence Data; D009510:New Caledonia; D009586:Nitrogen Fixation; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D010944:Plants / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000737:chemistry; D012231:Rhizobium / Q000378:metabolism; D058441:Rhizosphere; D017262:Siderophores / Q000378:metabolism; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000378:metabolism
chemical_list: D007210:Indoleacetic Acids; D019216:Metals, Heavy; D008903:Minerals; D000644:Quaternary Ammonium Compounds; D012336:RNA, Ribosomal, 16S; D017262:Siderophores; D012989:Soil Pollutants; C030737:indoleacetic acid; C033634:1-aminocyclopropane-1-carboxylate deaminase; D019755:Carbon-Carbon Lyases