Screening beneficial rhizobacteria from Spartina maritima for phytoremediation of metal polluted salt marshes: comparison of gram-positive and gram-negative strains

Abstract

The aim of our work was the isolation and characterization of bacteria from the rhizosphere of Spartina maritima in the metal contaminated Odiel estuary (Huelva, SW Spain). From 25 strains, 84 % were identified as gram-positive, particularly Staphylococcus and Bacillus. Gram-negative bacteria were represented by Pantoea and Salmonella. Salt and heavy metal tolerance, metal bioabsorption, plant growth promoting (PGP) properties, and biofilm formation were investigated in the bacterial collection. Despite the higher abundance of gram-positive bacteria, gram-negative isolates displayed higher tolerance toward metal(loid)s (As, Cu, Zn, and Pb) and greater metal biosorption, as deduced from ICP-OES and SEM-EDX analyses. Besides, they exhibited better PGP properties, which were retained in the presence of metals and the ability to form biofilms. Gram-negative strains Pantoea agglomerans RSO6 and RSO7, together with gram-positive Bacillus aryabhattai RSO25, were selected for a bacterial consortium aimed to inoculate S. maritima plants in metal polluted estuaries for phytoremediation purposes.

Effect of Plant Growth-Promoting Rhizobacteria on Salicornia ramosissima Seed Germination under Salinity, CO2 and Temperature Stress

“…Salt tolerance was expressed as the maximum tolerable concentration (MTC) of NaCl, namely the maximum concentration of NaCl not affecting bacterial growth. As for plant growth-promoting (PGP) traits of rhizobacteria, the same methodology as described in detail in [29] was used. Briefly, bacterial growth in NFb (nitrogen free bromothymol blue) medium was used to test nitrogen fixation [32].…”

“…In all cases, plates were incubated during 72 h at 28 • C before analyzing the results. The synthesis of IAA (indole-3-acetic acid) was colorimetrically estimated as explained in [29]. In the same line, capability of biofilm formation was measured by an adhesion capacity assay in wells of 96-wellmicrotitre plates and further absorbance measures (detailed in [29]).…”

“…The synthesis of IAA (indole-3-acetic acid) was colorimetrically estimated as explained in [29]. In the same line, capability of biofilm formation was measured by an adhesion capacity assay in wells of 96-wellmicrotitre plates and further absorbance measures (detailed in [29]). Presence of bacterial ACC (1-Aminocyclopropane-1-Carboxylate) deaminase activity was detected following again a colorimetrically method that quantifies the amount of α-ketobutyric acid generated from the cleavage of ACC [35].…”

“…under salinity stress [20]. However, screening of PGPR in halophytes are scarce to date [21][22][23][24][25][26][27][28][29]. Also, no studies of the effect of PGPR in Salicornia under NaCl, CO 2 and temperature stress have been carried out.…”

A Genetic and Metabolomic Perspective on the Production of Indole-3-Acetic Acid by Pantoea agglomerans and Use of Their Metabolites as Biostimulants in Plant Nurseries

“…Classification of P. agglomerans into the biosecurity group 2 and the fact that sometimes this species causes human infections particularly in immunocompromised people prevent its utilization as bioinoculant in Europe ( Dutkiewicz et al, 2016a ; Büyükcam et al, 2018 ). However, increasing evidence has shown that selected members of the P. agglomerans species can have a great potential as plant growth–promoting bacteria ( Paredes-Páliz et al, 2016a , b , 2017 ) and comprise strains that are agronomically relevant for their growth-promoting or biocontrol traits and have been increasingly regarded as ideal candidates among plant growth–promoting rhizobacteria to be used as a biocontrol agent ( Dutkiewicz et al, 2016b ).…”