Rhizosphere response to nickel in a facultative hyperaccumulator

Area of Science:

• Environmental Microbiology
• Biotechnology
• Plant Science

Background:

• The facultative nickel-hyperaccumulator Alyssoides utriculata harbors a unique rhizosphere microbiota.
• Understanding this microbiota is crucial for developing strategies for nickel (Ni) phytoextraction.
• Serpentine and non-serpentine soils exhibit distinct elemental compositions affecting plant-microbe interactions.

Purpose of the Study:

• To characterize the culturable bacterial and fungal microbiota associated with Alyssoides utriculata.
• To isolate and identify microbial strains with potential applications in nickel phytoextraction.
• To assess the nickel tolerance and plant growth-promoting (PGPR) activities of isolated strains.

Main Methods:

• Collection of soil, root, and shoot samples from A. utriculata at serpentine and non-serpentine sites.
• Isolation and genotypic/phenotypic characterization of rhizobacteria and fungi.
• Elemental analysis of soil and plant tissues using Inductively Coupled Plasma Mass Spectrometry (ICP-MS).
• Determination of nickel tolerance and PGPR activities (ACC deaminase, IAA, siderophores, phosphate solubilization).

Main Results:

• Significant differences in Ni, Cobalt (Co), and Calcium (Ca) concentrations were observed between serpentine and non-serpentine sites.
• Rhizosphere soils showed higher bacterial and fungal abundance compared to bare soils, dominated by genera like Arthrobacter, Bacillus, Streptomyces, Penicillium, and Mucor.
• Specific strains, including Pseudomonas, Streptomyces, Trichoderma harzianum group, and Penicillium ochrochloron, exhibited high nickel tolerance (up to 15-20 mM).
• Eight serpentine bacterial isolates from five genera demonstrated PGPR activities, with Pantoea, Pseudomonas, and Streptomyces showing notable potential.

Conclusions:

• The study successfully characterized the culturable microbiota of A. utriculata, identifying key genera.
• Several bacterial and fungal strains possess high nickel tolerance and plant growth-promoting capabilities.
• These identified microorganisms are promising candidates for bioaugmentation strategies in nickel phytoextraction.