title: Combined endophytic inoculants enhance nickel phytoextraction from serpentine soil in the hyperaccumulator Noccaea caerulescens.
abstract: This study assesses the effects of specific bacterial endophytes on the phytoextraction capacity of the Ni-hyperaccumulator Noccaea caerulescens, spontaneously growing in a serpentine soil environment. Five metal-tolerant endophytes had already been selected for their high Ni tolerance (6 mM) and plant growth promoting ability. Here we demonstrate that individual bacterial inoculation is ineffective in enhancing Ni translocation and growth of N. caerulescens in serpentine soil, except for specific strains Ncr-1 and Ncr-8, belonging to the Arthrobacter and Microbacterium genera, which showed the highest indole acetic acid production and 1-aminocyclopropane-1-carboxylic acid-deaminase activity. Ncr-1 and Ncr-8 co-inoculation was even more efficient in promoting plant growth, soil Ni removal, and translocation of Ni, together with that of Fe, Co, and Cu. Bacteria of both strains densely colonized the root surfaces and intercellular spaces of leaf epidermal tissue. These two bacterial strains also turned out to stimulate root length, shoot biomass, and Ni uptake in Arabidopsis thaliana grown in MS agar medium supplemented with Ni. It is concluded that adaptation of N. caerulescens in highly Ni-contaminated serpentine soil can be enhanced by an integrated community of bacterial endophytes rather than by single strains; of the former, Arthrobacter and Microbacterium may be useful candidates for future phytoremediation trials in multiple metal-contaminated sites, with possible extension to non-hyperaccumulator plants.
authors: Department of Life Sciences, University of Parma Parma, Italy.
authors: Giovanna
authors: G
authors: Visioli
authors: Department of Agronomy, Food, Natural Resources, Animals and the Environment, University of Padova Padova, Italy.
authors: Teofilo
authors: T
authors: Vamerali
authors: Department of Chemistry, University of Parma Parma, Italy.
authors: Monica
authors: M
authors: Mattarozzi
authors: Department of Life Sciences, University of Parma Parma, Italy.
authors: Lucia
authors: L
authors: Dramis
authors: Department of Life Sciences, University of Parma Parma, Italy.
authors: Anna M
authors: AM
authors: Sanangelantoni
keywords: Arabidopsis thaliana; Noccaea caerulescens; nickel; phytoextraction; plant growth-promoting endophytic bacteria (PGPE); serpentine soil; tissue colonization