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.

Responses of the Endophytic Bacterial Communities of Juncus acutus to Pollution With Metals, Emerging Organic Pollutants and to Bioaugmentation With Indigenous Strains

“…Bioaugmentation with indigenous endophytic bacteria influenced positively metal concentration in plant tissues at both levels of mixed pollution; they significantly enhanced Zn concentrations inside the plant while they also increased Ni concentrations to a lesser extent ( Supplementary Figures S2 – S4 ). Earlier, it was also shown that bioaugmentation with endophytic bacteria stimulates the host to uptake metals ( Ma et al, 2015 , 2016b ; Visioli et al, 2015 ) while at the same time no effect of metal accumulation was demonstrated by other studies ( Mesa et al, 2015 ). Metal tolerant bacteria expressing plant growth properties (ACC deaminase, siderophores, IAA) were inoculated to J. acutus as they may enhance its ability to accumulate Zn and Ni in the internal tissues by reducing the stress caused by metal toxicity.…”

Endophytic Cultivable Bacteria of the Metal Bioaccumulator Spartina maritima Improve Plant Growth but Not Metal Uptake in Polluted Marshes Soils

“…Hence, attention has focused in the last years on the role of endophytic bacteria in phytoremediation of contaminated soils (reviewed by Newman and Reynolds, 2005 ; Doty, 2008 ) and their use has been reported by several authors (reviewed in Rajkumar et al, 2009 ). The interactions between endophytes and hyperaccumulator plants have attracted the attention of several researchers, allowing the study of bacterial communities living on a naturally contaminated environment and their possible biotechnological applications for bioremediation (reviewed in Lodewyckx et al, 2002 ; Sessitsch et al, 2013 ; Visioli et al, 2014 , 2015 ; Ma et al, 2015 ).…”

Exploitation of Endophytic Bacteria to Enhance the Phytoremediation Potential of the Wetland Helophyte Juncus acutus

“…Adding nickel resistant root endophytic inoculants negatively influenced the root biomass and nickel accumulation in the Ni-hyperaccumulator Noccaea caerulescens ; however, co-inoculation of specific strains had positive effects on plant biomass and Ni translocation to internal tissues ( Visioli et al, 2015 ). Similarly, the dry weight of J. acutus inoculated with the consortium was not significantly different from that of the unexposed plants ( Figure 6A ).…”

“…Endophytes are known to possess PGP traits and degradation genes that assist their host plant to cope with various environmental stresses. Once they are inside, they can contribute in planta to the detoxification of organic contaminants by degrading them and/or enhance the metal translocation providing a potential toward sustainable treatment of mixed contaminations ( Babu et al, 2013 ; Ho et al, 2013 ; Visioli et al, 2015 ). There exist a limited number of studies that highlight the use of endophytic bacteria in terms of enhancing the performance of wetlands treating sewage effluent ( Ijaz et al, 2015 ) or textile effluent ( Shehzadi et al, 2014 ).…”