Rhizobacteria and plant symbiosis in heavy metal uptake and its implications for soil bioremediation

Abstract

Certain species of plants can benefit from synergistic effects with plant growth-promoting rhizobacteria (PGPR) that improve plant growth and metal accumulation, mitigating toxic effects on plants and increasing their tolerance to heavy metals. The application of PGPR as biofertilizers and atmospheric nitrogen fixators contributes considerably to the intensification of the phytoremediation process. In this paper, we have built a system consisting of rhizospheric Azotobacter microbial populations and Lepidium sativum plants, growing in solutions containing heavy metals in various concentrations. We examined the ability of the organisms to grow in symbiosis so as to stimulate the plant growth and enhance its tolerance to Cr(VI) and Cd(II), to ultimately provide a reliable phytoremediation system. The study was developed at the laboratory level and, at this stage, does not assess the inherent interactions under real conditions occurring in contaminated fields with autochthonous microflora and under different pedoclimatic conditions and environmental stresses. Azotobacter sp. bacteria could indeed stimulate the average germination efficiency of Lepidium sativum by almost 7%, average root length by 22%, average stem length by 34% and dry biomass by 53%. The growth of L. sativum has been affected to a greater extent in Cd(II) solutions due its higher toxicity compared to that of Cr(VI). The reduced tolerance index (TI, %) indicated that plant growth in symbiosis with PGPR was however affected by heavy metal toxicity, while the tolerance of the plant to heavy metals was enhanced in the bacteria-plant system. A methodology based on artificial neural networks (ANNs) and differential evolution (DE), specifically a neuro-evolutionary approach, was applied to model germination rates, dry biomass and root/stem length and proving the robustness of the experimental data. The errors associated with all four variables are small and the correlation coefficients higher than 0.98, which indicate that the selected models can efficiently predict the experimental data.

Effect of Enterobacter sp. CS2 and EDTA on the Phytoremediation of Ni-contaminated Soil by Impatiens balsamina

“…Plants subjected to Ni stress showed reduced quantities of carotenoids and chl 'a' and chl 'b' contents. These results indicate that metal toxicity impedes metabolic activities of inoculated and un-inoculated plants, resulting in decreased biomass production in plants under metal stress [27]. The increased metal uptake in contaminated soils reduces plant growth [28].…”

Exploration of NPK Activity Showing Chromium Resistant Bacteria from Sukinda Mining Area

“…(Table 4). Moreover, several studies have reported utilization of chromium resistant and plant growth promoting rhizobacteria (PGPR) for the bioremediation of toxic metals (Samuel et al, 2013;Sobariu et al, 2016;Ndeddy and Babalola, 2016) to reclaim and restore soil properties.…”

“…Such activities of soil microbes are largely affected by pollutants released to the soil, as plant growth is regulated by soil fertility (Hansda et al, 2014). Several studies have reported the utilization of plant growth promoting rhizobacteria (PGPR) for the bioremediation of toxic metals (Samuel et al, 2013;Sobariu et al, 2016;Ndeddy and Babalola, 2016 …”

EVALUATION OF IAA AND PHAs PRODUCTION BY CHROMIUM RESISTANT BACTERIAL ISOLATES

“…strain HU38 were also isolated from rhizospheric soil of P. juliflora (Khan et al, 2015). Thus, utilization of these metal resistant bacteria for bioremediation can overcome toxic effect of Cr(VI) as well as increase plant growth (Hansda et al, 2014;Sobariu et al, Figure 1 (a) IAA (b) production by Cr(VI) resistant bacterial isolates. …”