Rhizobacteria and plant symbiosis in heavy metal uptake and its implications for soil bioremediation.
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.
"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania.
Dana Luminița
DL
Sobariu
"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania.
Daniela Ionela Tudorache
DIT
Fertu
"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania.
Mariana
M
Diaconu
"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania; "Gheorghe Asachi" Technical University of Iasi, Faculty of Hydrotechnical Engineering, Geodesy and Environmental Engineering, Department of Hydrology and Environmental Protection, 65 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania.
Lucian Vasile
LV
Pavel
"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania.
Raluca-Maria
RM
Hlihor
"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Chemical Engineering, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania.
Elena Niculina
EN
Drăgoi
"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Chemical Engineering, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania.
Silvia
S
Curteanu
University of Applied Sciences and Arts Northwestern Switzerland, School of Life Science, Institute for Ecopreneurship, Gruendenstrasse 40, 4132 Muttenz, Switzerland; Sub-Department of Environmental Technology, Wageningen University, 6700 EV Wageningen, The Netherlands.
Markus
M
Lenz
University of Applied Sciences and Arts Northwestern Switzerland, School of Life Science, Institute for Ecopreneurship, Gruendenstrasse 40, 4132 Muttenz, Switzerland.
Philippe François-Xavier
PF
Corvini
"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, 73 Prof. Dr. Docent D. Mangeron Street, 700050 Iasi, Romania; Academy of Romanian Scientists, 54 Splaiul Independentei, RO-050094 Bucharest, Romania. Electronic address: mgav@tuiasi.ro.
Maria
M
Gavrilescu
D001395:Azotobacter / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism*; D001673:Biodegradation, Environmental; D029686:Lepidium / Q000254:growth & development / Q000378:metabolism*; D019216:Metals, Heavy / Q000378:metabolism*; D008962:Models, Theoretical; D016571:Neural Networks, Computer; D058441:Rhizosphere; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000302:isolation & purification; D013559:Symbiosis
D019216:Metals, Heavy; D012987:Soil; D012989:Soil Pollutants
Azotobacter sp.; Cadmium; Chromium; Lepidium sativum; Rhizobacteria; Tolerance