AUTHOR=Supel Paulina , Śliwa-Cebula Marta , Miszalski Zbigniew , Kaszycki Paweł 

TITLE=Cadmium-Tolerant Rhizospheric Bacteria of the C3/CAM Intermediate Semi-Halophytic Common Ice Plant (Mesembryanthemum crystallinum L.) Grown in Contaminated Soils

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.820097

DOI=10.3389/fpls.2022.820097

ISSN=1664-462X

ABSTRACT=<p>The common ice plant, <italic>Mesembryanthemum crystallinum</italic> L., has recently been found as a good candidate for phytoremediation of heavy-metal polluted soils. This semi-halophyte is a C<sub>3</sub>/CAM (Crassulacean acid metabolism) intermediate plant capable of tolerating extreme levels of cadmium in the soil. The aim of the work was to obtain and characterize novel, Cd-tolerant microbial strains that populate the root zone of <italic>M. crystallinum</italic> performing different types of photosynthetic metabolism and growing in Cd-contaminated substrates. The plants exhibiting either C<sub>3</sub> or CAM photosynthesis were treated for 8 days with different CdCl<sub>2</sub> doses to obtain final Cd concentrations ranging from 0.82 to 818 mg⋅kg<sup>–1</sup> of soil d.w. The CAM phase was induced by highly saline conditions. After treatment, eighteen bacterial and three yeast strains were isolated from the rhizosphere and, after preliminary Cd-resistance <italic>in vitro</italic> test, five bacterial strains were selected and identified with a molecular proteomics technique. Two strains of the species <italic>Providencia rettgeri</italic> (W6 and W7) were obtained from the C<sub>3</sub> phase and three (one <italic>Paenibacillus glucanolyticus</italic> S7 and two <italic>Rhodococcus erythropolis</italic> strains: S4 and S10) from the CAM performing plants. The isolates were further tested for Cd-resistance (treatment with either 1 mM or 10 mM CdCl<sub>2</sub>) and salinity tolerance (0.5 M NaCl) in model liquid cultures (incubation for 14 days). <italic>Providencia rettgeri</italic> W7 culture remained fully viable at 1 mM Cd, whereas <italic>Rh. erythropolis</italic> S4 and S10 together with <italic>P. glucanolyticus</italic> S7 were found to be resistant to 10 mM Cd in the presence of 0.5 M NaCl. It is suggested that the high tolerance of the common ice plant toward cadmium may result from the synergic action of the plant together with the Cd/salt-resistant strains occurring within rhizospheral microbiota. Moreover, the isolated bacteria appear as promising robust microorganisms for biotechnological applications in bio- and phytoremediation projects.</p>