# Potential of Halophytes-Associated Microbes for the Phytoremediation of Metal-Polluted Saline Soils
## 3 Selection of Microbes for the Phytoremediation of Metal Contaminated Saline Soils
### Metal Tolerance and Metal Inactivation Capacities
#### 3.2.2 Production of Exopolysaccharideacharides  
In the study of [PERSON] et al. previously mentioned [92], _Kocuria flava_ and _Bacillus vietnamensis_ strains were also able to adsorb As at their surface and accumulate this element intracellularly (2 mM As) under hypersaline conditions (from 0.5 to 2 M NaCl). The two strains were able to improve plant growth while reducing As accumulation in plants. For the authors, this could be due to their capacities of producing exopolysaccharides (EPSs). These molecules play an important role in the resistance of bacteria to stresses such as extreme pH, temperature, high salinity, and high metal contents [43]. EPSs surround cells by forming a capsule or a viscous gangue in solution and can protect bacteria by neutralizing toxic Na\({}^{+}\) and metallic cations thanks to their negatively charged residues [132, 133]. In the work by [PERSON] et al. [90], the production of EPS by a halophilic strain of _Halobacillus_ isolated from Lake Qarum in Egypt was measured in the presence of 0 to 5 mM Cu, Zn, Cd, Pb, and Ni. Bacterial growth and EPS concentrations decreased with increasing metal concentrations, suggesting that the production of EPS could be related to the survival of the bacteria. The structure and biochemical properties of EPS and their contribution to the stabilization of metals have been studied and reviewed [7, 44, 57, 90, 115, 128, 134, 135]. As it can reduce metal bioavailability and toxicity, the production of EPS is often considered to be a PGP effect and is frequently investigated in the development of bioaugmented phytoremediation techniques. These polymers are useful to control metal ions' flow into the roots. Their binding properties can vary along diverse parameters. [PERSON] and [PERSON] [128] showed that the binding capacity for Pb and Cu of the EPSs produced by a _Marinobacter_ strain was impacted by pH and salinity and differed between the two metal species. Metals and salt stress can stimulate their production. For instance, _Halomonas_ bacteria isolated from the rhizosphere of _Avicennia marina_ (a mangrove species) have been used to inoculate rice seedlings and showed PGP effects under salt and arsenic stress. Bacteria produced a greater amount of EPS with increasing salt or As concentrations [136]. Owing to their good metal binding properties, these biopolymers can be used in diverse forms to remediate metal contaminated soils and waters (application of activated sludge containing pure or mixed bacterial culture(s), application of dead biomass EPS, application of EPS immobilized in alginate or agar beads, or, more scarcely, application of chemically modified and enhanced EPS). The effectiveness of such treatments has been reviewed [133]. EPS are often found in bacterial biofilms as it influences the architecture and provides a stability of the biofilm [132]. Biofilm contains diverse molecules that bind metals, and this binding ability is another commonly investigated feature for the selection of metal-chelating compounds producing bacteria [45, 46, 92, 125, 137]. [PERSON] et al. [46] tested different bacteria from the rhizosphere of _Spartina maritina_ living in the metal-contaminated Odiel estuary. In the presence of As, Cu, Zn, and Pb, the Gram-negative strains of _Pantoea agglomerants_ produced significantly higher amounts of biofilm than the Gram-positive _Bacillus argabhattai_.