# Potential of Halophytes-Associated Microbes for the Phytoremediation of Metal-Polluted Saline Soils
## 1 Introduction
However, microbes could also accelerate and improve the phytoremediation yield [25; 26]. Many plant-associated microbes are known to increase plant growth and stress resistance. Microbial remediation, the process for removal of environmental contaminants with the use of microorganisms [27; 28], can be combined with phytoremediation. Indeed, microbe-assisted phytoremediation techniques involving bacteria and/or fungi and plants have been proposed as a cost-effective and reliable approach to improve the intrinsic bioaccumulation capacities in plants [7; 29; 30]. Bioleaching, biosorption, bioaccumulation, bioprecipitation, and biotransformation represent the main strategies evolved by microbes in order to cope with contaminants from the soils. Hence, microbes are often prospected as interesting potential candidates in bioremediation [21]. The abilities of haplotypes to cope with high levels of metals have been widely studied [31; 32; 33; 34; 35; 36; 37]. Indeed, by using the search item \"halophyte OR halophytes AND (metal OR metals)\" on Scholar Google ([[http://scholar.google.com](http://scholar.google.com)]([http://scholar.google.com](http://scholar.google.com)), accessed on 12 March 2023), we found 27,400 results. Representing 1-2% of the world's flora [38; 39], this plant group harbors numerous interesting properties for several application fields (including food, pharmacology, and energy) [40], and some species are already recommended for the phytostabilization or phytoextraction of organic and inorganic pollutants. In the 2000s, researchers began to study halophytes-associated microbes for their bioremediation potential, and the number of publications on their use as plant-inoculants only increased in the late 2000s/early 2010s, but studies mainly focused on saline-affected soils rather than metal-contaminated saline soils. However, numerous papers dedicated to the restoration of agricultural soil functions affected by salt show interesting plant-growth-promoting (PGP) properties of halotolerant microbes that could also benefit plants under metal stress [41; 42; 43; 44]. Owing to their halophilic/halotolerant adaptations, these microbes unfold multiple PGP effects and metal-tolerance strategies [45; 46; 47], thus emphasizing their potential in metal-contaminated saline soils' treatments [15; 48; 49; 50; 51]. Nevertheless, microbe-assisted phytoremediation applied to metal-contaminated coastal environments still lack in knowledge to be properly used, despite the warnings about the impacts of the contaminants spread in the oceans. Furthermore, despite a substantial number of experiments conducted for this purpose, no specific review has, to our knowledge, focused on the use of halophyte-associated microbes as inoculants to improve the effectiveness of halophyte phytoremediation of metal contaminated saline soils. Indeed, research on PGP microbes was mainly reviewed in the context of metal contamination in non-saline sites [52; 53; 54; 55; 56; 57; 58]. Some reviews concerned applications to salt-affected sites by using halotolerant bacteria for agriculture [41; 42; 43; 44; 59; 60] but did not develop their potential for the improvement of metal phytoremediation. In this review, we focus on the current research on (i) the potential of halophytes and their associated microbes in the phytoremediation of metals; (ii) the mechanisms employed by these halotolerant microbes to deal with metals and to improve plant growth; (iii) how using a microbial inoculum combining bacteria and fungi can benefit plants and (iv) the in situ applications of microbe-assisted phytoremediation, including their limitations and benefits. As several publications described the PGP effects commonly screened in microbes, the most common ones will be briefly presented here to better contextualize their implication in the optimization of metal-phytoremediation techniques applied to saline environments.