# Potential of Halophytes-Associated Microbes for the Phytoremediation of Metal-Polluted Saline Soils
## 5 Complementary Effects of Microbial Associations  
The literature on PGP effects in saline environments revealed a disparity both in terms of in vitro/in vivo studies and between bacteria and fungi (compared to bacteria, fungi has received less attention). [PERSON] et al. [7] perceived a weaker interest in using fungi in bioremediation. According to the authors, the reason is that research on bioremediation \"tends to disregard the ecological demands of fungi and often uses ecologically displaced organisms in competition with bacteria more suited to the polluted environment\". Bacteria are easier to study, and numerous articles mentioned impressive capacities of bacteria to produce large quantities of EPS, to form biofilms, and to produce diverse phytohormones, as well as their capacities for high resistance to multiple stressors. However, fungi can also present many advantages. Fungal morphology is plastic and can adapt under metal stress. For example, they can produce pigments and thicken their cell wall by producing more chitin in response to metal stress [171]. Some AMF showed insensitivity to seasonality when colonizing roots under metal stress [141]. Some fungi, including AMF, can also produce organic acids that solubilize metals [172] and thus facilitate their phytoextraction in contrast with exopolysaccharideadroducing bacteria that rather stabilize metals. However, some bacteria have also been recognized for their metal-modilizing properties [173; 174]. Fungi easily can transport nutrients and contaminants for longer distances than bacteria [7]. Moreover, some bacteria can be inappropriate despite having interesting PGP capacities. For example, [PERSON] and [PERSON] [128] investigated a _Marinobacter_ strain which could produce high amount of EPS. However, the authors showed that these EPS represented a source of nutrients for _Hediste diversicolor_, a benthic polychaete, thus leading to a transfer of metals to higher trophic levels. The synergic effects of the association between some fungi and bacteria sometimes help them to survive in stressful environments, thus preserving their respective positive effects on soil and plants. According to [PERSON] et al. [21], facing constantly changing parameters in mixed polluted soils requires the combination of several methods to ensure an efficient remediation of metals. Saline soils are strongly influenced by winds, waves, tides, and temperature variations due to the opening of these environments and consequently fluctuate a lot in regard to their structural and chemical characteristics along time and space [122]. Their strong heterogeneity can compromise the establishment of microbes that need specific conditions to develop. Moreover, bacteria motility can be limited by soil physical barriers (air-filled pores, dense aggregates, etc.) [7]. The use of fungi can be complementary to bacterial activities, as their highly branched mycelian filaments network can facilitate their spread in soils, as demonstrated by [PERSON] et al. [175]. Reciprocally, [PERSON] et al. [176] emphasized the beneficial effects of Mycorrhiza Helper Bacteria (MHB) on the establishment of ectomycorrhizal symbiosis. In an agricultural soil affected by salt and Cd, a greenhouse experiment was conducted on _Cajanus cajan_ pretreated with a _Sinorhizobium fredii_ strain and the AMF _Glomus mosseae_[177]. The phytotoxicity of Cd was increased, but the fungal symbiont was able to protect the _Sinorhizobium_ nodules exposed to NaCl and Cd stress by mediating interactions between toxic ions and plants and reducing oxidative damages. They suggested an adaptation of the nodules of the _S. fredii_ strain to mycorrhizal, thus enhancing their salt and metal resistance [177]. Microbes can also be complementary between them. For instance, [PERSON] et al. [178] showed an interesting way of designing a cadmium-resistant autochthonous bacterial consortia inoculum by selecting the cultivable fraction of the rhizospheric microbiome of _Juncus maritimus_ and _Phragmites australis_.