## 3 Lactic Acid Bacteria (LAB): An Emerging Group of PGPR
### Biofertilization and Bioremediation Effects of LAB  
The ability of LAB to synthesize metabolites, including organic acids, phenolic acids and their flavonoid derivatives, phytohormones, and antimicrobial substrates, has already been reported [19; 105; 106; 107]. LAB have been reported to have a high capacity to solubilize insoluble forms of phosphate [19; 108; 109] and potassium [18], to biologically fix nitrogen [110], and to produce iron-chelating compounds [111] and siderophores [112]. They are also involved in soil biochemical cycles through regulating soil organic matter content and detoxifying hazardous chemicals [111]. Heavy metal biosorption mechanisms of LAB have been previously reported, involving bacterial surface-associated functional groups, including carboxyl, hydroxyl, and phosphate [111; 113]. Previous studies on food technology outlined the critical role of LAB in breaking down organic macromolecules and indigestible polysaccharides and converting disfavored flavor compounds [114]. In addition, it has already been suggested that shifts in the microbiome in response to environmental changes may imply the plasticity of the available microbial genetic pool in aiding plant adaptation to environmental stress [115; 116]. Accordingly, the finding of a rich diversity of LAB in the rhizosphere of plants grown in deserts [93; 97] can confirm the role of LAB in improving the tolerance of associated plants. It can also be assumed that LAB conferring a specific stress tolerance can be derived from holobionts thriving under similar stress conditions. Improved tolerance of LAB-treated plants to abiotic stresses has been correlated with changes in plant metabolic responses related to proline content, phenolic acids, and antioxidant enzymes [97; 117]. Such reported findings can support the assumption that LAB are effective as biofertilizers by increasing nutrient bioavailability and as biostimulants to stimulate plant growth or seed germination by alleviating diverse environmental stresses [97; 118; 119]. The beneficial outcomes of the application of LAB treatment in several plant species have been summarized in Table 2. A scheme of the biofertilization, bioprotection, and biodegradation potential of LAB is shown in Figure 2.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**LAB Species** & \begin{tabular}{c} **Experimental** \\ **Condition** \\ \end{tabular}  & \multicolumn{2}{c}{**Summary of Results**} & **Reference** \\ \hline \multirow{8}{*}{Pot} & \multicolumn{3}{c}{Commercial inoculants of \(L\). _plantarum_ reduced eight} \\  & & potato pathogen infestations, including _Pectobacterium_ & \multirow{2}{*}{[PERSON] et al. [120]} \\  & & _carrotovorum_, _Streptomyces scabici_, _Alternaria solani_, _A. tenuissima_, _A. alternata_, _Phoma exigua_, & [120] \\  & & _Rhizoctonia solani_, and _Colletotrichum cccc_. & \\  & & Improving cucumber plant growth indirectly through organic acid (succiciic and lactic acid) production and & \\  & & increasing the bioavailability of mineral nutrients in the soil in comparison with the commercial inoculants of & [PERSON] et al. [121] \\  & & _L. plantarum_. & \\ \hline \multirow{8}{*}{_Lactiplantibacillus plantarum_} & \multicolumn{3}{c}{Reducing the Fusarium head blight index in wheat plants via the synthesis of organic acids and plantaricin in response to \(L\). _plantarum_ SLG17 application. & [PERSON] et al. [122] \\  & & Increasing the percentage of germination rate and & \\  & & improving the length of shoot and roots of tomato in & [PERSON] et al. [123] \\  & & response to inoculation with \(L\). _plantarum_ ONU12. & \\  & & \(L\). _plantarum_ JCM1149 showed antibacterial activity and & \\  & & suppressed soft rot caused by _Pectobacterium catovorum_ & \\  & & subsp. carorotovorum in cabbage, onion, potato, tomato, & [PERSON] et al. [124] \\  & & and radish. & \\ \hline \multirow{8}{*}{In vitro} & \multicolumn{3}{c}{The \(L\). _plantarum_ MF042018 strain’s ability as a reassuring biosorbent for removing heavy metals from industrial wastewater is approved.}