# Bioremediation Methods for the Recovery of Lead-Contaminated Soils: A Review
## 5 Bioaugmentation-Assisted Phytoremediation  
Phytoremediation processes can be assisted by fungi and bacteria, so improving the extractive performance of plants and mitigating the main drawback of this remediation strategy, namely, the long application times required to obtain satisfactory results [45; 46; 47]. In particular, phytoextraction can be strengthened through the use of microorganisms capable of increasing plant biomass or favoring the metals uptake thanks to the production of enzymes, organic acids, biosurfactants, or siderophores [83]. [PERSON] et al. [84] combined the phytoextraction of cadmium and lead by _Zea mays_ species with the addition of some bacteria capable of producing siderophores, namely _Pseudomonas aeruginosa, Pseudomonas fluorescens_, and _Ralstonia metallidurans_. The bacteria were inoculated using different approaches, such as free cells or immobilization in Ca-alginate beads to ensure good survival of microorganisms by reducing the processes of grazing, desiccation, and competition with indigenous bacteria. Furthermore, skim milk was added to enhance the concentration of bacteria in the soil. Lead concentration in maize shoots increased by a factor of 3.4 in the case of free cells and of 3.8 for immobilized cells of _P. aeruginosa_ added with skim milk, and a rise of a factor of 3.2 was observed in the case of immobilized cells of _R. metallidurans_ supplied with skim milk. The bioaugmentation with free cells of _P. fluorescens_ supplied with skim milk increased the lead concentration in roots, but if we consider the other bacteria at work and inoculation conditions, the bioaugmentation caused a reduction in the amount of Pb in roots. In general, the inoculation of bacteria induced a decrease in the total uptake of Pb by maize, but an increase in TF from the roots to the aerial parts. In addition, [PERSON] et al. [84] determined the mobility of lead in the soil by analyzing the first two fractions of the Tessier protocol, and they evidenced an increase in metal mobility caused by the presence of bacteria. This behavior was probably connected to its removal from the interception zone of plant roots and at the same time to an increased translocation of metal from the roots. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Study** & **Species** & **Mechanism** \\ \hline \multirow{6}{*}{B bioremediation by fungi} & [PERSON] et al. [69] & _P. jacunicus_ & Precipitation of lead as \\  & & _M. anisopliae_ & chloropyyromorphite \\ \cline{2-4}  & & _A. niger_ & \\  & & _P. chrysogenum_ & \\  & & _T. viride_ & phosphate and biosorption \\ \cline{2-4}  & & _A. niger_ & \\  & & _P. bliae_ & Chelation with LMWOAs \\  & & _P._ sp & \\ \cline{2-4}  & & _A. niger_ & Biosorption \\ \cline{2-4}  & & & Chelation with active \\  & & & functional groups \\  & & & Binding with humic \\  & & & substances, \\  & & & pH increase, and solubility \\  & & & reduction \\ \hline \multirow{3}{*}{Bioremediation by bacteria} & [PERSON] et al. [77] & _R. sharerides_ & Immobilization as inert forms \\  & [PERSON] et al. [78] & _L. alexarboxylata_ & Binding with EPS \\ \cline{1-1}  & [PERSON] et al. [79] & _[PERSON]. [PERSON]_ & Chelation by calcite \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary table of studies on the bioremediation of lead via fungi and bacteria. [PERSON] et al. [85] verified the effect of the bioaugmentation of the indigenous fungi _Trichoderma asperellum_ in a soil rich in lead and Na+ and Ca2+ ions (high salinity) on the phytoremediation by the _Suada salsa_ plant cultivated in flowerpots. The results showed that the chosen plant was able to grow in the contaminated soil and that the bioaugmentation caused an increase in the growth rate and decreased oxidative stress of the plant. Despite this, the BF and TF values below 1 have shown that _S. salsa_ is not particularly efficient in the accumulation of lead and in the translocation of lead from the roots to the aerial parts.