# Fungi and Arsenic: Tolerance and Bioaccumulation by Soil Saprotrophic Species
## 4 Discussion
In general, the arsenic content and concentration in fungal biomass increased as arsenic concentrations increased in media (Table 5). Along with As, Sb concentration also increased. It is important to note that Sb showed the same behavior of As because it was present as an impurity (<0.5%) in the sodium arsenite added in the culture media. This behavior is mainly due to the chemical similarities between the two metalloids, both belonging to Group 15 of the periodic table [80], which usually leads them to follow similar accumulation pathways [81]. However, even if Sb was present at a relatively low concentration, it was highly accumulated by all of the tested species, thus revealing the outstanding Sb accumulation ability of these strains, which merits further investigation. Moreover, increasing As concentrations in both culture media did not affect the accumulation in the fungal biomass of trace and ultra-trace elements (Cd, Cu, Cr, Mn, Ni, Pb, and Sn). Results in Supplementary Materials Table S1 confirmed that in both culture media, _C. nanum_ was the species able to accumulate the highest concentrations of As and Sb, while _A. spinosa_ was found to be the strain with the lowest accumulation ability of both elements, which was also observable in the plots obtained by principal component analysis. Bioaccumulation of As was reported in several works in the presence of trivalent or pentavalent arsenic with fungi belonging to different genera (e.g., _Apergillus, Penicillin_, and _Trichoderma_[11; 19; 44; 68; 69; 70]. For instance, after five days of growth with 50 mg/L As(V), As bioaccumulation in _Penicillium janthhellum_ was 87.0 ug/g [70]. The highest As removal in _Apergillus candidus_ were observed after three days of growth in the presence of 25 mg/L or 50 mg/L of trivalent or pentavalent arsenic [44]. Iron-coated fungal biomass of a _Paicolomyces_ sp. successfully removed As(III) from aqueous solution by biosorption [82]. Arsenic can be transported inside fungal cells via specific or non-specific transport processes (e.g., via specific and non-specific phosphate, glycerol, or hexose transporters) and mechanisms involved in As bioaccumulation in fungi can include surface association (e.g., biosorption to cell wall components), vacuolar compartmentalization, chelation, immobilization, and sequestration by metal-binding peptides (e.g., glutathione) [67; 68]. In _Saccharomyces cerevisiae_, the arsenate, taken up by phosphate transporter, is reduced to arsenite inside the fungal cell, conjugated with glutathione, and transported into vacuoles [83]. According to [PERSON] and [PERSON] [84], similar mechanisms were also reported in the arsenate-hypertolerant _Apergillus_ sp. P37. In fungi, As can be methylated, resulting in As volatilization, and As efflux can occur by arsenite extrusion through the arsenite carrier protein in the plasma membrane (e.g., Acr3p channel in _S. cerevisiae_) [2; 19; 67; 68; 69; 67; 69; 83]. These mechanisms can influence arsenic mobilization in the environment. Since the mobilization of As from rocks, minerals, soils, and other substrates by fungi and other organisms can also be caused by the production of siderophores [67], they may represent feasible, environmentally-friendly bioresources for bioremediation application [24; 85]. In this study, the tested species showed the production of siderophores with a high affinity for Fe complexation, while low or no affinity for As (Table 6). In _A. spinosa_ and _C. nanum_, albeit to a very small extent, siderophore activity in chelating As was observed. In contrast, _P. ilacinum_ and _M. marquandii_ showed OD values greater than the reference value. This may be explained by the presence of secondary metabolites in the culture filtrates, interfering with the assay and by a low affinity of siderophores for As. With reference to the secondary metabolites, some pigments in _P. ilacinum_ and _M. marquandii_ have been isolated and characterized [86; 87; 88] and may have influenced the assay.