Potential of glomalin-related soil protein on metal sequestration in lead-contaminated sites

CÁCERES-MAGO K., SALAZAR M.J., BECERRA A.G

Congreso; XIX CONGRESO DE LA SOCIEDAD ARGENTINA DE MICROBIOLOGÍA GENERAL; 2024

Heavy metals (HM) accumulation in the soil represents a risk to the environment,food safety, and human health due to their toxic nature and potential to mobilizebetween environmental compartments. The remediation of contaminated sites iscomplex, leading to the proposal of phytoremediation as a key tool for restoringaffected areas. Therefore, this study aimed to evaluate the amount of glomalinrelatedsoil protein (GRSP), produced by arbuscular mycorrhizal fungi (AMF),and its contribution to Pb sequestration. Twenty soil samples were randomlycollected from the vicinity of an abandoned acid battery recycling plant,specifically from the rhizosphere of the predominant plant species (Sorghumhalepense, Bidens pilosa, and Tagetes minuta) growing in Pb-contaminatedsoils, and three soil samples were taken from a nearby uncontaminated site. ThePb concentration in soils was determined in dried soil samples using an X-rayFluorescence Analyzer. GRSP was extracted using citrate buffer and autoclavingand quantified by the Bradford protein assay. To determine the Pb content in theGRSP extracts by flame atomic absorption spectrometry (AAS), the followingsteps were performed: protein precipitation at pH 2.5 with HCl, resuspension,dialysis against water, lyophilization, and digestion in HNO3. The Pbconcentration in GRSP was determined in mg g-1, and the percentage of Pbretention in GRSP, defined as the proportion of the total Pb in the soil that isbound to glomalin, was calculated. The Pb concentration in soil from thecontaminated sites showed significant variation, with values ranging from 149.28to 77,588.77 ?g g?¹, forming a concentration gradient. The values found in theuncontaminated sites ranged from 19.95 to 27.87 ?g g?¹. GRSP was found at allevaluated sites (between 1.25 and 3.89 mg g-1), but no increasing or decreasingtrend was observed associated with soil Pb content with a weak negativecorrelation (r = -0.24). The amount of Pb bound to GRSP (ranging from 2.03 to548.54 mg g?¹) tended to increase with the rise in soil Pb concentration, showinga strong positive correlation between these variables (r = 0.84). This representeda Pb retention percentage in GRSP of up to 23.3 %, which decreased to 1.04 %as the total soil Pb increased, showing a moderate negative correlation (r = -0.56). This study considered very high levels of Pb in the soil, which had notpreviously been evaluated in this context. As a result, the contribution of GRSPto element stabilization may be reduced in percentage terms at highlycontaminated sites. However, similar amounts of GRSP bound 77 times more Pbat the most contaminated site compared to the least contaminated site.Therefore, for AMF-assisted phytoremediation, it would be essential to develop strategies that lead to an increase in soil glomalin levels to mitigate the adverseeffects of soils highly contaminated with heavy metals.