QUANTIFICATION OF GLOMALIN FRACTIONS IN THE RHIZOSPHERE OF A METALLOPHYTIC PLANT AT LEAD-CONTAMINATED SITES

CÁCERES-MAGO K, SALAZAR MJ, BECERRA AG

Los Cocos

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Sociedad Argentina de Microbiología General SAMIGE

Bower is a town located south of Córdoba city (Argentina), where an acid battery recycling plant dedicated to the recovery of lead (Pb) operated between 1984 and 2005. The lack of emission control and inadequate waste disposal caused a severe accumulation of Pb over an extensive zone, leading to numerous cases of poisoning. Given that this situation remains a potential toxicological risk, it is necessary to apply recovery measures such as phytoremediation, considering tolerant plants and microorganisms that could represent a key tool in the restoration of ecosystems affected by these contaminants. The introduced plant Sorghum halepense is a metalophytic species that grows in this area, and arbuscular mycorrhizal fungi (AMF) are able to alleviate the toxicity of metals in the plant through various mechanisms, such as the production of glomalin that binds to some heavy metals sequestering them in the soil. Therefore, the aim of this study was to evaluate the content of easily extractable glomalin (EEG) and total glomalin (TG) in Pb-contaminated soils in Bower. Rhizospheric soil samples of S. halepense were taken from six sites in the vicinity of the factory that differed in Pb content (μg g-1): Pb0 (14 ± 1), Pb1 (89 ± 6); Pb2 (365 ± 23); Pb3 (544 ± 33); Pb4 (965 ± 56); Pb5 (2938 ± 150); and Pb6 (16,186 ± 686). The uncontaminated site Pb0 was located 2.7 km from the factory area. EEG and TG were extracted using citric acid buffer and autoclaving, and quantified by Bradford protein assay. At all evaluated sites, glomalin was found indicating that there is AMF activity in Pb-contaminated soils, but no increasing or decreasing trend associated with increased Pb content was observed. Pb1 and Pb5 had the highest EEG values, while Pb1, Pb3 and Pb5 had the highest TG content. Interestingly, the sites with the highest TG coincided with the highest values of other soil variables such as organic matter (SOM), carbon (C) and total nitrogen (TN), suggesting that glomalin could contribute to C and N pools, represent a source of SOM, and favor its retention through the stability of soil aggregates. The increased TG in Pb3 could be related to a higher hyphal density and to the spore number (the second highest of the gradient) reported at this site, since glomalin is a wall component of these AMF structures. Furthermore, changes in AMF communities were previously reported as a consequence of Pb contamination in the study sites, which could also imply changes in glomalin production rates and explain the variations observed here. This preliminary study shows that the presence of glomalin could contribute to one of the mechanisms of phytoremediation of Pb-contaminated soils, strategically using the combination of plants growing on the site with native AMF that show tolerance to Pb soil contamination.