Mycoremediation of citrus wastewater by white-rot fungi immobilized in Luffa cylindrica

BENITEZ, SILVANA FLORENCIA; SAGUCHI, EVELYN YURIKO; ACOSTA, GABRIELA ALEJANDRA; ZAPATA, PEDRO DARIO; SADAÑOSKI, MARCEL ALEJANDRA; LEVIN, LAURA NOEMÍ; FONSECA, MARIA ISABEL

Los Cocos

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Sociedad Argentina de Microbiología General (SAMIGE)

Citrus-processing industries produce large volumes of wastewater (WW) characterized by a high content of organic matter, presence of pesticides, and terpenes. Although several strategies were developed for their treatment, white-rot fungi (WRF) have emerged as a promising alternative owing to their high tolerance and ability to degrade xenobiotics. WW can inhibit fungal growth due to the presence of toxic compounds and/or bacterial proliferation, therefore fungal immobilization on low-cost lignocellulosic materials is proposed as an effective approach to increase their stability. The aim of this work was to evaluate two WRF immobilized on lignocellulosic material for the mycoremediation of real citrus WW. The strains Phlebia brevispora BAFC 633 and Pleurotus pulmonarius LBM 105 were immobilized on Luffa cylindrica. Citrus WW and L. cylindrica were kindly provided by Cooperativa Citrícola Agroindustrial de Misiones Ltda. (Leandro N. Alem, Misiones) and Espudela (Jardín América, Misiones), respectively. The L. cylindrica was washed with tap water, rinsed with distilled water, oven-dried at 40 ± 2 °C, and cut into 1 cm3 pieces. All the experiments were carried out in triplicate in 250 mL Erlenmeyer flasks containing 1 g of L. cylindrica. Initial moisture was adjusted to 75 % w/w with Czapek medium (sucrose 30 g/L; K2HPO4 1 g/L; KCl 0.5 g/L; MgSO4 7H2O 0.5 g/L; NaNO3 20 g/L). Autoclave-sterilized flasks were inoculated with three agar plugs (~7 mm ⌀) of each strain and were incubated for different time periods (0, 3, 6, 9, and 12 days) at 28 ± 1 °C under static conditions. After incubation, 50 mL of filtered citrus WW was added to the cultures, and flasks were incubated for 10 extra days (treatment), destructive samples were taken every 48 h. The control consisted in WW without immobilized fungi. Supernatants were obtained by centrifugation at 4600 xg for 10 min. Chemical oxygen demand (COD) and toxicity were determined following standard protocols (open reflux method and Lactuca sativa seed germination/root elongation test, respectively). COD variation was estimated as:% COD=((A-B))/A*100 where A and B are COD before and after treatment respectively. A significant COD reduction was observed for both strains. P. brevispora BAFC 633 reached 83.01 ± 1.81 COD reduction after 10 days of treatment without prior incubation. For P. pulmonarius LBM 105 a 92.82 ± 5.18 % COD reduction was determined after 10 days of treatment without prior incubation, and 94.26 ± 5.18 % with 9 days of incubation. However, toxicity test showed that the treatment with P. pulmonarius LBM 105 without prior incubation was the most efficient for toxicity reduction. Treatments with P. brevispora BAFC 633 were not able to reduce toxicity probably due to the persistence and/or production of toxic metabolites. Therefore, these results show that the treatment with P. pulmonarius LBM 105 immobilized in L. cylindrica is a promising alternative strategy for the mycoremediation of real citrus WW.Keywords: Bioremediation-Pleurotus pulmonarius-Phlebia brevispora-COD-Ecotoxicity