Tolerance and laccase enzyme secretion in citrus industry wastewater of white-rot fungi native of Misiones

ANIBAL SEBASTIÁN CHELALICHE; LAURA NOEMÍ LEVIN; SILVANA FLORENCIA BENITEZ; MARCELA ALEJANDRA SADAÑOSKI; PEDRO DARIO ZAPATA; MARÍA ISABEL FONSECA

Encuentro; LVI SAIB Meeting XV SAMIGE Meeting; 2020

Citrus-processing industries produce large volumes of wastewater (WW) characterized by high content of organic matter, color, presence of pesticides and terpenes. Due to their potential hazardous effect, several treatment systems have been proposed. In this regard, biological treatments are considered a low-cost and eco-friendly alternative. Bioremediation using white-rot fungi (WRF) was proved to be an effective strategy. Their ability to metabolize a variety of pollutants is attributed to the secretion of lignin-modifying enzymes, especially laccases (Lac). In this context, exploring isolates capable of tolerate and potentially bioremediate WW would contribute to the bioremediation and WW management research. The aim of this work was to assess the tolerance and Lac enzyme secretion of Irpex lacteus LBM 037, Phlebia brevispora LBM 036, Pleurotus pulmonarius LBM 105 and Trametes sanguinea LBM 023 in media supplemented with citrus WW. Tolerance in solid media was evaluated in 85 mm ø Petri dishes containing 12 mL of MEA (malt extract 12.7 g/L, agar 20 g/L) supplemented with WW (15, 30, 50 %). One agar plug (5 mm ø) was inoculated; fungal radial growth was measured daily and analyzed using predictive mycology (Sadañoski et al. 2018). Fungal growth τ (time to attain half the plate) was standardized as Δτ = τWWx ? τC, where τWWx were the values from supplemented media (x=concentration) and τC were the values from control without WW. A positive value of Δτ proved fungal growth inhibition. Assays in liquid media were performed in 250 mL Erlenmeyer flasks with 50 mL of ME (malt extract 12.7 g/L) supplemented with WW (15, 30, 50 %). Flasks were inoculated with one agar plug and incubated for 10 d. Biomass production was assessed by mycelium dry weight. Lac activity in supernatants was determined according to Fonseca et al. (2014). All assays were incubated under static conditions at 28 ± 1 °C. T. sanguinea and I. lacteus were able to grow with 15 % of WW. In solid media a positive value of Δτ proved growth inhibition for both fungi (Δτ15=0.9; Δτ15=1.48, respectively). However, in liquid media biomass production was higher in the presence of WW reaching 4.20 ± 0.22 mg/mL for T. sanguinea and 2.73 ± 0.20 for I. lacteus. P. brevispora tolerated up to 50 and 30 % of WW in solid and liquid media respectively. In solid media growth inhibition increased with WW concentration (Δτ15=0.15; Δτ30=0.85; Δτ50=2.15). In liquid media there was a slight inhibition on biomass production but with no significant difference among concentrations. As for Lac activity, P. brevispora presented the highest activity with 30 % of WW. T. sanguinea was able to secrete Lac in the presence of 15 % WW similar to the control. Lac activity for I. lacteus was not detected in WW or controls. P. pulmonarius LBM 105 was not able to grow or secrete Lac in the presence of WW. This study allowed us to select P. brevispora as a promissory bioremediation agent for citrus WW treatment strategies.