Characterization of Penicillium oxalicum SL2 isolated from indoor air and its application to the removal of hexavalent chromium

Abstract

Removal of toxic Cr(VI) by microbial reduction is a promising approach to reducing its ecotoxicological impact. To develop bioremediation technologies, many studies have evaluated the application of microorganisms isolated from Cr(VI)-contaminated sites. Nonetheless, little attention has been given to microbes from the environments without a history of Cr(VI) contamination. In this study, we aimed to characterize the Cr(VI) tolerance and removal abilities of a filamentous fungus strain, SL2, isolated from indoor air. Based on phenotypic characterization and rDNA sequence analysis, SL2 was identified as Penicillium oxalicum, a species that has not been extensively studied regarding Cr(VI) tolerance and reduction abilities. SL2 showed high tolerance to Cr(VI) on solid and in liquid media, facilitating its application to Cr(VI)-contaminated environments. Growth curves of SL2 in the presence of 0, 100, 400, or 1000 mg/L Cr(VI) were well simulated by the modified Gompertz model. The relative maximal colony diameter and maximal growth rate decreased as Cr(VI) concentration increased, while the lag time increased. SL2 manifested remarkable efficacy of removing Cr(VI). Mass balance analysis indicated that SL2 removed Cr(VI) by reduction, and incorporated 0.79 mg of Cr per gram of dry biomass. In electroplating wastewater, the initial rate of Cr(VI) removal was affected by the initial contaminant concentration. In conclusion, P. oxalicum SL2 represents a promising new candidate for Cr(VI) removal. Our results significantly expand the knowledge on potential application of this microorganism.

Fig 1. Microscopic examination of Penicillium oxalicum strain SL2, focusing on conidiophores and conidia (400× magnification).

Fig 2. The tolerance index of SL2 in PDA solid media containing different concentrations of Cr(VI).

Fig 3. The tolerance index of SL2 in PDL media containing different concentrations of Cr(VI).

Fig 4. Micrographs of strain SL2 grown in PDL under Cr(VI) stress.

Panels a, b, and c are images of strain SL2 grown for 48 h in the PDL medium containing 0, 100, or 1000 mg/L Cr(VI), respectively. Panels d, e, and f are images of SL2 grown for 144 h in the PDL medium containing 0, 100, or 1000 mg/L Cr(VI), respectively.

Fig 5. Cr(VI) removal and pH change during the incubation of SL2 in the PDL medium.

Fig 6. Cr(VI) removal by SL2 at different dilutions of electroplating wastewater.

C-217.1, C-96.1, and C-40.6 represent treatments with initial Cr(VI) concentrations of 217.1, 96.1, and 40.6 mg/L, respectively.

Fig 7. The initial rate of Cr(VI) removal by SL2 at different dilutions of electroplating wastewater.

C-217.1, C-96.1, and C-40.6 represent treatments with initial Cr(VI) concentrations of 217.1, 96.1, and 40.6 mg/L, respectively. Error bars represent standard deviation. Treatments marked with the same letter are not significantly different.