The pellet-formation factors of Aspergillus niger RAF106 and its application in the biosorption of crystal violet

Abstract:

[Background] Aspergillus niger, a typical filamentous fungus, can produce valuable metabolites, such as enzymes, organic acids, antibiotics, and is widely used in food fermentation, environment protection and so on. Its physiological characters including fungal metabolism and productivity are closely associated with fungal morphologies. However, the relationship between fungal morphologies and the biosorption of dyes and heavy metals is little known. [Objective] To study the pellet-formation factors of A. niger RAF106 and its application in the biosorption of crystal violet. [Methods] The dynamic processes of pellet formation, the effects of the initial pH, temperature, spore inoculum level, agitation frequency, and different carbon and nitrogen sources on pellet formation, and the effects of different morphologies on the biosorption of crystal violet were investigated in tea-derived A. niger RAF106 when incubated in the medium of potato dextrose broth (PDB). [Results] Both conidia and hypha can aggregate and then form pellets in A. niger RAF106. The diameters of pellets were inversely proportional to the initial pH values ranging from 4.0 to 10.0 and spore inoculum levels ranging from 5×10⁴ to 5×10⁶ but had nothing to do with agitation frequency. Moreover, the diameters increased with the increase of culture temperature ranging from 25℃ to 35℃ but decreased with the increase of culture temperature ranging from 35℃ to 40℃, and pellets can not be formed at 45℃. Additionally, the diameters of pellets in the group of glucose are the biggest among the tested groups treated with different carbon sources, but the addition of exogenous nitrogen sources inhibited the diameters. In addition, the fungal biomass was not affected by tested initial pH, temperature, and agitation frequency but positively correlated with spore inoculum levels, and affected by different carbon and nitrogen sources. Furthermore, more crystal violet can be absorbed by smaller pellets than that in bigger pellets, and hypha was the most effective one. [Conclusion] The diameters of pellets are affected by temperature, initial pH, inoculum levels as well as carbon and nitrogen source but not shaker speed. The adsorption of crystal violet depends on fungal morphologies in A. niger RAF106. These results will be helpful to control the fungal morphologies and optimize the wastewater treatment system associated with A. niger.