The use of microorganisms to remove Fe (oxyhydr)oxides from kaolins has the potential to be an effective method for upgrading the whiteness and brightness, and therefore the commercial value, of the kaolin. The purpose of the present study was to compare kaolin products obtained by currently used chemical leaching methods with a bioleaching treatment using Aspergillus niger in order to remove Fe from kaolin (from Canakkale, Turkey). The effects of pulp density, temperature, and oxalic acid concentration on the chemical leaching experiments were investigated using the ANOVA-Yates test. The greatest degree of removal of Fe from the kaolin sample (at 15% w/v pulp density, temperature of 80°C, oxalic acid concentration of 0.2 M, and a particle size of <63 µm) was found to be 94.89% in 120 min of leaching. The Fe content decreased from 1.723%) Fe2O3 to 0.088% Fe2O3. In a shake flask, bioleaching of kaolin by Aspergillus niger resulted in removal of 77.13% of the total Fe, suggesting that this strain is effective at removing Fe impurities from kaolin. The removal efficiency generally decreased with increased pulp density. The Fe content of the kaolin decreased from 1.723% Fe2O3 to 0.394% Fe2O3 (at 1% w/v pulp density, temperature of 25°C, Aspergillus niger 3 × 107 spores, and particle size of <63 µm) after 21 days of bioleaching.

Degradation of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-yl)amino] carbonyl] benzenesulfonamide} in acidic and alkaline soils was evaluated using plant bioassay and high-performance liquid chromatography (HPLC) radiotracer techniques. Soil sterilization with either ethylene oxide (Et0) or gamma irradiation significantly reduced breakdown of chlorsulfuron; the ability for degradation was restored by reinoculation with indigenous soil microorganisms. Streptomyces griseolus (a soil actinomycete), Aspergillus niger, and Penicillium sp. (soil fungi) were demonstrated to degrade 14C-chlorsulfuron in pure culture. In addition to microbial breakdown, chemical hydrolysis was an important factor in the disappearance of chlorsulfuron from soil. The contribution of chemical hydrolysis to total degradation was a function of soil pH, with hydrolysis occurring most rapidly in acidic soils. Both dissipation processes slowed markedly at low temperatures.

Clitoria ternatea is known for its antimicrobial activity but the antifungal effects of leaf extract on growth and morphogenesis of Aspergillus niger have not been observed. The extract showed a favorable antifungal activity against A. niger with a minimum inhibition concentration 0.8 mg/mL and minimum fungicidal concentration 1.6 mg/mL, respectively. The leaf extract exhibited considerable antifungal activity against filamentous fungi in a dose-dependent manner with 0.4 mg/mL IC50 value on hyphal growth of A. niger. The main changes observed under scanning electron microscopy after C. ternatea extract treatment were loss of cytoplasm in fungal hyphae and the hyphal wall and its diameter became markedly thinner, distorted, and resulted in cell wall disruption. In addition, conidiophore alterations were also observed when A. niger was treated with C. ternatea leaf extract.

A parent strain of Aspergillus niger LW-1 producing β-mannanase, preserved in our laboratory, was isolated. A strain, N-9, was screened out and further treated with vacuum microwave irradiation and ethyl methane sulphonate (EMS). A mutant strain, E-30, producing a high and stable yield of β-mannanase was obtained through screening by solid-state cultivation on the basic fermentation medium and several generations of bevel subculture. Its enzyme activity (36 675 U/g) was increased by 2.15 times compared to that of A. niger LW-1 (17 048 U/g). The production of high-yield β-mannanase by E-30 remained stable when maintained at 4°C for 2 months.