Mineralization of mono-nitrophenols by Bjerkandera adusta and Lentinus squarrosulus and their extracellular ligninolytic enzymes

Recent advances in biological removal of nitroaromatics from wastewater

Various nitroaromatic compounds (NACs) released into the environment cause potential threats to humans and animals. Biological treatment is valued for cost-effectiveness, environmental friendliness, and availability when treating wastewater containing NACs. Considering the significance and wide use of NACs, this review focuses on recent advances in biological treatment systems for NACs removal from wastewater. Meanwhile, factors affecting biodegradation and methods to enhance removal efficiency of NACs are discussed. The selection of biological treatment system needs to consider NACs loading and cost, and its performance is affected by configuration and operation strategy. Generally, sequential anaerobic-aerobic biological treatment systems perform better in mineralizing NACs and removing co-pollutants. Future research on mechanism exploration of NACs biotransformation and performance optimization will facilitate the large-scale application of biological treatment systems.

The roles of Pleurotus ostreatus HAUCC 162 laccase isoenzymes in decolorization of synthetic dyes and the transformation pathways

Fungal laccases have shown great potential in industrial and environmental applications. They are generally produced as laccase isoenzymes. Thus, to further study the properties of different laccase isoenzymes and their performance in bio-remediation is essential for a deep understanding of laccase function and application. In this study, three Pleurotus ostreatus HAUCC 162 laccase isoenzymes were heterologously expressed, and the effects of different inhibitors, metal ions, and organic solvents on the activity of recombinant laccases were evaluated. In the dye decolorization test, LACC6 showed the highest ability to remove Malachite green (MG), Remazol Brilliant Blue R (RBBR), Bromophenol blue (BB), and Methyl orange (MO) among the three recombinant laccases. Removal rates within 24 h were 91.5%, 84.9%, 79.1%, and 73.1% for MG (100 mg/L), RBBR (100 mg/L), BB (100 mg/L), and MO (100 mg/L), respectively. The MG and RBBR transformation pathways were proposed by using High Performance Liquid Chromatography-Mass Spectrometry (LC-MS) analysis. Based on the results of this work, the production of recombinant LACC6 or improving the portion of LACC6 in the crude extracellular laccase may advance synthetic dye removal.

Heterologous expression and characterization of three laccases obtained from Pleurotus ostreatus HAUCC 162 for removal of environmental pollutants

Chlorophenols (CPs), nitrophenols (NPs), and sulfonamide antibiotics (SAs) are three types of environmental pollutants that are of great concern because of their prevalence and toxicity. In this study, three laccase isoenzymes obtained from Pleurotus ostreatus HAUCC 162 were heterologously expressed and characterized with respect to their ability to degrade CPs, NPs, and, SAs. The three recombinant laccases can efficiently degrade the three types of considered pollutants using a laccase-mediator system (LMS). Their specific efficiencies for the removal of 2NP, 3NP, 4NP, 4CP, 2,4-dichlorophenol (DCP), 2,6-DCP, sulfadiazine (SDZ), sulfamethazine (SMZ), and sulfamethoxazole (SMX) over 60min were 59.21%, 47.91%, 60.24%, 74.9%, 28.9%, 35.1%, 98.1%, 97.5%, and 97.8%, respectively. Based on the analysis of the oxidation products of the CPs, NPs, and SAs, pollutant removal pathways are proposed, namely, the production of 3-nitromuconate and 3-chloromuconate as the key intermediates of 4-NP and 2, 4-DCP; and oxidative coupling for the transformation of SDZ by LMS. The results of present work indicated the laccases could efficiently remove NPs, CPs, and SAs in LMS, which offers an opportunity to apply P. ostreatus HAUCC 162 laccase in the field of environmental biotechnology.

Hexavalent molybdenum reduction to mo-blue by a sodium-dodecyl-sulfate-degrading Klebsiella oxytoca strain DRY14

Bacteria with the ability to tolerate, remove, and/or degrade several xenobiotics simultaneously are urgently needed for remediation of polluted sites. A previously isolated bacterium with sodium dodecyl sulfate- (SDS-) degrading capacity was found to be able to reduce molybdenum to the nontoxic molybdenum blue. The optimal pH, carbon source, molybdate concentration, and temperature supporting molybdate reduction were pH 7.0, glucose at 1.5% (w/v), between 25 and 30 mM, and 25°C, respectively. The optimum phosphate concentration for molybdate reduction was 5 mM. The Mo-blue produced exhibits an absorption spectrum with a maximum peak at 865 nm and a shoulder at 700 nm. None of the respiratory inhibitors tested showed any inhibition to the molybdenum-reducing activity suggesting that the electron transport system of this bacterium is not the site of molybdenum reduction. Chromium, cadmium, silver, copper, mercury, and lead caused approximately 77, 65, 77, 89, 80, and 80% inhibition of the molybdenum-reducing activity, respectively. Ferrous and stannous ions markedly increased the activity of molybdenum-reducing activity in this bacterium. The maximum tolerable concentration of SDS as a cocontaminant was 3 g/L. The characteristics of this bacterium make it a suitable candidate for molybdenum bioremediation of sites cocontaminated with detergent pollutant.

The tropical white rot fungus, Lentinus squarrosulus Mont.: lignocellulolytic enzymes activities and sugar release from cornstalks under solid state fermentation

Lentinus squarrosulus Mont., a high temperature tolerant white rot fungus that is found across sub-Saharan Africa and many parts of Asia, is attracting attention due to its rapid mycelia growth and potential for use in food and biodegradation. A solid state fermentation (SSF) experiment with L. squarrosulus (strain MBFBL 201) on cornstalks was conducted. The study evaluated lignocellulolytic enzymes activity, loss of organic matter (LOM), exopolysaccharide content, and the release of water soluble sugars from degraded substrate. The results showed that L. squarrosulus was able to degrade cornstalks significantly, with 58.8% LOM after 30 days of SSF. Maximum lignocellulolytic enzyme activities were obtained on day 6 of cultivation: laccase = 154.5 U/L, MnP = 13 U/L, peroxidase = 27.4 U/L, CMCase = 6.0 U/mL and xylanase = 14.5 U/mL. L. squarrosulus is a good producer of exopolysaccharides (3.0-5.13 mg/mL). Glucose and galactose were the most abundant sugars detected in the substrate during SSF, while fructose, xylose and trehalose, although detected on day zero of the experiment, were absent in treated substrates. The preference for hemicellulose over cellulose, combined with the high temperature tolerance and the very fast growth rate characteristics of L. squarrosulus could make it an ideal candidate for application in industrial pretreatment and biodelignification of lignocellulosic biomass.