Biodegradation of PAHs by Ligninolytic Fungi Hypoxylon Fragiforme and Coniophora Puteana

Immobilized enzyme with sustainable chestnut biochar to remediate polycyclic aromatic hydrocarbons contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) contaminated soil severely and are difficult to remediate. In this study, acid-modified chestnut inner shell biochar with abundant pore channels was used as the main raw materials for the immobilization of white-rot fungal crude enzyme. The maximum immobilization rate of crude enzymes (97.25%±6.20%) could be achieved under the optimal conditions of 24 h immobilization of 10 U/mL crude enzymes by 1 g biochar at 25℃ and pH = 5. Meanwhile, immobilization improved the stability of the crude enzyme. The relative activity of the immobilized crude enzyme increased by 59.32% and 49.73% (compared to the free crude enzymes) after 5 weeks of storage at 4°C and 25°C, respectively. It has been verified that chestnut-based immobilized crude enzyme can degrade 37% of benzo[a]pyrene in 10 days for PAHs-contaminated soils. An efficient, feasible, and low-cost remediation method for PAHs-contaminated soils was explored, which provides technical support for the application of crude enzymes in organic contaminated soils.

Endophytic, extremophilic and entomophilic fungi strains biodegrade anthracene showing potential for bioremediation

Anthropogenic activities have been increasing Polycyclic Aromatic Hydrocarbons (PAHs) release, promoting an urgent need for decontamination methods. Therefore, anthracene biodegradation by endophytic, extremophilic, and entomophilic fungi was studied. Moreover, a salting-out extraction methodology with the renewable solvent ethanol and the innocuous salt K₂HPO₄ was employed. Nine of the ten employed strains biodegraded anthracene in liquid medium (19-56% biodegradation) after 14 days at 30 °C, 130 rpm, and 100 mg L^-1. The most efficient strain Didymellaceae sp. LaBioMMi 155, an entomophilic strain, was employed for optimized biodegradation, aiming at a better understanding of how factors like pollutant initial concentration, pH, and temperature affected this process. Biodegradation reached 90 ± 11% at 22 °C, pH 9.0, and 50 mg L^-1. Futhermore, 8 different PAHs were biodegraded and metabolites were identified. Then, experiments with anthracene in soil ex situ were performed and bioaugmentation with Didymellaceae sp. LaBioMMi 155 presented better results than natural attenuation by the native microbiome and biostimulation by the addition of liquid nutrient medium into soil. Therefore, an expanded knowledge about PAHs biodegradation processes was achieved with emphasis to the action of Didymellaceae sp. LaBioMMi 155, which can be further employed for in situ biodegradation (after strain security test), or for enzyme identification and isolation aiming at oxygenases with optimal activity under alkaline conditions.

Current and emerging trends in bioaugmentation of organic contaminated soils: A review

Organic contaminated soils constitute an important environmental problem, whereas field applicability of existing physical-chemical methods has encountered numerous obstacles, such as high chemical cost, large energy consumption, secondary pollution, and soil degradation. Bioaugmentation is an environmentally friendly and potentially economic technology that efficiently removes toxic pollutants from organic contaminated soils by microorganisms or their enzymes and bioremediation additives. This review attempted to explore the recent advances in bioaugmentation of organic contaminated soils and provided a comprehensive summary of various bioaugmentation methods, including bacterial, fungus, enzymes and bioremediation additives. The practical application of bioaugmentation is frequently limited by soil environmental conditions, microbial relationships, enzyme durability and remediation cycles. To tackle these problems, the future of bioaugmentation can be processed from sustainability of broad-spectrum bioremediation carriers, microbial/enzyme agents targeting combined contaminants, desorption of environmentally friendly additives and small molecular biological stimulants. Findings of this research are expected to provide new references for bioaugmentation methods that are practically feasible and economically potential.

Efficacy of antifungal substances of three Streptomyces spp. against different plant pathogenic fungi

Background

Soil-borne plant pathogenic fungi with a wide host range of crops cause a significant limitation on the global production of agronomic crops. Applications of synthetic pesticides are an important tool for managing plant diseases, but have deleterious influences on the environment as well as its incompatibility with organic agriculture. Recently, Streptomyces spp. became one of the best bio-control agents as a promising environmentally eco-friendly method for effective management of plant diseases.

Results

In a previous research, three species of Streptomyces spp., i.e., S. griseus (MT210913 “DG5”), S. rochei (MN700192 “DG4”) and S. sampsonii (MN700191 “DG1” strains) were identified, as exhibiting potent antifungal activities against plant pathogenic fungus, Sclerotinia sclerotiorum in vitro and greenhouse. GC–Mass analysis revealed the presence of 44, 47 and 54 substances of S. sampsonii DG1, S. griseus DG5 and S. rochei DG4, respectively. GC–MS revealed substances, with bio-control activity, were categorized as volatile organic compounds (VOCs), fatty acids and plant growth regulators, etc. GC–MS analysis exhibited the presence of 7, 13 and 20 volatile compounds produced by S. sampsonii, S. rochei and S. griseus, respectively. These substances exhibited potent antifungal activity against various plant pathogenic fungi, i.e., Botrytis cinerea, Macrophomina phaseolina, Rhizoctonia solani and S. sclerotiorum in vitro, by dual-culture assay. The three strains inhibited all the pathogenic fungi in dual-culture assay in the range of 30–73.67%. Also, the produced substances were applied in vivo (in the field) and supported their potential biocontrol agent against S. sclerotiorum as well as possessed significant biological properties for plant health and growth. Applying Streptomyces spp. culture broth in the field enhanced physiological responses of phenols, sugar, chlorophyll, protein contents and parameters as well as the yield of bean plants.

Conclusion

In field experiments, foliar application of Streptomyces spp. and their metabolites proved to be a great potential, as promising biocontrol agents, for controlling S. sclerotiorum and enhanced plant growth and yield. S. rochei and S. griseus proved to be strong antifungal, plant growth promoters and environmentally eco-friendly fungicides.

Surfactant-aided mycoremediation of soil contaminated with polycyclic aromatic hydrocarbons

Remediation of persistent polycyclic aromatic hydrocarbons (PAHs) contaminated soil has become a major challenge in recent years. Further, conventional application of bioaugmentation strategies for PAHs remediation require continuous supply of microbial specific nutrients, which makes these processes less feasible. Hence, the present study focused on PAHs remediation using surfactants along with wood assisted fungal system in a microcosm set up. In this study, in absence of surfactants, a saturation in PAHs degradation was noted in bioaugmentation with wood assisted fungal system (BAW) with 61 ± 1.25% degradation, followed by bioaugmentation with free fungi system (BAF) (54 ± 0.46%). However, with addition of 1500 mg/L of surface-active compounds (SAC), a maximum PAHs degradation in BAW (100%) and BAF (86 ± 1.30%) strategies were noted on 21st day. Irrespective of the strategies, presence of SAC and rhamnolipids enhanced PAHs degradation by increasing the enzymes production in Trametes hirsuta when compared to Triton x-100 and sodium dodecyl sulphate (SDS). Among the detected PAHs, 100% degradation within 17 days was noted for naphthalene and acenaphthene in SAC-supplemented BAW system. Further, ecotoxicity analysis established showed the LC50 of sediment soil at 26.5 ± 0.24%, which was reduced by an average of 71% after soil remediation. Hence, the current microcosm system proved that the application of SAC with BAW enhanced the PAHs remediation rate, which supports its application in real time soil remediation.

Impact of lignocellulosic waste-immobilised white-rot fungi on enhancing the development of 14C-phenanthrene catabolism in soil

In this study, an investigation was carried out to explore the the impact of white-rot fungi (WRF) on enhancing the development of phenanthrene catabolism in soil over time (1, 25, 50, 75 and 100 d). The WRF were immobilised on spent brewery grains (SBG) prior to inoculation to the soil. The results showed that SBG-immobilised WRF-amended soils reduced the lag phases and increased the extents of ¹⁴C-phenanthrene mineralisation. Greater reductions in the lag phases and increases in the rates of mineralisation were observed in immobilised Trametes versicolor-amended soil compared to the other WRF-amendments. However, the presence of Pleurotus ostreatus and Phanerochaete chrysosporium influenced biodegradation more strongly than the other fungal species. In addition, fungal enzyme activities increased in the amended soils and positively correlated with the extents of ¹⁴C-phenanthrene mineralisation in all soil amendments. Maximum ligninolytic enzyme activities were observed in P. ostreatus-amended soil. Microbial populations increased in all amended soils while PAH-degrading fungal numbers increased with increased soil-PAH contact time and strongly positively correlated with fastest rates of mineralisation. The findings presented in this study demonstrate that inoculating the soil with these immobilised WRFs generally enhanced the mineralisation of the ¹⁴C-phenanthrene in soil. This has the potential to be used to stimulate or enhance PAH catabolism in field-contaminated soils.

Biological machinery for polycyclic aromatic hydrocarbons degradation: A review

Polycyclic aromatic hydrocarbons (PAHs) are hazardous environmental pollutants with widespread and well-recognized health concerns. Amidst more than a hundred known PAHs, 16 are categorized as priority pollutants. Use of widely diverse biological machinery comprising bacteria, fungi, and algae harnessed from contaminated sites has emerged as an ecologically safe and sustainable approach for PAH degradation. The potential of these biological systems has been thoroughly examined to maximize the degradation of specific PAHs by understanding their detailed biochemical pathways, enzymatic system, and gene organization. Recent advancements in microbial genetic engineering and metabolomics using modern analytical tools have facilitated the bioremediation of such xenobiotics. This review explores the role of microbes, their biochemical pathways, genetic regulation of metabolic pathways, and the effect of biosurfactants against the backdrop of PAH substrate structures.