A Comprehensive Review of the Mycelial Pellet: Research Status, Applications, and Future Prospects

Immobilization of ammonia-oxidizing bacteria using mycelial pellets: Preparation, characteristics, and application for nitritation

Ammonia-oxidizing bacteria (AOB) sourced from an aerobic granular sludge (AGS) process were rapidly enriched by progressively increasing ammonia nitrogen (NH4+-N) loads, achieving a Nitrosomonas abundance of 20.7 % and a nitrite accumulation rate exceeding 80 %. Mycelial pellets formed by Cladosporium, isolated from the same AGS system, provided a porous surface structure for the immobilization of the enriched AOB, creating mycelial pellet/AOB composites. Robust microbial colonization and aggregation in mycelial pellet porous matrix were facilitated by a higher level of extracellular polymeric substances (EPS) compared to conventional AGS. Static tests showed a maximum NH4+-N oxidation rate of 17.7 mg/(gMLVSS·h), higher than free AOB (8.5 mg/(gMLVSS·h)). In multi-recycling tests, the composites maintained 96.6 % NH4+-N oxidation, demonstrating superior repeatability and stability. The results highlight advantages of mycelial pellets as biocompatible carriers in immobilizing AOB sourced from the same system, offering insights into improved nitritation performance and durability, making them promising for practical wastewater treatment.

Development and characterization of starch/polyvinyl alcohol active films with slow-release property by utilizing Mucorracemosus Fresenius mycelium to load with clove essential oil

The controlled release active packaging film represents a novel technology that always can effectively slow down the release of active agents, extending their efficacy. Mucorracemosus Fresenius (MF) mycelium was prepared and used as an adsorption carrier to load clove essential oil (CEO). The CEO/MF complexes were incorporated into the starch/polyvinyl alcohol (Starch/PVA) matrix to develop active films. The effects of MF content on the films' properties were investigated. MF exhibited the internal hollow structure with diaphragm inside and showed antioxidant activity. The adsorption rate of MF on CEO was 238.09 %. As MF increased, the tensile strength, water contact angle and gas barrier properties (water vapor and oxygen) of the films containing CEO enhanced. The release rate of CEO from the films into food simulant (10 % ethanol) slowed down significantly with increasing of MF. Compared to the film without MF, the film with highest MF delayed 33 h to reach equilibrium. The films with different content of MF showed different antioxidant and antibacterial activities, and different preservation effects on shrimp. It showed a great prospect to develop controlled release active films by utilizing MF mycelium as an adsorption material, which enriched the technical solutions for developing controlled release active packaging films.

Direct development of microalgae-bacterial granular sludge system by seeding pre-made microalgae-dewatered sludge granules: Performance and mechanism analysis

Microalgae-bacterial granular sludge (MBGS) process has great potential in achieving carbon neutrality and energy neutrality, but rapidly cultivating MBGS remains challenging. To address this challenge, this study proposes a new strategy to develop MBGS systems using pre-made granules from microalgae and dewatered sludge. The results indicate that using pre-made microalgae-dewatered sludge granules (M-DSG) as inoculants can directly develop MBGS system, with M-DSG maintaining a relatively stable granular structure, and ultimately achieving pollutant removal efficiencies of 94.0% for chemical oxygen demand (COD), 99.7% for ammonium nitrogen (NH4+-N), and 86.0% for total inorganic nitrogen (TIN). Extracellular polymeric substances (EPS) play a dominant role in maintaining the structure of granules, while filamentous bacteria/algae provide additional reinforcement. The adhesion of microalgae to granules possibly relies on polysaccharides in tightly bound extracellular polymeric substances (TB-EPS) and proteins in loosely bound extracellular polymeric substances (LB-EPS). Microbial community analysis reveals that the target algae (Chlorella) remain the primary algae, and heterotrophic nitrifying bacteria (HNB) and denitrifying bacteria are enriched.

Unveiling the potential of Aspergillus terreus SJP02 for zinc remediation and its driving mechanism

In present study, 15 morphologically different fungi isolated from rhizopheric soils of an industrial area were screened for their Zn2+ removal efficiency from aqueous solution. Isolate depicting highest potential was molecularly identified as Aspergillus terreus SJP02. Effect of various process parameters viz. biosorbent dose, contact time, temperature, agitation rate, pH and initial Zn2+ concentration on the fungal sorption capacity were studied. The biosorbent exhibited maximum Zn2+ sorption capacity of 10.7 ± 0.2 mg g- 1 in 60 min. Desorption studies showed 71.46% Zn2+ recovery rate in 120 min with 0.01 N HNO3, indicating efficient metal recovery for reuse and subsequent reutilization of spent mycosorbents. Acid digestion study suggested adsorption being the primary mechanism accounting for 87% Zn2+removal. It was further confirmed by the FE-SEM and EDX analysis. FTIR analysis suggested involvement of amino, hydroxyl, carbonyl, and phosphate functional groups of fungal cell wall in adsorption. The experimental results were in accordance with the tested isotherm and kinetic models, and suggested the role of physical adsorption for Zn2+ removal. Noteworthy, the present study showed better sorption capacity in considerably shorter equilibration time compared to previous reports and advocate potential utilization of A. terreus SJP02 for bioremediation of Zn2+ contaminated wastewater at industrial scale.

Resource recovery and treatment of wastewaters using filamentous fungi

Industrial wastewater, often characterized by its proximity to neutral pH, presents a promising opportunity for fungal utilization despite the prevalent preference of fungi for acidic conditions. This review addresses this discrepancy, highlighting the potential of certain industrial wastewaters, particularly those with low pH levels, for fungal biorefinery. Additionally, the economic implications of biomass recovery and compound separation, factors that require explicit were emphasized. Through an in-depth analysis of various industrial sectors, including food processing, textiles, pharmaceuticals, and paper-pulp, this study explores how filamentous fungi can effectively harness the nutrient-rich content of wastewaters to produce valuable resources. The pivotal role of ligninolytic enzymes synthesized by fungi in wastewater purification is examined, as well as their ability to absorb metal contaminants. Furthermore, the diverse benefits of fungal biorefinery are underscored, including the production of protein-rich single-cell protein, biolipids, enzymes, and organic acids, which not only enhance environmental sustainability but also foster economic growth. Finally, the challenges associated with scaling up fungal biorefinery processes for wastewater treatment are critically evaluated, providing valuable insights for future research and industrial implementation. This comprehensive analysis aims to elucidate the potential of fungal biorefinery in addressing industrial wastewater challenges while promoting sustainable resource utilization.

Flow modeling and structural characterization in fungal pellets

Fungal pellets are hierarchical systems that can be found in an ample variety of applications. Modeling transport phenomena in this type of systems is a challenging but necessary task to provide knowledge-based processes that improve the outcome of their biotechnological applications. In this work, an upscaled model for total mass and momentum transport in fungal pellets is implemented and analyzed, using elements of the volume averaging and adjoint homogenization methods departing from the governing equations at the microscale in the intracellular and extracellular phases. The biomass is assumed to be composed of a non-Newtonian fluid and the organelles impervious to momentum transport are modeled as a rigid solid phase. The upscaled equations contain effective-medium coefficients, which are predicted from the solution of adjoint closure problems in a three-dimensional periodic domains representative of the microstructure. The construction of these domains was performed for Laccaria trichodermophora based on observations of actual biological structures. The upscaled model was validated with direct numerical simulations in homogeneous portions of the pellets core. It is shown that no significant differences are observed when the dolipores are open or closed to fluid flow. By comparing the predictions of the average velocity in the extracellular phase resulting from the upscaled model with those from the classical Darcy equation (i.e., assuming that the biomass is a solid phase) the contribution of the intracellular fluid phase was evidenced. This work sets the foundations for further studies dedicated to transport phenomena in this type of systems.

Ultra-rapid development of 'solid' aerobic granular sludge by stable transition/filling of inoculated 'hollow' mycelial pellets in hypersaline wastewater

To overcome the long start-up period in cultivating aerobic granular sludge (AGS) under hypersaline environment, mycelial pellets (MPs) of halotolerant fungus Cladosporium tenuissimum NCSL-XY8 were inoculated to try to realize the ultra-rapid development of salt-tolerant AGS by stable transition of 'hollow' MPs into 'solid' AGS without apparent fragmentation. The granules directly met the standard of AGS after inoculating MPs (Day 0), and it basically satisfied relatively strict standards of AGS (SVI30 < 50 mL/g, D50 > 300 μm, D10 > 200 μm and SVI30/SVI5 > 0.9) under anaerobic/aerobic mode during whole cultivation processes. Microstructure of the granular cross section clarified that MPs with hollow/loose inner layer transitioned into solid/dense AGS under anaerobic/aerobic mode within 7 days, while formed skin-like floating pieces and unstable double-layer hollow granules under aerobic mode. Organics removal reached relatively stable within 13 days under anaerobic/aerobic mode, 6 days faster than aerobic mode. This study provided a strategy for ultra-rapid and stable development of AGS, which showed the shortest granulation period in various AGS-cultivation strategies.

Manipulation of co-pelletization for Chlorela vulgaris harvest by treatment of Aspergillus niger spore

The co-pelletization of microalgae with filamentous fungi was a promising approach for microalgae harvest. However, the real conditions of microalgae growth limited the arbitrary optimization of co-pellets formation with filamentous fungi. Therefore, it is urgent to develop an approach to manipulate the co-pelletization through treatment of A. niger spores. In this study, Aspergillus niger and Chlorella vulgaris were used as the model species of filamentous fungi and microalgae to investigate co-pellets formation using A. niger spores after by different pH solutions treatment, swelling, snailase treatment. The importance of spore treatments on C. vulgaris harvest in sequence was claimed based on response surface methodology analysis. The pH solutions treatment, swelling, snailase treatment of A. niger spore contributed 21.0%, 10.5%, 40.7% of harvest ratio of C. vulgaris respectively, which guided the application of spore treatment into co-pelletization. Treatment of spore was showed as an efficient approach to manipulate co-pelletization for microalgae harvest in diverse microalgae condition. This results promoted the application of co-pelletization technology in microalgae harvest of various conditions.

Functional fungal pellets self-immobilized by mycelium fragments of Irpex lacteus WRF-IL for efficient degradation of sulfamethazine as the sole carbon source

In order to achieve an efficient microbial material with dual functions of self-immobilization and sulfamethazine (SMZ) degradation, this study explored the pelletization technique utilizing mycelium fragments of Irpex lacteus WRF-IL and systematically examined the pellets formation conditions and degradation capability. The Box-Behnken design results demonstrated that pure mycelium fragments, broken by frosted glass beads, could be rapidly self-immobilized to form white rot mycelial pellets (WRMPs) within 24 h, serving as the pelleting core. These WRMPs could completely remove SMZ as the sole carbon source within 20 h. The addition of sucrose expedited this process, achieving complete removal within only 14 h. Kinetic analysis showed that WRMPs could potentially remove SMZ at higher concentrations (>25 mg/L). Biodegradation was the primary pathway of SMZ removal. Seven intermediates were identified by QTOF LC/MS, and three transformation pathways initiated by SO₂ overflow, molecular rearrangement, and aniline moiety oxidation were deduced.

Extracellular vesicles in phytopathogenic fungi

Extracellular vesicles (EVs) are nano-sized lipid compartments that mediate the intercellular transport of lipids, proteins, nucleic acids and metabolites. During infectious diseases, EVs released by host cells promote immune responses, while those released by pathogens attempt to subvert host immunity. There is a growing body of research investigating the role of fungal EVs in plant pathosystems. It is becoming clear that EVs released by fungal phytopathogens play a role during infection through the transport of protein effectors, toxic metabolites and RNA. Here, we discuss recent findings on EVs in fungal phytopathogens, including the methods employed in their isolation, their characterization, contents and functionality, as well as the key questions remaining to be addressed.

A rapid and simplified method for evaluating the performance of fungi-algae pellets: A hierarchical analysis model

Microbial pellets technology has undergone extensive research recently and has increasingly matured, showing significant promise. However, the performance of microbial pellets cannot be predicted quickly by the current evaluating methods because they are complicated to operate, take a long time, and pose a risk to the environment. In this study, a representative microbial pellet, fungi-algae pellet, was selected as the research object. Eight evaluation parameters and four evaluation indices were chosen to construct the performance evaluation system of the fungal-algal pellets using the analytic hierarchy process (AHP) and weighting method. Combining the correlation analysis and expert opinion, we found that among the eight parameters selected, the adsorption saturation rate of mycelial pellets on algae had the most significant influence weight on the performance of fungi-algae pellet, followed by algal culture time and fungal incubation time. This research proposes and validates the Performance Evaluation Value (PEV) of fungi-algae pellet and its calculation method. We also discuss the effectiveness of this new evaluation system in saving time, cost, and emission reductions. The results of this paper enable the rapid evaluation of fungi-algae pellets and promote the better development of fungi-algae pellets technology and even other multi-microbial symbiotic pellet technologies.

Evaluating the role of algae in algal-bacterial granular sludge: Nutrient removal, microbial community and granular characteristics

Algal-bacterial granular sludge (ABGS) and bacterial granular sludge (BGS, control group) were operated over 240 days to investigate the role of algae in treating synthetic municipal wastewater. The results showed that algae significantly improved the removal efficiency of total nitrogen (TN). The nitrogen removal load of ABGS was 2.6 mg-N/g-VSS/day (22.8 %, light) and 1.1 mg-N/g-VSS/day (9.6 %, dark) higher than that of BGS, respectively, which was attributed to algae enhanced NH₃-N removal capacity in the anaerobic stage and increased the utilization efficiency of organics in denitrification. Algae increased the relative abundance of denitrifying bacteria, and ABGS (28.83 %) was higher than BGS (14.28 %). Moreover, the dominant phylum of algae was Chlorophyta (98.39 %), the chlorophyll-a was sustained at 1.28 ± 0.26 mg/g-VSS. Algae significantly increased the content of extracellular polymeric substances (EPS), and the increased polysaccharide came from the tightly bound EPS. This study expands the understanding of the role of algae in ABGS.

Assessing Edible Filamentous Fungal Carriers as Cell Supports for Growth of Yeast and Cultivated Meat

The growth and activity of adherent cells can be enabled or enhanced through attachment to a solid surface. For food and beverage production processes, these solid supports should be food-grade, low-cost, and biocompatible with the cell of interest. Solid supports that are edible can be a part of the final product, thus simplifying downstream operations in the production of fermented beverages and lab grown meat. We provide proof of concept that edible filamentous fungal pellets can function as a solid support by assessing the attachment and growth of two model cell types: yeast, and myoblast cells. The filamentous fungus Aspergillus oryzae was cultured to produce pellets with 0.9 mm diameter. These fugal pellets were inactivated by heat or chemical methods and characterized physicochemically. Chemically inactivated pellets had the lowest dry mass and were the most hydrophobic. Scanning electron microscope images showed that both yeast and myoblast cells naturally adhered to the fungal pellets. Over 48 h of incubation, immobilized yeast increased five-fold on active pellets and six-fold on heat-inactivated pellets. Myoblast cells proliferated best on heat-treated pellets, where viable cell activity increased almost two-fold, whereas on chemically inactivated pellets myoblasts did not increase in the cell mass. These results support the use of filamentous fungi as a novel cell immobilization biomaterial for food technology applications.

Bio-flocculation of Microcystis aeruginosa by using fungal pellets of Aspergillus oryzae: Performance and mechanism

Algal blooms caused by eutrophication are global phenomena that seriously threaten the sustainable use of freshwater resources. Traditional water treatment chemicals often typically lead to high levels of residue and cause damage to the morphology of algal cells. This study investigated an eco-friendly fungal bio-flocculant, Aspergillus oryzae, to remove the representative microalgae (Microcystis aeruginosa). Furthermore, it explored crucial flocculation parameters, adsorption kinetics, and thermodynamics of microalgae using A. oryzae. Accordingly, a flocculation efficiency of >95% was achieved when the fungus was cultured for six days, flocculant dosage was 11 g/L, rotation speed was 100 rpm, temperature was 25 °C, flocculation time was 5 h, and pH ranged between 4.0 and 9.0. KEGG analysis based on the genomic data, and chemical composition analysis revealed that proteins and polysaccharides were the major components of metabolites. Zeta potential analysis, scanning electron microscopy, three-dimensional fluorescence, X-ray spectroscopy, and infrared spectroscopy, electrostatic attraction revealed that electrostatic attraction promoted the destabilization and aggregation of microalgae. Additionally, hyphal surface adsorption and chemisorption from extracellular proteins and exopolysaccharides aided in the removal of microalgae. Therefore, fungi-based bio-flocculants have the potential to remove microalgae in a simple, effective, and eco-friendly manner without the complex extraction of extracellular metabolites.

Unravelling the biodegradation performance and mechanisms of acid orange 7 by aerobic granular sludge at different salinity levels

Azo dyes wastewater is characterized by high-salinity, however, the biodegradation performance and mechanisms of azo dyes by aerobic granular sludge (AGS) under different salinity levels are still unclear. Herein, the results showed that the reactor performance was almost unaffected at low-salinity levels (0.5%-1.0% salinity), and the removal efficiency of acid orange 7 (AO7) was increased by 2.6%-19.1%, possibly due to the excessive secretion of extracellular polymeric substances (EPS) and the enrichment of functional bacteria. Nevertheless, the microbial cell viability was negatively affected by high-salinity level (2.0% salinity), leading to the deterioration of AO7 and nutrient removal efficiencies. The AO7 removal was achieved by rapid adsorption and slow biodegradation. The biodegradation pathway indicated that AO7 was gradually mineralized in the AGS system through desulfurization, deamination, decarboxylation and hydroxylation. Altogether, this work provides an important reference for the application of AGS technology for treating saline azo dye wastewaters.

A review on mycelial pellets as biological carriers: Wastewater treatment and recovery for resource and energy

Mycelial pellets, a new environment friendly biological carrier, have received wide attention from researchers due to porosity, stability and unique biocompatibility. In this article, the theoretical basis and mechanism of mycelial pellets as a biological carrier were analyzed from the properties of mycelial pellets and the interaction between mycelial pellets and other microorganisms. This article aims to collate and present the current application and development trend of mycelial pellets as biological carriers in wastewater treatment, resource and energy recovery, especially the symbiotic particle system formed by mycelial pellets and microalgae is an important way to break through the technical bottleneck of biodiesel recovery from wastewater. This review also analyzes the research hotspots and trends of mycelial pellets as carriers in recent years, discusses the challenges faced by this technology, and puts forward corresponding solutions.

Microalgal-bacterial granular sludge for municipal wastewater treatment: From concept to practice

Recently, increasing interest has been placed in microalgal-bacterial granular sludge (MBGS) in the journey towards the energy and carbon neutrality of municipal wastewater treatment. Different from aerobic granular sludge, the performance of MBGS is mainly determined by the mutualism and symbiosis between coexisting microalgae and bacteria. It appears from the literature that most of studies on MBGS were conducted at small benchtop scales under controlled conditions with synthetic wastewater. Therefore, this article attempts to look into the major engineering gaps between the knowledge generated from numerous laboratory research works and the large-scale application of MBGS, including massive production of MBGS, type of bioreactor, effect of alternate photo and dark metabolisms on effluent quality, resource recovery from waste MBGS, etc. It is clearly demonstrated that MBGS is still at its infant stage, and more effort is strongly needed to identify the technological bottlenecks of full-scale applications, while providing corresponding engineering solutions.

A novel strategy for rapid development of a self-sustaining symbiotic algal-bacterial granular sludge: Applying algal-mycelial pellets as nuclei

Algal-bacterial granular sludge (ABGS) is a promising technology for wastewater treatment, benefiting from the synergetic interactions between algae and bacteria. However, the rapid start-up of the ABGS system is not trivial. Herein, a novel strategy was proposed by applying the algal-mycelial pellets (AMPs) as the primary nuclei for accelerating the development of a self-sustaining symbiotic ABGS system. The results indicated that by using this strategy complete granulation was shortened to 12 days, much shorter than the control system without AMPs dosage (28 days). The ABGS had a large particle diameter (3.3 mm), compact granular structure (1.0253 g/mL), and excellent settleability (SVI30 of 53.2 mL/g). Moreover, 98.6% of COD, 80.8% of TN and 80.0% of PO43--P were removed by the ABGS. The nuclei of targeted algae (Chlorella) and filamentous fungi (Aspergillus niger), the enhanced production of extracellular polymeric substances (especially proteins) and the enrichment of functional bacteria (such as Neomegalonema and Flavobacterium) facilitated the granules development. The low surface free energy (-69.56 mJ/m2) and energy barrier (89.93 KT) were the inherent mechanisms for the strong surface hydrophobicity, the easy bacterial adhesion, and the short granulation period. This study provides an economically feasible approach to accelerate ABGS granulation and sustain system stability.

Morphologically favorable mutant of Trichoderma reesei for low viscosity cellulase production

Metabolite production by filamentous fungi hampered because of high viscosity generated during growth. Low viscosity fermentation by mold is one of the preferred ways of large scale enzymes production. Cellulolytic enzymes play a key role during the process of lignocellulosic biomass conversion. In this study a mutant RC-23-1 was isolated through mutagenesis (diethyl sulfate followed by UV) of T. reesei RUT-C30. RC-23-1 not only gave higher cellulase production but also generated lower viscosity during enzyme production. Viscosity of mutant growth was more than three times lower than parent strain. RC-23-1 shows unique, yeast like colony morphology on solid media and small pellet like growth in liquid media. This mutant did not spread like mold on solid media. This mutant produces cellulases constitutively when grown in sugars. Using only glucose, the cellulase production was 4.1 FPU/ml. Among polysaccharides (avicel, xylan and pectin), avicel gave maximum of 6.2 FPU/ml and pretreated biomass (rice straw, wheat straw and sugarcane bagasse) produced 5.1-5.8 FPU/ml. At 7L scale reactor, fed-batch process was designed for cellulase production using different carbon and nitrogen sources. Maximum yield of cellulases was 182 FPU/g of lactose consumed was observed in fed-batch process. The produced enzyme used for hydrolysis of acid pretreated rice straw (20% solid loading) and maximum of 60 % glucan conversion was observed. RC-23-1 mutant is good candidate for large scale cellulase production and could be a model strain to study mold to yeast-like transformation. This article is protected by copyright. All rights reserved.

Biosorption of Precious Metals Present at Dilute Concentrations on Fungal Pellets

Biosorption on fungal pellets constitutes a promising way of removing precious metals, which are often present at dilute concentrations in wastewater. Herein, we studied the Ag and Au biosorption by Aspergillus tabacinus and Cladosporium cladosporioides pellets. For A. tabacinus pellets the optimum pH values for the biosorption of Ag and Au were 5 and 4, respectively, while for C. cladosporioides granules, the best-suited values were 3 and 4, respectively. Biosorption kinetics of both metals were also studied at low adsorbate concentrations (1 mg/L) and the pH values mentioned above, and the contact times that allow maximum recovery of the two metals were defined. At the pH values estimated as optimum, A. tabacinus pellets adsorbed greater amounts of Ag than C. cladosporioides pellets, while for Au the opposite occurred. We found that the pseudo-second-order model adequately represents Ag and Au biosorption kinetics under the conditions tested. Due to the growing demand and limited availability of these metals, their recovery from aqueous residual solutions is economically attractive and desirable in the expanding circular economy scheme.

Colonization of biofilm in wastewater treatment: A review

The attachment and colonization process of microorganisms on a carrier is an interdisciplinary research field. Through a series of physical, chemical, and biological actions, the microorganisms can eventually reproduce on the carrier. This article introduces biofilm start-up and its applications, and explores the current issues to look forward to future development directions. Firstly, the mechanism of microbial film formation is analyzed from the microbial community colonization and reproduction process. Secondly, when analyzing the factors influencing microbial membrane formation, the effect of microbial properties (e.g., genes, proteins, lipids) and external conditions (i.e., carrier, operating environment, and regulation mechanism among microbial communities) were discussed in depth. Aimed at exploring the mechanisms and influencing factors of biofilm start-up, this article proposes the application measures to strengthen this process. Finally, the problems encountered and the future development direction of the technology are analyzed and prospected.