Enhancement in multiple lignolytic enzymes production for optimized lignin degradation and selectivity in fungal pretreatment of sweet sorghum bagasse

Decisional tool development and application for techno-economic analysis of fungal laccase production

Textile and medical effluents causing bioaccumulation and biomagnification have been successfully biodegraded by fungal laccases. Here, a decision-making tool was developed and applied to evaluate 45 different laccase production strategies which determined the best potential source from a techno-economical perspective. Laccase production cost was calculated with a fixed output of 109 enzymatic units per batch (USD$per109U) and a sensitivity analysis was performed. Results indicate that optimization of enzymatic kinetics for each organism is essential to avoid exceeding the fermentation time point at which production titer reaches its peak and, therefore, higher production costs. Overall, the most cost-effective laccase-producing strategy was obtained when using Pseudolagarobasidium acaciicola with base production cost of USD $42.46 per 109 U. This works serves as platform for decision-making to find the optimal laccase production strategy based on techno-economic parameters.

Under explored roles of microbial ligninolytic enzymes in aerobic polychlorinated biphenyl transformation

Polychlorinated biphenyls (PCBs) are persistent organic pollutants in the environment that are responsible for many adverse health effects. Bioremediation appears to be a healthy and cost-effective alternative for remediating PCB-contaminated environments. While some microbial species have been observed to be capable of transforming PCBs, only two different microbial pathways (rdh and bph pathways) have been described to be involved in PCB transformations. Ligninolytic enzymes have been observed or are under suspicion in some microbial PCB transformations. However, the role of these promising PCB-transforming enzymes, which are produced by fungi and some aerobic bacteria, is still unclear. The present review describes their role by identifying microbial PCB-transforming species and their reported ligninolytic enzymes whether proven or suspected to be involved in PCB transformations. There are several lines of evidence that ligninolytic enzymes are responsible for PCB transformations such as (1) the ability of purified laccases from Myceliophthora thermophila, Pycnoporus cinnabarinus, Trametes versicolor, Cladosporium sp, and Coprinus cumatus to transform hydroxy-PCBs; (2) the increased production of laccases and peroxidases by many fungi in the presence of PCBs; and (3) the enhanced PCB transformation by Pseudomonas stutzeri and Sinorhizobium meliloti NM after the addition of ligninolytic enzyme enhancers. However, if the involvement of ligninolytic enzymes in PCB transformation is clearly demonstrated in some fungal species, it does not seem to be implicated in all microbial species suggesting other still unknown metabolic pathways involved in PCB transformation and different from the bph and rdh pathways. Therefore, PCB transformation may involve several metabolic pathways, some involving ligninolytic enzymes, bph or rdh genes, and some still unknown, depending on the microbial species. In addition, current knowledge does not fully clarify the role of ligninolytic enzymes in PCB oxidation and dechlorination. Therefore, further studies focusing on purified ligninolytic enzymes are needed to clearly elucidate their role in PCB transformation.

Efficient crop straws biotreatment using the fungus Cerrena Unicolor GC.u01

Lignin is main composition of agricultural biomass which can be decomposed through enzymatic hydrolysis by fungi. However, there are still needs to identify more efficient and effective fungal stain for biomass valorization. In this study, lignin degrading fungi from birch forest were screened for sustainable degradation of waste agricultural straws. The most effective strain was identified as Cerrena unicolor GC.u01 using 18 S rDNA gene-sequencing technology. Three different crop straws (corn stalk, rice and wheat straws) were used for the biotreatment studies. The activities of lignin degrading enzymes, laccase (Lac), cellulase and xylanase, secreted by C. unicolor were also determined. Scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analyzer (TGA) were further used to monitor the effects of the biotreatment process. The results showed that C. unicolor degraded 34.3% rice straw lignin, a percentage which was higher than other isolated strains after 15 d straw liquid fermentation. The highest Lac activity (8.396 U•mL- 1) was observed with corn stalk on the 7 d. Cellulase and xylanase activities, in the same biomass, were higher than those of wheat and rice straws after 15 d. Furthermore, SEM, FTIR and TGA analyses showed that C. unicolor pretreatment process had significant effects on corn stalk, rice and wheat straws' structures. The newly isolated stain of C. unicolor demonstrated high lignin degradation potential that can provide effective, ecofriendly means of valorizing biomass to industrial useable raw-material.

Laccase-Based Self-Amplifying Catalytic System Enables Efficient Antibiotic Degradation for Sustainable Environmental Remediation

Antibiotic contamination poses potential risks to ecosystems and human health. Laccase (LAC) has emerged as a promising biocatalyst for the oxidation of environmentally toxic contaminants with high catalytic efficiency; however, its large-scale application is hindered by enzyme costs and dependency on redox mediators. Herein, a novel self-amplifying catalytic system (SACS) for antibiotic remediation that does not require external mediators is developed. In SACS, a natural mediator-regenerating koji with high-activity LAC, derived from lignocellulosic waste, initiates the chlortetracycline (CTC) degradation. Subsequently, an intermediate product, CTC327, identified as an active mediator for LAC via molecular docking, is formed and then starts a renewable reaction cycle, including CTC327-LAC interaction, stimulated CTC bioconversion, and self-amplifying CTC327 release, thus enabling highly efficient antibiotic bioremediation. In addition, SACS exhibits excellent performance in producing lignocellulose-degrading enzymes, highlighting its potential for lignocellulosic biomass deconstruction. To demonstrate its effectiveness and accessibility in the natural environment, SACS is used to catalyze in situ soil bioremediation and straw degradation. The resulting CTC degradation rate is 93.43%, with a straw mass loss of up to 58.35% in a coupled process. This mediator regeneration and waste-to-resource conversion in SACS provides a promising route for environmental remediation and sustainable agricultural practices.

Overproduction of Laccase by Trametes versicolor and Pycnoporus sanguineus in Farnesol-Pineapple Waste Solid Fermentation

The effect of farnesol, a sesquiterpene alcohol, on the production of laccases by Trametes versicolor and Pycnoporus sanguineus in pineapple waste solid-state fermentation was evaluated. Extracellular laccase production reached a maximum of 77.88 ± 5.62 U/g (236% above control) in farnesol-induced cultures of T. versicolor on the 17th day, whereas in a similar P. sanguineus culture, a maximal laccase activity of 130.95 ± 2.20 U/g (159% increase) was obtained on the 17th day. A single 45 KDa laccase was produced by both fungi under the influence of farnesol. These and other data allow us to conclude that farnesol acted as an inducer of the same form of laccase in both fungi. Farnesol disfavored fungal growth by increasing the lag phase, but it also clearly improved the oxidative state of the cultures. Contrary to the results obtained previously in submerged cultures, farnesol did not promote hyperbranching in the fungal mycelia. This is the first demonstration that farnesol is an excellent inducer of laccases in T. versicolor and P. sanguineus in solid-state cultivation. In quantitative terms, the results can be regarded as an excellent starting point for developing industrial or at least pre-industrial procedures to produce laccases using T. versicolor and P sanguineus under the stimulus of farnesol.

Enhanced lignin degradation of paddy straw and pine needle biomass by combinatorial approach of chemical treatment and fungal enzymes for pulp making

Paddy straw (PS) and pine needles (PN) are one of the challenging biomasses in terms of disposal and compost making due to their high silica and tannin contents. Particulate air pollution, loss of biodiversity and respiratory impairments are some of disastrous outcomes caused by burning. However, high percentage of cellulose and hemicellulose makes them potential substrate for paper and pulp industries. The main aim of work was to study and utilize a combinatorial approach of weak chemical treatment and lignin degrading fungal species as agents of effective production of lignin modifying enzymes (LME's) for lignin depolymerisation from the biomasses. Phanerochaete chrysosporium was found to be the best degrader of lignin (47.11 % in PS + PN in 28 days) with maximum LME's production between 10th-17th days. Efficient lignin degradation in the PS and PN biomass will aid further application in pulp production supporting the transition to a circular economy in a greener way.

Conversion sweet sorghum biomass to produce value-added products

Currently, most biotechnological products are produced from sugar- or starch-containing crops via microbial conversion, but accelerating the conflict with food supply. Thus, it has become increasingly interesting for industrial biotechnology to seek alternative non-food feedstock, such as sweet sorghum. Value-added chemical production from sweet sorghum not only alleviates dependency and conflict for traditional starch feedstocks (especially corn), but also improves efficient utilization of semi-arid agricultural land resources, especially for China. Sweet sorghum is rich in components, such as fermentable carbohydrates, insoluble lignocellulosic parts and bioactive compounds, making it more likely to produce value-added chemicals. Thus, this review highlights detailed bioconversion methods and its applications for the production of value-added products from sweet sorghum biomass. Moreover, strategies and new perspectives on improving the production economics of sweet sorghum biomass utilization are also discussed, aiming to develop a competitive sweet sorghum-based economy.

Use of Anthracophyllum Discolor and Stereum Hirsutum as a Suitable Strategy for Delignification and Phenolic Removal of Olive Mill Solid Waste

This study evaluated the use of the white-rot fungi (WRF) Anthracophyllum discolor and Stereum hirsutum as a biological pretreatment for olive mill solid mill waste (OMSW). The WRF strains proposed were added directly to OMSW. The assays consisted of determining the need to add supplementary nutrients, an exogenous carbon source or use agitation systems, and evaluating WRF growth, enzyme activity, phenolic compound removal and lignin degradation. The highest ligninolytic enzyme activity was found at day 10, reaching 176.7 U/L of manganese-independent peroxidase (MniP) produced by A. discolor, and the highest phenolic removal (more than 80% with both strains) was reached after 24 days of incubation. The confocal laser scanning microscopy analysis (CLSM) confirmed lignin degradation through the drop in lignin relative fluorescence units (RFU) from 3967 for untreated OMSW to 235 and 221 RFU, showing a lignin relative degradation of 94.1% and 94.4% after 24 days of treatment by A. discolor and S. hirsutum, respectively. The results demonstrate for the first time that A. discolor and S. hirsutum were able to degrade lignin and remove phenolic compounds from OMSW using this as the sole substrate without adding other nutrients or using agitation systems. This work indicates that it could be possible to design an in situ pretreatment of the valorization of OMSW, avoiding complex systems or transportation. In this sense, future research under non-sterile conditions is needed to evaluate the competition of WRF with other microorganisms present in the OMSW. The main drawbacks of this work are associated with both the low reaction time and the water addition. However, OMSW is seasonal waste produced in one season per year, being stored for a long time. In terms of water addition, the necessary optimization will be addressed in future research.

Endophytic fungi: a potential source of industrial enzyme producers

Microbial enzymes have gained interest for their widespread use in various industries and medicine due to their stability, ease of production, and optimization. Endophytic fungi in plant tissues produce a wide range of secondary metabolites and enzymes, which exhibit a variety of biological activities. The present review illustrates promising applications of enzymes produced by endophytic fungi and discusses the characteristic features of the enzymes, application of the endophytic fungal enzymes in therapeutics, agriculture, food, and biofuel industries. Endophytic fungi producing ligninolytic enzymes have possible biotechnological applications in lignocellulosic biorefineries. The global market of industrially important enzymes, challenges, and future prospects are illustrated. However, the commercialization of endophytic fungal enzymes for industrial purposes is yet to be explored. The present review suggests that endophytic fungi can produce various enzymes and may become a novel source for upscaling the production of enzymes of industrial use.

Recent Developments in the Immobilization of Laccase on Carbonaceous Supports for Environmental Applications - A Critical Review

Τhe ligninolytic enzyme laccase has proved its potential for environmental applications. However, there is no documented industrial application of free laccase due to low stability, poor reusability, and high costs. Immobilization has been considered as a powerful technique to enhance laccase's industrial potential. In this technology, appropriate support selection for laccase immobilization is a crucial step since the support could broadly affect the properties of the resulting catalyst system. Through the last decades, a large variety of inorganic, organic, and composite materials have been used in laccase immobilization. Among them, carbon-based materials have been explored as a support candidate for immobilization, due to their properties such as high porosity, high surface area, the existence of functional groups, and their highly aromatic structure. Carbon-based materials have also been used in culture media as supports, sources of nutrients, and inducers, for laccase production. This study aims to review the recent trends in laccase production, immobilization techniques, and essential support properties for enzyme immobilization. More specifically, this review analyzes and presents the significant benefits of carbon-based materials for their key role in laccase production and immobilization.

Ammonia Fiber Expansion Combined with White Rot Fungi to Treat Lignocellulose for Cultivation of Mushrooms

In order to improve the degradation efficiency of lignocellulose while increasing the yield of mushrooms, white rot fungi treatment (Pleurotus ostreatus, Pleurotus eryngii, and Pleurotus geesteranus) combined with ammonia fiber expansion was proposed as a method for treating lignocellulose (Pennisetum sinese, salix chips, and pine chips) for mushroom cultivation. Compared with treatment using either ammonia fiber expansion or white rot fungus, the combined treatment significantly improved lignocellulose degradation rate by 10-20% and reduced the time required significantly. Among them, P. geesteranus was the most effective bacterium for the combined treatment of lignocellulose. Ammonia fiber expansion-treated lignocellulose contributed to mycelial growth and increased the activity of three lignin hydrolase enzymes (laccase, manganese peroxidase, and lignin peroxidase) and mushroom yield. The mushroom yield was increased by 44.6%. The combined treatment method proposed in our study improves lignocellulose resource utilization and is therefore useful in the treatment of agricultural solid organic waste.

Degradation of lignocelluloses in straw using AC-1, a thermophilic composite microbial system

In composting, the degradation of lignocellulose in straw is problematic due to its complex structures such as lignin. A common solution to this problem is the addition of exogenous inoculants. AC-1, a stable thermophilic microbial composite, was isolated from high temperature compost samples that can decompose lignocellulose at 50–70 °C. AC-1 had a best degradation efficiency of rice straw at 60 °C (78.92%), of hemicellulose, cellulose and lignin were 82.49%, 97.20% and 20.12%, respectively. It showed degrad-ability on both simple (filter paper, absorbent cotton) and complex (rice straw) cellulose materials. It produced acetic and formic acid during decomposition process and the pH had a trend of first downward then upward. High throughput sequencing revealed the main bacterial components of AC-1 were Tepidimicrobium, Haloplasma, norank-f-Limnochordaceae, Ruminiclostridium and Rhodothermus which provides major theoretical basis for further application of AC-1.

Recent advances in removal of lignin from paper industry wastewater and its industrial applications - A review

Pulp and paper mill wastewater contains lignin related synthetic, aromatic and chlorinated chemical compounds. Extracting lignin from pulp and paper mill wastewater is one way of recovering valuable organic material. Due to its complex structure, lignin is difficult to break and provides economical and technical provocations in biomass recovery. The conventional wastewater treatment processes are seldom efficacious for the complete removal of lignin from paper mill effluents. A wide range of thermal, mechanical and physico-chemical methods have been reported for the removal of lignin. Moreover, biological method of lignin removal employed microorganisms including bacteria and fungi as a one-step treatment and/or amalgamation of various physico-chemical techniques. Compared with other methods, biological process for degradation of lignin is regarded as eco-friendly, cost-effective and sustainable. Therefore, this review will provide insight into the recent breakthroughs and future trends in lignin removal with special emphasis on biological treatment and scope of lignin utilization.

A novel lignin degradation bacteria-Bacillus amyloliquefaciens SL-7 used to degrade straw lignin efficiently

Using tobacco straw (Ts) and lignin as the sole carbon source, a strain was isolated from Ts and identified as Bacillus amyloliquefaciens SL-7 by 16S rDNA gene-sequencing technology.7-day incubation of Bacillus amyloliquefaciens SL-7 can reduce the chemical oxygen demand (COD) by 69.35% in lignin mineral salt medium. The activity of Manganese peroxidase (MnP) reached maximum level 258.57 U L^-1, and Lignin peroxidase (Lip) was 422.68 U L^-1 at 4th day. The highest Laccase (Lac) activity (55.95 U L^-1) was observed at 3th day. After straw-liquid fermentation degradation of 15 days, the bacterial could degrade 28.55% lignin of the straw which was close to that of fungi. Compared with the control group and effective microorganisms (EM) group, the lignin degradation rate in Bacillus amyloliquefaciens SL-7 group increased by 22.26% and 11.70% at 41-day compost fermentation of tobacco straw. These show the strain has strong lignin degradation performance.

Fungal Laccase Production from Lignocellulosic Agricultural Wastes by Solid-State Fermentation: A Review

Laccases are copper-containing oxidase enzymes found in many fungi. They have received increasing research attention because of their broad substrate specificity and applicability in industrial processes, such as pulp delignification, textile bleaching, phenolic removal, and biosensors. In comparison with traditional submerged fermentation (SF), solid-state fermentation (SSF) is a simpler technique for laccase production and has many advantages, including higher productivity, efficiency, and enzyme stability as well as reduced production costs and environmental pollution. Here, we review recent advances in laccase production technology, with focus on the following areas: (i) Characteristics and advantages of lignocellulosic agricultural wastes used as SSF substrates of laccase production, including detailed suggestions for the selection of lignocellulosic agricultural wastes; (ii) Comparison of fungal laccase production from lignocellulosic substrates by either SSF or SF; (iii) Fungal performance and strain screening in laccase production from lignocellulosic agricultural wastes by SSF; (iv) Applications of laccase production under SSF; and (v) Suggestions and avenues for future studies of laccase production by fungal SSF with lignocellulosic materials and its applications.

A perspective on the biotechnological applications of the versatile tyrosinase

Tyrosinase (E.C. 1.14.18. 1) is a type of Cu-containing oxidoreductase which has bifunctional activity for various phenolic substrates: ortho-hydroxylation of monophenols to diphenols (a cresolase activity) and oxidation of diphenols to quinones (a catecholase activity). Based on the broad substrate spectrum, tyrosinase has been used in bioremediation of phenolic pollutants, constructing biosensors for identifying phenolic compounds, and L-DOPA synthesis. Furthermore, not only tyrosinase has been used to produce useful polyphenol derivatives, but also it is recently revealed that the promiscuous activity of tyrosinase is closely related with delignification in the biorefinery. Accordingly, tyrosinase might be a potential biocatalyst for industrial applications (e.g., electroenzymatic L-DOPA production, but its long-term stability and reusability should be further explored. In this review, we emphasize the versatility of tyrosinase, which includes conventional applications, and suggest new perspectives as an industrial biocatalyst (e.g., electroenzymatic L-DOPA production). Especially, this review focuses on and comprehensively discusses recent innovative studies.

Depolymerization of lignocellulose of oil palm empty fruit bunch by thermophilic microorganisms from tropical climate

Previous studies on screening of lignin-degrading bacteria mainly focused on the ligninolytic ability of the isolated bacteria for the utilization of lignin monomers. In this study, we focused on the depolymerization of alkali lignin to prove the ability of the isolated thermophilic bacterial strains to utilize and depolymerize more than a monomer of alkali lignin within 7 days of incubation. Indigenous thermophilic bacterial isolates from the palm oil plantation were used to evaluate the depolymerization and utilization of alkali lignin. The confirmation of the bacterium-mediated depolymerization of oil palm empty fruit bunch was achieved through the removal of silica bodies, as observed with scanning electron microscopy. Stenotrophomonas sp. S2 and Bacillus subtilis S11Y were able to reduce approximately 50% and 20% of alkali lignin at 7 days of incubation without the requirement for additional carbon sources.

Two-stage autohydrolysis and mechanical treatment to maximize sugar recovery from sweet sorghum bagasse

Modified autohydrolysis combined with mechanical refining has been suggested to recover free sugars from sweet sorghum bagasse and facilitates enzyme access to cellulose in bagasse for enhancing its conversion to fermentable sugars. The amount of total available sugars in sweet sorghum bagasse was found to be 76.1% and this value was used to evaluate the efficiency of the process suggested. Total sugar recovery was achieved up to 68.1% through the single-stage autohydrolysis at 170 °C for 60 min, followed by mechanical refining and enzymatic hydrolysis; however, the sugar recovery through partial degradation of free sugars induced by high-temperature autohydrolysis was lower than expected. A modified two-stage autohydrolysis was suggested to prevent sugar degradation and the total sugar recovery using this process reached 83.9% of total available sugars in sweet sorghum bagasse.

Optimization of a pretreatment and hydrolysis process for the efficient recovery of recycled sugars and unknown compounds from agricultural sweet sorghum bagasse stem pith solid waste

Background

Sweet sorghum bagasse (SSB), comprising both a dermal layer and pith, is a solid waste generated by agricultural activities. Open burning was previously used to treat agricultural solid waste but is harmful to the environment and human health. Recent reports showed that certain techniques can convert this agricultural waste into valuable products. While SSB has been considered an attractive raw material for sugar extraction and the production of value-added products, the pith root in the SSB can be difficult to process. Therefore, it is necessary to pretreat bagasse before conventional hydrolysis.

Methods

A thorough analysis and comparison of various pretreatment methods were conducted based on physicochemical and microscopic approaches. The responses of agricultural SSB stem pith with different particle sizes to pretreatment temperature, acid and alkali concentration and enzyme dosage were investigated to determine the optimal pretreatment. The integrated methods are beneficial to the utilization of carbohydrate-based and unknown compounds in agricultural solid waste.

Results

Acid (1.5−4.5%, v/v) and alkali (5−8%, w/v) reagents were used to collect cellulose from different meshes of pith at 25–100 °C. The results showed that the use of 100 mesh pith soaked in 8% (w/v) NaOH solution at 100 °C resulted in 32.47% ± 0.01% solid recovery. Follow-up fermentation with 3% (v/v) acid and 6.5% (w/v) alkali at 50 °C for enzymolysis was performed with the optimal enzyme ratio. An analysis of the surface topography and porosity before and after pretreatment showed that both the pore size of the pith and the amount of exposed cellulose increased as the mesh size increased. Interestingly, various compounds, including 42 compounds previously known to be present and 13 compounds not previously known to be present, were detected in the pretreatment liquid, while 10 types of monosaccharides, including D-glucose, D-xylose and D-arabinose, were found in the enzymatic solution. The total monosaccharide content of the pith was 149.48 ± 0.3 mg/g dry matter.

Discussion

An integrated technique for obtaining value-added products from sweet sorghum pith is presented in this work. Based on this technique, lignin and hemicellulose were effectively broken down, amorphous cellulose was obtained and all sugars in the sweet sorghum pith were hydrolysed into monosaccharides. A total of 42 compounds previously found in these materials, including alcohol, ester, acid, alkene, aldehyde ketone, alkene, phenolic and benzene ring compounds, were detected in the pretreatment pith. In addition, several compounds that had not been previously observed in these materials were found in the pretreatment solution. These findings will improve the transformation of lignocellulosic biomass into sugar to create a high-value-added coproduct during the integrated process and to maximize the potential utilization of agricultural waste in current biorefinery processing.