Biodelignification of rice straw by Phanerochaete chrysosporium in the presence of dirhamnolipid

Optimizing fungal treatment of lignocellulosic agro-industrial by-products to enhance their nutritional value

This study delves into the dynamic interaction between various fungal strains, substrates, and treatment durations to optimize the nutritional value of these by-products. Six fungi, including Penicillium chrysogenum, Fusarium sp., Fusarium oxysporum, Fusarium solani, Penicillium crustosum, and Cosmospora viridescens, were evaluated across three substrates: wheat straw (WS), cedar sawdust (CW), and olive pomace (OP) over treatment periods of 4, 8, and 12 weeks. The study discerned profound impacts of these fungi across multiple parameters, including cellulose variation (C.var), lignin variation (L.var), and in vitro true digestibility variation (IVTD.var). Our results demonstrated that the various fungi had a significant effect on all parameters (p < .001). Noteworthy, F. oxysporum and F. solani emerged as exemplars, displaying notable lignin degradation, cellulose liberation, and IVTD enhancement. Importantly, P. crustosum demonstrated substantial cellulose degradation, exhibiting optimal efficacy in just 4 weeks for all substrates. Notably, F. sp. excelled, yielding favorable results when treating WS. P. chrysogenum achieved optimal outcomes with 8-week treatment for WS. Both Fusarium sp. and P. chrysogenum exhibited slight cellulose release, with remarkable reduction of WS lignin compared to other substrates. Especially, WS and OP displayed superior digestibility enhancements relative to CW. It should be noted that the treatment duration further shaped these outcomes, as prolonged treatment (12 weeks) fostered greater benefits in lignin degradation and digestibility, albeit with concomitant cellulose degradation. These findings underscore the intricate balance between fungal strains, substrates, and treatment durations in optimizing the nutritional value of lignocellulosic agro-industrial by-products. The outcomes of this study lead to the enhancement in the overall value of by-products, promoting sustainable livestock feed and advancing agricultural sustainability.

Screening the Carbon Source Type in Solid-State Fermentation with Phanerochaete chrysosporium to Improve the Forage Value of Corn Straw and Rice Straw

Poor quality straw can be made more digestible and palatable through delignification using white rot fungi as a biological treatment in SSF. The decomposition of organic matter by white rot fungi is improved when a carbon source is added. Reducing the fermentation cycle can also help retain more nutrients in straw feed. To increase rumen digestibility and nutrient utilization, corn straw and rice straw were subjected to SSF with white rot fungi (Phanerochaete chrysosporium) for 21 days. The type of carbon source (glucose, sucrose, molasses, or soluble starch) was optimized, and the nutrient composition and in vitro fermentation parameters of the fermented straw were assessed. In the fermented corn straw and rice straw supplemented with different carbon sources, the results showed a decrease in lignin content, dry matter, cellulose, and hemicellulose loss, and an increase in crude protein content after 21 days. Total volatile fatty acid and ammonium nitrogen concentrations increased significantly (p < 0.01) during in vitro fermentation. Overall, the most enhanced nutritional values for corn straw and rice straw were observed after 14 days of SSF in the groups using molasses or glucose as a carbon source.

Biodelignification of lignocellulose using ligninolytic enzymes from white-rot fungi

Lignocellulose is the most abundant biomass available on earth, including wood and agricultural wastes such as rice straw, corn cobs, and oil palm empty bunches. The biopolymer content in lignocellulose has a great potential as feedstock for producing industrial raw materials such as glucose, sorbitol, xylose, xylitol, and other pharmaceutical excipients. Currently, scientists and governments agree that the enzymatic delignification method is an environmentally friendly green method to be applied. This review attempts to explain the proper preparation of the enzymes laccase, lignin peroxidase, and manganese peroxidase, as well as the important factors influencing their activity. The recent applications of the enzymes for detoxification of hazardous substances, proper enzyme immobilization technique, and future prospect combination with DESs extraction of lignin are also discussed.

Extraction of Vanillin Following Bioconversion of Rice Straw and Its Optimization by Response Surface Methodology

Value-added chemicals, including phenolic compounds, can be generated through lignocellulosic biomass conversion via either biological or chemical pretreatment. Currently vanillin is one of the most valuable of these products that has been shown to be extractable on an industrial scale. This study demonstrates the potential of using rice straw inoculated with Serpula lacrymans, which produced a mixture of high value bio-based compounds including vanillin. Key extraction conditions were identified to be the volume of solvent used and extraction time, which were optimized using response surface methodology (RSM). The vanillin compounds extracted from rice straw solid state fermentation (SSF) was confirmed through LC-ESI MS/MS in selective ion mode. The optimum concentration and yield differed depending on the solvent, which was predicted using 60 mL ethyl acetate for 160 min were 0.408% and 3.957 μg g⁻¹ respectively. In comparison, when ethanol was used, the highest concentration and yields of vanillin were 0.165% and 2.596 μg g⁻¹. These were achieved using 40 mL of solvent, and extraction time increased to 248 min. The results confirm that fungal conversion of rice straw to vanillin could consequently offer a cost-effect alternative to other modes of production.

Biological pretreatment of corn straw for enhancing degradation efficiency and biogas production

In order to explore the effect of pretreatment on corn straw degradation and biogas production, corn straw was pretreated with mixed microbes and composting at 30°C for 14 days. The characteristics of material were measured and analyzed in the pretreatment process. Then, the pretreated and untreated corn straw was digested by anaerobic fermentation. Gas production and methane content of corn straw were analyzed. The results showed that the biological pretreatment process with mixed microbes could accelerate the degradation rate of straw and increase the degradation efficiency of lignin. The pH value of material was more stable, and the content of organic matter in the material was higher in the pretreatment process of corn straw with mixed microbes. The Scanning Electron Microscope (SEM) images showed that the structure of the lignocellulose was changed by mixed microbes, increasing the exposed area of cellulose and hemicellulose, which was beneficial to improve the utilization efficiency of straw. The degradation rates of hemicellulose, cellulose and lignin were 44.4%, 34.9% and 39.2%, respectively, after the pretreatment process with mixed microbes. Pretreatment was more helpful to increase the methane content in the anaerobic fermentation process of corn straw pretreated with mixed microbes, and could also shorten the fermentation period.

Performance evaluation of a biotrickling filter for the removal of gas-phase 1,2-dichlorobenzene: Influence of rhamnolipid and ferric ions

The aim of this study was to evaluate the influence of rhamnolipid (RL) and ferric ions on the performance of a biotrickling filter (BTF) for the removal of gas-phase 1,2-dichlorobenzene (o-DCB). A comprehensive investigation of microbial growth, pollutant solubility, extracellular polymeric substances (EPS) and enzymatic activity in o-DCB degradation by an isolated strain Bacillus cereus DL-1 with/without RL and Fe³⁺ were carried out using batch microcosm experiments. In addition, o-DCB removal performance, biofilm morphology, and microbial community structures in two identical lab-scale biotrickling filters (named BTF1 and BTF2) inoculated with strain DL-1 were studied. The batch microcosm experiments demonstrated that 120 mg L^-1 RL and 4 mg L^-1 Fe³⁺ could enhance the biodegradation of o-DCB, which may be due to promotion on bacterial growth, o-DCB solubilization, C₁₂O enzyme activity, and polysaccharide (PS) and protein (PN) in EPS. Fourier transform infrared (FTIR) spectra indicated that the addition of RL with Fe³⁺ had notable effects on the functional groups of PS and PN in EPS. The experimental results in BTFs indicate that the removal efficiency of o-DCB decreased from 100% to 56.4% for BTF1, which was not fed with RL and Fe³⁺, and from 100% to 80.3% for BTF2, which was fed with RL and Fe³⁺, when the inlet loading rate increased from 4.88 to 102 g m^-3 h^-1 at an empty bed residence time of 60 s. In addition, the microbial adhesive strength and the microbial community structure were different among both BTFs, highlighting the positive effects of RL and Fe³⁺.

Effect of Rhamnolipids on Microbial Biomass Content and Biochemical Parameters in Soil Contaminated with Coal Tar Creosote

The objective of the present study was to compare the effect of rhamnolipids on the microbial biomass content and the activity of dehydrogenases (DHA), acid phosphatase (ACP), alkaline phosphatase (ALP), and urease (URE) in soil contaminated with two types of coal tar creosote: type C and type GX-Plus. The experiment was carried out on samples of sandy clay loam under laboratory conditions. Coal tar creosote was added to soil samples at a dose of 0 and 10 g·kg⁻¹ DM, along with rhamnolipids at a dose of 0, 10, 100, and 1000 mg·kg⁻¹ DM. The humidity of the samples was brought to 60% maximum water holding capacity, and the samples were incubated at 20°C. Microbial and biochemical parameters were determined on days 1, 7, 21, and 63. The obtained results demonstrated that the addition of rhamnolipids did not result in any significant changes in the activity of the determined parameters in the uncontaminated soil. However, it was observed that the application of these biosurfactants, particularly at the dose of 1000 mg·kg⁻¹ DM, largely decreased the effect of coal tar creosote on the determined parameters. Moreover, the microbial biomass and the activity of ALP and URE were found to be the best indicator of bioremediation of soil contaminated with coal tar creosote.

Evaluation of Screened Lignin-degrading Fungi for the Biological Pretreatment of Corn Stover

The biological pretreatment of lignocellulosic biomass is a low-cost and eco-friendly method for facilitating enzymatic hydrolysis. In this study, strains with lignin depletion capability were screened using a high-throughput screening method. Sixty-three strains were screened out and Myrothecium verrucaria secreted three lignin-degrading enzymes simultaneously during the bio-pretreatment process. The activity levels of laccase, lignin peroxidase and manganese peroxidase were 6.61, 0.78 and 1.31 U g⁻¹ dry biomass. The content of lignin in corn stover decreased by 42.30% after bio-pretreatment, and the conversion rate increased by 123.84% during the subsequent saccharification process in comparison with the untreated corn stover. Furthermore, the effects of bio-pretreatment on the structure of corn stover were presented using a scanning electron microscope (SEM), Brunauer-Emmet-Teller (BET), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). The results showed that M.V. is a promising lignin-degrading fungus. This research demonstrated an efficient pretreatment approach for enhancing the enzymatic saccharification of corn stover.

Effects of rhamnolipids on microorganism characteristics and applications in composting: A review

Biosurfactant rhmnolipids have been applied in many fields, especially in environmental bioremediation. According to previous researches, many research groups have studied the influence of rhamnolipids on microorganism characteristics and/or its application in composting. In this review, the effects of rhamnolipids on the cell surface properties of microorganisms was discussed firstly, such as cell surface hydrophobicity (CSH), electrical, surface compounds, etc. Moreover, the deeper mechanisms were also discussed, such as the effects of rhamnolipids on the structural characteristics and functional characteristics of the cell membrane, and the effects of rhamnolipids on the related enzymes and genes. Additionally, the application of rhamnolipids in composting was discussed, which is an important way for pollutant biodegradation and resource reutilization. It is believed that rhamnolipids will play more and more important role in composting.

Effects of Rhamnolipid and Microbial Inoculants on the Vermicomposting of Green Waste with Eisenia fetida

The effects of adding the biosurfactant rhamnolipid, the lignolytic and cellulolytic fungus Phanerochete chrysosporium, and the free-living nitrogen-fixing bacterium Azotobacter chrococcum on vermicomposting of green waste with Eisenia fetida was investigated. The addition of rhamnolipid and/or either microorganism alone or in all combinations significantly increased E. fetida growth rate, the number of E. fetida juveniles and cocoons, the population densities of cellulolytic fungi and Azotobacter bacteria, and cellulase and urease activities in the vermicomposts. The quality of the final vermicompost (in terms of electrical conductivity, nutrient content, C/N ratio, humic acid content, lignin and cellulose contents, and phytotoxicity to germinating seeds) was enhanced by addition of rhamnolipid and/or microorganisms. The physical characteristics of vermicomposts produced with rhamnolipid and/or microorganisms were acceptable for agricultural application. The best quality vermicompost was obtained with the combined addition of P. chrysosporium, A. chrococcum, and rhamnolipid.

Microbial utilization of lignin: available biotechnologies for its degradation and valorization

Lignocellulosic biomasses, either from non-edible plants or from agricultural residues, stock biomacromolecules that can be processed to produce both energy and bioproducts. Therefore, they become major candidates to replace petroleum as the main source of energy. However, to shift the fossil-based economy to a bio-based one, it is imperative to develop robust biotechnologies to efficiently convert lignocellulosic streams in power and platform chemicals. Although most of the biomass processing facilities use celluloses and hemicelluloses to produce bioethanol and paper, there is no consolidated bioprocess to produce valuable compounds out of lignin at industrial scale available currently. Usually, lignin is burned to provide heat or it remains as a by-product in different streams, thus arising environmental concerns. In this way, the biorefinery concept is not extended to completion. Due to Nature offers an arsenal of biotechnological tools through microorganisms to accomplish lignin valorization or degradation, an increasing number of projects dealing with these tasks have been described recently. In this review, outstanding reports over the last 6 years are described, comprising the microbial utilization of lignin to produce a variety of valuable compounds as well as to diminish its ecological impact. Furthermore, perspectives on these topics are given.

Malachite green bioremoval by a newly isolated strain Citrobacter sedlakii RI11; enhancement of the treatment by biosurfactant addition

Citrobacter sedlackii RI11, isolated from acclimated textile effluent after selective enrichment on synthetic dyes, was assessed for malachite green (MG) biotreatment potency. Results indicate that this bacterium has potential for use in effective treatment of MG contaminated wastewaters under shaking conditions at neutral and alkaline pH value, characteristic of typical textile effluents. Also, the newly isolated strain can tolerate higher doses of dye and decolorize up to 1,000 mg/l of dye. When used as microbial surfactant to enhance MG biodecolorization, Bacillus subtilis SPB1-derived lipopeptide accelerated the decolorization rate and maximized the decolorization efficiency at an optimal concentration of biosurfactant of about 0.075%. Studies ensured that MG removal by this strain could be due to biodegradation and/or adsorption. Results on germination potencies of different seeds using the treated dyes under different conditions favor the use of SPB1 biosurfactant for the treatment of MG.

Effect of the combined physical and chemical treatments with microbial fermentation on corn straw degradation

In order to improve corn straw degradation, steam explosion, sodium hydroxide soaking and Aspergillus oryzae fermentation were used. The optimal sodium hydroxide pretreatment condition for lignin degradation was obtained. The degradation rates of hemicellulose, cellulose and lignin were 54.68%, 17.76% and 33.14% for the exploded straw (P<0.05); 67.92%, 2.44% (P>0.05) and 76.54% for the alkali-treated straw (P<0.05); 75.98%, 39.93% and 77.88% for the exploded and alkali-treated straw (P<0.05), respectively. The following microbial fermentation could degrade hemicellulose and cellulose further (P<0.05). Cellulase, amylase and protease activities produced during microbial fermentation in the pretreated corn straw were lower than that in the untreated one (P<0.05); however, glucose content was increased by microbial fermentation (P<0.05). It can be concluded that the combined treatments of steam explosion, sodium hydroxide and microbial fermentation will be a good method for straw degradation.

Effects of phosphorus concentration on the growth and enzyme production of Phanerochaete chrysosporium

The effects of different phosphorus concentrations in culture media on the growth and enzyme production of Phanerochaete chrysosporium was investigated at a glucose concentration of 10 g L(-1). The results showed that the optimal KH(2)PO(4) concentration was 2.0 g L(-1). Optimal phosphorus content not only supported robust growth of P. chrysosporium, but also helped produce higher yields of manganese-dependent peroxidase (MnP) (324.9 U L(-1)). In addition, the results revealed that a relationship between the consumption of total phosphorus (TP) and fungal growth and enzyme production existed in P. chrysosporium cultures. Over a range of 0-0.5 g L(-1) KH(2)PO(4) concentration in the medium, the biomass and MnP activity increased in proportion to phosphorus concentration. When the KH(2)PO(4) concentration reached 0.5 g L(-1), it was generally found that the increase in biomass gradually slowed down, while MnP production decreased greatly with an increase in phosphorus concentration.

Effect of steam explosion and microbial fermentation on cellulose and lignin degradation of corn stover

In order to increase nutrient values of corn stover, effects of steam explosion (2.5 MPa, 200 s) and Aspergillus oryzae (A. oryzae) fermentation on cellulose and lignin degradation were studied. The results showed the contents of cellulose, hemicellulose and lignin in the exploded corn stover were 8.47%, 50.45% and 36.65% lower than that in the untreated one, respectively (P<0.05). The contents of cellulose and hemicellulose in the exploded and fermented corn stover (EFCS) were decreased by 24.36% and 69.90%, compared with the untreated one (P<0.05); decreased by 17.35% and 38.59%, compared with the exploded one (P<0.05). The scanning electron microscope observations demonstrated that the combined steam explosion and fermentation destructed corn stover. The activities of enzymes in EFCS were increased. The metabolic experiment showed that about 8% EFCS could be used to replace corn meal in broiler diets, which made EFCS become animal feedstuff possible.

Structural changes of lignocelluloses by a nonionic surfactant, Tween 20, and their effects on cellulase adsorption and saccharification

In this work, we found that Tween 20 treatment (0-8 mM) contributed to the cell wall collapse of most samples except for those with high lignin contents and high crystallinity. Cell wall collapse contributed to the formation of 10- to 50-nm pores and not only increased the monolayer saturation amount of adsorbed cellulase about 3-3.6 times but also increased the cellulase adsorption rate (D(e)/r(2)) about 160-880 times. Moreover, cellulose conversion at 72 h was also increased 8.7-21.5% by Tween 20 treatment. On the other hand, the adsorption of Tween 20 on Avicel (microcrystalline cellulose) hindered the cellulase reaction (adsorption and saccharification). The effect of Tween 20 treatment on the crystalline part was insignificant for both lignocelluloses and Avicel. It was found that some degree of pretreatment (e.g. lignin removal) that enhances Tween 20 diffusion into samples is necessary to obtain the structural effects of Tween 20.