Enhanced anaerobic digestion performance by two artificially constructed microbial consortia capable of woody biomass degradation and chlorophenols detoxification

Bioanode boosts efficacy of chlorobenzenes-powered microbial fuel cell: Performance, kinetics, and mechanism

Microbial fuel cell (MFC) is a promising device for water decontamination and energy generation. However, the correlation between power generation and pollutant degradation has not been clarified. Herein, a ruthenium-activated carbon (Ru-AC) bioanode was constructed for chlorobenzenes (CBs) treatment. The pollutant tolerance was improved by Ru-AC anode, and the minimum removal efficiencies of CB and ortho-dichlorobenzene (o-DCB) reached 75.1 % and 69.3 %, respectively, which were considerably higher than those of other MFCs (16.3 %-39.7 %). Correspondingly, the maximum output voltage reached 360.7 mV for the Ru-AC anode, whereas the values obtained from others reached 45.2-149.6 mV. Interaction models were introduced to quantify the relationship between power generation and pollutant degradation. The conversion of highly toxic chlorophenols to organic acids could be accelerated by boosting the mass and electron transfer, thereby simultaneously enhancing CBs removal and power generation. This work provided important insights into pollutant-powered MFC development.

Degradation of Triazole Fungicides by Plant Growth-Promoting Bacteria from Contaminated Agricultural Soil

The widespread application of triazole fungicides (TFs) in agricultural practices can result in the considerable accumulation of active compound residues in the soil and a subsequent negative impact on the soil microbiota and crop health. In this study, we isolated three TF-degrading bacterial strains from contaminated agricultural soils and identified them as Klebsiella sp., Pseudomonas sp., and Citrobacter sp. based on analysis of morphological characteristics and 16S rRNA gene sequences. The strains used three common TFs, namely hexaconazole, difenoconazole, and propiconazole, as their only sources of carbon and energy for growth in a liquid mineral salt medium, with high concentrations (~ 500 mg/l) of each TF. In addition to the ability to degrade fungicides, the isolates also exhibited plant growth-promoting characteristics, such as nitrogen fixation, indole acetic acid production, phosphate dissolution, and cellulose degradation. The synergistic combination of three bacterial isolates significantly improved plant growth and development with an increased survival rate (57%), and achieved TF degradation ranging from 85.83 to 96.59% at a concentration of approximately 50 mg/kg of each TF within 45 days in the soil-plant system. Based on these findings, the three strains and their microbial consortium show promise for application in biofertilizers, to improve soil health and facilitate optimal plant growth.

Bioproduction and optimization of newly characterized melanin pigment from Streptomyces djakartensis NSS-3 with its anticancer, antimicrobial, and radioprotective properties

BACKGROUND

Melanin is a natural pigment that is considered a promising biomaterial for numerous biotechnological applications across several industries. Melanin has biomedical applications as antimicrobial, anticancer, and antioxidant properties. Additionally, in the pharmaceutical and cosmetic industries, it is used in drug delivery and as a radioprotective agent. Also, melanin has environmental uses in the fields of bioremediation and the food industry. The biosynthesis of melanin pigment is an area of interest for researchers due to its multifunctionality, high compatibility, and biodegradability. Therefore, our present work is the first attempt to characterize and optimize the productivity of melanin pigment from Streptomyces djakartensis NSS-3 concerning its radioprotection and biological properties.

RESULTS

Forty isolates of soil actinobacteria were isolated from the Wadi Allaqui Biosphere Reserve, Egypt. Only one isolate, ACT3, produced a dark brown melanin pigment extracellularly. This isolate was identified according to phenotypic properties and molecular phylogenetic analysis as Streptomyces djakartensis NSS-3 with accession number OP912881. Plackett-Burman experimental design (PBD) and response surface methodology (RSM) using a Box-Behnken design (BBD) were performed for optimum medium and culturing conditions for maximum pigment production, resulting in a 4.19-fold improvement in melanin production (118.73 mg/10 mL). The extracted melanin pigment was purified and characterized as belonging to nitrogen-free pyomelanin based on ultraviolet-visible spectrophotometry (UV-VIS), Fourier transform infrared (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and NMR studies. Purified melanin demonstrated potent scavenging activity with IC50 values of 18.03 µg/mL and revealed high potency as sunscreens (in vitro SPF = 18.5). Moreover, it showed a nontoxic effect on a normal cell line (WI38), while it had a concentration-dependent anticancer effect on HCT116, HEPG, and MCF7 cell lines with IC50 = 108.9, 43.83, and 81.99 µg/mL, respectively. Also, purified melanin had a detrimental effect on the tested MDR bacterial strains, of which PA-09 and SA-04 were clearly more susceptible to melanin compared with other strains with MICs of 6.25 and 25 µg/mL, respectively.

CONCLUSION

Our results demonstrated that the newly characterized pyomelanin from Streptomyces djakartensis NSS-3 has valuable biological properties due to its potential photoprotective, antioxidant, anticancer, antimicrobial, and lack of cytotoxic activities, which open up new prospects for using this natural melanin pigment in various biotechnological applications and avoiding chemical-based drugs.

Core taxa, co-occurrence pattern, diversity, and metabolic pathways contributing to robust anaerobic biodegradation of chlorophenol

It is hard to achieve robustness in anaerobic biodegradation of trichlorophenol (TCP). We hypothesized that specific combinations of environmental factors determine phylogenetic diversity and play important roles in the decomposition and stability of TCP-biodegrading bacteria. The anaerobic bioreactor was operated at 35 °C (H condition) or 30 °C (L condition) and mainly fed with TCP (from 28 μM to 180 μM) and organic material. Metagenome sequencing was combined with 16S rRNA gene amplicon sequencing for the microbial community analysis. The results exhibited that the property of robustness occurred in specific conditions. The corresponding co-occurrence and diversity patterns suggest high collectivization, degree and evenness for robust communities. Two types of core functional taxa were recognized: dechlorinators (unclassified Anaerolineae, Thermanaerothrix and Desulfovibrio) and ring-opening members (unclassified Proteobacteria, Methanosarcina, Methanoperedens, and Rubrobacter). The deterministic process of the expansion of niche of syntrophic bacteria at higher temperatures was confirmed. The reductive and hydrolytic dechlorination mechanisms jointly lead to C-Cl bond cleavage. H ultimately adapted to the stress of high TCP loading, with more abundant ring-opening enzyme (EC 3.1.1.45, ∼55%) and hydrolytic dechlorinase (EC 3.8.1.5, 26.5%) genes than L (∼47%, 10.5%). The functional structure (based on KEGG) in H was highly stable despite the high loading of TCP (up to 60 μM), but not in L. Furthermore, an unknown taxon with multiple functions (dechlorinating and ring-opening) was found based on genetic sequencing; its functional contribution of EC 3.8.1.5 in H (26.5%) was higher than that in L (10.5%), and it possessed a new metabolic pathway for biodegradation of halogenated aromatic compounds. This new finding is supplementary to the robust mechanisms underlying organic chlorine biodegradation, which can be used to support the engineering, regulation, and design of synthetic microbiomes.

Biodegradation of willow sawdust by novel cellulase-producing bacterial consortium from wood-feeding termites for enhancing methane production

This study was designed to develop a cellulase-producing bacterial consortium (CBC) from wood-feeding termites that could effectively degrade willow sawdust (WSD) and consequently enhance methane production. The bacterial strains Shewanella sp. SSA-1557, Bacillus cereus SSA-1558, and Pseudomonas mosselii SSA-1568 exhibited significant cellulolytic activity. Their CBC consortium showed positive effects on cellulose bioconversion, resulting in accelerated WSD degradation. After nine days of pretreatment, the WSD had lost 63%, 50%, and 28% of its cellulose, hemicellulose, and lignin, respectively. The hydrolysis rate of treated WSD (352 mg/g) was much higher than that of untreated WSD (15.2 mg/g). The highest biogas production (66.1 NL/kg VS) with 66% methane was observed in the anaerobic digester M-2, which contained a combination of pretreated WSD and cattle dung in a 50/50 ratio. The findings will enrich knowledge for the development of cellulolytic bacterial consortia from termite guts for biological wood pretreatment in lignocellulosic anaerobic digestion biorefineries.

Taxonomic and enzymatic basis of the cellulolytic microbial consortium KKU-MC1 and its application in enhancing biomethane production

Lignocellulosic biomass is a promising substrate for biogas production. However, its recalcitrant structure limits conversion efficiency. This study aims to design a microbial consortium (MC) capable of producing the cellulolytic enzyme and exploring the taxonomic and genetic aspects of lignocellulose degradation. A diverse range of lignocellulolytic bacteria and degrading enzymes from various habitats were enriched for a known KKU-MC1. The KKU-MC1 was found to be abundant in Bacteroidetes (51%), Proteobacteria (29%), Firmicutes (10%), and other phyla (8% unknown, 0.4% unclassified, 0.6% archaea, and the remaining 1% other bacteria with low predominance). Carbohydrate-active enzyme (CAZyme) annotation revealed that the genera Bacteroides, Ruminiclostridium, Enterococcus, and Parabacteroides encoded a diverse set of cellulose and hemicellulose degradation enzymes. Furthermore, the gene families associated with lignin deconstruction were more abundant in the Pseudomonas genera. Subsequently, the effects of MC on methane production from various biomasses were studied in two ways: bioaugmentation and pre-hydrolysis. Methane yield (MY) of pre-hydrolysis cassava bagasse (CB), Napier grass (NG), and sugarcane bagasse (SB) with KKU-MC1 for 5 days improved by 38-56% compared to non-prehydrolysis substrates, while MY of prehydrolysed filter cake (FC) for 15 days improved by 56% compared to raw FC. The MY of CB, NG, and SB (at 4% initial volatile solid concentration (IVC)) with KKU-MC1 augmentation improved by 29-42% compared to the non-augmentation treatment. FC (1% IVC) had 17% higher MY than the non-augmentation treatment. These findings demonstrated that KKU-MC1 released the cellulolytic enzyme capable of decomposing various lignocellulosic biomasses, resulting in increased biogas production.

Enhancement of Biomass Conservation and Bioethanol Production of Sweet Sorghum Silage by Constructing Synergistic Microbial Consortia

The efficient storage of materials before bioethanol production could be key to improving pretreatment protocol and facilitating biodegradation, in turn improving the cost-effectiveness of biomass utilization. Biological inoculants were investigated for their effects on ensiling performance, biodegradability of silage materials, and final bioethanol yield from sweet sorghum. Two cellulolytic microbial consortia (CF and PY) were used to inoculate silages of sweet sorghum, with and without combined lactic acid bacteria (Xa), for up to 60 days of ensiling. We found that the consortia notably decreased pH and ammonia nitrogen content while increasing lactic acid/acetic acid ratios. The microbes also functioned in synergy with Xa, significantly reducing lignocellulose content and improving biomass preservation. First-order exponential decay models captured the kinetics of nonstructural carbohydrates and suggested high water-soluble carbohydrate (grams per kilogram dry matter [DM]) preservation potential in PY-Xa (33.48), followed by CF-Xa (30.51). Combined addition efficiently improved enzymatic hydrolysis and enhanced bioethanol yield, and sweet sorghum treated with PY-Xa had the highest ethanol yield (28.42 g L-1). Thus, combined bioaugmentation of synergistic microbes provides an effective method of improving biomass preservation and bioethanol production from sweet sorghum silages. IMPORTANCE Ensiling is an effective storage approach to ensure stable year-round supply for downstream biofuel production; it offers combined facilities of storage and pretreatment. There are challenges in ensiling sweet sorghum due to its coarse structure and high fiber content. This study provides a meaningful evaluation of the effects of adding microbial consortia, with and without lactic acid bacteria, on changes in key properties of sweet sorghum. This study highlighted the bioaugmented ensiling using cellulolytic synergistic microbes to outline a cost-effective strategy to store and pretreat sweet sorghum for bioethanol production.

Environmental and Human Health Impact of Disposable Face Masks During the COVID-19 Pandemic: Wood-Feeding Termites as a Model for Plastic Biodegradation

The ongoing COVID-19 pandemic has resulted in an unprecedented form of plastic pollution: personal protective equipment (PPE). On the eve of the COVID-19 pandemic, there is a tremendous increase in the production of plastic-based PPE. To control the spread of the virus, face masks (FMs) are used as primary PPE. Thus, the production and usage of FM significantly increased as the COVID-19 pandemic was still escalating. The primary raw materials for the manufacturing of FMs are non-biodegradable synthetic polymers derived from petrochemicals. This calls for an urgent need to develop novel strategies for the efficient degradation of plastics. Furthermore, most of these masks contain plastic or other derivatives of plastic. The extensive usage of FM generates millions of tons of plastic waste for the environment in a short span of time. However, their degradation in the environment and consequences are poorly understood. Therefore, the potential impacts of disposable FM on the environment and human health during the COVID-19 pandemic are clarified in the present study. Despite structural and recalcitrance variations, lignocellulose and plastic polymers have physicochemical features, including carbon skeletons with comparable chemical bonds as well as hydrophobic properties in amorphous and crystalline regions. In this review, we argue that there is much to be learned from termites by transferring knowledge from research on lignocellulose degradation by termites to that on plastic waste.

Mitigation of hazards and risks of emerging pollutants through innovative treatment techniques of post methanated distillery effluent - A review

Distillery wastewater has high biological and chemical oxygen demand and requires additional treatment before it can be safely discharged into receiving water. It is usually processed through a biomethanation digester and the end product is the post-methanated distillery effluent (PMDE). Research have shown that PMDE released by molasses-based distilleries is a hazardous effluent that can cause harm to the biota and the environment; it contains elevated amount of total dissolved solids (TDS), total suspended solids (TSS) and excess levels of persistent organic compounds (POPs), heavy metals, phenolic compounds, and salts. The practice of wastewater reuse for irrigation in many water scarce countries necessitates the proper treatment of PMDE before it is discharged into receiving water. Convention methods have been in practice for decades, but innovative technologies are needed to enhance the efficiency of PMDE treatment. Advance physical treatment such as membrane separation technology using graphene, ion-exchange and ultrafiltration membranes; chemical treatment such as advanced oxidation methods, electrocoagulation and photocatalytic technologies; biological treatment such as microbial and enzymatic treatment; and hybrid treatment such as microbial-fuel cell (MFC), genetically modified organisms (GMO) and constructed wetland technologies, are promising new methods to improve the quality of PMDE. This review provides insight into current accomplishments evaluates their suitability and discusses future developments in the detoxification of PMDE. The consolidated knowledge will help to develop a better management for the safe disposal and the reuse of PMDE wastewater.

Exploring the potential of a newly constructed manganese peroxidase-producing yeast consortium for tolerating lignin degradation inhibitors while simultaneously decolorizing and detoxifying textile azo dye wastewater

MnP-YC4, a newly constructed manganese peroxidase-producing yeast consortium, has been developed to withstand lignin degradation inhibitors while degrading and detoxifying azo dye. MnP-YC4 tolerance to major biomass-derived inhibitors was promising. MnP induced by lignin was found to be highly related to dye decolorization by MnP-YC4. Simulated azo dye-containing wastewater supplemented with a lignin co-substrate (3,5-Dimethoxy-4-hydroxybenzaldehyde) decolorized up to 100, 91, and 76% at final concentrations of 20, 40, and 60%, respectively. MnP-YC4 effectively decolorized the real textile wastewater sample, reaching up to 91.4%, and the COD value decreased significantly during the decolorization, reaching 7160 mg/l within 7 days. A possible dye biodegradation pathway was proposed based on the degradation products identified by UV-vis, FTIR, GC/MS, and HPLC techniques, beginning with azo bond cleavage and eventually mineralized to CO₂ and H₂O. When compared to the phytotoxic original dye, the phytotoxicity of MnP-YC4 treated dye-containing wastewater samples confirmed the nontoxic nature.

Could termites be hiding a goldmine of obscure yet promising yeasts for energy crisis solutions based on aromatic wastes? A critical state-of-the-art review

Biodiesel is a renewable fuel that can be produced from a range of organic and renewable feedstock including fresh or vegetable oils, animal fats, and oilseed plants. In recent years, the lignin-based aromatic wastes, such as various aromatic waste polymers from agriculture, or organic dye wastewater from textile industry, have attracted much attention in academia, which can be uniquely selected as a potential renewable feedstock for biodiesel product converted by yeast cell factory technology. This current investigation indicated that the highest percentage of lipid accumulation can be achieved as high as 47.25% by an oleaginous yeast strain, Meyerozyma caribbica SSA1654, isolated from a wood-feeding termite gut system, where its synthetic oil conversion ability can reach up to 0.08 (g/l/h) and the fatty acid composition in yeast cells represents over 95% of total fatty acids that are similar to that of vegetable oils. Clearly, the use of oleaginous yeasts, isolated from wood-feeding termites, for synthesizing lipids from aromatics is a clean, efficient, and competitive path to achieve "a sustainable development" towards biodiesel production. However, the lacking of potent oleaginous yeasts to transform lipids from various aromatics, and an unknown metabolic regulation mechanism presented in the natural oleaginous yeast cells are the fundamental challenge we have to face for a potential cell factory development. Under this scope, this review has proposed a novel concept and approach strategy in utilization of oleaginous yeasts as the cell factory to convert aromatic wastes to lipids as the substrate for biodiesel transformation. Therefore, screening robust oleaginous yeast strain(s) from wood-feeding termite gut system with a set of the desirable specific tolerance characteristics is essential. In addition, to reconstruct a desirable metabolic pathway/network to maximize the lipid transformation and accumulation rate from the aromatic wastes with the applications of various "omics" technologies or a synthetic biology approach, where the work agenda will also include to analyze the genome characteristics, to develop a new base mutation gene editing technology, as well as to clarify the influence of the insertion position of aromatic compounds and other biosynthetic pathways in the industrial chassis genome on the expressional level and genome stability. With these unique designs running with a set of the advanced biotech approaches, a novel metabolic pathway using robust oleaginous yeast developed as a cell factory concept can be potentially constructed, integrated and optimized, suggesting that the hypothesis we proposed in utilizing aromatic wastes as a feedstock towards biodiesel product is technically promising and potentially applicable in the near future.

Biosynthesis of Silver Nanoparticles by Marine Actinobacterium Nocardiopsis dassonvillei and Exploring Their Therapeutic Potentials

Nanoparticles have recently emerged as a popular research topic. Because of their potential applications in therapeutic applications, biosynthesized silver nanoparticles (Bio-AgNPs) have gained much attention in recent years. Cell-free extracts (CFE) from a marine culture of actinobacteria and silver nitrate were used to reduce Ag+ ions and create Bio-AgNPs. Nocardiopsis dasonvillei KY772427, a new silver-tolerant actinomycete strain, was isolated from marine water and used to synthesize AgNPs. In order to characterize Bio-AgNPs, UV-Vis spectral analysis, Fourier transform infrared (FTIR), transmission electron microscopy (TEM), and dynamic light scattering spectroscopy (DLS) were all utilized. Using UV-Vis spectroscopy, a peak in the surface plasmon resonance (SPR) spectrum at 430 nm revealed the presence of Bio-AgNPs. The TEM revealed spherical AgNPs with a diameter of 29.28 nm. DLS determined that Bio-AgNPs have a diameter of 56.1 nm and a negative surface charge (-1.46 mV). The minimum inhibitory concentration (MIC) of Bio-AgNPs was determined against microbial strains. Using resazurin-based microtiter dilution, the synergistic effect of Bio-AgNPs with antimicrobials was investigated. Pseudomonas aeruginosa had the lowest MIC of Bio-AgNPs (4 μg/ml). Surprisingly, the combination of antimicrobials and Bio-AgNPs had a significant synergistic effect on the tested strains. The insecticidal activity of Bio-AgNPs (200 μg/ml) against Macrosiphum rosae was found to be maximal after 36 h. Additionally, Bio-AgNPs demonstrated significant scavenging activity against 2,2'-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl (OH - ) radicals, with IC 50 values of 4.08 and 8.9 g/ml, respectively. In vitro studies using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay revealed a concentration-dependent decrease in cell viability when CaCo2 cells were exposed to Bio-AgNPs. With the decrease in cell viability, lactate dehydrogenase leakage (LDH) increased. The findings of this study open up a new avenue for the use of marine Nocardiopsis dasonvillei to produce Bio-AgNPs, which have significant antimicrobial, antioxidant, insecticidal, and anticancer potential.

Microbial Consortia Are Needed to Degrade Soil Pollutants

Soil pollution is one of the most serious environmental problems globally due to the weak self-purification ability, long degradation time, and high cost of cleaning soil pollution. The pollutants in the soil can be transported into the human body through water or dust, causing adverse effects on human health. The latest research has shown that the clean-up of soil pollutants through microbial consortium is a very promising method. This review provides an in-depth discussion on the efficient removal, bio-adsorption, or carbonated precipitation of organic and inorganic pollutants by the microbial consortium, including PAHs, BPS, BPF, crude oil, pyrene, DBP, DOP, TPHP, PHs, butane, DON, TC, Mn, and Cd. In view of the good degradation ability of the consortium compared to single strains, six different synergistic mechanisms and corresponding microorganisms are summarized. The microbial consortium obtains such activities through enhancing synergistic degradation, reducing the accumulation of intermediate products, generating the crude enzyme, and self-regulating, etc. Furthermore, the degradation efficiency of pollutants can be greatly improved by adding chemical materials such as the surfactants Tween 20, Tween 80, and SDS. This review provides insightful information regarding the application of microbial consortia for soil pollutant removal.

Bioaugmented degradation of rice straw combining two novel microbial consortia and lactic acid bacteria for enhancing the methane production

Two consortia of lignocellulolytic microbes (CL and YL) were isolated from the rumen of ruminants. Their ability to facilitate the degradation of rice straw and enhance methane (CH₄) production were evaluated, both individually and combined with lactic acid bacteria (LAB). After 30 days of degradation, rice straw powders (RSPs) were observed to change in physical structure and also displayed a significant reduction in lignocellulose content. Combined application of microbial consortia with LAB efficiently improved enzymatic hydrolysis of RSPs, increasing organic acid as well as mono- and disaccharide contents. Synergistic action between microbial consortia and LAB enhanced CH₄ yield, and rice straw treated with YL + LAB had the highest CH₄ production (357.53 mL CH₄/g VS), more than fivefold of the control. The newly identified microbial consortia are capable of efficiently degrading lignocellulosic biomass. Functioning synergistically with LAB, they provide a feasible way biodegrade rice straw and enhance methane production from agricultural wastes.

Wood-feeding termite gut symbionts as an obscure yet promising source of novel manganese peroxidase-producing oleaginous yeasts intended for azo dye decolorization and biodiesel production

BACKGROUND

The ability of oxidative enzyme-producing micro-organisms to efficiently valorize organic pollutants is critical in this context. Yeasts are promising enzyme producers with potential applications in waste management, while lipid accumulation offers significant bioenergy production opportunities. The aim of this study was to explore manganese peroxidase-producing oleaginous yeasts inhabiting the guts of wood-feeding termites for azo dye decolorization, tolerating lignocellulose degradation inhibitors, and biodiesel production.

RESULTS

Out of 38 yeast isolates screened from wood-feeding termite gut symbionts, nine isolates exhibited high levels of extracellular manganese peroxidase (MnP) activity ranged between 23 and 27 U/mL after 5 days of incubation in an optimal substrate. Of these MnP-producing yeasts, four strains had lipid accumulation greater than 20% (oleaginous nature), with Meyerozyma caribbica SSA1654 having the highest lipid content (47.25%, w/w). In terms of tolerance to lignocellulose degradation inhibitors, the four MnP-producing oleaginous yeast strains could grow in the presence of furfural, 5-hydroxymethyl furfural, acetic acid, vanillin, and formic acid in the tested range. M. caribbica SSA1654 showed the highest tolerance to furfural (1.0 g/L), 5-hydroxymethyl furfural (2.5 g/L) and vanillin (2.0 g/L). Furthermore, M. caribbica SSA1654 could grow in the presence of 2.5 g/L acetic acid but grew moderately. Furfural and formic acid had a significant inhibitory effect on lipid accumulation by M. caribbica SSA1654, compared to the other lignocellulose degradation inhibitors tested. On the other hand, a new MnP-producing oleaginous yeast consortium designated as NYC-1 was constructed. This consortium demonstrated effective decolorization of all individual azo dyes tested within 24 h, up to a dye concentration of 250 mg/L. The NYC-1 consortium's decolorization performance against Acid Orange 7 (AO7) was investigated under the influence of several parameters, such as temperature, pH, salt concentration, and co-substrates (e.g., carbon, nitrogen, or agricultural wastes). The main physicochemical properties of biodiesel produced by AO7-degraded NYC-1 consortium were estimated and the results were compared to those obtained from international standards.

CONCLUSION

The findings of this study open up a new avenue for using peroxidase-producing oleaginous yeasts inhabiting wood-feeding termite gut symbionts, which hold great promise for the remediation of recalcitrant azo dye wastewater and lignocellulosic biomass for biofuel production.

Two novel screened microbial consortia and their application in combination with Lactobacillus plantarum for improving fermentation quality of high-moisture alfalfa

AIMS

To enrich lignocellulolytic microbial consortia and evaluate whether a combination of these consortia and Lactobacillus plantarum can facilitate degradation of structural carbohydrates and improve fermentation quality of high-moisture alfalfa silage.

METHODS AND RESULTS

Two novel microbial consortia (CL and YL) with high lignocellulolytic potential were enriched, and had higher enzyme activities at slightly acidic conditions (pH 3.5-6.5). Two consortia were inoculated with and without combined L. plantarum (LP) to alfalfa for up to 120 days of ensiling. The two consortia alone or combined with LP significantly (p < 0.05) increased lactic-to-acetic acid ratios and decreased contents of volatile organic acids and NH₃ -N as compared to the control. Treatments that combining microbial consortia and LP further resulted in the higher contents of lactic acid (LA), water soluble carbohydrates (WSC) and crude protein, dry matter (DM) recovery, and lower neutral detergent fibre, acid detergent lignin and cellulose contents, with YLP silage showing the lowest pH (4.41) and highest LA content (76.72 g kg^-1  DM) and the conversion of WSC into LA (184.03%).

CONCLUSIONS

The addition of lignocellulolytic microbial consortia (CL or YL) to alfalfa silages as attractive silage inoculants could improve fermentation quality, and that their combination with L. plantarum appeared more effective on the degradation of structural carbohydrates and conversion of soluble carbohydrates into LA.

SIGNIFICANCE AND IMPACT OF THE STUDY

High-moisture alfalfa is difficult to ensile due to its high buffering capacity and low readily fermentable carbohydrate contents. Microbial consortia (CL and YL) can encode a broad selection of multi-functional CAZymes, and their combination with LP could be promising for the degradation of structural carbohydrates simultaneously with improvement fermentation quality, with high performance in LA production.

Characterization and identification of a novel microbial consortium M2 and its effect on fermentation quality and enzymatic hydrolysis of sterile rice straw

AIMS

To isolate and enrich lignocellulolytic microbial consortia from yak (Bos grunniens) rumen and evaluate their effects on the fermentation characteristics and enzymatic hydrolysis in rice straw silage.

METHODS AND RESULTS

A novel microbial consortium M2 with high CMCase and xylanase activities was enriched and observed to be prone to use natural carbon sources. Its predominant genus was Enterococcus, and most carbohydrate-active enzyme (CAZyme) genes belonged to the glycosyl hydrolases class. The consortium M2 was introduced with or without combined lactic acid bacteria (XA) to rice straw silage for 60 days. Inoculating the consortium M2 notably decreased the structural carbohydrate contents and pH of rice straw silages. Treatment that combines consortium M2 and XA resulted in the highest levels of lactic acid and lignocellulose degradation. The consortium M2 alone or combined with XA significantly (p < 0.01) increased water-soluble carbohydrates (WSCs), mono- and disaccharides contents compared with the XA silage. Combined addition obviously improved the enzymatic conversion efficiency of rice straw silage with higher glucose and xylose yields (23.39 and 12.91 w/w% DM, respectively).

CONCLUSIONS

Ensiling pretreatment with the microbial consortium M2 in sterile rice straw improved fermentation characteristics. The combined application of consortium M2 with XA had synergistic effects on promoting the degradation of structural carbohydrates and enzymatic hydrolysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Rice straw is difficult to ensile because of its low WSC and high structural carbohydrate contents. The microbial consortium M2 identified herein exhibits great potential for degrading fibrous substrates, and their combination with XA provides a faster and more effective synergistic strategy for biorefinery of lignocellulosic biomass.

Wood‑feeding termites as an obscure yet promising source of bacteria for biodegradation and detoxification of creosote-treated wood along with methane production enhancement

This study aims to explore distinct bacterial strains from wood-feeding termites and to construct novel bacterial consortium for improving the methane yield during anaerobic digestion by degrading birchwood sawdust (BSD) and removing creosote (CRO) compounds simultaneously. A novel bacterial consortium CTB-4 which stands for the molecularly identified species Burkholderia sp., Xanthomonas sp., Shewanella sp., and Pseudomonas mosselii was successfully developed. The CTB-4 consortium showed high efficiency in the removal of naphthalene and phenol. It also revealed reduction in lignin, hemicellulose, and cellulose by 19.4, 52.5, and 76.8%, respectively. The main metabolites after the CRO degradation were acetic acid, succinate, pyruvate, and acetaldehyde. Pretreatment of treated BSD mixed with CRO enhanced the total methane yield (162 L/kg VS) by 82.7% and biomass reduction by 54.7% compared to the untreated substrate. CRO showed a toxicity decrease of >90%, suggesting the efficiency of constructed bacterial consortia in bioremediation and biofuel production.

Construction of a novel microbial consortium valued for the effective degradation and detoxification of creosote-treated sawdust along with enhanced methane production

Lignocellulosic biomass represents an unlimited and ubiquitous energy source, which can effectively address current global challenges, including climate change, greenhouse gas emissions, and increased energy demand. However, lignocellulose recalcitrance hinders microbial degradation, especially in case of contaminated materials such as creosote (CRO)-treated wood, which necessitates appropriate processing in order to eliminate pollution. This study might be the first to explore a novel bacterial consortium SST-4, for decomposing birchwood sawdust, capable of concurrently degrading lignocellulose and CRO compounds. Afterwards, SST-4 which stands for molecularly identified bacterial strains Acinetobacter calcoaceticus BSW-11, Shewanella putrefaciens BSW-18, Bacillus cereus BSW-23, and Novosphingobium taihuense BSW-25 was evaluated in terms of biological sawdust pre-treatment, resulting in effective lignocellulose degradation and 100% removal of phenol and naphthalene. Subsequently, the maximum biogas production observed was 18.7 L/kg VS, while cumulative methane production was 162.8 L/kg VS, compared to 88.5 without microbial pre-treatment. The cumulative energy production from AD-I and AD-II through biomethanation was calculated as 3177.1 and 5843.6 KJ/kg, respectively. The pretreatment process exhibited a significant increase in the energy yield by 83.9%. Lastly, effective CRO detoxification was achieved with EC₅₀ values exceeding 90%, showing the potential for an integrated process of effective contaminated wood management and bioenergy production.

Plastic wastes biodegradation: Mechanisms, challenges and future prospects

The growing accumulation of plastic wastes is one of the main environmental challenges currently faced by modern societies. These wastes are considered a serious global problem because of their effects on all forms of life. There is thus an urgent need to demonstrate effective eco-environmental techniques to overcome the hazardous environmental impacts of traditional disposal paths. However, our current knowledge on the prevailing mechanisms and the efficacy of synthetic plastics' biodegradation still appears limited. Under this scope, our review aims to comprehensively highlight the role of microbes, with special emphasis on algae, on the entire plastic biodegradation process focusing on the depolarization of various synthetic plastic types. Moreover, our review emphasizes on the ability of insects' gut microbial consortium to degrade synthetic plastic wastes. In this view, we discuss the schematic pathway of the biodegradation process of six types of synthetic plastics. These findings may contribute to establishing bio-upcycling processes of plastic wastes towards biosynthesis of valuable metabolic products. Finally, we discuss the challenges and opportunities for microbial valorization of degraded plastic wastes.

Degradation of conventional plastic wastes in the environment: A review on current status of knowledge and future perspectives of disposal

Accumulation of plastic wastes has been recently recognized as one of the most critical environmental challenges, affecting all life forms, natural ecosystems and economy, worldwide. Under this threat, finding alternative environmentally-friendly solutions, such as biodegradation instead of traditional disposal, is of utmost importance. However, up to date, there is limited knowledge on plastic biodegradation mechanisms and efficiency. From this point of view, the purpose of this review is to highlight the negative effects of the accumulation of the most conventional plastic waste (polyethylene, polypropylene, polystyrene, polyvinylchloride, polyethylene terephthalate and polyurethane) on the environment and to present their degradability potential through abiotic and biotic processes. Furthermore, the ability of different microbial species for degradation of these polymers is thoroughly discussed. The present review also addresses the contribution of invertebrates, such as insects, in plastic degradation process, highlighting the vital role that they could play in the future. In total, a schematic pathway of an innovative approach to improve the disposal of plastic wastes is proposed, with view to establishing an effective and sustainable practice for plastic waste management.

Biodegradation of creosote-treated wood by two novel constructed microbial consortia for the enhancement of methane production

Lignocellulose biodegradation is limited because of its recalcitrant structure particularly when polluted by toxic and carcinogenic compounds such as creosote oil (CRO). As far as we know, this might be the first report that explores the biodegradation of creosote treated wood (CTW) to serve biomethane production. Two novel CTW-degrading microbial consortia, designated as CTW-1 and CTW-2, were screened and constructed to enhance methane production from CRO-treated pine sawdust. After 12 days of biological pretreatment by CTW-1 and CTW-2, a significant reduction in lignocellulosic content of CTW was recorded; estimated as 49 and 43%, respectively. More than 64 and 91% of cumulative biogas and methane yields were obtained from biodegraded CTW over control. Ecotoxicity of treated and untreated CTW was compared by Microtox test. The biodegraded CTW hydrolysates showed a toxicity decrease of more than 80%, suggesting the promising role of constructed microbial consortia for biofuel production and bioremediation.

Valorizing lignin-like dyes and textile dyeing wastewater by a newly constructed lipid-producing and lignin modifying oleaginous yeast consortium valued for biodiesel and bioremediation

Construction of a multipurpose yeast consortium suitable for lipid production, textile dye/effluent removal and lignin valorization is critical for both biorefinery and bioremediation. Therefore, a novel oleaginous consortium, designated as OYC-Y.BC.SH has been developed using three yeast cultures viz. Yarrowia sp. SSA1642, Barnettozyma californica SSA1518 and Sterigmatomyces halophilus SSA1511. The OYC-Y.BC.SH was able to grow on different carbon sources and accumulate lipids, with its highest lipid productivity (1.56 g/L/day) and lipase activity (170.3 U/mL) exhibited in xylose. The total saturated fatty acid content was 36.09 %, while the mono-unsaturated and poly-unsaturated fatty acids were 45.44 and 18.30 %, respectively, making OYC-Y.BC.SH valuable for biodiesel production. The OYC-Y.BC.SH showed its highest decolorization efficiency of Red HE3B dye (above 82 %) in presence of sorghum husk as agricultural co-substrate, suggesting its feasibility for simultaneous lignin valorization. The significant higher performance of OYC-Y.BC.SH on decolorizing the real dyeing effluent sample at pH 8.0 suggests its potential and suitability for degrading most of the wastewater textile effluents. Clearly, toxicological studies underline the additional advantage of using OYC-Y.BC.SH for bioremediation of industrial dyeing effluents in terms of decolorization and detoxification. A possible mechanism of Red HE3B biodegradation and ATP synthesis was also proposed.

Construction of a new lipase- and xylanase-producing oleaginous yeast consortium capable of reactive azo dye degradation and detoxification

A new oleaginous yeast consortium Y-BC-SH which stands for molecularly identified species Yarrowia sp., Barnettozyma californica and Sterigmatomyces halophilus was successfully constructed in this study. This multipurpose oleaginous yeast consortium was developed based on its higher ability to accumulate large amounts of lipids in the form of triacylglycerol, grow on xylose, produce lipase and xylanase and it could rapidly decolorize and degrade commonly-used textile reactive azo dyes. The specific enzyme activities of lipase, xylanase, xylan esterase, β-xylosidase, CMCase, β-glucosidase and cellobiohydrolase produced by Y-BC-SH were significantly higher than that of individual strains. As chemical oxygen demand reduction had occurred in the dye mixture solutions, it was evidence of their color removal and mineralization by Y-BC-SH. The significant induction of oxidoreductive enzymes by Y-BC-SH was probably due to the coordinated metabolic interactions of the individual strains. Phytotoxicity assay confirmed that metabolites generated after dye degradation by Y-BC-SH are non-toxic.

The Effects of Halogenated Compounds on the Anaerobic Digestion of Macroalgae

The urgent need to replace fossil fuels has seen macroalgae advancing as a potential feedstock for anaerobic digestion. The natural methane productivity (dry weight per hectare) of seaweeds is greater than in many terrestrial plant systems. As part of their defence systems, seaweeds, unlike terrestrial plants, produce a range of halogenated secondary metabolites, especially chlorinated and brominated compounds. Some orders of brown seaweeds also accumulate iodine, up to 1.2% of their dry weight. Fluorine remains rather unusual within the chemical structure. Halogenated hydrocarbons have moderate to high toxicities. In addition, halogenated organic compounds constitute a large group of environmental chemicals due to their extensive use in industry and agriculture. In recent years, concerns over the environmental fate and release of these halogenated organic compounds have resulted in research into their biodegradation and the evidence emerging shows that many of these compounds are more easily degraded under strictly anaerobic conditions compared to aerobic biodegradation. Biosorption via seaweed has become an alternative to the existing technologies in removing these pollutants. Halogenated compounds are known inhibitors of methane production from ruminants and humanmade anaerobic digesters. The focus of this paper is reviewing the available information on the effects of halogenated organic compounds on anaerobic digestion.

Ecofriendly biodegradation of Reactive Black 5 by newly isolated Sterigmatomyces halophilus SSA1575, valued for textile azo dye wastewater processing and detoxification

A total of seven yeast strains from 18 xylanolytic and/or xylose-fermenting yeast species isolated from the wood-feeding termite Reticulitermes chinenesis could efficiently decolorize various azo dyes under high-salt conditions. Of these strains, a novel and unique azo-degrading and halotolerant yeast, Sterigmatomyces halophilus SSA1575, has been investigated in this study. This strain could significantly decolorize four combinations of a mixture of dyes. It showed a high capability for decolorizing Reactive Black 5 (RB5) even at 1,500 mg L⁻¹. The strain SSA1575 still showed a high capability for decolorizing a 50 mg L⁻¹ RB5 with a salt mixing at a NaCl concentration of up to 80 g L⁻¹. It also exhibited significant ability to decolorize repeated additions of dye aliquots, with a reduction in time of up to 18 h. Most of the tested carbon and nitrogen sources could significantly enhance a RB5 decolorization. However, this process was inhibited by the addition of sucrose and sodium nitrate. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase were determined as the key reductase and oxidase of S. halophilus SSA1575. Finally, strain SSA1575, can effectively detoxify RB5 into non-toxic products. Overall, S. halophilus SSA1575, might be a promising halotolerant yeast valued for the treatment of various textile effluents with high salinity.

Aerobic biodegradation of p-nitrophenol in a nitrifying sludge bioreactor: System performance, sludge property and microbial community shift

The system performance, sludge property and microbial community shift were evaluated in a nitrifying sludge (NS) bioreactor for simultaneous treating p-Nitrophenol (PNP) and high ammonia wastewater. After long-term acclimation for 80 days, the removal efficiencies of PNP and NH₄⁺-N reached to 99.9% and 99.5%, respectively. Meanwhile, the effluent PNP gradually decreased from 7.9 to 0.1 mg/L by acclimation of sludge. The particle size of NS increased from 115.2 μm to 226.3 μm accompanied by the decreased zeta potential as a self-protection strategy. The presence of PNP exposure altered the effluent soluble microbial products (SMP) fluorescent components and molecular composition. The increase in the relative abundance of Thauera, Nitrospiraceae and Nitrosomonas indicated the nitrification and denitrification capacities of NS increased, which maybe the PNP cometabolic biodegradation effect. Moreover, Ignavibacteria and Aeromonas were responsible as the dominant bacteria for degrading PNP in the nitrifying system.

Performance of a Newly Isolated Salt-Tolerant Yeast Strain Sterigmatomyces halophilus SSA-1575 for Azo Dye Decolorization and Detoxification

The effective degradation of hazardous contaminants remains an intractable challenge in wastewater processing, especially for the high concentration of salty azo dye wastewater. However, some unique yeast symbionts identified from the termite gut system present an impressive function to deconstruct some aromatic compounds, which imply that they may be valued to work on the dye degradation for various textile effluents. In this investigation, a newly isolated and unique yeast strain, Sterigmatomyces halophilus SSA-1575, was identified from the gut system of a wood-feeding termite (WFT), Reticulitermes chinensis. Under the optimized ambient conditions, the yeast strain SSA-1575 showed a complete decolorization efficiency on Reactive Black 5 (RB5) within 24 h, where this azo dye solution had a concentration of a 50 mg/L RB5. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase (LiP) were determined as the key reductase and oxidase of S. halophilus SSA-1575. Enhanced decolorization was recorded when the medium was supplemented with carbon and energy sources, including glucose, ammonium sulfate, and yeast extract. To understand a possible degradation pathway well, UV-Vis spectroscopy, FTIR and Mass Spectrometry analyses were employed to analyze the possible decolorization pathway by SSA-1575. Determination of relatively high NADH-DCIP reductase suggested that the asymmetric cleavage of RB5 azo bond was mainly catalyzed by NADH-DCIP reductase, and finally resulting in the formation of colorless aromatic amines devoid of any chromophores. The ecotoxicology assessment of RB5 after a decolorization processing by SSA-1575, was finally conducted to evaluate the safety of its metabolic intermediates from RB5. The results of Microtox assay indicate a capability of S. halophilus SSA-1575, in the detoxification of the toxic RB5 pollutant. This study revealed the effectiveness of halotolerant yeasts in the eco-friendly remediation of hazardous pollutants and dye wastewater processing for the textile industry.