Corrigendum: Acidic Versus Alkaline Bacterial Degradation of Lignin Through Engineered Strain E. coli BL21(Lacc): Exploring the Differences in Chemical Structure, Morphology, and Degradation Products

[This corrects the article DOI: 10.3389/fbioe.2020.00671.].

Acidic Versus Alkaline Bacterial Degradation of Lignin Through Engineered Strain E. coli BL21(Lacc): Exploring the Differences in Chemical Structure, Morphology, and Degradation Products

There is increasing interest in research on lignin biodegradation compounds as potential building blocks in applications related to renewable products. More attention is necessary to evaluate the effects of the initial pH conditions during the bacterial degradation of lignin. In this study we performed experiments on lignin biodegradation under acidic and mild alkaline conditions. For acidic biodegradation, lignin was chemically pretreated with hydrogen peroxide. Alkaline biodegradation was achieved by developing the bacterial growth on Luria and Bertani medium with alkali lignin as the sole carbon source. The mutant strain Escherichia coli BL21(Lacc) was used to carry out lignin biodegradation over 10 days of incubation. Results demonstrated that under acidic conditions there was a predominance of aliphatic compounds of the C₃–C₄ type. Alkaline biodegradation was produced in the context of oxidative stress, with a greater abundance of aryl compounds. The final pH values of acidic and alkaline biodegradation of lignin were 2.53 and 7.90, respectively. The results of the gas chromatography mass spectrometry analysis detected compounds such as crotonic acid, lactic acid and 3-hydroxybutanoic acid for acidic conditions, with potential applications for adhesives and polymer precursors. Under alkaline conditions, detected compounds included 2-phenylethanol and dehydroabietic acid, with potential applications for perfumery and anti tumor/anti-inflammatory medications. Size-exclusion chromatography analysis showed that the weight-average molecular weight of the alkaline biodegraded lignin increased by 6.75-fold compared to the acidic method, resulting in a repolymerization of its molecular structure. Lignin repolymerization coincided with an increase in the relative abundance of dehydroabietic acid and isovanillyl alcohol, from 2.70 and 3.96% on day zero to 13.43 and 10.26% on 10th day. The results of the Fourier-transformed Infrared spectroscopy detected the presence of C = O bond and OH functional group associated with carboxylic acids in the acidic method. In the alkaline method there was a greater preponderance of signals related to skeletal aromatic structures, the amine functional group and the C – O – bond. Lignin biodegradation products from E. coli BL21(Lacc), under different initial pH conditions, demonstrated a promising potential to enlarge the spectrum of renewable products for biorefinery activities.

Recent Development of Extremophilic Bacteria and Their Application in Biorefinery

The biorefining technology for biofuels and chemicals from lignocellulosic biomass has made great progress in the world. However, mobilization of laboratory research toward industrial setup needs to meet a series of criteria, including the selection of appropriate pretreatment technology, breakthrough in enzyme screening, pathway optimization, and production technology, etc. Extremophiles play an important role in biorefinery by providing novel metabolic pathways and catalytically stable/robust enzymes that are able to act as biocatalysts under harsh industrial conditions on their own. This review summarizes the potential application of thermophilic, psychrophilic alkaliphilic, acidophilic, and halophilic bacteria and extremozymes in the pretreatment, saccharification, fermentation, and lignin valorization process. Besides, the latest studies on the engineering bacteria of extremophiles using metabolic engineering and synthetic biology technologies for high-efficiency biofuel production are also introduced. Furthermore, this review explores the comprehensive application potential of extremophiles and extremozymes in biorefinery, which is partly due to their specificity and efficiency, and points out the necessity of accelerating the commercialization of extremozymes.

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.

Cellulose Nanofibrils Filled Poly(Lactic Acid) Biocomposite Filament for FDM 3D Printing

As direct digital manufacturing, 3D printing (3DP) technology provides new development directions and opportunities for the high-value utilization of a wide range of biological materials. Cellulose nanofibrils (CNF) and polylactic acid (PLA) biocomposite filaments for fused deposition modeling (FDM) 3DP were developed in this study. Firstly, CNF was isolated by enzymatic hydrolysis combined with high-pressure homogenization. CNF/PLA filaments were then prepared by melt-extrusion of PLA as the matrix and CNF as the filler. Thermal stability, mechanical performance, and water absorption property of biocomposite filaments and 3D-printed objects were analyzed. Findings showed that CNF increased the thermal stability of the PLA/PEG600/CNF composite. Compared to unfilled PLA FDM filaments, the CNF filled PLA biocomposite filament showed an increase of 33% in tensile strength and 19% in elongation at break, suggesting better compatibility for desktop FDM 3DP. This study provided a new potential for the high-value utilization of CNF in 3DP in consumer product applications.

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

Catalpa sawdust (CSW) is a promising biomass-based biofuel. However, the complex lignocellulosic structure limits its efficient utilization in biorefinery applications. It is even more so when chlorophenols (CPs), highly toxic organic substances widely used as wood preservatives, are present. Hence, it is crucial to develop effective and eco-friendly approaches to attain deconstruction of lignocellulose and chlorophenols simultaneously as well as to improve methane (CH4) production efficiently. This study might be the first to explore the performance of the novel constructed microbial consortia CS-5 and BC-4 on woody biomass degradation and CPs detoxification simultaneously with CH4 production. After the degradation of CSW and CPs for 15 days by C5-5 or BC-4, significant reduction in lignocellulosic components and CPs mixture was realized with a total weight loss of 69.2 and 56.3 % and CPs degradation of 89 and 95 %, respectively. The toxicity of individual or mixed CPs after 15 days of degradation was reduced by approximately 90 %. The synergistic action of CS-5 and BC-4 enhanced biogas and CH4 yields over 76 and 64 % respectively, higher than control. Furthermore, CH4 production increased by 113.7 % at the peak phase of AD process. Methanosataceae represented 45.1 % of the methanogenic Archaea in digester G-III.

Construction of novel microbial consortia CS-5 and BC-4 valued for the degradation of catalpa sawdust and chlorophenols simultaneously with enhancing methane production

This study might be the first to explore the novel constructed microbial consortia CS-5 and BC-4 for enhancing methane (CH₄) production during anaerobic digestion (AD) with simultaneous degradation of catalpa sawdust and chlorophenols (CPs). Significant reduction in cellulose, hemicellulose and lignin contents was achieved after the biodegradation of catalpa sawdust for 15 days by CS-5 and BC-4, with a total weight loss of 69.2 and 56.3%, respectively. The synergistic microbial consortia enhanced cumulative biogas and CH₄ yields by 76.3 and 64.3%, respectively higher than the corresponding control at the end of AD. More than 90% of CH₄ was produced within 18 days of AD as a result of microbial pretreatment of catalpa sawdust. These consortia resulted in remarkably higher energy conversion efficiency of 44.3% (218.1 L_N CH₄/kg TS) over the control. CS-5 and BC-4 removed more than 69 and 77% of the total amount of CPs tested after 15 days.

Molecular characterization of virulence and drug resistance genes-producing Escherichia coli isolated from chicken meat: Metal oxide nanoparticles as novel antibacterial agents

Escherichia coli is a major global foodborne pathogen, infecting a wide range of animals and contaminating their meat products. E. coli, can lead to high morbidity and mortality with a huge economic loss especially if foodborne diseases are associated with multidrug resistant (MDR)- and multivirulent-producing pathogens. Due to the increased resistance to common antimicrobials used to treat livestock animals and human infections, the discovery of new and innovative nanomaterials are in high demand. Recently, metal oxides can be considered as effective inorganic agents with antimicrobial features. Hence, this study might be the first to evaluate the efficiency of metal oxide nanoparticles (MO-NPs) as novel antibacterial agents against MDR/multivirulent E. coli pathogens isolated from chicken meat. The occurrence of pathogenic E. coli was determined in fresh warm chicken meat parts (breast, thigh, liver and gizzard). Ninety-one of 132 (69%) chicken meat parts were Escherichia -positive with E. coli as the only species isolated. Out of identified 240 E. coli strains, 72.5% (174/240) were classified as MDR E. coli strains. Fifty-five profile patterns were obtained. From each pattern, one strain was randomly selected for further analysis of virulence and resistance genes. Extracted DNA was assessed for the presence of antibiotic resistance genes (bla_IMP-7, bla_IMP-25, bla_TEM, bla_SHV, bla_OXA-2, tetA, aadA, and aac(3)-IV) and virulence genes (stx1, stx2, hlyA, eaeA, aggR, eltB, estIb, papA, afa and hlyD). Clustering analyses revealed that 10 E. coli harboring the highest number of virulence and resistance genes were shifted together into one cluster designated as cluster X. The average activities of zinc peroxide nanoparticles (ZnO₂-NPs) were higher than that of zinc oxide nanoparticles (ZnO-NPs) and titanium dioxide nanoparticles (TiO₂-NPs) by 20% and 29%, respectively. The anti-inflammatory activity of ZnO₂-NPs in comparison with aspirin was assessed using membrane stabilization, albumin denaturation, and proteinase inhibition methods. Significant anti-inflammatory activity of ZnO₂-NPs was achieved at concentration levels of 500-1000 μg/ml. It seems that MO-NPs are effective alternative agents, since they exhibited a competitive antibacterial capability against MDR/multivirulent-producing E. coli pathogens isolated from chicken meat. Hence, ZnO₂-NPs are a promising nanoparticles-based material for controlling foodborne pathogens, thereby valued for food safety applications.

Impairment of the Glymphatic Pathway and Putative Meningeal Lymphatic Vessels in the Aging Human

OBJECTIVE

Aging is a major risk factor for numerous neurological disorders, and the mechanisms underlying brain aging remain elusive. Recent animal studies demonstrated a tight relationship between impairment of the glymphatic pathway, meningeal lymphatic vessels, and aging. However, the relationship in the human brain remains uncertain.

METHODS

In this observational cohort study, patients underwent magnetic resonance imaging before and at multiple time points after intrathecal administration of a contrast agent. Head T1-weighted imaging was performed to assess the function of the glymphatic pathway and head high-resolution T2-fluid attenuated inversion recovery imaging to visualize putative meningeal lymphatic vessels (pMLVs). We measured the signal unit ratio (SUR) of 6 locations in the glymphatic pathway and pMLVs, defined the percentage change in SUR from baseline to 39 hours as the clearance of the glymphatic pathway and pMLVs, and then analyzed their relationships with aging.

RESULTS

In all patients (N = 35), the SUR of the glymphatic pathway and pMLVs changed significantly after intrathecal injection of the contrast agent. The clearance of both the glymphatic pathway and pMLVs was related to aging (all p < 0.05). The clearance of pMLVs was significantly related to the clearance of the glymphatic pathway (all p < 0.05), and the clearance of the glymphatic pathway was significantly faster in patients with early filling of pMLVs than those with late filling (all p < 0.05).

INTERPRETATION

We revealed that both the glymphatic pathway and pMLVs might be impaired in the aging human brain through the novel, clinically available method to simultaneously visualize their clearance. Our findings also support that in humans, pMLVs are the downstream of the glymphatic pathway. Ann Neurol 2020;87:357-369.

Understanding the association between psychomotor processing speed and white matter hyperintensity: A comprehensive multi-modality MR imaging study

Cognitive processing speed is crucial for human cognition and declines with aging. White matter hyperintensity (WMH), a common sign of WM vascular damage in the elderly, is closely related to slower psychomotor processing speed. In this study, we investigated the association between WMH and psychomotor speed changes through a comprehensive assessment of brain structural and functional features. Multi-modal MRIs were acquired from 60 elderly adults. Psychomotor processing speeds were assessed using the Trail Making Test Part A (TMT-A). Linear regression analyses were performed to assess the associations between TMT-A and brain features, including WMH volumes in five cerebral regions, diffusivity parameters in the major WM tracts, regional gray matter volume, and brain activities across the whole brain. Hierarchical regression analysis was used to demonstrate the contribution of each index to slower psychomotor processing speed. Linear regression analysis demonstrated that WMH volume in the occipital lobe and fractional anisotropy of the forceps major, an occipital association tract, were associated with TMT-A. Besides, resting-state brain activities in the visual cortex connected to the forceps major were associated with TMT-A. Hierarchical regression showed fractional anisotropy of the forceps major and regional brain activities were significant predictors of TMT-A. The occurrence of WMH, combined with the disruption of passing-through fiber integrity and altered functional activities in areas connected by this fiber, are associated with a decline of psychomotor processing speed. While the causal relationship of this WMH-Tract-Function-Behavior link requires further investigation, this study enhances our understanding of these complex mechanisms.

Scaled-up biodiesel synthesis from Chinese Tallow Kernel oil catalyzed by Burkholderia cepacia lipase through ultrasonic assisted technology: A non-edible and alternative source of bio energy

In East Asia, for thousands of years, the fruit of Chinese tallow tree (Sapium sebiferum) has been used for multiple purposes because of its chemical composition; the presence of high amounts of lipids is remarkable, showing potential to be used as substrate for biodiesel synthesis. Previously have been reported the use of alkaline and enzymatic catalysts, microwave technology and the use of ionic liquids as co-solvents with the lipids of this tree species to produce biodiesel. This study shows the results of the use of Burkholderia cepacia lipase as enzymatic catalyst for transesterification of Chinese Tallow Kernel oil (CTK), extracted from the fruit of Chinese tallow tree, into biodiesel, with the use of ultrasonic assisted technology and without the usage of solvents. The optimal operational parameters were determined and the reactions were developed in a batch reactor with the use of ultrasonic irradiation and emulsification to enhance the mass transfer. The scaled-up experiments, in an especially designed 3 L capacity reactor, showed promising results, obtaining 55.20% biodiesel and a kinematic viscosity of 10.31 mm².s^-1 in only 4 h, in comparison with previously published (in vitro) methods. The valorization of this non-edible source of oil represents an opportunity to use as an alternative source for bioenergy and also to tackle the uncontrolled expansion of this oleaginous tree species in some ecologically fragile ecosystems.

Syzygium aromaticum L.: Traditional herbal medicine against cagA and vacA toxin genes-producing drug resistant Helicobacter pylori

The Pan-Drug Resistant (PDR), Helicobacter pylori remains an intractable challenge in public health worldwide and this pathogenicity is mainly due to the presence of a cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA). On the other hand, plant extracts such as Syzygium aromaticum contain a diverse array of secondary metabolites, which could be potentially used to combat H. pylori pathogens. To our knowledge, this is the first report on the biomedical potential of S. aromaticum extract against cytotoxin-associated genes producing PDR H. pylori. In this investigation, out of 45 gastric antral biopsy specimens of dyspeptic patients, 20 strains were confirmed as H. pylori. Eight (40%) out of 20 strains were PDR H. pylori while the rest of the strains were Multi-Drug Resistant (MDR) strains. Genotypic analyses of PDR H. pylori strains showed that cagA and vacA genes were found to be 75% and 87.5%, respectively and m2s2 was the most common subtype of vacA gene. S. aromaticum showed a significant higher anti-H. pylori activity compared to that of Cinnamomum zeylanicum and Thymus vulgaris. Eugenol was the major phenolic compound (28.14%) detected in the methanolic extract of S. aromaticum. Clearly, results of the toxicological assessment confirmed the safety of S. aromaticum for use. Hence, these results suggest that S. aromaticum could be a new useful natural antimicrobial agent that could potentially combat cytotoxin genes-producing drug-resistant H. pylori. Moreover, these findings provide a scientific basis for the development of antimicrobial agents from traditional herbal medicines for gastroprotection against gastric ulcer.

•

Helicobacter pylori remains an intractable challenge in public health worldwide.

•

CagA and VacA genes are H. pylori pathogenicity dependent.

•

Eight strains of H. pylori were proven to pan-drug resistant.

•

The cagA and vacA genes were found to be 75% and 87.5%, respectively.

•

Syzygium aromaticum extract showed a significant higher anti-H. pylori activity.

Lycium shawii Roem. & Schult.: A new bioactive antimicrobial and antioxidant agent to combat multi-drug/pan-drug resistant pathogens of wound burn infections

The Multidrug Drug Resistance (MDR) and Pan-Drug Resistance (PDR) remain an intractable challenge issue in public health, worldwide. Plant extracts-based biological macromolecules containing a diverse array of secondary metabolites could be potentially used as alternative approaches to control or limit MDR/PDR infections. Plants of the Solanaceae family exhibit a wide variety of secondary metabolites with antioxidant and antimicrobial properties, which render them a significant role in food and pharmaceutical applications. To our knowledge, this is the first report on phytochemical constituents, antioxidant, antimicrobial activities and in vivo toxicological safety of Lycium shawii leaf extracts. Results revealed that phenolics and flavonoids were found to be the most abundant compounds in all extracts. Antioxidant activity of extracts was measured using DPPH^• and ABTS^•+ assays and the methanol extract displayed superior scavenging activity (IC₅₀ = 0.06 and 0.007 mg/mL for DPPH^• and ABTS^•+, respectively). Results of the GC-MS analysis revealed the identity of 10 compounds. Moreover, in vivo toxicological assessment can confirm the safety of L. shawii for use. Overall, L. shawii leaves are a promising natural source for the development of novel antimicrobial and antioxidant agents that could potentially combat clinical MDR/PDR pathogens.

•

The drug resistance remains an intractable challenge in public health.

•

Phenolics and flavonoids were the most abundant compounds in all extracts.

•

Methanol extract was the most antioxidant and antimicrobial agent.

•

p-coumaric acid, apigenin, and fisetin are the major identified compounds.

•

In vivo toxicological assessment can confirm the safety of L. shawii for use.

Genomics and biochemistry investigation on the metabolic pathway of milled wood and alkali lignin-derived aromatic metabolites of Comamonas serinivorans SP-35

BACKGROUND

The efficient depolymerization and utilization of lignin are one of the most important goals for the renewable use of lignocelluloses. The degradation and complete mineralization of lignin by bacteria represent a key step for carbon recycling in land ecosystems as well. However, many aspects of this process remain unclear, for example, the complex network of metabolic pathways involved in the degradation of lignin and the catabolic pathway of intermediate aromatic metabolites. To address these subjects, we characterized the deconstruction and mineralization of lignin with milled wood lignin (MWL, the most representative molecule of lignin in its native state) and alkali lignin (AL), and elucidated metabolic pathways of their intermediate metabolites by a bacterium named Comamonas serinivorans SP-35.

RESULTS

The degradation rate of MWL reached 30.9%, and its particle size range was decreased from 6 to 30 µm to 2-4 µm-when cultured with C. serinivorans SP35 over 7 days. FTIR analysis showed that the C-C and C-O-C bonds between the phenyl propane structures of lignin were oxidized and cleaved and the side chain structure was modified. More than twenty intermediate aromatic metabolites were identified in the MWL and AL cultures based on GC-MS analysis. Through genome sequencing and annotation, and from GC-MS analysis, 93 genes encoding 33 enzymes and 5 regulatory factors that may be involved in lignin degradation were identified and more than nine metabolic pathways of lignin and its intermediates were predicted. Of particular note is that the metabolic pathway to form the powerful antioxidant 3,4-dihydroxyphenylglycol is described for the first time in bacteria.

CONCLUSION

Elucidation of the β-aryl ether cleavage pathway in the strain SP-35 indicates that the β-aryl ether catabolic system is not only present in the family of Sphingomonadaceae, but also other species of bacteria kingdom. These newly elucidated catabolic pathways of lignin in strain SP-35 and the enzymes responsible for them provide exciting biotechnological opportunities for lignin valorization in future.

Drug resistance profile and molecular characterization of extended spectrum beta-lactamase (ESβL)-producing Pseudomonas aeruginosa isolated from burn wound infections. Essential oils and their potential for utilization

OBJECTIVES

Pseudomonas aeruginosa producing extended spectrum β-lactamase (ESβL) enzyme had the ability for antimicrobial resistance mechanisms and its multidrug-resistant (MDR) phenotype, has been increasingly reported as a major clinical concern worldwide. The aim of this study was to (i) characterize ESβL-producing MDR P. aeruginosa isolated from burn wound infections phenotypically and molecularly, (ii) evaluate the antibacterial activity of some essential oils (EOs) against selected ESβL-producing drug resistant P. aeruginosa and (iii) characterize a promising EO.

METHODS

Identification and antibiotic susceptibility tests were performed for all isolates. ESβL production was detected phenotypically by an initial screening test (IST) and a phenotypic confirmatory test (PCT). Additionally, ESβL-producing isolates were also characterized molecularly. The antibacterial activity was detected using a disc diffusion method. Mechanisms of antibacterial action, the fatty acid profile, and functional groups characterization of the promising EO were analyzed using scanning and transmission electron microscopy (SEM & TEM), gas chromatography-mass spectrometry (GC-MS), and Fourier transform infrared (FTIR) spectroscopy, respectively.

RESULTS

A total of 50 non duplicated P. aeruginosa isolates from the wound samples of burn patients were identified. Of these, MDR and pan-drug resistance (PDR) showed a high prevalence in 38 (76%) isolates obtained from 10 clusters, while 21 (42%) were identified as ESβL-producing MDR or PDR P. aeruginosa isolates. Phenotypic detection of ESβL production showed that 20% were considered positive ESβL-producing P. aeruginosa using the IST, and were increased to 56% by the PCT. The most prevalent ESβL-encoding gene was blaOXA-2 (60.7%), followed by blaIMP-7 (53.6%) and blaOXA-50 (42.8%). Ginger oil is the most efficient antibacterial agent and its antibacterial action mechanism is attributed to the morphological changes in bacterial cells. The oil characterization revealed that 9,12-Octadecadienoic acid methyl ester is the major fatty acid (50.49%) identified.

CONCLUSION

The high incidence of drug-resistance in ESβL-producing P. aeruginosa isolated from burn wounds is alarming. As proven in vitro, EOs may represent promising natural alternatives against ESβL-producing PDR or MDR P. aeruginosa isolates.

Transcriptome analysis of the digestive system of a wood-feeding termite (Coptotermes formosanus) revealed a unique mechanism for effective biomass degradation

BACKGROUND

Wood-feeding termite, Coptotermes formosanus Shiraki, represents a highly efficient system for biomass deconstruction and utilization. However, the detailed mechanisms of lignin modification and carbohydrate degradation in this system are still largely elusive.

RESULTS

In order to reveal the inherent mechanisms for efficient biomass degradation, four different organs (salivary glands, foregut, midgut, and hindgut) within a complete digestive system of a lower termite, C. formosanus, were dissected and collected. Comparative transcriptomics was carried out to analyze these organs using high-throughput RNA sequencing. A total of 71,117 unigenes were successfully assembled, and the comparative transcriptome analyses revealed significant differential distributions of GH (glycosyl hydrolase) genes and auxiliary redox enzyme genes in different digestive organs. Among the GH genes in the salivary glands, the most abundant were GH9, GH22, and GH1 genes. The corresponding enzymes may have secreted into the foregut and midgut to initiate the hydrolysis of biomass and to achieve a lignin-carbohydrate co-deconstruction system. As the most diverse GH families, GH7 and GH5 were primarily identified from the symbiotic protists in the hindgut. These enzymes could play a synergistic role with the endogenous enzymes from the host termite for biomass degradation. Moreover, twelve out of fourteen genes coding auxiliary redox enzymes from the host termite origin were induced by the feeding of lignin-rich diets. This indicated that these genes may be involved in lignin component deconstruction with its redox network during biomass pretreatment.

CONCLUSION

These findings demonstrate that the termite digestive system synergized the hydrolysis and redox reactions in a programmatic process, through different parts of its gut system, to achieve a maximized utilization of carbohydrates. The detailed unique mechanisms identified from the termite digestive system may provide new insights for advanced design of future biorefinery.

Effective bio-pretreatment of sawdust waste with a novel microbial consortium for enhanced biomethanation

Anaerobic digestion (AD) is considered an efficient cost-effective technology for sustainable biogas production from lignocellulosic wastes. A novel lignocellulosic degradation microbial consortium (LCDC) was isolated from rotten sawdust, and further used for sawdust pretreatment prior to AD. Results showed that pretreatment of sawdust for 10days led to significant reduction in cellulose, hemicelluloses, and lignin contents by 37.5%, 39.6%, and 56.7%, respectively, with respect to the control. In addition, the pretreatment enhanced cumulative biogas yield, which reached its maximum value of 312.0Lkg^-1VS after 28days of AD (25.6% higher than the corresponding control). Moreover, the maximum significant cumulative methane yield was recorded after 28days of AD of the pretreated sawdust (155.2Lkg^-1VS), which represented 72.6% higher than the corresponding control. Significantly higher biomethane yield from sawdust pretreated with LCDC confirms that this process is more economical than the previous reports.

Screening and characterizing of xylanolytic and xylose-fermenting yeasts isolated from the wood-feeding termite, Reticulitermes chinensis

The effective fermentation of xylose remains an intractable challenge in bioethanol industry. The relevant xylanase enzyme is also in a high demand from industry for several biotechnological applications that inevitably in recent times led to many efforts for screening some novel microorganisms for better xylanase production and fermentation performance. Recently, it seems that wood-feeding termites can truly be considered as highly efficient natural bioreactors. The highly specialized gut systems of such insects are not yet fully realized, particularly, in xylose fermentation and xylanase production to advance industrial bioethanol technology as well as industrial applications of xylanases. A total of 92 strains from 18 yeast species were successfully isolated and identified from the gut of wood-feeding termite, Reticulitermes chinensis. Of these yeasts and strains, seven were identified for new species: Candida gotoi, Candida pseudorhagii, Hamamotoa lignophila, Meyerozyma guilliermondii, Sugiyamaella sp.1, Sugiyamaella sp. 2, and Sugiyamaella sp.3. Based on the phylogenetic and phenotypic characterization, the type strain of C. pseudorhagii sp. nov., which was originally designated strain SSA-1542^T, was the most frequently occurred yeast from termite gut samples, showed the highly xylanolytic activity as well as D-xylose fermentation. The highest xylanase activity was recorded as 1.73 and 0.98 U/mL with xylan or D-xylose substrate, respectively, from SSA-1542^T. Among xylanase-producing yeasts, four novel species were identified as D-xylose-fermenting yeasts, where the yeast, C. pseudorhagii SSA-1542^T, showed the highest ethanol yield (0.31 g/g), ethanol productivity (0.31 g/L·h), and its fermentation efficiency (60.7%) in 48 h. Clearly, the symbiotic yeasts isolated from termite guts have demonstrated a competitive capability to produce xylanase and ferment xylose, suggesting that the wood-feeding termite gut is a promising reservoir for novel xylanases-producing and xylose-fermenting yeasts that are potentially valued for biorefinery industry.

First Assessment of NOx Sources at a Regional Background Site in North China Using Isotopic Analysis Linked with Modeling

Nitrogen oxides (NO_x, including NO and NO₂) play an important role in the formation of atmospheric particles. Thus, NO_x emission reduction is critical for improving air quality, especially in severely air-polluted regions (e.g., North China). In this study, the source of NO_x was investigated by the isotopic composition (δ¹⁵N) of particulate nitrate (p-NO₃^-) at Beihuangcheng Island (BH), a regional background site in North China. It was found that the δ¹⁵N-NO₃^- (n = 120) values varied between -1.7‰ and +24.0‰ and the δ¹⁸O-NO₃^- values ranged from 49.4‰ to 103.9‰. On the basis of the Bayesian mixing model, 27.78 ± 8.89%, 36.53 ± 6.66%, 22.01 ± 6.92%, and 13.68 ± 3.16% of annual NO_x could be attributed to biomass burning, coal combustion, mobile sources, and biogenic soil emissions, respectively. Seasonally, the four sources were similar in spring and fall. Biogenic soil emissions were augmented in summer in association with the hot and rainy weather. Coal combustion increased significantly in winter with other sources showing an obvious decline. This study confirmed that isotope-modeling by δ¹⁵N-NO₃^- is a promising tool for partitioning NO_x sources and provides guidance to policymakers with regard to options for NO_x reduction in North China.

Village energy survey reveals missing rural raw coal in northern China: Significance in science and policy

Burning coal for winter heating has been considered a major contributor to northern China's winter haze, with the district heating boilers holding the balance. However a decade of intensive efforts on district heating boilers brought few improvements to northern China's winter air quality, arousing a speculation that the household heating stoves mainly in rural area rather than the district heating boilers mainly in urban area dominate coal emissions in winter. This implies an extreme underestimation of rural household coal consumption by the China Energy Statistical Yearbooks (CESYs), although direct evidence supporting this speculation is lacking. A village energy survey campaign was launched to gather the firsthand information on household coal consumption in the rural areas of two cities, Baoding (in Hebei province) and Beijing (the capital of China). The survey data show that the rural raw coal consumption in Baoding (5.04 × 10³ kt) was approximately 6.5 times the value listed in the official CESY 2013 and exceeded the rural total of whole Hebei Province (4668 kt), revealing a huge amount of raw coal missing from the current statistical system. More importantly, rural emissions of particulate matter (PM) and SO₂ from raw coal, which had never been included in widely distributing environmental statistical reports, were found higher than those from industrial and urban household sectors in the two cities in 2013, which highlights the importance of rural coal burning in creating northern China's heavy haze and helps to explain why a number of modeling predictions on ambient pollutant concentrations based on normal emission inventories were more bias-prone in winter season than in other seasons. We therefore recommend placing greater emphasis on the "missing" rural raw coal to help China in its long-term ambition to achieve clean air in the context of rapid economic development.