Co-digestion of Biowastes to Enhance Biological Hydrogen Process by Defined Mixed Bacterial Cultures

Nonsterile Process for Biohydrogen Production: Recent Updates, Challenges, and Opportunities

Hydrogen (H2), a clean and versatile energy carrier, has recently gained significant attention as a potential solution for reducing carbon emissions and promoting sustainable energy systems. The yield and efficiency of the biological H2 production process primarily depend on sterilization conditions. Various strategies, such as heat inactivation and membrane-based sterilization, have been used to achieve desirable yields via microbial fermentation. Almost every failed biotransformation process is linked to nonsterile conditions at any reaction stage. Therefore, the production of renewable biofuels as alternatives to fossil fuels is more attractive. Pure sugars have been widely documented as a costly feedstock for H2 production under sterile conditions. Biotransformation under nonsterile conditions is more desirable for stable and sustainable operation. Low-cost feeds, such as biowaste, are considered suitable alternatives, but they require appropriate sterilization to overcome the limitations of inherited or contaminating microbes during H2 production. This article describes the status of microbial fermentative processes for H2 production under nonsterile conditions and discusses strategies to improve such processes for sustainable, cleaner production.

Genome mining discovery of hydrogen production pathway of Klebsiella sp. WL1316 fermenting cotton stalk hydrolysate

Genome sequencing was used to identify key genes for the generation of hydrogen gas through cotton stalk hydrolysate fermentation by Klebsiella sp. WL1316. Genome annotation indicated that the genome size was 5.2 Mb with GC content 57.6%. Xylose was metabolized in the pentose phosphate pathway via the conversion of xylose to xylulose in Klebsiella sp. WL1316. This strain contained diverse formate-hydrogen lyases and hydrogenases with gene numbers higher than closely related species. A metabolic network involving glucose, xylose utilisation, and fermentative hydrogen production was reconstructed. Metabolic analysis of key node metabolites showed that glucose and xylose metabolism influenced biomass synthesis and biohydrogen production. Formic acid accumulated during fermentation at 24-48 h but decreased sharply after 48 h, illustrating the splitting of formic acid to hydrogen gas during early-to-mid fermentation. The Kreb's cycle was the main competitive metabolic branch of biohydrogen synthesis at 24 h of fermentation. Lactic and acetic acid fermentation and late ethanol accumulation competed the carbon skeleton of biohydrogen synthesis after 72 h of fermentation, indicating that these competitive pathways are regulated in middle-to-late fermentation (48-96 h). This study is the first to elucidate the metabolic mechanisms of mixed sugar utilisation and biohydrogen synthesis based on genomic information.

Nano-Biocatalysts: Potential Biotechnological Applications

Biocatalysts are a biomolecule of interest for various biotechnological applications. Non-reusability and poor stability of especially enzymes has always limited their applications in large-scale processing units. Nanotechnology paves a way by conjugating the biocatalysts on different matrices. It predominantly enables nanomaterials to overcome the limited efficacy of conventional biocatalysts. Nanomaterial conjugated nanobiocatalyst have enhanced catalytic properties, selectivity, and stability. Nanotechnology extended the flexibility to engineer biocatalysts for various innovative and predictive catalyses. So developed nanobiocatalyst harbors remarkable properties and has potential applications in diverse biotechnological sectors. This article summaries various developments made in the area of nanobiocatalyst towards their applications in biotechnological industries. Novel nanobiocatalyst engineering is an area of critical importance for harnessing the biotechnological potential.

Biomolecules Production from Greenhouse Gases by Methanotrophs

Harmful effects on living organisms and the environment are on the rise due to a significant increase in greenhouse gas (GHG) emissions through human activities. Therefore, various research initiatives have been carried out in several directions in relation to the utilization of GHGs via physicochemical or biological routes. An environmentally friendly approach to reduce the burden of significant emissions and their harmful effects is the bioconversion of GHGs, including methane (CH4) and carbon dioxide (CO2), into value-added products. Methanotrophs have enormous potential for the efficient biotransformation of CH4 to various bioactive molecules, including biofuels, polyhydroxyalkanoates, and fatty acids. This review highlights the recent developments in methanotroph-based systems for methanol production from GHGs and proposes future perspectives to improve process sustainability via biorefinery approaches.

Anaerobic Digestion of Agri-Food Wastes for Generating Biofuels

Presently, fossil fuels are extensively employed as major sources of energy, and their uses are considered unsustainable due to emissions of obnoxious gases on the burning of fossil fuels, which can lead to severe environmental complications, including human health. To tackle these issues, various processes are developing to waste as a feed to generate eco-friendly fuels. The biological production of fuels is considered to be more beneficial than physicochemical methods due to their environmentally friendly nature, high rate of conversion at ambient physiological conditions, and less energy-intensive. Among various biofuels, hydrogen (H₂) is considered as a wonderful due to high calorific value and generate water molecule as end product on the burning. The H₂ production from biowaste is demonstrated, and agri-food waste can be potentially used as a feedstock due to their high biodegradability over lignocellulosic-based biomass. Still, the H₂ production is uneconomical from biowaste in fuel competing market because of low yields and increased capital and operational expenses. Anaerobic digestion is widely used for waste management and the generation of value-added products. This article is highlighting the valorization of agri-food waste to biofuels in single (H₂) and two-stage bioprocesses of H₂ and CH₄ production.

Photocatalytic TiO2/CdS/ZnS nanocomposite induces Bacillus subtilis cell death by disrupting its metabolism and membrane integrity

Titanium dioxide (TiO₂) is widely characterized for its application in clinical diagnostics, therapeutics, cosmetics, nutrition, and environment management. Despite enormous potential, its dependence on ultraviolet (UV) light for photocatalytic activity limits its commercialization. Accordingly in the present study, a photo catalytically superior ternary complex of TiO₂ with Cadmium sulfide/Zinc sulfide (CdS/ZnS) has been synthesized, as well as, characterized for photo-induced antimicrobial activity. The band gap of crystalline TiO₂/CdS/ZnS nanocomposite has been reduced (2.26 eV) and nanocomposite has shown the optimal photo-activation at 590 nm. TiO₂ nanocomposite has significant bactericidal activity in visible light (P < 0.01). Exposure of the TiO₂ nanocomposite affected the cellular metabolism by altering the 1681 metabolic features (P < 0.001) culminating in poor cellular survivability. Additionally, photo-induced reactive oxygen species generation through nanocomposite disrupts the microbial cellular structure. The present study synthesized photocatalytic nanocomposite as well as unveiled the holistic cellular effect of theTiO₂/CdS/ZnS nanocomposite. Additionally, the present study also indicated the potential application of TiO₂/CdS/ZnS nanocomposite for sustainable environment management, therapeutics, and various industries.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-021-00973-z.

Wild Halophytic Phragmites karka Biomass Saccharification by Bacterial Enzyme Cocktail

Biofuel derived from halophytic biomass is getting attention owing to the concerns of energy versus food crisis. The disadvantages associated with edible bioenergy resources necessitate the need to explore new feedstocks for sustainable biofuel production. In this study, biomass from locally available abundant halophytes (Panicum antidotale, Phragmites karka, Halopyrum mucronatum, and Desmostachya bipinnata) was screened for saccharification by an enzyme cocktail composed of cellulase, xylanase, and pectinase from Brevibacillus borstelensis UE10 and UE27, Bacillus aestuarii UE25, Aneurinibacillus thermoaerophilus UE1, and Bacillus vallismortis MH 1. Two types of pretreatment, i.e., with dilute acid and freeze-thaw, were independently applied to the halophytic biomass. Saccharification of acid-pretreated P. karka biomass yielded maximum reducing sugars (9 mg g^-1) as compared to other plants. Thus, the factors (temperature, pH, substrate concentration, and enzyme units) affecting its saccharification were optimized using central composite design. This statistical model predicted 49.8 mg g^-1 of reducing sugars that was comparable to the experimental value (40 mg g^-1). Scanning electron microscopy and Fourier-transform infrared spectroscopy showed significant structural changes after pretreatment and saccharification. Therefore, halophytes growing in saline, arid, and semi-arid regions can be promising alternative sources for bioenergy production.

Biotin and Zn2+ Increase Xylitol Production by Candida tropicalis

In this study, the medium requirements to increase the production of xylitol by using Candida tropicalis (CT) have been investigated. The technique of single addition or omission of medium components was applied to determine the nutritional requirements. The addition of amino acids such as Asp, Glu, Gln, Asn, Thr, and Gly had no significant effect on CT growth. However, in the absence of other metal ions, there was a higher concentration of cell growth and xylitol production when only Zn2+ was present in the medium. The analysis of various vitamins unveiled that biotin and thiamine were the only vitamins required for the growth of CT. Surprisingly, when only biotin was present in the medium as a vitamin, there was less growth of CT than when the medium was complete, but the amount of xylitol released was significantly higher. Overall, this study will increase the xylitol production using the single omission or addtion technique.

Removal of Petroleum Contaminants Through Bioremediation with Integrated Concepts of Resource Recovery: A Review

There is an upsurge in industrial production to meet the rising demands of the rapidly growing population globally. The enormous energy demand of the growing economies still depends upon petroleum. It has also resulted in environmental pollution due to the release of petroleum origin pollutants. Soil and aquifers, especially in the direct impact zones of petroleum refineries, are the worst hit. The integrated concept of bioremediation and resource recovery offers a sustainable solution to mitigate environmental pollution. It involves biodegradation, a benign utilization of toxic wastes, and the recycling of natural resources. Bioremediation is considered an integral contributor to the emerging concepts of bio-economy and sustainable development goals. This review article aims to provide an updated overview of bioremediation involving petroleum-based contaminants. Microbial degradation is discussed as a promising strategy for petroleum refinery effluent and sludge treatment. The review also provides an insight into resource reuse and recovery as a holistic approach towards sustainable refinery waste treatment. Furthermore, the integrated technologies that deserve in-depth exploration for future study in the refinery sector are highlighted in the present study.

Biosynthesis of Lactobionic Acid in Whey-Containing Medium by Microencapsulated and Free Bacteria of Pseudomonas taetrolens

The aim of this research was to develop a method of its production from whey using bacteria of the species Pseudomonas taetrolens. Analyses of the lactobionic acid production method from whey showed that the following factors have a significant effect on its efficiency: the frequency of whey batch feeding, pH and the type of bacteria application, i.e. microencapsulated vs. free. Lactose and lactobionic acid were assayed using high performance liquid chromatography (HPLC) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC–ESI–MS). The highest concentration of lactobionic acid of 22.03 mg/cm³ was obtained when whey was batch fed at 72-h intervals, pH was maintained at 6.25 and bacteria were enclosed in alginate microcapsules.

Epigenetic Regulation of Gut Microbial Dysbiosis

Microbiota inside the gut plays a vital role in maintaining human health. Microbial dysbiosis is associated with various complications leading to a range of diseases. Epigenetic changes enforced by various environmental and lifestyle factors lead to heritable modifications. These epigenetic modifications include DNA methylation, histone modifications, chromatin remodelling, and ribonucleic acid-based mechanisms. This review summarizes the impacts of environmental factors on the gut microbiome, epigenetic modifications, and their role in cardiovascular diseases.

Concrete Crack Restoration Using Bacterially Induced Calcium Metabolism

Concrete structures are prone to develop cracks and cause devastation. Repair and renovation are not enough to ensure complete eradication of crack development. The entire process is costly and laborious. The microbiologically induced calcium carbonated precipitation can be effective in restoring the cracks. The calcium-based nutrients along with specific bacterial strain have been used in the present investigation. The pellets of calcium as per Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy are deposited in the cracks of the concrete over a period of 7 days of incubation. The presence of bacteria in the calcium precipitates as demonstrated by scanning electron microscope provides adequate strength and adhering quality to the pellets. The effective filling of cracks is confirmed with the help ultrasonic pulse velocity test also. Since, elephantine heritage and high sky buildings have high maintenance costs, the use of present technique will cut down the cost and duration of restoration.

Supplementary Information

The online version of this article (10.1007/s12088-020-00916-0) contains supplementary material, which is available to authorized users.

Rhus vernicifera Laccase Immobilization on Magnetic Nanoparticles to Improve Stability and Its Potential Application in Bisphenol A Degradation

In the present study, Rhus vernicifera laccase (RvLac) was immobilized through covalent methods on the magnetic nanoparticles. Fe₂O₃ and Fe₃O₄ nanoparticles activated by 3-aminopropyltriethoxysilane followed with glutaraldehyde showed maximum immobilization yields and relative activity up to 81.4 and 84.3% at optimum incubation and pH of 18 h and 5.8, respectively. The maximum RvLac loading of 156 mg/g of support was recorded on Fe₂O₃ nanoparticles. A higher optimum pH and temperature of 4.0 and 45 °C were noted for immobilized enzyme compared to values of 3.5 and 40 °C for free form, respectively. Immobilized RvLac exhibited better relative activity profiles at various pH and temperature ranges. The immobilized enzyme showed up to 16-fold improvement in the thermal stability, when incubated at 60 °C, and retained up to 82.9% of residual activity after ten cycles of reuses. Immobilized RvLac exhibited up to 1.9-fold higher bisphenol A degradation efficiency potential over free enzyme. Previous reports have demonstrated the immobilization of RvLac on non-magnetic supports. This study has demonstrated that immobilization of RvLac on magnetic nanoparticles is very efficient especially for achieving high loading, better pH and temperature profiles, and thermal- and solvents-stability, high reusability, and higher degradation of bisphenol A.

Conversion of biogas to methanol by methanotrophs immobilized on chemically modified chitosan

In this study, chitosan modified with glutaraldehyde (GLA), 3-aminopropyltriethoxysilane (APTES), polyethyleneimine, and APTES followed by GLA (APTES-GLA) as a support material was used to improve methanol production from biogas. Among these support materials, chitosan-APTES-GLA showed the highest increase in immobilization yield and relative efficiency of Methylomicrobium album up to 56.4% and 97.7%, respectively. Maximum cell loading of 236 mg dry cell mass per g-support was observed for M. album., which is 7.7-fold higher than that of chitosan. The immobilized M. album maintained a 23.9-fold higher methanol production compared to free cells after 8 cycles of reuse; it also produced 6.92 mmol·L^-1 methanol from biogas that originated from anaerobic digestion of rice straw, thereby validating its industrial application. This is the first report on the immobilization of methanotrophs on chemically modified chitosans to improve cell loading and relative efficiency, and its potential applications in the conversion of greenhouse gases to methanol.

Evaluation of the Fermentative Capacity of Saccharomyces cerevisiae CAT-1 and BB9 Strains and Pichia kudriavzevii BB2 at Simulated Industrial Conditions

The search for promising yeasts that surpass the fermentative capacity of commercial strains, such as Saccharomyces cerevisiae CAT-1, is of great importance for industrial ethanol processes in the world. Two yeasts, Pichia kudriavzevii BB2 and Saccharomyces cerevisiae BB9, were evaluated in comparison to the industrial yeast S. cerevisiae CAT-1. The objective was to evaluate the performance profile of the three studied strains in terms of growth, substrate consumption, and metabolite formation, aiming to determine their behaviour in different media and pH conditions. The results showed that under cultivation conditions simulating the medium used in the industrial process (must at 22° Brix at pH 3.0) the highest ethanol productivity was 0.41 g L^-1 h^-1 for S. cerevisiae CAT-1, compared to 0.11 g L^-1 h^-1 and 0.16 g L^-1 h^-1 for P. kudriavzevii and S. cerevisiae BB2, respectively. S. cerevisiae CAT-1 produced three times more ethanol in must at pH 3.0 (28.30 g L^-1) and in mineral medium at pH 3.0 (29.17 g L^-1) and 5.0 (30.70 g L^-1) when compared to the value obtained in sugarcane must pH 3.0 (9.89 g L^-1). It was concluded that S. cerevisiae CAT-1 was not limited by the variation in pH in the mineral medium due to its nutritional composition, guaranteeing better performance of the yeast even in the presence of stressors. Only S. cerevisiae CAT-1 expressed he constitutive invertase enzyme, which is responsible for hydrolysing the sucrose contained in the must.

Characterization of Cellobiohydrolases from Schizophyllum commune KMJ820

A novel cellobiohydrolase (CBH)-generating fungi have been isolated and categorized as Schizophyllum commune KMJ820 based on morphology and rDNA gene sequence. Cellulose powder was used as carbon source, the total enzyme activity was 11.51 U/ml is noted; which is among the highest amounts of CBH-generating microbes studied. CBH have been purified to homogenize, with pursual of serial chromatography using S. commune supernatants and two different CBHs were found; CBH 1 and 2. The filtered CBHs showed greater activity (V max = 51.4 and 20.8 U/mg) in contrast to CBHs from earlier studies. The MW (molecular weights) of S. commune CBH 1 and 2 were verified to be approximately 50 kDa and 150 kDa, respectively, by size exclusion chromatography. Even though CBHs have been evaluated from other sources, but S. commune CBH is prominent in comparison to other CBHs by its high enzyme activity.

Biomethanol Production from Methane by Immobilized Co-cultures of Methanotrophs

Methanol production by co-culture of methanotrophs Methylocystis bryophila and Methyloferula stellata was examined from methane, a greenhouse gas. Co-culture exhibited higher methanol yield of 4.72 mM at optimum ratio of M. bryophila and M. stellata (3:2) compared to individual cultures. The immobilized co-culture within polyvinyl alcohol (PVA) showed relative efficiency of 90.1% for methanol production at polymer concentration of 10% (v/v). The immobilized co-culture cells within PVA resulted in higher bioprocess stability over free cells at different pH, and temperatures. Free and encapsulated co-cultures showed maximum methanol production of 4.81 and 5.37 mM under optimum conditions, respectively. After five cycles of reusage under batch conditions, free and encapsulated co-cultures retained methanol production efficiency of 23.8 and 61.9%, respectively. The present investigation successfully revealed the useful influence of co-culture on the methanol production over pure culture. Further, encapsulation within the polymeric matrix proved to be a better approach for the enhanced stability of the bioprocess.

Mapping Microbial Capacities for Bioremediation: Genes to Genomics

Bioremediation is a process wherein the decontamination strategies are designed so that a site could achieve the environmental abiotic and biotic parameters close to its baseline. In the process, the driving force is the available microbial genetic degradative capabilities, which are supported by required nutrients so that the desired expression of these capabilities could be exploited in favour of removal of pollutants. With genomics tools not only the available abilities could be estimated but their dynamic performance could also be established. These tools are now playing important role in bioprocess optimization, which not only derive the bio-stimulation plans but also could suggest possible genetic bio-augmentation options.

Solvent-Tolerant Acyltransferase from Bacillus sp. APB-6: Purification and Characterization

Amidase from Bacillus sp. APB-6 with very good acyltransferase activity was purified to homogeneity with a purification fold of 3.68 and 53.20% enzyme yield. The purified protein's subunit molecular mass was determined approximately 42 kDa. Hyperactivity of the enzyme was observed at pH 7.5 (150 mM, potassium-phosphate buffer) and 50 °C of incubation. An enhancement in activity up to 42% was recorded with ethylenediaminetetraacetic acid and dithiothreitol. The kinetic parameter K _m values for substrates: acetamide and hydroxylamine-hydrochloride were 73.0 and 153 mM, respectively. Further, the V _max for acyltransferase activity was 1667 U/mg of protein and the K _i for acetamide was calculated as 37.0 mM. The enzyme showed tolerance to various organic solvents (10%, v/v) and worked well in the biphasic reaction medium. The acyltransferase activity in presence of solvents i.e. biphasic medium may prove highly favorable for the transformation of hydrophobic amides, which otherwise is not possible in simple aqueous phase.

Aligning Microbial Biodiversity for Valorization of Biowastes: Conception to Perception

Generation of biowastes is increasing rapidly and its uncontrolled, slow and persistent fermentation leads to the release of Green-house gases (GHGs) into the environment. Exploration and exploitation of microbial diversity for degrading biowastes can result in producing diverse range of bioactive molecules, which can act as a source of bioenergy, biopolymers, nutraceuticals and antimicrobials. The whole process is envisaged to manage biowastes, and reduce their pollution causing capacity, and lead to a sustainable society. A strategy has been proposed for: (1) producing bioactive molecules, and (2) achieving a zero-pollution emission by recycling of the GHGs through biological routes.