Biodiesel Industry Waste: A Potential Source of Bioenergy and Biopolymers

Exploiting Polyhydroxyalkanoates for Biomedical Applications

Polyhydroxyalkanoates (PHA) are biodegradable plastic. Numerous bacteria produce PHAs under environmental stress conditions, such as excess carbon-rich organic matter and limitations of other nutritional elements such as potassium, magnesium, oxygen, phosphorus, and nitrogen. In addition to having physicochemical properties similar to fossil-fuel-based plastics, PHAs have unique features that make them ideal for medical devices, such as easy sterilization without damaging the material itself and easy dissolution following use. PHAs can replace traditional plastic materials used in the biomedical sector. PHAs can be used in a variety of biomedical applications, including medical devices, implants, drug delivery devices, wound dressings, artificial ligaments and tendons, and bone grafts. Unlike plastics, PHAs are not manufactured from petroleum products or fossil fuels and are, therefore, environment-friendly. In this review, a recent overview of applications of PHAs with special emphasis on biomedical sectors, including drug delivery, wound healing, tissue engineering, and biocontrols, are discussed.

Multiple Effects of Different Nickel Concentrations on the Stability of Anaerobic Digestion of Molasses

Molasses is a highly thick by-product produced after sugarcane crystallization constitutes large amounts of biodegradable organics. These organic compounds can be converted to renewable products through anaerobic digestion. Nevertheless, its anaerobic digestion is limited due to its high chemical oxygen demand (COD) and ion concentration. The effects of nickel (Ni2+) on the stability of anaerobic digestion of molasses were established by studying the degradation of organic matter (COD removal rate), biogas yield, methane content in the biogas, pH, and alkalinity. The results showed that there were no significant effects on the stability of pH and alkalinity. Increased COD removal rate and higher methane content was observed by 2–3% in the digesters receiving 2 and 4 mg/L of Ni2+ in the first phase of the experiment. Ni2+ supplemented to reactors at concentration 2 mg/L enhanced biogas yield. Overall, it is suggested that the addition of Ni2+ has some effects on the enhancement of biogas yield and methane contents but has no obvious effects on the long-lasting stability of the molasses digestion.

Integrated Approach for Wastewater Treatment and Biofuel Production in Microalgae Biorefineries

The increasing world population generates huge amounts of wastewater as well as large energy demand. Additionally, fossil fuel’s combustion for energy production causes the emission of greenhouse gases (GHG) and other pollutants. Therefore, there is a strong need to find alternative green approaches for wastewater treatment and energy production. Microalgae biorefineries could represent an effective strategy to mitigate the above problems. Microalgae biorefineries are a sustainable alternative to conventional wastewater treatment processes, as they potentially allow wastewater to be treated at lower costs and with lower energy consumption. Furthermore, they provide an effective means to recover valuable compounds for biofuel production or other applications. This review focuses on the current scenario and future prospects of microalgae biorefineries aimed at combining wastewater treatment with biofuel production. First, the different microalgal cultivation systems are examined, and their main characteristics and limitations are discussed. Then, the technologies available for converting the biomass produced during wastewater treatment into biofuel are critically analyzed. Finally, current challenges and research directions for biofuel production and wastewater treatment through this approach are outlined.

Waste based hydrogen production for circular bioeconomy: Current status and future directions

The present fossil fuel-based energy sector has led to significant industrial growth. On the other hand, the dependence on fossil fuels leads to adverse impact on the environment through releases of greenhouse gases. In this scenario, one possible substitute is biohydrogen, an eco-friendly energy carrier as high-energy produces. The substrates rich in organic compounds like organic waste/wastewater are very useful for improved hydrogen generation through the dark fermentation. Thus, this review article, initially, the status of biohydrogen production from organic waste and various strategies to enhance the process efficiency are concisely discussed. Then, the practical confines of biohydrogen processes are thoroughly discussed. Also, alternate routes such as multiple process integration approach by adopting biorefinery concept to increase overall process efficacy are considered to address industrial-level applications. To conclude, future perspectives besides with possible ways of transforming dark fermentation effluent to biofuels and biochemicals, which leads to circular bioeconomy, are discussed.

Biochemical conversion of biodiesel by-product into malic acid: A way towards sustainability

Crude glycerol, one of the ever-growing by-product of biodiesel industry and is receiving the closest review in recent times because direct disposal of crude glycerol may emerge ecological issues. The renewability, bioavailability and typical structure of glycerol, therefore, discover conceivable application in serving the role of carbon and energy source for microbial biosynthesis of high value products. This conceivable arrangement could find exploitation of crude glycerol as a renewable building block for bio-refineries as it is economically as well as environmentally profitable. In this review, we summarize the uptake and catabolism of crude glycerol by different wild and recombinant microorganism. The chemical and biochemical transformation of crude glycerol into high esteem malic acid by various microbial pathways is also additionally discussed. An extensive investigation in the synthesis of high-value malic acid production from various feed stock which finds applications in cosmeceutical and chemical industries, food and beverages, and to some extent in the field of medical science is also likewise studied. Finally, the open doors for unrefined crude glycerol in serving as a promising abundant energy source for malic acid production in near future have been highlighted.

Promotion of compound K production in Saccharomyces cerevisiae by glycerol

BACKGROUND

Ginsenoside compound K (CK), one of the primary active metabolites of protopanaxadiol-type ginsenosides, is produced by the intestinal flora that degrade ginseng saponins and exhibits diverse biological properties such as anticancer, anti-inflammatory, and anti-allergic properties. However, it is less abundant in plants. Therefore, enabling its commercialization by construction of a Saccharomyces cerevisiae cell factory is of considerable significance.

RESULTS

We induced overexpression of PGM2, UGP1, and UGT1 genes in WLT-MVA5, and obtained a strain that produces ginsenoside CK. The production of CK at 96 h was 263.94 ± 2.36 mg/L, and the conversion rate from protopanaxadiol (PPD) to ginsenoside CK was 64.23 ± 0.41%. Additionally, it was observed that the addition of glycerol was beneficial to the synthesis of CK. When 20% glucose (C mol) in the YPD medium was replaced by the same C mol glycerol, CK production increased to 384.52 ± 15.23 mg/L, which was 45.68% higher than that in YPD medium, and the PPD conversion rate increased to 77.37 ± 3.37% as well. As we previously observed that ethanol is beneficial to the production of PPD, ethanol and glycerol were fed simultaneously in the 5-L bioreactor fed fermentation, and the CK levels reached 1.70 ± 0.16 g/L.

CONCLUSIONS

In this study, we constructed an S. cerevisiae cell factory that efficiently produced ginsenoside CK. Glycerol effectively increased the glycosylation efficiency of PPD to ginsenoside CK, guiding higher carbon flow to the synthesis of ginsenosides and effectively improving CK production. CK production attained in a 5-L bioreactor was 1.7 g/L after simultaneous feeding of glycerol and ethanol.

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.

Poultry slaughterhouse anaerobic ponds as a source of inoculum for biohydrogen production

Several waste sources have been studied as substrate sources for the production of biogas rich in hydrogen and for the isolation of bacteria capable of fermenting several substrates for the same purpose. Nonetheless, to simplify the process and minimize production costs, it is important to seek alternatives both for the use of microbial consortia using crude waste and for the use of substrates also in their crude form, without the need for purification. The aim of this study was to use only waste as inoculum and substrate for the biological production of hydrogen. Thus, samples from anaerobic ponds of a poultry slaughterhouse were used as inoculum. Sucrose, pure glycerol (in initial tests) and crude glycerol (inserted in blends with pure glycerol) were used as substrates. H₂ production experiments were conducted in batches, using a reactor kept in an anaerobic environment for 11 days, at 35°C, under orbital agitation at 150 rpm. To analyse the composition of the biogas and the presence of soluble metabolic products (SMPs), samples of the headspace gases generated and of the reaction medium were collected. The results using sucrose as substrate indicated that the inoculum under study has potential for bio-H₂ production, as it produced CH₄-free biogas containing 50-60% H₂. The inoculum was also shown to be adaptable to the use of glycerine as a substrate, producing biogas with similar characteristics to those obtained from sucrose degradation; however, it required a longer acclimatization period, and thus more in-depth study is required.

Bioremediation of wastewater through a quorum sensing triggered MFC: A sustainable measure for waste to energy concept

A mission for fast advancement has constrained us to unpredictably tap various natural assets. The reckless utilisation of fossil fuels led unmanageable wastes which have greatly affected our health and environment. Endeavours to address these difficulties have conveyed to the frontal area certain creative natural solutions particularly the utilisation of microbial digestion systems. In the previous two decades, the microbial fuel cell (MFC) innovation has caught the consideration of the researchers. The MFCs is a kind of bio-electrochemical framework with novel highlights, for example, power production, wastewater treatment, and biosensor applications. Lately, dynamic patterns in MFC inquire about on its synthetic, electrochemical, and microbiological perspectives have brought about its observable applications. The MFCs have begun as a logical interest, and in numerous regards, these remaining parts to be the situation. This is especially a result of the multidimensional uses of this eco-accommodating innovation. The innovation relies upon the electroactive microorganisms, prominently known as exoelectrogens. In the first place, it is the main innovation that can create energy out of waste, without the contribution of outer/extra energy. Modification of electrodes with nanomaterials, for example, gold nanoparticles and iron oxide nanoparticles or pretreatment techniques, for example, sonication and autoclave disinfection have indicated promising outcomes in improving MFC execution for power generation and wastewater treatment. The MFC innovation has been likewise explored for the remediation of different heavy metals and hazardous components, and to recognize the poisonous components in wastewater. What's more, the MFCs can be adjusted into microbial electrolysis cells to produce hydrogen energy from different natural sources. This article gives a thorough and cutting-edge appraisal of the novel magnitudes of the MFC.

Cloning, Sequencing and In Silico Analysis of phbC Gene from Pseudomonas spp

We report here isolation and analysis of PCR amplified phbC gene from Pseudomonas spp. strain phbmbb15-B3. This strain was previously developed from mutations of landfill isolates and found to be an efficient Poly Hydroxy butyrate (PHB) producer. The fragment was cloned into pTZ57R/T cloning vector and then the gene has been sequenced and submitted to GenBank (Accession Number KT933807). The sequence results confirmed the clone to be phbC homologue and the ORF was 910 base pairs long and coded for 303 amino acids, which shared 92-99% amino acid sequence identity with the available bacterial sequences in Gene Bank. We could also predict the primary and secondary structural features of the expected phbC protein. Phylogenetic analysis also revealed its similarity with several pseudomonads. The results of the present study shall provide a stable foundation for further research on modeling studies of PHB synthase and developing PHB a commercial technology.

Valorization of polyhydroxyalkanoates production process by co-synthesis of value-added products

Polyhydroxyalkanoates (PHAs) are the only polyesters that are completely synthesized biologically and possess features equivalent to petroleum-based plastics besides being biodegradable. PHA based materials may certainly prove helpful in addressing the concerns caused due to the indiscriminate use of synthetic plastics. However, the cost of producing these polymers on a large scale is still uneconomical. Various approaches have been developed to tackle this issue through usage of agro-industrial wastes, co-production of high market value products, polymer extraction using green solvents, etc. The advent of recombineering and CRISPR technologies has broadened the scope of constructing a microbe capable of synthesizing multiple products with economic feasibility. Quite a few high-market value chemicals are possible to synthesize along with the favorable accumulation of PHA. The present article attempts to review all PHA polymer co-production processes with other chemicals reported till date and discusses the opportunities for their large-scale operation in future.

Exploring nutrient limitation for polyhydroxyalkanoates synthesis by newly isolated strains of Aeromonas sp. using biodiesel-derived glycerol as a substrate

Aeromonas spp. strains isolated from activated sludge in a municipal wastewater treatment plant were found to be able to synthesize polyhydroxyalkanoates (PHA) utilizing pure and crude glycerol. The 16S rRNA gene sequence of the isolates exhibited similarity to Aeromonas hydrophila, A. aquatica, and A. salmonicida. Our results confirmed that the adequate supply of nitrogen and phosphorus during culture in 250-ml shake flasks did not stimulate the synthesis of PHAs. The results indicate that the PHA content of cells was higher under a phosphorus-limiting environment compared to nitrogen starvation. In the two-stage cultivation using glucose (in the first step) and crude glycerol from biodiesel industry (in the second step) as a component of the growth medium, the analyzed strains grew to 3.06 g/l of cell dry weight containing up to 22% of PHAs. Furthermore, during the same culture strategy up to 42% of PHAs were extracted, when in the second step of the process, Aeromonas sp. AC_03 was grown on pure glycerol under phosphorus limitation. The purified biopolymer was confirmed to be polyhydroxybutyrate. Aeromonas sp. AC_02 was also capable to accumulate the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer when pure glycerol was added as a substrate under nitrogen-deficiency one-step bioprocess. Our results confirm that due to the biopolymer productivity, newly isolated strains could be exploited for obtaining valuable biopolymers using wastes generated from biodiesel industry.

Bioprocessing of Biodiesel Industry Effluent by Immobilized Bacteria to Produce Value-Added Products

Biodiesel industrial effluent rich in crude glycerol (CG) was processed to produce value-added product. Under continuous culture system, Bacillus amyloliquefaciens strain CD16 immobilized within its biofilm, produced 3.2 L H₂/day/L feed, over a period of 60 days at a hydraulic retention time of 2 days. The effective H₂ yield by B. amyloliquefaciens strain CD16 was 165 L/L CG. This H₂ yield was 1.18-fold higher than that observed with non-biofilm forming Bacillus thuringiensis strain EGU45. Bioprocessing of the effluent released after this stage, by recycling it up to 25% did not have any adverse effect on H₂ production by strain EGU45; however, a 25% reduction in yield was recorded with strain CD16. Biofilm forming H₂ producers thus proved effective as self-immobilizing system leading to enhanced process efficiency.

Co-production of polyhydroxyalkanoates and carotenoids through bioconversion of glycerol by Paracoccus sp. strain LL1

Polyhydroxyalkanoates (PHA) have emerged as a potential alternative to synthetic plastics, although its large-scale production is limited by the expenditure incurred in feed materials. Co-production of various valuable bioproducts along with PHA has been proposed to alleviate the overall production cost. Here, high-yield co-production of PHA and carotenoids was achieved in single step fermentation by Paracoccus sp. LL1. The halophilic bacterial strain could metabolize a wide range of substrates including methanol, lactose, galactose, glycerol, fructose, mannitol, etc. Under batch fermentation using mineral media supplemented with 2% glycerol, Paracoccus sp. LL1 synthesized 3.77gL^-1 PHA with concomitant production of 3.6mgL^-1 of carotenoids after 96h. An enhancement of 2.2-folds in total dry cell weight (DCW) was achieved through cell retention culture of Paracoccus sp. LL1, resulting in a maximum DCW (24.2gL^-1) containing PHA (39.3%, ww^-1) with concomitant enhancement in the production of total carotenoids. Paracoccus sp. LL1 could convert glycerol into carotenoids and PHA to a level of 7.14mgL^-1 and 9.52gL^-1, respectively. It is the first report showing value addition in PHA production process through co-production of high value carotenoids by Paracoccus sp. using glycerol as substrate.

Polyhydroxyalkanoate Production and Degradation Patterns in Bacillus Species

Bacteria under stress conditions of excess of carbon (C) and limitations of nutrients divert its metabolism towards C storage as energy reservoir-polyhydroxyalkanoate (PHA). Different Bacillus species-B. cereus and B. thuringiensis, were monitored to produce PHA from different C sources-glucose, crude glycerol and their combination at 37 °C for period up to 192 h. PHA production and its composition was found to vary with feed and bacterial strains. PHA production on crude glycerol continued to increase up to 120 h, reaching a maximum of 2725 mg/L with an effective yield of 71% of the dry cell mass. Depolymerization of PHA was observe to initiate after 96 h of incubation up to 192 h. PHA degradation products have been envisaged to be applied in medical field: tissue engineering, drug carriers, memory enhancers, antiosteoporosis, biodegradable implants. The PHA production and degradation cycle for 192 h has not been reported previously in literature.

Biomedical Applications of Polyhydroxyalkanoates

Polyhydroxyalkanoates (PHA) are produced by a large number of microbes under stress conditions such as high carbon (C) availability and limitations of nutrients such as nitrogen, potassium, phosphorus, magnesium, and oxygen. Here, microbes store C as granules of PHAs-energy reservoir. PHAs have properties, which are quite similar to those of synthetic plastics. The unique properties, which make them desirable materials for biomedical applications is their biodegradability, biocompatibility, and non-toxicity. PHAs have been found suitable for various medical applications: biocontrol agents, drug carriers, biodegradable implants, tissue engineering, memory enhancers, and anticancer agents.

Integrative Approach for Producing Hydrogen and Polyhydroxyalkanoate from Mixed Wastes of Biological Origin

In this study, an integrative approach to produce biohydrogen (H2) and polyhydroxyalkanoates (PHA) from the wastes of biological origin was investigated. A defined set of mixed cultures was used for hydrolysis and the hydrolysates were used to produce H2. The effluent from H2 production stage was used for PHA production. Under batch culture, a maximum of 62 l H2/kg of pure potato peels (Total solid, TS 2 %, w/v) and 54 l H2/kg of mixed biowastes (MBW1) was recorded. Using effluent from the H2 production stage of biowaste mixture (MBW1), Bacillus cereus EGU43 could produce 195 mg PHA/l and 15.6 % (w/w). Further, supplementation of GM-2 medium (0.1×) and glucose (0.5 %) in H2 production stage effluents, resulted in significant improvements of up to 11 and 41.7 % of PHA contents, respectively. An improvement of 3.9- and 17-fold in PHA yields as compared to with and without integrative H2 production from the MBW1 has been recorded. This integrative approach seems to be a suitable process to improve the yields of H2 and PHA by mixing biowastes.

Biorefinery for Glycerol Rich Biodiesel Industry Waste

The biodiesel industry has the potential to meet the fuel requirements in the future. A few inherent lacunae of this bioprocess are the effluent, which is 10 % of the actual product, and the fact that it is 85 % glycerol along with a few impurities. Biological treatments of wastes have been known as a dependable and economical direction of overseeing them and bring some value added products as well. A novel eco-biotechnological strategy employs metabolically diverse bacteria, which ensures higher reproducibility and economics. In this article, we have opined, which organisms and what bioproducts should be the focus, while exploiting glycerol as feed.

Production of co-polymers of polyhydroxyalkanoates by regulating the hydrolysis of biowastes

Production of polyhydroxyalkanoate (PHA) co-polymers by Bacillus spp. was studied by feeding defined volatile fatty acids (VFAs) obtained through controlled hydrolysis of various wastes. Eleven mixed hydrolytic cultures (MHCs) each containing 6 strains could generate VFA from slurries of (2% total solids): pea-shells (PS), potato peels (PP), apple pomace (AP) and onion peels (OP). PS hydrolysates (obtained with MHC2 and MHC5) inoculated with Bacillus cereus EGU43 and Bacillus thuringiensis EGU45 produced co-polymers of PHA at the rate of 15-60mg/L with a 3HV content of 1%w/w. An enhancement in PHA yield of 3.66-fold, i.e. 205-550mg/L with 3HV content up to 7.5%(w/w) was observed upon addition of OP hydrolysate and 1% glucose (w/v) to PS hydrolysates. This is the first demonstration, where PHA co-polymer composition, under non-axenic conditions, could be controlled by customizing VFA profile of the hydrolysate by the addition of different biowastes.

Bioconversion of Raw Glycerol Generated from the Synthesis of Biodiesel by Different Oleaginous Yeasts: Lipid Content and Fatty Acid Profile of Biomass

In this work, 12 different yeast strains were evaluated to gauge their ability to accumulate lipids using raw glycerol as the main carbon source. Lipomyces lipofer NRRL Y-1155 stood out above the other strains, achieving 9.48 g/l biomass, 57.64 % lipid content and 5.46 g/l lipid production. The fatty acid profile was similar to vegetable oils commonly used in the synthesis of biodiesel, with the predominance of polyunsaturated acids, especially linoleic acid, reaching 68.3 % for Rhodotorula glutinis NRRL YB-252. The occurrence of palmitic acid (39.3 % for Lipomyces starkeyi NRRL Y-11557) was also notable. Thus, yeast biomass with high lipid content can be a sustainable and renewable alternative as a raw material for the biodiesel industry.

Comparison of Different Strategies for Selection/Adaptation of Mixed Microbial Cultures Able to Ferment Crude Glycerol Derived from Second-Generation Biodiesel

Objective of this study was the selection and adaptation of mixed microbial cultures (MMCs), able to ferment crude glycerol generated from animal fat-based biodiesel and produce building-blocks and green chemicals. Various adaptation strategies have been investigated for the enrichment of suitable and stable MMC, trying to overcome inhibition problems and enhance substrate degradation efficiency, as well as generation of soluble fermentation products. Repeated transfers in small batches and fed-batch conditions have been applied, comparing the use of different inoculum, growth media, and Kinetic Control. The adaptation of activated sludge inoculum was performed successfully and continued unhindered for several months. The best results showed a substrate degradation efficiency of almost 100% (about 10 g/L glycerol in 21 h) and different dominant metabolic products were obtained, depending on the selection strategy (mainly 1,3-propanediol, ethanol, or butyrate). On the other hand, anaerobic sludge exhibited inactivation after a few transfers. To circumvent this problem, fed-batch mode was used as an alternative adaptation strategy, which led to effective substrate degradation and high 1,3-propanediol and butyrate production. Changes in microbial composition were monitored by means of Next Generation Sequencing, revealing a dominance of glycerol consuming species, such as Clostridium, Klebsiella, and Escherichia.

Challenges and Opportunities for Customizing Polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) as an alternative to synthetic plastics have been gaining increasing attention. Being natural in their origin, PHAs are completely biodegradable and eco-friendly. However, consistent efforts to exploit this biopolymer over the last few decades have not been able to pull PHAs out of their nascent stage, inspite of being the favorite of the commercial world. The major limitations are: (1) the high production cost, which is due to the high cost of the feed and (2) poor thermal and mechanical properties of polyhydroxybutyrate (PHB), the most commonly produced PHAs. PHAs have the physicochemical properties which are quite comparable to petroleum based plastics, but PHB being homopolymers are quite brittle, less elastic and have thermal properties which are not suitable for processing them into sturdy products. These properties, including melting point (Tm), glass transition temperature (Tg), elastic modulus, tensile strength, elongation etc. can be improved by varying the monomeric composition and molecular weight. These enhanced characteristics can be achieved by modifications in the types of substrates, feeding strategies, culture conditions and/or genetic manipulations.

Diversity of the Intestinal Bacteria of Cattle Fed on Diets with Different Doses of Gelatinized Starch-Urea

Gelatinized starch-urea (Starea, SU) is an effective and economical source of urea for ruminants. Here we assessed the influence of dietary supplementation with gelatinized starch-urea on the diversity of intestinal bacteria in finishing cattle. Fifty steers were randomly allotted to five treatments with diets supplemented with different doses of Starea [0 % (SU0), 8 % (SU8), 16 % (SU16), 24 % (SU24), and 32 % (SU32) of urea-N in total nitrogen]. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes was used to examine the effect of dietary supplementation of Starea on intestinal bacterial flora. Shannon-Weaver and Simpson diversity indices consistently showed the lowest bacterial diversity in the SU0 treatment. Increasing doses of Starea increased the diversity up to SU24 after which, diversity decreased. Cluster analysis of 16S rRNA gene DGGE profiles indicates that the intestinal bacterial communities associated with cattle that were not supplemented with Starea in feed differed in composition and structure from those supplemented with Starea. The amount of Starea supplemented in cattle diets influenced the abundance of several key species affiliated with Lachnospiraceae, Ruminococcaceae, Peptostreptococcaceae, Comamonadaceae and Moraxellaceae. These results suggest that Starea influences the composition and structure of intestinal bacteria which may play a role in promoting ruminant health and production performance.

Dark fermentative bioconversion of glycerol to hydrogen by Bacillus thuringiensis

Biodiesel manufacturing units discharge effluents rich in glycerol. The need is to convert crude glycerol (CG) into useful products such as hydrogen (H2). Under batch culture, Bacillusthuringiensis EGU45 adapted on pure glycerol (PG, 2% v/v) resulted in an H2 yield of 0.646 mol/mol glycerol consumed on minimal media (250 mL) supplemented with 1% ammonium nitrate at 37°C over 4 days. Here, H2 constituted 67% of the total biogas. Under continuous culture, at 2 days of hydraulic retention time, B. thuringiensis immobilized on ligno-cellulosic materials (banana leaves - BL, 10% v/v) resulted in a H2 yield of 0.386 mol/mol PG consumed. On CG, the maximal H2 yield of 0.393 mol/mol feed consumed was recorded. In brief, B. thuringiensis could transform CG, on limited resources - minimal medium with sodium nitrate, by immobilizing them on cheap and easily available biowaste, which makes it a suitable candidate for H2 production on a large scale.

Contemplating 3-Hydroxypropionic Acid Biosynthesis in Klebsiella pneumoniae

3-Hydroxypropionic acid (3-HP) is a commercially valuable platform chemical from which an array of C3 compounds can be generated. Klebsiella pneumoniae has been considered a promising species for biological production of 3-HP. Despite a wealth of reports related to 3-HP biosynthesis in K. pneumoniae, its commercialization is still in infancy. The major hurdle hindering 3-HP overproduction lies in the poor understanding of glycerol dissimilation in K. pneumoniae. To surmount this problem, this review aims to portray a picture of 3-HP biosynthesis, involving 3-HP-synthesizing strains, biochemical attributes, metabolic pathways and key enzymes. Inspired by the state-of-the-art advances in metabolic engineering and synthetic biology, here we advocate protocols for overproducing 3-HP in K. pneumoniae. These protocols range from cofactor regeneration, alleviation of metabolite toxicity, genome editing, remodeling of transport system, to carbon flux partition via logic gate. The feasibility for these protocols was also discussed.