Abstract: Pre-treatment to increase cellulose enzymatic hydrolyzability is a prerequisite step for bioconversion of lignocellulosic biomass. The final objective of pre-treatment is to increase cellulose accessibility to cellulase enzymes, which can be done by either removing hemicelluloses or delignification or modifying lignin structure. Organosolv fractionating pre-treatment (OFP) achieves a fractionation of biomass in a one-pot process with greatly increased cellulose digestibility. In this review, the research progress in recent years on the acid and alkali-catalyzed OFP processes has been discussed, in terms of the process modes, chemistry, pre-treatment kinetics as well as substrate structures. It is concluded that OFP not only improves cellulose digestibility but also shows great promise as an entry to biomass biorefining for co-producing various chemicals and fuels; however, the economic feasibility of the OFP process has to be improved by reducing the energy consumption for solvent recovery and developing more products with higher added values. Finally, the challenge and perspective of OFP are further discussed. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd

Abstract: Xylans are the most abundant noncellulosic polysaccharides in lignified secondary cell walls of woody dicots and in both primary and secondary cell walls of grasses. These polysaccharides, which comprise 20–35% of terrestrial biomass, present major challenges for the efficient microbial bioconversion of lignocellulosic feedstocks to fuels and other value-added products. Xylans play a significant role in the recalcitrance of biomass to degradation, and their bioconversion requires metabolic pathways that are distinct from those used to metabolize cellulose. In this review, we discuss the key differences in the structural features of xylans across diverse plant species, how these features affect their interactions with cellulose and lignin, and recent developments in understanding their biosynthesis. In particular, we focus on how the combined structural and biosynthetic knowledge can be used as a basis for biomass engineering aimed at developing crops that are better suited as feedstocks for the bioconversion industry.

Abstract: CO, H2, and CO2 are major components of syngas and some industrial CO-rich waste gases (e.g. waste gases from steel industries), besides some additional minor compounds. It was recently shown that those gases can be bioconverted, by acetogenic/solventogenic bacteria, into ethanol and higher alcohols such as butanol, but also hexanol, through the so-called HBE fermentation. That process presents some advantages over existing chemical conversion processes. This paper reviews HBE fermentation from C1-gases after briefly describing the more conventional ABE (acetone-butanol-ethanol) fermentation from carbohydrates by Clostridium acetobutylicum, in order to allow for comparison of both processes. Although acetone may appear in carbohydrate fermentation, alcohols are the only major end-metabolites in the HBE process with Clostridium carboxidivorans. The few acetogenic bacteria known to metabolize C1-gases and produce butanol or higher alcohols are described. Clostridium carboxidivorans has been used in most cases. Bioconversion of the gaseous substrates takes place in two stages, namely acidogenesis (production of acids) followed by solventogenesis (production of alcohols), characterized by different optimal fermentation conditions. Major parameters affecting each bioconversion stage as well as the overall fermentation process are analyzed. Although it has been claimed that acidification is required in ABE fermentation to initiate the solventogenic stage, strong acidification seems to some extent not to be a prerequisite for solventogenesis in the HBE process. Bioreactors potentially suitable for this type of bioconversion process are described as well. © 2017 Society of Chemical Industry

Abstract: Products that bear the label "natural" have gained more attention in the marketplace. In this approach, the production of aroma compounds through biotransformation or bioconversion has been receiving more incentives in economic and research fields. Among the substrates used in these processes, terpenes can be highlighted for their versatility and low cost; some examples are limonene, α-pinene, and β-pinene. This work focused on the biotransformation of the two bicyclic monoterpenes, α-pinene and β-pinene; the use of different biocatalysts; the products obtained; and the conditions employed in the process.

Abstract: Currently, one of the major problem affecting the world is solid waste management, predominantly petroleum-based plastic and fish solid waste (FSW). However, it is very difficult to reduce the consumption of plastic as well as fish products, but it is promising to convert FSW to biopolymer to reduce eco-pollution. On account of that, the bioconversion of FSW extract to polyhydroxybutyrate (PHB) was undertaken by using Bacillus subtilis (KP172548). Under optimized conditions, 1.62 g/L of PHB has been produced by the bacterium. The purified compound was further characterized by advanced analytical technologies to elucidate its chemical structure. Results indicated that the biopolymer was found to be PHB, the most common homopolymer of polyhydroxyalkanoates (PHAs). This is the first report demonstrating the efficacy of B. subtilis to utilize FSW extract to produce biopolymer. The biocompatibility of the PHB against murine macrophage cell line RAW264.7 demonstrated that, it was comparatively less toxi...

Abstract: Lignin depolymerization mainly involves redox reactions relying on the effective electron transfer. Even though electron mediators were previously used for delignification of paper pulp, no study has established a bioprocess to fragment and solubilize the lignin with an effective laccase–mediator system, in particular, for subsequent microbial bioconversion. Efficient lignin depolymerization was achieved by screening proper electron mediators with laccase to attain a nearly 6-fold increase of kraft lignin solubility compared to the control kraft lignin without laccase treatment. Chemical analysis suggested the release of a low molecular weight fraction of kraft lignin into the solution phase. Moreover, NMR analysis revealed that an efficient enzyme–mediator system can promote the lignin degradation. More importantly, the fundamental mechanisms guided the development of an efficient lignin bioconversion process, where solubilized lignin from laccase–HBT treatment served as a superior substrate for bioconve...

Abstract: Termites are xylophages, being able to digest a wide variety of lignocellulosic biomass including wood with high lignin content. This ability to feed on recalcitrant plant material is the result of complex symbiotic relationships, which involve termite-specific gut microbiomes. Therefore, these represent a potential source of microorganisms for the bioconversion of lignocellulose in bioprocesses targeting the production of carboxylates. In this study, gut microbiomes of four termite species were studied for their capacity to degrade wheat straw and produce carboxylates in controlled bioreactors. All of the gut microbiomes successfully degraded lignocellulose and up to 45% w/w of wheat straw degradation was observed, with the Nasutitermes ephratae gut-microbiome displaying the highest levels of wheat straw degradation, carboxylate production and enzymatic activity. Comparing the 16S rRNA gene diversity of the initial gut inocula to the bacterial communities in lignocellulose degradation bioreactors revealed important changes in community diversity. In particular, taxa such as Spirochaetes and Fibrobacteres that were highly abundant in the initial gut inocula were replaced by Firmicutes and Proteobacteria at the end of incubation in wheat straw bioreactors. Overall, this study demonstrates that termite-gut microbiomes constitute a reservoir of lignocellulose-degrading bacteria that can be harnessed in artificial conditions for biomass conversion processes that lead to the production of useful molecules.

Abstract: Bioprocesses in conventional second generation biorefineries are mainly based on the fermentation of sugars obtained from lignocellulosic biomass or agro-industrial wastes. An alternative to this process consists in gasifying those same feedstocks or even other carbon-containing materials to obtain syngas which can also be fermented by some anaerobic bacteria to produce chemicals or fuels. Carbon monoxide, carbon dioxide and hydrogen, which are the main components of syngas, are also found in some industrial waste gases, among others in steel industries. Clostridium carboxidivorans is able to metabolise such gases to produce ethanol and higher alcohols, i.e. butanol and hexanol, following the Wood–Ljungdahl pathway. This does simultaneously allow the removal of volatile pollutants involved in climate change. The bioconversion is a two step process in which organic acids (acetate, butyrate, hexanoate) are produced first, followed by the accumulation of alcohols; although partial overlap in time of acids and alcohols production may sometimes take place as well. Several parameters, among others pH, temperature, or gas-feed flow rates in bioreactors, affect the bioconversion process. Besides, the accumulation of high concentrations of alcohols in the fermentation broth inhibits the growth and metabolic activity of C. carboxidivorans.

Abstract: 3-Hydroxypropionic acid (3-HP) is an important platform chemical which can be produced biologically from glycerol. Klebsiella pneumoniae is an ideal biocatalyst for 3-HP because it can grow well on glycerol and naturally synthesize the essential coenzyme B12. On the other hand, if higher yields and titers of 3-HP are to be achieved, the sustained regeneration of NAD+ under anaerobic conditions, where coenzyme B12 is synthesized sustainably, is required. In this study, recombinant K. pneumoniae L17 overexpressing aldehyde dehydrogenase (AldH) was developed and cultured in a bioelectrochemical system (BES) with the application of an electrical potential to the anode using a chronoamperometric method (+0.5 V vs. Ag/AgCl). The BES operation resulted in 1.7-fold enhancement of 3-HP production compared to the control without the applied potential. The intracellular NADH/NAD+ ratio was significantly lower when the L17 cells were grown under an electric potential. The interaction between the electrode and overexpressed AldH was enhanced by electron shuttling mediated by HNQ (2-hydroxy-1,4-naphthoquinone). Enhanced 3-HP production by the BES was achieved using recombinant K. pneumoniae L17. The quinone-based electron transference between the electrode and L17 was investigated by respiratory uncoupler experiments. This study provides a novel strategy to control the intracellular redox states to enhance the yield and titer of 3-HP production as well as other bioconversion processes.

Abstract: Background Methane is the major component of natural and shale gas. Methane can be converted into methanol via a bioprocess using methanotrophs, and methanol is a valuable chemical feedstock for the production of value-added chemicals. This work demonstrates highly effective bioconversion of methane to methanol using a newly isolated novel methanotroph, Methylomonas sp. DH-1. Results A novel methanotroph strain was isolated from activated sludge from a brewery plant and characterized using phylogenetic analysis, electron microscopy and chemotaxonomic analysis. This aerobic, Gram-negative, non-motile rod-shaped type I methanotroph was designated as Methylomonas sp. DH-1. The growth condition of Methylomonas sp. DH-1 and batch methane-to-methanol bioconversion conditions such as methane concentration, pH, biocatalyst loading, concentration of formate and MDH inhibitor were analyzed and optimized. Methanol was produced from methane with a 1.340 g L−1 titer, a 0.332 g L−1 h−1 volumetric conversion rate and a 0.0752 g g−1 cell h−1 specific methanol conversion rate. Conclusion It was demonstrated that isolation and application of a new methanotroph strain is a practical way of improving bioconversion efficiency in the conversion of methane to methanol. Moreover, one promising feature of Methylomonas sp. DH-1 for methanol production was its extremely high tolerance to methanol up to 7%(v/v), which is advantageous for high-titer methanol production. © 2016 Society of Chemical Industry

Abstract: Lignocellulosic biomass has been considered as the second generation feedstock for biorefinery to produce biofuels and bio-based products. Bioconversion is one of the major pathways involved in the development of biorefinery. However, it is significantly hindered by the structural and chemical complexity of biomass, which makes cellulosic biofuel economically unfit. Fermentable sugars of biomass carbohydrates such as cellulose and hemicellulose necessary for fermentation are trapped inside the cross-linking structure of the lignocellulose. Therefore, pretreatment of biomass is always required to convert lignocellulosic biomass from its native form, in which it is recalcitrant to biodegradation by enzymatic and microbial attacks, into a form amenable to biodegradation. The pretreatment itself is one of key cost contributors to the economics of biofuels while it also affects the cost efficiency of the downstream bioconversion processes. As a result, extensive research has been done on pretreatment. This chapter reviews currently existing pretreatment methods including physical, chemical and biological pretreatment with the focus on the principles, advantages/disadvantages, characteristics and recent development. In addition, we also cover the impact of biomass structural and compositional features on the pretreatment, the current status and challenges of pretreatment research and the future research targets.

Abstract: Urban municipal solid waste in India are 75–85% organic. Uncontrolled dumping of this waste is a major health concern. Degradation of organic waste by use of a microbial consortium is safe, efficient and economic. Therefore, this study was taken up to recycle the organic solid waste into effective compost using a microbial consortium. Bacterial consortia were developed using antagonism assay. Concomitant enzyme production by the consortia was determined. The best consortium was further employed for degradation of 30 kg of organic solid waste. Compost analysis of 30 kg of wastes was done to determine the level of C, N, K, P and S. In this study, of the four consortia proposed, consortia no. 2 had the highest degrading capability. It exhibited consistent degrading capabilities of 30 kg waste. The volume of the waste was reduced to 82%, with a reduction in mass and moisture content to 65 and 42%, respectively, after 30 days of degradation study. The compost produced after 30 days had a dark colour and grainy texture without any crustacean population and lacked foul smell. Compost analysis of 30kg wastes inoculated with consortium 2 showed C:N ratio of 22:1 compared to 32:1 in control, and increased percentage of K, P and S which are required for enhancement of soil fertility. Therefore, we can conclude that consortium 2 can serve as a biological tool for the removal of organic solid wastes from the environment, and the compost generated from the degradation can be applied to increase the fertility of the soil.

Abstract: Biofuels are the imperative commodities influential in future bioeconomy that can be made sustainable by utilizing hemicelluloses which are the primary unutilized residues obtained from a lignocellulosic ethanol refinery. The abundant fraction in these hemicelluloses include pentoses (mainly xylose). The rationale behind the huge loss of hemicellulosic fraction is their heteropolymeric nature, low fermentability, lack of pentose specific transporters and enzyme cascades required for pentose fermentation by natural yeast strains. These lacunae lead to lower overall yield and productivity of ethanol thus rendering the entire process uneconomical. However, improvements in the conventional cellulose to ethanol know-how can trigger evolution towards bioeconomy. For industrial implementation of process technology, hemicellulosic stream should be integrated as a primary fraction along with celluloses for converting into ethanol. Thus, a novel hexose and pentose co-fermenting yeast strain is essential for...

Abstract: Vinasse, a residue from bioethanol production containing high organic matter concentration, was used as substrate in submerged fermentation of Pseudomonas aeruginosa PA1 for biosurfactant production. About 2.7 g/L of rhamnolipids was obtained, with surface tension of 29.2 mN/m and critical micelle concentration of 80.3 mg/L. After separation of rhamnolipid and biomass, residual fermentation media were submitted to anaerobic biodegradation in mesophilic conditions. The residual medium derived from fermentation with vinasse diluted to 1 : 1, without addition of nitrogen, C : N 21, and for 168 h, led to 63.2% chemical oxygen demand (COD) removal and 97.6 mL CH4/g . Compared to results obtained with fresh vinasse (73.7% COD removal and 112.4 mL CH4/g ), it could be concluded that both processes can be integrated in order to add value to the residue and obtain energy, reducing production costs and at the same time environmental impacts related to vinasse disposal.

Abstract: Conjugated linoleic acids (CLAs) have been found to have beneficial effects on human health when used as dietary supplements. However, their availability is limited because pure, chemistry-based production is expensive, and biology-based fermentation methods can only create small quantities. In an effort to enhance microbial production of CLAs, four genetically modified strains of the oleaginous yeast Yarrowia lipolytica were generated. These mutants presented various genetic modifications, including the elimination of β-oxidation (pox1-6∆), the inability to store lipids as triglycerides (dga1∆ dga2∆ are1∆ lro1∆), and the overexpression of the Y. lipolytica ∆12-desaturase gene (YlFAD2) under the control of the constitutive pTEF promoter. All strains received two copies of the pTEF-oPAI or pPOX-oPAI expression cassettes; PAI encodes linoleic acid isomerase in Propionibacterium acnes. The strains were cultured in neosynthesis or bioconversion medium in flasks or a bioreactor. The strain combining the three modifications mentioned above showed the best results: when it was grown in neosynthesis medium in a flask, CLAs represented 6.5% of total fatty acids and in bioconversion medium in a bioreactor, and CLA content reached 302 mg/L. In a previous study, a CLA degradation rate of 117 mg/L/h was observed in bioconversion medium. Here, by eliminating β-oxidation, we achieved a much lower rate of 1.8 mg/L/h.

Abstract: The dicarboxylic acid malic acid synthesized as part of the tricarboxylic acid cycle can be produced in excess by certain microorganisms. Although malic acid is produced industrially to a lesser extent than citric acid, malic acid has industrial applications in foods and pharmaceuticals as an acidulant among other uses. Only recently has the production of this organic acid from coproducts of industrial bioprocessing been investigated. It has been shown that malic acid can be synthesized by microbes from coproducts generated during biofuel production. More specifically, malic acid has been shown to be synthesized by species of the fungus Aspergillus on thin stillage, a coproduct from corn-based ethanol production, and on crude glycerol, a coproduct from biodiesel production. In addition, the fungus Ustilago trichophora has also been shown to produce malic acid from crude glycerol. With respect to bacteria, a strain of the thermophilic actinobacterium Thermobifida fusca has been shown to produce malic acid from cellulose and treated lignocellulosic biomass. An alternate method of producing malic acid is to use agricultural biomass converted to syngas or biooil as a substrate for fungal bioconversion. Production of poly(β-l-malic acid) by strains of Aureobasidium pullulans from agricultural biomass has been reported where the polymalic acid is subsequently hydrolyzed to malic acid. This review examines applications of malic acid, metabolic pathways that synthesize malic acid and microbial malic acid production from biofuel-related coproducts, lignocellulosic biomass and poly(β-l-malic acid).

Abstract: Growing scientific interest in mixed microbial culture-based anaerobic biotechnologies for the production of value-added chemicals and fuels from waste organic residues requires a parallel focus on the development and implementation of strategies to control products distribution. This study examined the feasibility of an electro-fermentation approach, based on the introduction of a polarized (-700 mV vs. the standard hydrogen electrode) graphite electrode in the fermentation medium, to steer products distribution during the conversion of organic substrates (glucose, ethanol, and acetate supplied as single compounds or in mixtures) by undefined mixed microbial cultures. As a main result, in batch experiments the polarized electrode triggered a nearly 20-fold increase (relative to open circuit controls) in the yield of i-butyrate production (0.43±0.01 vs. 0.02±0.02 mol/ mol glucose) during the anaerobic fermentation of the ternary mixture of substrates, without adversely affecting the rate of substrate bioconversion. The observed change in the fermentative metabolism was most likely triggered by the (potentiostatic) regulation of the oxidation-reduction potential of the reaction medium rather than by the electrode serving as an electron donor.