Bioprocessing of waste biomass for sustainable product development and minimizing environmental impact

Fungal xylanolytic enzymes: Diversity and applications

As important polysaccharide degraders in nature, fungi can diversify their extensive set of carbohydrate-active enzymes to survive in ecological habitats of various composition. Among these enzymes, xylanolytic ones can efficiently and sustainably degrade xylans into (fermentable) monosaccharides to produce valuable chemicals or fuels from, for example relevant for upgrading agro-food industrial side streams. Moreover, xylanolytic enzymes are being used in various industrial applications beyond biomass saccharification, e.g. food, animal feed, biofuel, pulp and paper. As a reference for researchers working in related areas, this review summarized the current knowledge on substrate specificity of xylanolytic enzymes from different families of the Carbohydrate-Active enZyme database. Additionally, the diversity of enzyme sets in fungi were discussed by comparing the number of genes encoding xylanolytic enzymes in selected fungal genomes. Finally, to support bio-economy, the current applications of fungal xylanolytic enzymes in industry were reviewed.

Propionic acid-rich fermentation (PARF) production from organic wastes: A review

Nowadays, increasing attention has been drawn to biological valorization of organic wastes. Wherein, propionic acid-rich fermentation (PARF) has become a focal point of research. The objective of this review is to make a thorough investigation on the potential of PARF production and give future outlook. By discussing the key factors affecting PARF including substrate types, pH, temperature, retention time, etc., and various improving methods to enhance PARF including different pretreatments, inoculation optimization and immobilization, a comprehensive summary on how to achieve PARF from organic waste is presented. Then, current application of PARF liquid is concluded, which is found to play an essential role in the efficient denitrification and phosphorus removal of wastewater and preparation of microbial lipids. Finally, the environmental performance of PARF production is reviewed through life cycle assessment studies, and environmentally sensitive sectors are summarized for process optimization, providing a reference for waste management in low carbon scenarios.

Burkholderia sacchari (synonym Paraburkholderia sacchari): An industrial and versatile bacterial chassis for sustainable biosynthesis of polyhydroxyalkanoates and other bioproducts

This is the first review presenting and discussing Burkholderia sacchari as a bacterial chassis. B. sacchari is a distinguished polyhydroxyalkanoates producer strain, with low biological risk, reaching high biopolymer yields from sucrose (0.29 g/g), and xylose (0.38 g/g). It has great potential for integration into a biorefinery using residues from biomass, achieving 146 g/L cell dry weight containing 72% polyhydroxyalkanoates. Xylitol (about 70 g/L) and xylonic acid [about 390 g/L, productivity 7.7 g/(L.h)] are produced by the wild-type B. sacchari. Recombinants were constructed to allow the production and monomer composition control of diverse tailor-made polyhydroxyalkanoates, and some applications have been tested. 3-hydroxyvalerate and 3-hydroxyhexanoate yields from substrate reached 80% and 50%, respectively. The genome-scale reconstruction of its metabolic network, associated with the improvement of tools for genetic modification, and metabolic fluxes understanding by future research, will consolidate its potential as a bioproduction chassis.

Industrial applications of cold-adapted enzymes: challenges, innovations and future perspective

Extreme cold environments are potential reservoirs of microorganisms producing unique and novel enzymes in response to environmental stress conditions. Such cold-adapted enzymes prove to be valuable tools in industrial biotechnology to meet the increasing demand for efficient biocatalysts. The inherent properties like high catalytic activity at low temperature, high specific activity and low activation energy make the cold-adapted enzymes well suited for application in various industries. The interest in this group of enzymes is expanding as they are the preferred alternatives to harsh chemical synthesis owing to their biodegradable and non-toxic nature. Irrespective of the multitude of applications, the use of cold-adapted enzymes at the industrial level is still limited. The current review presents the unique adaptive features and the role of cold-adapted enzymes in major industries like food, detergents, molecular biology and bioremediation. The review highlights the significance of omics technology i.e., metagenomics, metatranscriptomics and metaproteomics in enzyme bioprospection from extreme environments. It further points out the challenges in using cold-adapted enzymes at the industrial level and the innovations associated with novel enzyme prospection strategies. Documentations on cold-adapted enzymes and their applications are abundant; however, reports on the role of omics tools in exploring cold-adapted enzymes are still scarce. So, the review covers the aspect concerning the novel techniques for enzyme discovery from nature.

Production of R- and S-1,2-propanediol in engineered Lactococcus lactis

1,2-propanediol (1,2-PDO) is a versatile chemical used in multiple manufacturing processes. To date, some engineered and non-engineered microbes, such as Escherichia coli, Lactobacillus buchneri, and Clostridium thermosaccharolyticum, have been used to produce 1,2-PDO. In this study, we demonstrated the production of R- and S-1,2-PDO using engineered Lactococcus lactis. The L- and D-lactic acid-producing L. lactis strains NZ9000 and AH1 were transformed with the plasmid pNZ8048-ppy harboring pct, pduP, and yahK genes for 1,2-PDO biosynthesis, resulting in L. lactis LL1 and LL2, respectively. These engineered L. lactis produced S- and R-1,2-PDO at concentrations of 0.69 and 0.50 g/L with 94.4 and 78.0% ee optical purities, respectively, from 1% glucose after 72 h of cultivation. Both 1% mannitol and 1% gluconate were added instead of glucose to the culture of L. lactis LL1 to supply NADH and NADPH to the 1,2-PDO production pathway, resulting in 75% enhancement of S-1,2-PDO production. Production of S-1,2-PDO from 5% mannitol and 5% gluconate was demonstrated using L. lactis LL1 with a pH-stat approach. This resulted in S-1,2-PDO production at a concentration of 1.88 g/L after 96 h of cultivation. To our knowledge, this is the first report on the production of R- and S-1,2-PDO using engineered lactic acid bacteria.

Interdependence between lignocellulosic biomasses, enzymatic hydrolysis and yeast cell factories in biorefineries

Biorefineries have a pivotal role in the bioeconomy scenario for the transition from fossil‐based processes towards more sustainable ones relying on renewable resources. Lignocellulose is a prominent feedstock since its abundance and relatively low cost. Microorganisms are often protagonists of biorefineries, as they contribute both to the enzymatic degradation of lignocellulose complex polymers and to the fermentative conversion of the hydrolyzed biomasses into fine and bulk chemicals. Enzymes have therefore become crucial for the development of sustainable biorefineries, being able to provide nutrients to cells from lignocellulose. Enzymatic hydrolysis can be performed by a portfolio of natural enzymes that degrade lignocellulose, often combined into cocktails. As enzymes can be deployed in different operative settings, such as separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF), their characteristics need to be combined with microbial ones to maximize the process. We therefore reviewed how the optimization of lignocellulose enzymatic hydrolysis can ameliorate bioethanol production when Saccharomyces cerevisiae is used as cell factory. Expanding beyond biofuels, enzymatic cocktail optimization can also be pivotal to unlock the potential of non‐Saccharomyces yeasts, which, thanks to broader substrate utilization, inhibitor resistance and peculiar metabolism, can widen the array of feedstocks and products of biorefineries.

Supporting decision making to achieve circularity via a biodegradable waste-to-bioenergy and compost facility

Bioproducts, such as energy and fertilizers, are strongly interrelated with the biodegradable waste treatment processes, within a holistic management strategy. Although different forms of biological treatment technologies are available, anaerobic digestion represents a process of major importance in the overall management strategy of biodegradable waste. This paper presents a methodology to support decision making for efficient management of biodegradable waste. The decision support framework provides the background towards the selection and design of a biodegradable waste installation with emphasis on the recovery of energy and organic fertilizer. The discrete steps are analytically defined and illustrated to assist managers and policy makers to organize their decision making in the whole spectrum of procedures required to promote sustainable biodegradable waste management programs. The methodological approach developed can be generically applied by public authorities, producers and stakeholders following essential basic steps regarding safe and environmentally friendly production of high-quality final product. Moreover, a demonstration is performed for a real-case study for the Region of Serres, Greece. The proposed installation is expected to manage 3,285 t of biodegradable waste and generate approximately 160,000 m³/a of biogas, 400 MWh_el/a and 450 MWh_thermal/a. The final bioproduct exceeds 3 kt of digestate that will be valorized in arable land close to the installation. Crucial interactions and managerial insights are also highlighted. The decision support framework aims to assist the research community, the private sector and decision makers to produce affordable and sustainable compost/digestate recovered from waste, also supporting the transition to a low carbon future and sustainable -circular- development.

The Impact of Filler Geometry on Polylactic Acid-Based Sustainable Polymer Composites

Recently, biocomposites have emerged as materials of great interest to the scientists and industry around the globe. Among various polymers, polylactic acid (PLA) is a popular matrix material with high potential for advanced applications. Various particulate materials and nanoparticles have been used as the filler in PLA based matrix. One of the extensively studied filler is cellulose. However, cellulose fibres, due to their hydrophilic nature, are difficult to blend with a hydrophobic polymer matrix. This leads to agglomeration and creates voids, reducing the mechanical strength of the resulting composite. Moreover, the role of the various forms of pure cellulose and its particle shape factors has not been analyzed in most of the current literature. Therefore, in this work, materials of various shapes and shape factors were selected as fillers for the production of polymer composites using Polylactic acid as a matrix to fill this knowledge gap. In particular, pure cellulose fibres (three types with different elongation coefficient) and two mineral nanocomponents: precipitated calcium carbonate and montmorillonite were used. The composites were prepared by a melt blending process using two different levels of fillers: 5% and 30%. Then, the analysis of their thermomechanical and physico-chemical properties was carried out. The obtained results were presented graphically and discussed in terms of their shape and degree of filling.