Nadezhda A. Shavyrkina

The concept of bacterial nanocellulose (BNC) production from low-cost cellulosic raw materials is evolving across the world, as it reduces the production cost of this valuable polymer and expands its technical applications. Miscanthus × giganteus is a widely recognized energy crop with high cellulose content, but its potential as a feedstock for BNC production is underexplored. The cellulose content in the biomass of Miscanthus × giganteus from the Russian breeding stock was 54% in the present study. The Miscanthus × giganteus biomass was subjected to chemical pretreatment by four different techniques: classical alkaline delignification and three authors’ own methods using diluted nitric acid solutions at atmospheric pressure. The resultant substrates were then enzymatically hydrolyzed under identical conditions, yielding carbohydrate-based culture media on which bacterial nanocellulose biosynthesis was carried out using a SCOBY symbiotic culture. All the four chemical pretreatment methods were found to be extremely efficient because they provide a 28–31-fold increase in the biomass reactivity to enzymatic hydrolysis compared to untreated Miscanthus × giganteus. This study clearly demonstrates that it is most expedient to carry out the biomass pretreatment in a single stage using a dilute nitric acid solution in the BNC production technology from Miscanthus × giganteus. In this case, the substrate yield from the feedstock for subsequent hydrolysis was 50%, the recovery of reducing sugars from the Miscanthus × giganteus biomass reached its maximal value (65.2%), and the yield of BNC was 1.1–1.3 times higher compared to the other three methods of biomass pretreatment.

Biotechnological transformation of plant materials constitutes one of the most promising industrial processes for obtaining high-value products from inexpensive plant materials. The article analyzes the biotransformation of giant miscanthus (Miscanthus × giganteus) into high-value bacterial nanocellulose from the feedstock to the final product, i.e., presents the complete cycle of plant material processing. First, the chemical composition of giant miscanthus biomass was determined, and the content of cellulose was found to be 54%. After that, biotransformation was performed in three stages: in the first stage, the giant miscanthus biomass was pretreated using four methods; then, the obtained substrates were subjected to enzymatic hydrolysis under the same conditions, and carbohydrate growth media were obtained; in the final stage, bacterial nanocellulose was biosynthesized in the obtained growth media using Medusomyces gisevii Sa-12 symbiotic culture. The chemical pretreatment with dilute solutions of nitric acid and sodium hydroxide was found to be extremely effective and increase the reactivity to enzymatic hydrolysis by 28–31 times as compared to native miscanthus. It is shown that for the production of bacterial nanocellulose from giant miscanthus, biomass should undergo one-stage pretreatment with a dilute nitric acid solution. In this case, the substrate yield from the feedstock (for subsequent hydrolysis) amounts to 50%, the extraction of reducing sugars from miscanthus biomass is maximum (65.2%), and the yield of bacterial nanocellulose is 1.1–1.3 times higher than for the other three biomass pretreatment methods.

The study set out to investigate the chemical functionalization of bacterial cellulose as an alternative means of satisfying the high demand for nano-sized cellulose nitrates. Using a Medusomyces gisevii Sa-12 symbiotic culture as a microbial producer, bacterial cellulose having a polymerization degree of 3950 was obtained on a synthetic glucose medium. Nitration was carried out using mixed sulfuric-nitric acids differing in their water content, followed by stabilization of the synthesized bacterial cellulose nitrates. Subject to a varying water content (14, 16 and 20 %) in the nitrating mixture, the obtained bacterial cellulose nitrates exhibited a nitrogen mass content of 8.68–11.56 %, a solubility in alcohol-ether mixture of 16.5–91.0 % and a viscosity of 32–255 mPa×s. The bacterial cellulose nitrate fibers were shown to have a nanoscale nature. Coupled thermogravimetric and differential thermal analyses revealed the bacterial cellulose nitrates to have a high chemical purity and energy content. FTIR spectroscopy confirmed the high quality of the bacterial cellulose based on the presence of basic functional groups characteristic of conventional cellulose: 3371, 2943, 1633, 1428, 1371, 1163, and 1112 cm^-1. According to their infrared spectra, the detected basic functional groups corroborate that the synthesized products are low-substituted cellulose nitrate esters: 1660–1643, 1282-1276, 847–837, 752–749, and 691–690 cm^-1. The relationship between the properties of the synthesized bacterial cellulose nitrates and the water mass content in mixed sulfuric-nitric acids is shown to have a complex nature.

Valuable bacterial nanocellulose (BNC) was produced herein from the abundant, cheap, lignocellulosic feedstock Miscanthus giganteus of the variety Kamis from the Russian selection. Four methods using dilute solutions of nitric acid and sodium hydroxide were examined for pretreating M. giganteus for the first time. Further, the stages involving enzymatic hydrolysis of the resultant pulps and biosynthesis of BNC using symbiotic culture Kombucha were carried out under the same conditions. Through comparing the BNC yield using four pretreatment methods on the conversion of M. giganteus, and one-step nitric acid pretreatment was the best method. And the yield of BNC was 1.7 - 1.9 times higher than other pretreatment methods. Unlike the majority of similar works, the present study performed a complete conversion cycle from the Miscanthus into BNC and made a full calculation of the yield of intermediates and the target product.

Biodegradable bacterial nanocellulose (BNC) is a highly in-demand but expensive polymer, and the reduction of its production cost is an important task. The present study aimed to biosynthesize BNC on biologically high-quality hydrolyzate media prepared from miscanthus and oat hulls, and to explore the properties of the resultant BNC depending on the microbial producer used. In this study, three microbial producers were utilized for the biosynthesis of BNC: individual strains Komagataeibacter xylinus B-12429 and Komagataeibacter xylinus B-12431, and symbiotic Medusomyces gisevii Sa-12. The use of symbiotic Medusomyces gisevii Sa-12 was found to have technological benefits: nutrient media require no mineral salts or growth factors, and pasteurization is sufficient for the nutrient medium instead of sterilization. The yield of BNCs produced by the symbiotic culture turned out to be 44–65% higher than that for the individual strains. The physicochemical properties of BNC, such as nanofibril width, degree of polymerization, elastic modulus, Iα allomorph content and crystallinity index, are most notably dependent on the microbial producer type rather than the nutrient medium composition. This is the first study in which we investigated the biosynthesis of BNC on hydrolyzate media prepared from miscanthus and oat hulls under the same conditions but using different microbial producers, and showed that it is advisable to use the symbiotic culture. The choice of a microbial producer is grounded on the yield, production process simplification and properties. The BNC production from technical raw materials would cover considerable demands of BNC for technical purposes without competing with food resources.

Carbon neutrality is a requisite for industrial development in modern times. In this paper, we review information on possible applications of polymers from the energy crop Miscanthus in the global industries, and we highlight the life cycle aspects of Miscanthus in detail. We discuss the benefits of Miscanthus cultivation on unoccupied marginal lands as well as the rationale for the capabilities of Miscanthus regarding both soil carbon storage and soil remediation. We also discuss key trends in the processing of Miscanthus biopolymers for applications such as a fuel resources, as part of composite materials, and as feedstock for fractionation in order to extract cellulose, lignin, and other valuable chemicals (hydroxymethylfurfural, furfural, phenols) for the subsequent chemical synthesis of a variety of products. The potentialities of the biotechnological transformation of the Miscanthus biomass into carbohydrate nutrient media and then into the final products of microbiological synthesis are also examined herein.

Lignocellulosic biomass is of great interest as an alternative energy resource because it offers a range of merits. Miscanthus × giganteus is a lignocellulosic feedstock of special interest, as it combines a high biomass productivity with a low environmental impact, including CO₂ emission control. The chemical composition of lignocellulose determines the application potential for efficient industrial processing. Here, we compiled a sample collection of Miscanthus × giganteus that had been cultivated in different climate regions between 2019 and 2021. The chemical composition was quantified by the conventional wet methods. The findings were compared with each other and with the known data. Starting as soon as the first vegetation year, Miscanthus was shown to feature the following chemical composition: 43.2–55.5% cellulose content, 17.1–25.1% acid-insoluble lignin content, 17.9–22.9% pentosan content, 0.90–2.95% ash content, and 0.3–1.2% extractives. The habitat and the surrounding environment were discovered herein to affect the chemical composition of Miscanthus. The stem part of Miscanthus was found to be richer in cellulose than the leaf (48.4–54.9% vs. 47.2–48.9%, respectively), regardless of the planation age and habitat. The obtained findings broaden the investigative geography of the chemical composition of Miscanthus and corroborate the high value of Miscanthus for industrial conversion thereof into cellulosic products worldwide.

The processing of plant biomass into demanded and economically viable products is currently a recognized global trend. Among alternative energy directions, biomass conversion is the most predictable and sustainable carbon resource that can replace fossil fuels. Already today, plant biomass provides almost 25% of the world’s energy supply. This review provides information on the most promising areas of chemical and biotechnological processing of the biomass of such an energy plant as miscanthus. The choice of miscanthus is due to its high yield (up to 40 t/ha of sown area) and high energy yield (140–560 GJ/ha) compared to other plant materials. In addition, miscanthus is able to grow on marginal lands and does not require special agronomic measures, while in the process of its cultivation, the soil is enriched with organic substances and it is cleaned from pollutants. The review reflects the directions of processing of native biomass and pretreated biomass. Miscanthus biomass, in addition to processing into energy resources, can be fractionated and transformed into many high-value products - cellulose, cellulose nitrates, ethylene, hydroxymethylfurfural, furfural, phenols, ethylene glycol, cooking solutions after nitric acid pretreatment of miscanthus biomass can act as lignohumic fertilizers. In addition, on the basis of miscanthus cellulose hydrolysates, it is possible to obtain benign nutrient media for biotechnological transformation into bacterial nanocellulose, for the accumulation and isolation of various microbial enzymes.

The present paper is a fundamental study on the physicochemical properties and hydrolysis behavior of cellulose samples differing in origin: bacterial, synthetic, and vegetal. Bacterial cellulose was produced by Medusomyces gisevii Sa-12 in an enzymatic hydrolyzate derived from oat-hull pulp. Synthetic cellulose was obtained from an aqueous glucose solution by electropolymerization. Plant-based cellulose was isolated by treatment of Miscanthus sacchariflorus with dilute NaOH and HNO₃ solutions. We explored different properties of cellulose samples, such as chemical composition, degree of polymerization (DP), degree of crystallinity (DC), porosity, and reported infrared spectroscopy and scanning electron microscopy results. The hydrolysis behavior was most notable dependent on the origin of cellulose. For the bacterial cellulose sample (2010 DP, 90% DC, 89.4% RS yield), the major property affecting the hydrolysis behavior was its unique nanoscale reticulate structure promoting fast penetration of cellulases into the substrate structure. The study on enzymatic hydrolysis showed that the hydrolysis behavior of synthetic and Miscanthus celluloses was most influenced by the substrate properties such as DP, DC and morphological structure. The yield of reducing sugars (RS) by hydrolysis of synthetic cellulose exhibiting a 3140 DP, 80% DC, and highly depolymerization-resistant fibers was 27%. In contrast, the hydrolysis of Miscanthus-derived cellulose with a 1030 DP, 68% DC, and enzyme-accessible fibers provided the highest RS yield of 90%. The other properties examined herein (absence/presence of non-cellulosic impurities, specific surface, pore volume) had no considerable effect on the bioconversion of the cellulosic substrates.

One of the ways to enhance the yield of bacterial cellulose (BC) is by using dynamic aeration and different-type bioreactors because the microbial producers are strict aerobes. But in this case, the BC quality tends to worsen. Here we have combined static culture with aeration in the biosynthesis of BC by symbiotic Medusomyces gisevii Sa-12 for the first time. A new aeration method by feeding the air onto the growth medium surface is proposed herein. The culture was performed in a Binder-400 climate chamber. The study found that the air feed at a rate of 6.3 L/min allows a 25% increase in the BC yield. Moreover, this aeration mode resulted in BC samples of stable quality. The thermogravimetric and X-ray structural characteristics were retained: the crystallinity index in reflection and transmission geometries were 89% and 92%, respectively, and the allomorph Iα content was 94%. Slight decreases in the degree of polymerization (by 12.0% compared to the control―no aeration) and elastic modulus (by 12.6%) are not critical. Thus, the simple aeration by feeding the air onto the culture medium surface has turned out to be an excellent alternative to dynamic aeration. Usually, when the cultivation conditions, including the aeration ones, are changed, characteristics of the resultant BC are altered either, due to the sensitivity of individual microbial strains. In our case, the stable parameters of BC samples under variable aeration conditions are explained by the concomitant factors: the new efficient aeration method and the highly adaptive microbial producer―symbiotic Medusomyces gisevii Sa-12.