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Thermophilic enzyme systems are of major importance nowadays in all industrial processes due to their great performance at elevated temperatures. In the present review, an overview of the current knowledge on the properties of thermophilic and thermotolerant carbohydrate esterases and oxidative enzymes with great thermostability is provided, with respect to their potential use in biotechnological applications. A special focus is given to the lytic polysaccharide monooxygenases that are able to oxidatively cleave lignocellulose through the use of oxygen or hydrogen peroxide as co-substrate and a reducing agent as electron donor. Structural characteristics of the enzymes, including active site conformation and surface properties are discussed and correlated with their substrate specificity and thermostability properties.

MtLPMO9 and FoLPMO9 are two lytic polysaccharide monooxygenases (LPMOs), from the filamentous fungi Thermothelomyces thermophila and Fusarium oxysporum, respectively. In the present study an attempt has been made to achieve direct electron transfer between these enzymes and a glassy carbon electrode by immobilization in Nafion polyelectrolyte. The method used to ascertain the feasibility of direct electron transfer was large amplitude Fourier transform alternating current voltammetry (FTacV) and the formal potentials of these enzymes were determined at different temperatures. The findings of this paper indicate that LPMOs can be studied by direct electron transfer, which could be exploited in the near future for their biochemical characterization.

The aim of this work was to investigate the use of isobutanol as organic solvent for the efficient delignification and fractionation of beechwood through the OxiOrganosolv process in the absence of any catalyst. The results demonstrate that cellulose-rich solid pulp produced after pretreatment is a source of fermentable sugars that can be easily hydrolyzed and serve as a carbon source in microbial fermentations for the production of omega-3 fatty acids and D-lactic acid. The C5 sugars are recovered in the aqueous liquid fractions and comprise a fraction rich in xylo-oligosaccharides with prebiotic potential. The maximum production of optically pure D-lactic from Lactobacillus delbrueckii sp. bulgaricus reached 51.6 g/L (0.57 g/gbiomass), following a simultaneous saccharification and fermentation strategy. Crypthecodenium cohnii accumulated up to 52.1 wt% lipids with a DHA content of 54.1 %, while up to 43.3 % hemicellulose recovery in form of oligosaccharides was achieved in the liquid fraction.

The field of enzymatic degradation of lignocellulose is actively growing and the recent updates of the last few years indicate that there is still much to learn. The growing number of protein sequences with unknown function in microbial genomes indicates that there is still much to learn on the mechanisms of lignocellulose degradation. In this review, a summary of the progress in the field is presented, including recent discoveries on the nature of the structural polysaccharides, new technologies for the discovery and functional annotation of gene sequences including omics technologies, and the novel lignocellulose-acting enzymes described. Novel enzymatic activities and enzyme families as well as accessory enzymes and their synergistic relationships regarding biomass breakdown are described. Moreover, it is shown that all the valuable knowledge of the enzymatic decomposition of plant biomass polymers can be employed towards the decomposition and upgrading of synthetic polymers, such as plastics.

In this work, a lytic polysaccharide monooxygenase (LPMO) belonging to the AA9 family from the filamentous fungus Thermothelomyces thermophilus, MtLPMO9H, is immobilized on cobalt functionalized multi-walled carbon nanotubes modified glassy carbon electrode. The step of the binding of phosphoric acid swollen cellulose on this LPMO is studied using large amplitude fast Fourier transform alternating current voltammetry (FTacV) at different temperatures, extracting the corresponding kinetic constants, based on a model developed for the interaction of immobilized enzyme with free, in the solution, species.

Lactic acid bioconversion processes have numerous advantages over the chemical synthesis route, not only due to the high-titer yield of the final product with great optical purity, but also due to the possibility of utilizing lignocellulosic biomass feedstocks as carbon source in an economic and environmentally friendly way. In the present study, beechwood and pine were pretreated with a novel mild oxidative organosolv process to produce cellulose-rich solid fractions, which were tested for their ability to support the growth and high lactic acid productivity of Lactobacillus delbrueckii subsp. bulgaricus (ATCC® 11842). We employed a simultaneous saccharification and fermentation (SSF) strategy in batch cultures with 9% w v−1 solids loading. The results for beechwood showed the highest production of 62 g L−1 lactic acid after 72 h of incubation, corresponding to a yield of 0.69 g g−1 of biomass (82.7% of the theoretical maximum yield) and a productivity of 0.86 g L−1 h−1. In the case of pine, the productivity was lower at 0.51 g L−1 h−1, leading to accumulation of 36.4 g L−1 lactic acid, corresponding to a yield of 0.40 g g−1 of biomass (41.4% of the theoretical maximum yield). Our study suggests that L. delbrueckii subsp. bulgaricus is an efficient lactic acid bacterial strain for the production of optically pure d -lactic acid from non-edible, organosolv pretreated hardwood and softwood biomass for the synthesis of bio-based plastics and other products.