Paradigm shift in xylose isomerase usage: a novel scenario with distinct applications

Enhanced High-Fructose Corn Syrup Production: Immobilizing Serratia marcescens Glucose Isomerase on MOF (Co)-525 Reduces Co2+ Dependency in Glucose Isomerization to Fructose

The escalating demand for processed foods has led to the widespread industrial use of glucose isomerase (GI) for high-fructose corn syrup (HFCS) production. This reliance on GIs necessitates continual Co2+ supplementation to sustain high catalytic activity across multiple reaction cycles. In this study, Serratia marcescens GI (SmGI) was immobilized onto surfaces of the metal-organic framework (MOF) material MOF (Co)-525 to generate MOF (Co)-525-GI for use in catalyzing glucose isomerization to generate fructose. Examination of MOF (Co)-525-GI structural features using scanning electron microscopy-energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, and ultraviolet spectroscopy revealed no structural changes after SmGI immobilization and the addition of Co2+. Notably, MOF (Co)-525-GI exhibited optimal catalytic activity at pH 7.5 and 70 °C, with a maximum reaction rate (Vmax) of 37.24 ± 1.91 μM/min and Km value of 46.25 ± 3.03 mM observed. Remarkably, immobilized SmGI exhibited sustained high catalytic activity over multiple cycles without continuous Co2+ infusion, retaining its molecular structure and 96.38% of its initial activity after six reaction cycles. These results underscore the potential of MOF (Co)-525-GI to serve as a safer and more efficient immobilized enzyme technology compared to traditional GI-based food-processing technologies.

Impact of xylose epimerase on sugar assimilation and sensing in recombinant Saccharomyces cerevisiae carrying different xylose-utilization pathways

BACKGROUND

Over the last decades, many strategies to procure and improve xylose consumption in Saccharomyces cerevisiae have been reported. This includes the introduction of efficient xylose-assimilating enzymes, the improvement of xylose transport, or the alteration of the sugar signaling response. However, different strain backgrounds are often used, making it difficult to determine if the findings are transferrable both to other xylose-consuming strains and to other xylose-assimilation pathways. For example, the influence of anomerization rates between α- and β-xylopyranose in pathway optimization and sugar sensing is relatively unexplored.

RESULTS

In this study, we tested the effect of expressing a xylose epimerase in S. cerevisiae strains carrying different xylose-consuming routes. First, XIs originating from three different species in isogenic S. cerevisiae strains were tested and the XI from Lachnoclostridium phytofermentans was found to give the best performance. The benefit of increasing the anomerization rate of xylose by adding a xylose epimerase to the XI strains was confirmed, as higher biomass formation and faster xylose consumption were obtained. However, the impact of xylose epimerase was XI-dependent, indicating that anomer preference may differ from enzyme to enzyme. The addition of the xylose epimerase in xylose reductase/xylitol dehydrogenase (XR/XDH)-carrying strains gave no improvement in xylose assimilation, suggesting that the XR from Spathaspora passalidarum had no anomer preference, in contrast to other reported XRs. The reduction in accumulated xylitol that was observed when the xylose epimerase was added may be associated with the upregulation of genes encoding endogenous aldose reductases which could be affected by the anomerization rate. Finally, xylose epimerase addition did not affect the sugar signaling, whereas the type of xylose pathway (XI vs. XR/XDH) did.

CONCLUSIONS

Although xylose anomer specificity is often overlooked, the addition of xylose epimerase should be considered as a key engineering step, especially when using the best-performing XI enzyme from L. phytofermentans. Additional research into the binding mechanism of xylose is needed to elucidate the enzyme-specific effect and decrease in xylitol accumulation. Finally, the differences in sugar signaling responses between XI and XR/XDH strains indicate that either the redox balance or the growth rate impacts the SNF1/Mig1p sensing pathway.

Development of an enzymatic cascade to systematically utilize lignocellulosic monosaccharide

BACKGROUND

The fermentation valorization of two main lignocellulosic monosaccharides, glucose and xylose, is extensively developed; however, it is restricted by limited yield and process complexity. An in vitro enzymatic cascade reaction can be an alternative approach.

RESULTS

In this study, a three-stage, five-enzyme cascade was developed to convert pretreated biomass to valuable chemicals. First, a ribose-5-phosphate isomerase B mutant isomerized xylose to d-xylulose with high substrate specificity, and a d-arabinose dehydrogenase continued to reduce d-xylulose to d-arabitol. Simultaneously, glucose was utilized for the coenzyme regeneration catalyzed by a glucose dehydrogenase, generating useful gluconic acid and achieving 73% of total conversion rate after 36 h. Then, six kinds of pretreated biomass lignocellulose were hydrolyzed by cellulase and hemicellulase, and corn cob was identified as the initial substrate for providing the highest monosaccharide content. A 65% conversion rate of the lignocellulosic xylose was obtained after 24 h.

CONCLUSIONS

This study presents a proof of concept to convert main lignocellulosic monosaccharides systematically by an enzymatic cascade at stoichiometric ratio. © 2022 Society of Chemical Industry.

Biotechnologically potential genes in a polysaccharide-degrading epibiont of the Indonesian brown algae Hydroclathrus sp

BACKGROUND

Marine bacteria have recently attracted increasing attention to be harnessed for the production of valuable enzymes, vitamins, and bioactive compounds. Bacteria associated with the surfaces of marine macroalgae, called epibionts, are particularly interesting from ecological and biotechnological points of view, as they often exhibit antimicrobial activities to compete with pathogenic bacteria for nutrients and spaces. In search for biotechnologically potential genes from marine bacteria, we sequenced and analysed the genome of the epibiont HI03-3b, a polysaccharide-degrading bacterium associated with the surface of the Indonesian brown algae Hydroclathrus sp.

RESULTS

The algal epibiont HI03-3b has a genome of approximately 4,860,704 bp in size with 42.02 mol% G + C content, consisting of 5655 open reading frames (ORFs), 4409 genes coding for proteins (CDSs), 94 genes for tRNAs, and 32 genes for rRNAs. The genome sequence of HI03-3b was most closely related to that of Cytobacillus firmus NCTC10335 with the average amino acid identity (AAI) of 95.0 %, average nucleotide identity (ANI) of 94.1 %, and a recommended DNA-DNA hybridization (DDH) of 57.60 %. These scores are lower than the most frequently used standard for species demarcation (95% ANI cutoff) and the new species threshold (DDH > 70.0% for the same bacterial species). Some differences in genome features and gene composition were observed between HI03-3b and NCTC10335, such as genes encoding carbohydrate active enzymes. These suggest that HI03-3b is unique and likely a novel species within Cytobacillus genus, and we therefore proposed its name as Cytobacillus wakatobiense HI03-3b. Genome sequence analyses indicated the presence of genes involved not only in polysaccharide and protein degradation but also in vitamin and secondary metabolite biosynthesis. Some of them encode enzymes and compounds with biotechnological interest, such as protease, chitinase, subtilisin, pullulanase, and bacillolysin, which are often associated with antimicrobial or antibiofilm activities. This antimicrobial potential is supported by our finding that the extracellular protein fraction of this epibiont inhibited the growth of the bacterial pathogen Staphylococcus aureus.

CONCLUSION

The epibiont Cytobacillus HI03-3b harbours genes for polysaccharide and protein degradation as well as for natural product biosynthesis, suggesting its potential ecological roles in outcompeting other bacteria during biofilm formation as well as in protecting its algal host from predation. Due to the presence of genes for vitamin biosynthesis, it might also provide the algal host with vitamins for growth and development. Some of these metabolic genes are biotechnologically important, as they could become a platform for bioengineering to generate various seaweed-derived substances sustainably, such as antibiofilm agents and vitamins, which are beneficial for human health.