Sugar Substrates Research Articles

Parts-Per-Million Level Loading Cyclometalated Ru(II)-NHC Catalyzed Selective Oxidation of Olefins to Carbonyls.

Oxidative cleavage of olefins is a useful reaction in organic synthesis. The most well-known catalytic system is the osmium based Lemieux-Johnson catalyst, which generally requires high catalyst loading and tends to suffer from rapid overoxidation to produce the acid predominantly. Hence, the development of a mild, general, and selective method toward the oxidative cleavage of alkenes to carbonyl compounds is highly desired. In this work, a highly efficient ruthenium-based catalyst for olefin oxidation has been demonstrated by employing a fused π-conjugated imidazo[1,5-a]quinoxaline (ImQx) based NHC ligand with bidentate C(carbanion) CNHC motif. Strong C-donor ligands, paired with a rigid backbone and ruthenium redox activity, provided exceptionally high catalytic activity and a long lifetime for olefin oxidation. Complex showed high catalytic activity and a long lifetime, TONs are several million. The catalyst tolerates numerous functional groups and can be applicable to challenging biomass, natural products, sugar, amino acids, and fatty acid-derived substrates. Based on kinetic studies, thermodynamic activation parameters, and DFT study, the mechanistic finding demonstrated that [3+2] cycloaddition reaction is the key step in the oxidation process. The use of the by-product NaIO3 in the catalytic efficiency has been disclosed for the first time.

A novel esterase regulates Klebsiella pneumoniae hypermucoviscosity and virulence.

Klebsiella pneumoniae, an emerging multidrug-resistant pathogen, exhibits hypermucoviscosity (HMV) as a critical virulence trait mediated by its capsular polysaccharide (CPS). Recent discoveries have determined acetylation as a significant modification for CPS, although its impact on HMV and virulence was previously unknown. This study elucidates the roles of two enzymes: Klebsiella pneumoniae Acetylated CPS Esterase (KpACE), an esterase that removes acetyl groups from CPS, and WcsU, an acetyltransferase that adds acetyl groups to CPS. KpACE is highly upregulated in an ompR-deficient mutant lacking HMV, and its overexpression consistently reduces HMV and diminishes virulence in a mouse model of pneumonia. The esterase domain-containing KpACE effectively deacetylates model sugar substrates and CPS-K2. Site-directed mutagenesis of the conserved catalytic histidine residue at position 370 significantly reduces its enzymatic activity. This reduction correlates with decreased HMV, affecting key virulence traits including biofilm formation and serum resistance. Similarly, a deficiency in the wcsU gene abolishes CPS acetylation, and reduces HMV and virulence. These results highlight the importance of the delicate balance between CPS acetylation by WcsU and deacetylation by KpACE in regulating the pathogenicity of K. pneumoniae. Understanding this balance provides new insights into the modulation of virulence traits and potential therapeutic targets for combating K. pneumoniae infections.

Metabolic strategies in hypoxic plants.

Complex multicellular organisms have evolved in an oxygen-enriched atmosphere. Oxygen is therefore essential for all aerobic organisms including plants, for energy production through cellular respiration. However, plants can experience hypoxia following extreme flooding events and also under aerated conditions in proliferative organs or tissues characterized by high oxygen consumption. When oxygen availability is compromised, plants adopt different strategies to cope with hypoxia and limited aeration. A common feature among different plant species is the activation of an anaerobic fermentative metabolism to provide adenosine triphosphate (ATP) to maintain cellular homeostasis under hypoxia. Fermentation also requires many sugar substrates, which is not always feasible, and alternative metabolic strategies are thus needed. Recent findings have also shown that the hypoxic metabolism is also active in specific organs or tissues of the plant under aerated conditions. Here, we describe the regulatory mechanisms that control the metabolic strategies of plants and how they enable them to thrive despite challenging conditions. A comprehensive mechanistic understanding of the genetic and physiological components underlying hypoxic metabolism should help to provide opportunities to improve plant resilience under the current climate change scenario.

Limosilactobacillus reuteri DSM 17938 Produce Bioactive Components during Formulation in Sucrose.

Improved efficacy of probiotics can be achieved by using different strategies, including the optimization of production parameters. The impact of fermentation parameters on bacterial physiology is a frequently investigated topic, but what happens during the formulation, i.e., the step where the lyoprotectants are added prior to freeze-drying, is less studied. In addition to this, the focus of process optimization has often been yield and stability, while effects on bioactivity have received less attention. In this work, we investigated different metabolic activities of the probiotic strain Limosilactobacillus reuteri DSM 17938 during formulation with the freeze-drying protectant sucrose. We discovered that the strain consumed large quantities of the added sucrose and produced an exopolysaccharide (EPS). Using NMR, we discovered that the produced EPS was a glucan with α-1,4 and α-1,6 glycosidic bonds, but also that other metabolites were produced. The conversion of the lyoprotectant is hereafter designated lyoconversion. By also analyzing the samples with GCMS, additional potential bioactive compounds could be detected. Among these were tryptamine, a ligand for the aryl hydrocarbon receptor, and glycerol, a precursor for the antimicrobial compound reuterin (3-hydroxypropionaldehyde). To exemplify the bioactivity potential of lyoconversion, lyoconverted samples as well as purified EPS were tested in a model for immunomodulation. Both lyoconverted samples and purified EPS induced higher expression levels of IL-10 (2 times) and IL-6 (4-6 times) in peripheral blood mononuclear cells than non-converted control samples. We further found that the initial cultivation of DSM 17938 with sucrose as a sugar substrate, instead of glucose, improved the ability to convert sucrose in the lyoprotectant into EPS and other metabolites. Lyoconversion did not affect the viability of the bacteria but was detrimental to freeze-drying survival, an issue that needs to be addressed in the future. In conclusion, we show that the metabolic activities of the bacteria during the formulation step can be used as a tool to alter the activity of the bacteria and thereby potentially improve probiotic efficacy.

Structural and biochemical insights into the molecular mechanism of N-acetylglucosamine/N-Acetylmuramic acid kinase MurK from Clostridium acetobutylicum

MurK is a MurNAc- and GlcNAc-specific amino sugar kinase, phosphorylates MurNAc and GlcNAc at the 6-hydroxyl group in an ATP-dependent manner, and contributes to the recovery of both amino sugars during the cell wall turnover in Clostridium acetobutylicum. Herein, we determined the crystal structures of MurK in complex with MurNAc, GlcNAc, and glucose, respectively. MurK represents the V-shaped fold, which is divided into a small N-terminal domain and a large C-terminal domain. The catalytic pocket is located within the deep cavity between the two domains of the MurK monomer. We mapped the significant enzyme-substrate interactions, identified key residues involved in the catalytic activity of MurK, and found that residues Asp77 and Arg78 from the β4-α2-loop confer structural flexibilities to specifically accommodate GlcNAc and MurNAc, respectively. Moreover, structural comparison revealed that MurK adopts closed-active conformation induced by the N-acetyl moiety from GlcNAc/MurNAc, rather than closed-inactive conformation induced by glucose, to carry out its catalytic reaction. Taken together, our study provides structural and functional insights into the molecular mechanism of MurK for the phosphorylation of both MurNAc and GlcNAc, sugar substrate specificity, and conformational changes upon sugar substrate binding.

Biochar promotes compost humification by regulating bacterial and fungal communities.

Humus can be formed during composting through biological pathways, nonetheless, the mechanisms through which bacterial and fungal communities govern the development of humus in compost with the addition of biochar remain uncertain. In this study, compost with cow dung and maize stover as feedstock was employed as a control group, and compost with 10% biochar added on top of the feedstock was adopted as a treatment group to investigate the effect of bacterial and fungal communities on humus formation during biochar composting. The results demonstrated that the humic acid content increased by 24.82 and 25.10% at the cooling and maturation stages, respectively, after adding biochar. Besides, the degree of polymerization content in the maturation stage was elevated by 90.98%, which accelerated the humification process of the compost. During the thermophilic and maturity stages, there was a respective increase of 51.34 and 31.40% in reducing sugar content, suggesting that the inclusion of biochar could furnish ample reducing sugar substrate for the Maillard reaction. The addition of biochar reduced the number of humus precursor-associated genera by 35, increased the number of genera involved in humus synthesis by two, and enhanced the stability of the cross-domain network between bacteria and fungi, which confirms that microorganisms contribute to the humification process by decreasing humus precursor consumption as well as increasing humus synthesis with the addition of biochar. Additionally, adding biochar could enhance the humification capacity of the compost pile by dominating the Maillard reaction with reducing sugars as the substrate and strengthening the function of humus synthesis-associated genera. This study enhances our comprehension of the regulatory pathways of biochar in the humification process during composting.

Evaluating bioproducts production in a purple phototrophic biofilm photobioreactor: Fuel-synthesis wastewater vs. simple substrates

This study evaluated the influence of different carbon sources on purple non-sulphur bacteria (PNSB) biofilm formation, and the production of polyhydroxybutyrate (PHB) and other value-added bio-products. Higher PNSB growth and biofilm formation were observed in fuel-synthesis wastewater (FSW), followed by acetate. Both FSW and acetate cultures contained a large proportion of Rhizobiales, while sugar substrates led to yeast enrichment. Protein contents reached 40–41 % for acetate, which is suitable for single cell protein (SCP) use. The maximum PHB content from the suspended and biofilm growth was obtained from glucose (18.1 ± 0.10 %, 12.9 ± 1.11 %), followed by FSW (14.9 ± 0.25 %, 11.2 ± 0.50 %). FSW showed the highest overall productivity for both protein and PHB. Pigment concentrations were low for all substrates. The study underscores substrate influence on microbial community and bioproducts potential. It highlights FSW as a promising substrate for PNSB, suggesting its treatment integration for resource recovery.

Exploring stevioside binding affinity with various proteins and receptors actively involved in the signaling pathway and a future candidate for diabetic patients.

Introduction and Background: Diabetes is a chronic metabolic disease characterized by elevated blood glucose levels and is one of the main global health concerns. Synthetic sugar substrate has many side effects such as leukemia, bladder cancer, hepatotoxicity, breast cancer, headache, and brain toxicity. The WHO and FDA has recently banned some of the synthetic sugar alternatives due to their carcinogenic effects. Objective and Methodology: Therefore, the main objective of the current study was to investigate the safety and binding affinity of Stevioside with Glucose Transpoter-4 (GLUT-4), Akt, Insulin Receptor (IR) and Insulin Receptor Substrate-1 (IRS-1) to confirmed that Stevioside is one the potent natural sweetener/drug for diabetes. This study delves into the molecular interaction between Stevioside and key diabetic proteins: GLUT-4, Akt, IR and IRS-1. A precise molecular docking approach was used to simulate the binding affinity of Stevioside to these proteins. The pharmacokinetic properties of the molecule should be taken into consideration as important variables throughout the virtual screening process. Results: The result of active site analysis of GLUT-4, Akt, IR and IRS-1 showed a zone of 2158.359 Ǻ2, 579.259 Ǻ2, 762.651 Ǻ2, and 152.167 Ǻ2 and a volume of 2765.094 Ǻ³, 355.567 Ǻ³, 686.806 Ǻ³, and 116.874 Ǻ³, respectively. Docking analysis of the Stevioside compound showed the highest docking energy with scores of -9.9 with GLUT-4, -6.7 with Akt, -8.0 with IR and -8.8 with IRS-1. Studies indicated that it remains undigested by stomach acids and enzymes and is not absorbed in the upper small intestine. Further, tests revealed no hepatotoxicity, AMES toxicity, or skin sensitivity, making it a promising candidate for safe consumption as drug metabolism. Conclusion and Recommendations: Instead of other sugar alternatives, Stevioside will help diabetic patients with a lower chance of infections, lowered blood pressure/blood sugar, and increased glucose uptake in diabetic muscles. Stevioside is a natural sweetener, and the current study recommends its usage in various dietary products for diabetic patients.

The molecular basis of Human FN3K mediated phosphorylation of glycated substrate.

Glycation, a non-enzymatic post-translational modification occurring on proteins, can be actively reversed via site-specific phosphorylation of the fructose-lysine moiety by FN3K kinase, to impact the cellular function of target protein. A regulatory axis between FN3K and glycated protein targets has been associated with conditions like diabetes and cancer. However the molecular basis of this relationship has not been explored so far. Here, we determined a series of crystal structures of HsFN3K in apo-state, and in complex with different nucleotide analogs together with a sugar substrate mimic to reveal the features important for its kinase activity and substrate recognition. Additionally, the dynamics in sugar substrate binding during the kinase catalytic cycle provide important mechanistic insights into HsFN3K function. Our structural work provides the molecular basis for rationale small molecule design targeting FN3K.

Supported Ruthenium Phosphide as a Promising Catalyst for Selective Hydrogenation of Sugars

AbstractThis work demonstrates that supported ruthenium phosphides (RuP2) are attractive catalysts for selective production of alditols by sugar hydrogenation. In our studies, carbon supported RuP2 with a ruthenium content of 5 wt.– % led to the highest activity in xylose hydrogenation and to nearly 100 % yield for xylitol. ICP‐OES and XRD measurements revealed the stability of this novel RuP2/C catalyst under typical hydrogenation conditions (50 barH2, 120 °C) in aqueous phase. Furthermore, STEM‐EDX illustrated the close proximity of ruthenium and phosphorous on the catalyst site and the formation of nanoparticles in the size of 2–4 nm. The catalyst system was successfully applied for the selective hydrogenation of further sugar substrates, including glucose, fructose, and disaccharides, such as cellobiose and sucrose. Here, the RuP2/C revealed its bifunctional acidic/metallic character, enabling in a tandem reaction the hydrolysis of disaccharides, directly followed by a selective hydrogenation to form sugar alcohols in high yield.

The Chemical Profiles and Antioxidant Properties of Live Fruit or Vegetable Vinegars Available on the Polish Food Market.

Live vinegar is a product formed through a two-step fermentation process of a sugar substrate that has not been subjected to filtration or pasteurization. This is considered to preserve all nutrients and biologically active microorganisms, making it a product with a valuable composition and beneficial properties. Therefore, the purpose of this study was to analyze the chemical composition and antioxidant properties of the selected vinegars available on the Polish food market. The material in the study consisted of four live (naturally turbid, unfiltered, unpasteurized) fruit or vegetable vinegars: apple, pear, rhubarb, and lemon. Spectrophotometric, HPLC, and GC methods were used. Among the vinegars tested, lemon vinegar had the highest vitamin C content-15.95 mg/100 mL. Apple vinegar proved to be the best source of polyphenols and flavonoids (TPC-191.97 mg GAE/L, TFC-70.22 mg RE/L). All of the vinegars contained dihydroxybenzoic acid, 4-hydroxybenzoic acid, caffeic acid, 2-hydroxycinnamic acid, and myricetin. The acetic acid content of the tested vinegars ranged from 29.180 to 38.125 mM/L. The pH values ranged from 3.14 to 3.41. In conclusion, the most promising nutraceutical with potentially beneficial health-promoting properties seems to be apple vinegar.

Characterization of the ADP-β-d-manno-heptose biosynthetic enzymes from two pathogenic Vibrio strains

ADP-activated β-d-manno-heptoses (ADP-β-d-manno-heptoses) are precursors for the biosynthesis of the inner core of lipopolysaccharide in Gram-negative bacteria. Recently, ADP-d-glycero-β-d-manno-heptose (ADP-d,d-manno-heptose) and its C-6′′ epimer, ADP-l-glycero-β-d-manno-heptose (ADP-l,d-manno-heptose), were identified as potent pathogen-associated molecular patterns (PAMPs) that can trigger robust innate immune responses. Although the production of ADP-d,d-manno-heptose has been studied in several different pathogenic Gram-negative bacteria, current knowledge of ADP-β-d-manno-heptose biosynthesis in Vibrio strains remains limited. Here, we characterized the biosynthetic enzymes of ADP-d,d-manno-heptose and the epimerase that converts it to ADP-l,d-manno-heptose from Vibrio cholerae (the causative agent of pandemic cholera) and Vibrio parahaemolyticus (non-cholera pathogen causing vibriosis with clinical manifestations of gastroenteritis and wound infections) in comparison with their isozymes from Escherichia coli. Moreover, we discovered that β-d-mannose 1-phosphate, but not α-d-mannose 1-phosphate, could be activated to its ADP form by the nucleotidyltransferase domains of bifunctional kinase/nucleotidyltransferases HldEVC (from V. cholerae) and HldEVP (from V. parahaemolyticus). Kinetic analyses of the nucleotidyltransferase domains of HldEVC and HldEVP together with the E. coli–derived HldEEC were thus carried out using β-d-mannose 1-phosphate as a mimic sugar substrate. Overall, our works suggest that V. cholerae and V. parahaemolyticus are capable of synthesizing ADP-β-d-manno-heptoses and lay a foundation for further physiological function explorations on manno-heptose metabolism in Vibrio strains.Key points• Vibrio strains adopt the same biosynthetic pathway as E. coli in synthesizing ADP-β-d-manno-heptoses.• HldEs from two Vibrio strains and E. coli could activate β-d-mannose 1-phosphate to ADP-β-d-mannose.• Comparable nucleotidyltransfer efficiencies were observed in the kinetic studies of HldEs.

The energy-converting hydrogenase Ech2 is important for the growth of the thermophilic acetogen Thermoanaerobacter kivui on ferredoxin-dependent substrates.

Acetogens thrive by converting H2+CO2 to acetate. Under environmental conditions, this allows for only very little energy to be conserved (∆G'<-20 kJ mol-1). CO2 serves as a terminal electron acceptor in the ancient Wood-Ljungdahl pathway (WLP). Since the WLP is ATP neutral, energy conservation during growth on H2 + CO2 is dependent on the redox metabolism. Two types of acetogens can be distinguished, Rnf- and Ech-type. The function of both membrane-bound enzyme complexes is twofold-energy conversion and redox balancing. Ech couples the Fd-dependent reduction of protons to H2 to the formation of a proton gradient in the thermophilic bacterium Thermoanaerobacter kivui. This bacterium may be utilized in gas fermentation at high temperatures, due to very high conversion rates and the availability of genetic tools. The physiological function of an Ech hydrogenase in T. kivui was studied to contribute an understanding of its energy and redox metabolism, a prerequisite for future industrial applications.

Acid hydrolysis of Solanum tuberosum periderm for accumulation of polyhydroxyalkanoates in Pseudomonas putida MTCC 2475.

Polyhydroxyalkanoates are a class of biodegradable, biocompatible polymers composed of polyesters of R-hydroxyalkanoic acids and deposited intracellularly by a variety of microorganisms which have potential to serve as alternative to commercial plastic. Bioplastics are gaining attention due to sustainability, biodegradability, biocompatibility, and lower carbon footprint. Nevertheless, the commercialization of PHA is predominantly hindered by the elevated production expenses arising primarily from the use of a pure sugar substrate. Our study has established a feasible method for bioplastic formation applying Pseudomonas putida MTCC 2475 and Solanum tuberosum periderm as a carbon source. To optimize the sugar yield response surface methodology was used, which released 69.34% ± 0.25% reducing sugar. PHA production experiments were performed in hydrolysate containing media as well as commercial sugar containing mineral salt media. After 48h of fermentation of using this sugar, a biomass concentration of 2.19 gL-1, with a PHA production of 0.60 gL-1 (28.71% ± 0.55%) was obtained which was comparatively similar with synthetic media (2.56 gL-1 cell dry weight and 29.97% ± 0.45% PHA). Furthermore, the monomers of PHA produced by hydrolysate were characterized using Gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance. This investigation has identified three distinct monomers of medium-chain PHAs, namely, methyl 3-Hydroxydodecanoate, 3-Hydroxytetradecanoate, and Hexadecanoic acid 3-Hydroxy methyl esters. Hence this study concludes a sustainable production of bioplastics from S. tuberosum periderm waste.

Effect of depolymerized lignin on the cellulosic/hemicellulosic precursors for fungal secondary metabolite (kojic acid) production

There are very few reports on kojic acid production from lignocellulosic biomass and mostly unexplored why there was a low product yield. This study demonstrates the experimental evidence of the effect of lignin on utilizing lignocellulosic sugar substrates. The fungi Aspergillus flavus BU20S used in this study was able to produce kojic acid from glucose (2.50 ± 0.07 g/L), xylan (1.40 ± 0.09 g/L), and xylose (2.66 ± 0.24 g/L). The product formation was significantly reduced (> 90 %) in the presence of rice straw-derived lignin with glucose as well as with xylan and xylose. The screening of glucose (2–10 g/L) + lignin (500–1500 mg/L) combinations in a central composite design using Design Expert® v.12 also showed that the product response was lower when the lignin was high (1500 mg/L). It concludes that the secondary metabolic route in fungi is greatly affected in the presence of lignin in the medium.

Simultaneous glucose and xylose utilization by an Escherichia coli catabolite repression mutant.

As advances are made toward the industrial feasibility of mass-producing biofuels and commodity chemicals with sugar-fermenting microbes, high feedstock costs continue to inhibit commercial application. Hydrolyzed lignocellulosic biomass represents an ideal feedstock for these purposes as it is cheap and prevalent. However, many microbes, including Escherichia coli, struggle to efficiently utilize this mixture of hexose and pentose sugars due to the regulation of the carbon catabolite repression (CCR) system. CCR causes a sequential utilization of sugars, rather than simultaneous utilization, resulting in reduced carbon yield and complex process implications in fed-batch fermentation. A mutant of the gene encoding the cyclic AMP receptor protein, crp*, has been shown to disable CCR and improve the co-utilization of mixed sugar substrates. Here, we present the strain construction and characterization of a site-specific crp* chromosomal mutant in E. coli BL21 star (DE3). The crp* mutant strain demonstrates simultaneous consumption of glucose and xylose, suggesting a deregulated CCR system. The proteomics further showed that glucose was routed to the C5 carbon utilization pathways to support both de novo nucleotide synthesis and energy production in the crp* mutant strain. Metabolite analyses further show that overflow metabolism contributes to the slower growth in the crp* mutant. This highly characterized strain can be particularly beneficial for chemical production by simultaneously utilizing both C5 and C6 substrates from lignocellulosic biomass.IMPORTANCEAs the need for renewable biofuel and biochemical production processes continues to grow, there is an associated need for microbial technology capable of utilizing cheap, widely available, and renewable carbon substrates. This work details the construction and characterization of the first B-lineage Escherichia coli strain with mutated cyclic AMP receptor protein, Crp*, which deregulates the carbon catabolite repression (CCR) system and enables the co-utilization of multiple sugar sources in the growth medium. In this study, we focus our analysis on glucose and xylose utilization as these two sugars are the primary components in lignocellulosic biomass hydrolysate, a promising renewable carbon feedstock for industrial bioprocesses. This strain is valuable to the field as it enables the use of mixed sugar sources in traditional fed-batch based approaches, whereas the wild-type carbon catabolite repression system leads to biphasic growth and possible buildup of non-preferential sugars, reducing process efficiency at scale.

Correlating sugar transporter expression and activities to identify transporters for an orphan sugar substrate

Filamentous fungi like Neurospora crassa are able to take up and metabolize important sugars present, for example, in agricultural and human food wastes. However, only a fraction of all putative sugar transporters in filamentous fungi has been characterized to date, and for many sugar substrates, the corresponding transporters are unknown. In N. crassa, only 14 out of the 42 putative major facilitator superfamily (MFS)–type sugar transporters have been characterized so far. To uncover this hidden potential for biotechnology, it is therefore necessary to find new strategies. By correlation of the uptake profile of sugars of interest after different induction conditions with the expression profiles of all 44 genes encoding predicted sugar transporters in N. crassa, together with an exhaustive phylogenetic analysis using sequences of characterized fungal sugar transporters, we aimed to identify transporter candidates for the tested sugars. Following this approach, we found a high correlation of uptake rates and expression strengths for many sugars with dedicated transporters, like galacturonic acid and arabinose, while the correlation is loose for sugars that are transported by several transporters due to functional redundancy. Nevertheless, this combinatorial approach allowed us to elucidate the uptake system for the disaccharide lactose, a by-product of the dairy industry, which consists of the two main cellodextrin transporters CDT-1 and CDT-2 with a minor contribution of the related transporter NCU00809. Moreover, a non-MFS transporter involved in glycerol transport was also identified. Deorphanization of sugar transporters or identification of transporters for orphan sugar substrates by correlation of uptake kinetics with transporter expression and phylogenetic information can thus provide a way to optimize the reuse of food industry by-products and agricultural wastes by filamentous fungi in order to create economic value and reduce their environmental impact.Key points• The Neurospora crassa genome contains 30 uncharacterized putative sugar transporter genes.• Correlation of transporter expression and sugar uptake profiles can help to identify transporters for orphan sugar substrates.• CDT-1, CDT-2, and NCU00809 are key players in the transport of the dairy by-product lactose in N. crassa.

Kinetic modeling of cell growth and value-added products accumulation of Thraustochytrium striatum

A kinetic mathematical model was developed, calibrated, and validated to describe the fermentation performance of a marine protist, Thraustochytrium striatum. This model consists of equations describing substrate consumption, cell growth, and the accumulation of two important intracellular products (lipids and astaxanthin). Moreover, the substrate inhibition and the consumption of product lipids were also considered in the model. After calibration, this model can describe the fermentation performance of T. striatum with high fidelity (R2 values greater than 0.92) over a broad concentration range of individual (glucose 2.5–50 g/L, cellobiose 2.5–10 g/L, and xylose 2.5–10 g/L) and mixed sugar substrates (glucose/cellobiose/xylose, 10.0/2.5/2.5 g/L and 18.0/4.0/4.0 g/L, respectively). Besides synthetic substrates, this model was also proven to be able to simulate the utilization of natural sugar substrates (i.e., glucose, xylose, and cellobiose) generated from the enzymatic hydrolysate of corn stover. However, the presence of toxic compounds in corn stover hydrolysate might have slightly deviated the model prediction, indicating further improvement of this model is needed when it comes to the simulation of natural sugar substrates containing toxic compounds. This model is anticipated to serve as a fundamental framework to simulate and predict the fermentation performance of marine protist for upscaled applications.

Bioethanol Production from Non-Conventional Yeasts Wickerhamomyces anomalus (Pichia anomala) and Detection of ADH1 Gene

Bioethanol is an organic compound resulted from the fermentation of sugar substrates by microorganisms which is used as alternative energy sources. During bioethanol fermentation yeast are exposed to various fermentation stresses, including temperature, osmotic, and oxidative stresess. Such conditions may decrease ethanol production. We previously isolated fermentation-stress tolerance yeast isolates from traditional Balinese beverages, identified as Wickerhamomyces anomalus BT2, BT5, and BT6. However no data available regarding the bioethanol production of those isolates. Our study indicates that these strains could utilize various sugar substrates (glucose, xylose, maltose, sucrose) in oxidative fermentative media. The highest value of substrate utilization efficiency following 48 hours fermentation was shown by BT6 on glucose (61.02%), BT 2 on xylose (55.44%) and maltose (60.90%). Measurement of ethanol production by Gas Chromatography showed that the strains were able to produce higher ethanol on the glucose substrate than other substrates. For instance, BT6 could produce the highest ethanol production (5.00 g/L) amongst strains tested by using glucose as substrate. Yet, the particular strains could only produce 0.30 g/L and 0.65 g/L by using xylose and maltose, respectively. For further genetic engineering purposes, we detected ADH1 gene from all three isolates, with high homology to the alcohol dehydrogenase from Saccharomyces cerevisiae, Geobacillus stearothermophilus and Pseudomonas aeruginosa. Further strain development can be carried out targeting the ADH1 gene, important for ethanol fermentation.

Physicochemical, Microbiological and Organoleptic Characteristics of Rosella Water Kefir with Sucrose Sweetener

&lt;p&gt;Red rosella is one of the beneficial plants with its flower petals that have a distinctly sour taste. Using rosella in water kefir can enrich its functionality and taste. Rosella water kefir has acidic characteristics derived from rosella and sugar substrates. Sugars such as sucrose in the production of water kefir act as a carbon source for the metabolism of water kefir grains. The higher the added sugar causes the total of good microbes and organic acids in water kefir products to increase, but too high sugar can cause the death of these good microbes so it also affects the nutritional content and taste of the product. Therefore, the best concentration of sugar is needed. This study aims to obtain the best sucrose concentration in producing the best physicochemical, microbiological, and organoleptic characteristics of rosella water kefir. This study used the addition of sucrose at concentrations of 6%, 9%, 12%, and 15% (w/v) with the parameters observed in physicochemical characteristics including total dissolved solids, biomass, CO&lt;sub&gt;2&lt;/sub&gt; content, and total acid, microbiological characteristics including total lactic acid bacteria and total microbes, and organoleptic characteristics including sweet taste, sour taste, soda sensation, and aroma. The results obtained in this study indicate that increasing the concentration of sucrose in rosella water kefir had a significant effect (p&amp;lt;0.05) on the physicochemical, microbiological, and organoleptic characteristics of sweet and sour tastes. The addition of 12% sucrose was the limit—tolerance for the addition of sugar in rosella water kefir which is also the best treatment.&lt;/p&gt;