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1.
A cyclic di-GMP network is present in gram-positive Streptococcus and gram-negative Proteus species
Ying Liu, Changhan Lee, Fengyang Li, Janja Trček, Heike Bähre, Rey-Ting Guo, Chun-Chi Chen, Alexey Chernobrovkin, Roman Zubarev, Ute Römling, 2020, original scientific article

Abstract: The ubiquitous cyclic di-GMP (c-di-GMP) network is highly redundant with numerous GGDEF domain proteins as diguanylate cyclases and EAL domain proteins as c-di-GMP specific phosphodiesterases comprising those domains as two of the most abundant bacterial domain superfamilies. One hallmark of the c-di-GMP network is its exalted plasticity as c-di-GMP turnover proteins can rapidly vanish from species within a genus and possess an above average transmissibility. To address the evolutionary forces of c-di-GMP turnover protein maintenance, conservation, and diversity, we investigated a Gram-positive and a Gram-negative species, which preserved only one single clearly identifiable GGDEF domain protein. Species of the family Morganellaceae of the order Enterobacterales exceptionally show disappearance of the c-di-GMP signaling network, but Proteus spp. still retained one diguanylate cyclase. As another example, in species of the bovis, pyogenes, and salivarius subgroups as well as Streptococcus suis and Streptococcus henryi of the genus Streptococcus, one candidate diguanylate cyclase was frequently identified. We demonstrate that both proteins encompass PAS (Per-ARNT-Sim)-GGDEF domains, possess diguanylate cyclase catalytic activity, and are suggested to signal via a PilZ receptor domain at the C-terminus of type 2 glycosyltransferase constituting BcsA cellulose synthases and a cellulose synthase-like protein CelA, respectively. Preservation of the ancient link between production of cellulose(-like) exopolysaccharides and c-di-GMP signaling indicates that this functionality is even of high ecological importance upon maintenance of the last remnants of a c-di-GMP signaling network in some of today’s free-living bacteria.
Keywords: cellulose biosynthesis, cyclic di-GMP signaling, EAL domain, GGDEF domain, Proteus mirabilis, Streptococcus gallolyticus subsp. gallolyticus
Published in DKUM: 28.01.2025; Views: 0; Downloads: 10
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Antimicrobial activity of amino-modified cellulose nanofibrils decorated with silver nanoparticles
Vesna Lazić, Jovan Nedeljković, Vanja Kokol, 2024, original scientific article

Abstract: Silver nanoparticles (Ag NPs) conjugated with amino-functionalized cellulose nanofibrils (NH2−CNFs) were in situ-prepared by reducing silver ions with free amino groups from NH2−CNFs. The spectroscopy and transmission electron microscopy measurements confirmed the presence of non-agglomerated nanometer-in-size Ag NPs within micrometer-large NH2−CNFs of high (20 wt.-%) content. Although the consumption of amino groups during the formation of Ag NPs lowers the ζ-potential and surface charge of prepared inorganic–organic hybrids (from +31.3 to +19.9 mV and from 2.4 to 1.0 mmol/g at pH 7, respectively), their values are sufficiently positive to ensure electrostatic interaction with negatively charged cell walls of pathogens in acidic and slightly (up to pH ~8.5) alkaline solutions. The antimicrobial activity of hybrid microparticles against various pathogens (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans) is comparable with pristine NH2−CNFs. However, a long-timescale use of hybrids ensures the slow and controlled release of Ag+ ions to surrounding media (less than 1.0 wt.-% for one month).
Keywords: amino-modified cellulose nanofibrils, silver nanoparticles, hybrid microparticles, zeta-potential, antimicrobial activity
Published in DKUM: 09.12.2024; Views: 0; Downloads: 2
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Genetic diversity of exopolysaccharides from acetic acid bacteria isolates originating from apple cider vinegars
Tadeja Vajdič, 2022, original scientific article

Abstract: Acetic acid bacteria (AAB) produce acetic acid but are also gaining importance as safe microorganisms for producing extracellular polysaccharides (EPSs). The best-known homopolysaccharides among them are cellulose and levan. In addition, acetic acid bacteria also produce heteropolysaccharides, water-soluble acetans. Isolates from the broth of organic and conventional apple cider vinegar production were screened for biofilm production. Phenotypic and genomic diversity of EPS-producing isolates was assessed. The diversity of phenotypically different EPSs of apple cider vinegar isolates was investigated at the gene level for the following novel strains: Komagataeibacter (K.) melomenusus SI3083, K. oboediens SI3053, K. pomaceti SI3133, and Gluconacetobacter (Ga.) entanii SI2084. Strain K. melomenusus SI3083 possesses cellulose operons bcs1, bcs2, and bcs4 together with the type I acetan cluster in the absence of the levan operon, strain K. oboediens SI3053 has the operons bcs1, bcs2, bcs3, and bcs4, the levan operon, and the acetan cluster (type I), and the strains K. pomaceti SI3133 and Ga. entanii SI2084 both contain recently described novel ace-type II cluster in addition to the incomplete operon bcs1. A comparison of the genetic diversity of these EPSs to those of the reference strains suggests that the studied EPSs are not species-descriptive. The results of this study deepen our understanding of the genetic variability of the EPS genes in AAB, thereby enabling us to better characterize and exploit the various insoluble and soluble exopolysaccharides produced by AAB for biotechnological applications in the future.
Keywords: acetic acid bacteria genomes, apple cider vinegar microbiota, biofilm production, bacterial cellulose, acetan, Acetobacter, Komagataeibacter
Published in DKUM: 26.09.2024; Views: 0; Downloads: 13
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Dielectric and thermal conductive properties of differently structured ▫$Ti_3C_2T_x$▫ MXene-integrated nanofibrillated cellulose films
Subramanian Lakshmanan, Vida Jurečič, Vid Bobnar, Vanja Kokol, 2024, original scientific article

Abstract: The fabrication of nanocellulose-based substrates with high dielectric permittivity and anisotropic thermal conductivity to replace synthetic thermoplastics in flexible organic electronics remains a big challenge. Herein, films were prepared from native (CNF) and carboxylated (TCNF) cellulose nanofibrils, with and without the addition of thermally conductive multi-layered Ti3C2Tx MXene, to examine the impact of polar (− OH, − COOH) surface groups on the film morphological, moisturizing, dielectric, and thermal dissipation properties. The electrostatic repulsion and hydrogen bonding interaction between the hydrophilic surface/terminal groups on CNF/TCNF and MXene was shown to render their self-assembly distribution and organization into morphologically differently structured films, and, consequently, different properties. The pristine CNF film achieved high intrinsic dielectric permittivity (ε' ~ 9), which was further increased to almost ε' ~ 14 by increasing (50 wt%) the MXene content. The well-packed and aligned structure of thinner TCNF films enables the tuning of both the composite’s dielectric permittivity (ε' ~ 6) and through-plane thermal conductivity (K ~ 2.9 W/mK), which increased strongly (ε' ~ 17) at higher MXene loading giving in-plane thermal conductivity of ~ 6.3 W/mK. The air-absorbed moisture ability of the films contributes to heat dissipation by releasing it. The dielectric losses remained below 0.1 in all the composite films, showing their potential for application in electronics.
Keywords: nanofibrillated cellulose, Ti3C2T, Mxene, film preparation, moisture content, thermal conductivity
Published in DKUM: 03.09.2024; Views: 36; Downloads: 11
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Production efficiency and properties of bacterial cellulose membranes in a novel grape pomace hydrolysate by Komagataeibacter melomenusus ▫$AV436^T$▫ and Komagataeibacter xylinus LMG 1518
Selestina Gorgieva, Urška Jančič, Eva Cepec, Janja Trček, 2023, original scientific article

Abstract: The microbial production of cellulose using different bacterial species has been extensively examined for various industrial applications. However, the cost-effectiveness of all these biotechnological processes is strongly related to the culture medium for bacterial cellulose (BC) production. Herein, we examined a simple and modified procedure for preparing grape pomace (GP) hydrolysate, without enzymatic treatment, as a sole growth medium for BC production by acetic acid bacteria (AAB). The central composite design (CCD) was used to optimise the GP hydrolysate preparation toward the highest reducing sugar contents (10.4 g/L) and minimal phenolic contents (4.8 g/L). The experimental screening of 4 differently prepared hydrolysates and 20 AAB strains identified the recently described species Komagataeibacter melomenusus AV436T as the most efficient BC producer (up to 1.24 g/ L dry BC membrane), followed by Komagataeibacter xylinus LMG 1518 (up to 0.98 g/L dry BC membrane). The membranes were synthesized in only 4 days of bacteria culturing, 1 st day with shaking, followed by 3 days of static incubation. The produced BC membranes in GP-hydrolysates showed, in comparison to the membranes made in a complex RAE medium 34 % reduction of crystallinity index with the presence of diverse cellulose allomorphs, presence of GP-related components within the BC network responsible for the increase of hydrophobicity, the reduction of thermal stability and 48.75 %, 13.6 % and 43 % lower tensile strength, tensile modulus, and elongation, respectively. Here presented study is the first report on utilising a GP-hydrolysate without enzymatic treatment as a sole culture medium for efficient BC production by AAB, with recently described species Komagataeibacter melomenusus AV436T as the most efficient producer in this type of food-waste material. The scale-up protocol of the scheme presented here will be needed for the cost-optimisation of BC production at the industrial levels.
Keywords: grape pomace hydrolysate, bacterial cellulose, acetic acid bacteria, Komagataeibacter melomenusus
Published in DKUM: 26.07.2024; Views: 98; Downloads: 11
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Synthesis of betaine, choline and carnitine containing polymers for dermal wound healing
Lucija Jurko, 2024, doctoral dissertation

Abstract: In this study, we explored the development of cationized 2-hydroxyethyl cellulose (HEC) and succinylated polyallylamine (PAA) in conjunction with polyvinyl alcohol (PVA) for potential applications as antimicrobial wound dressings. Quaternary ammonium compounds are known for their broad-spectrum antimicrobial properties against both Gram-negative and Gram-positive bacteria, but their non-selectivity can lead to high cytotoxicity. To improve the biocompatibility of the cationic materials investigates two distinct approaches. The first approach involves reducing the cationic nature of protonated PAA at a pH below 8.3 through amidation reaction with succinic anhydride. Gradual reduction of the cationic charge is achieved by varying the molar ratios of succinic anhydride during the reaction process. Notably, this reaction can be carried out in an aqueous solution, eliminating potential issues associated with solvent removal. The second part of this thesis focuses on introducing cationic charge by covalently binding naturally occurring quaternary ammonium compounds, such as betaine hydrochloride (BET HCl), choline chloride (ChCl), and carnitine hydrochloride (carnitine). Using 1,1′-carbonyldiimidazole (CDI), we quaternized HEC in anhydrous DMSO, with a detailed investigation of the reaction mechanism by isolating and characterizing intermediate products. This same procedure was applied to form a cationic dimer between BET HCl and ChCl. The chemical structures of the resulting materials were characterized using attenuated total reflectance infrared spectroscopy (ATR-IR) and nuclear magnetic resonance (NMR). The quantification of cationic and total charge was determined through polyelectrolyte and potentiometric titration, respectively. While succinylated PAA exhibited the anticipated biological properties associated with the reduction of cationic characteristics, the same behaviour was not observed for quaternized materials. High cytotoxicity and low antimicrobial properties in the derivatized HEC may be attributed to inadequate purification and the sensitivity of fibroblasts. We produced electrospun non-woven mats incorporating PVA and these derived materials using a single-needle electrospinning machine. The average diameter of the fibres was determined through scanning electron microscopy (SEM) images. Despite the cytotoxicity and the absence of significant antimicrobial properties in these materials, they exhibit potential as effective cationic flocculants for wastewater treatment. Further investigations are pending to address purification issues and make slight adjustments to the procedure to potentially scale up production. These materials still hold promise for applications in both biomedical and environmental chemistry.
Keywords: cellulose, quaternary ammonium compounds, antimicrobial, cytotoxicity, electrospinning
Published in DKUM: 11.07.2024; Views: 127; Downloads: 39
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