Exopolysaccharides Production by Cultivating a Bacterial Isolate from the Hypersaline Environment of Salar de Uyuni (Bolivia) in Pretreatment Liquids of Steam-Exploded Quinoa Stalks and Enzymatic Hydrolysates of Curupaú Sawdust

Exploring biosynthesis strategies to boost the yield of exopolysaccharide-protein blend from Bacillus arachidis SY8(T), an isolated native strain, as a potent adsorbent for heavy metals removal

This investigation centers on the synthesis of a polysaccharide-protein blend produced by an isolated native strain (99.12 % phylogenetic affinity with Bacillus arachidis SY8(T)). The primary objective was to investigate the production of extracellular polymeric substances (EPS) under diverse stress conditions, encompassing exposure to heavy metal ions, salt, and toxic agents. Additionally, the impact of environmental parameters, namely pH, inoculation percentage, and time, on the production was investigated. Subsequently, the study examined the biosorption potential of the EPS produced for Pb(II), Cu(II), and Mn(II). The EPS obtained was thoroughly characterized via various tests. Rheological evaluations of an EPS solution (2 wt%) confirmed its pseudo-plastic and non-Newtonian fluid properties, while TGA analysis demonstrated its thermal stability up to 600 °C. Additional analyses, including GPC, FTIR, and H-NMR, provide further insights into the produced EPS. The best conditions for EPS production are determined: 5 % NaCl salt, serving as an effective stress inducer, and 37 °C, pH 6, with a 5 % inoculation, over 96 h. EPS demonstrates remarkable removal efficiencies of 99.9, 99.4 and 78.9 % for Pb(II), Cu(II), and Mn(II), respectively. These findings highlight the potential of EPS as an effective agent for removing heavy metal ions.

Community-forming traits play role in effective colonization of plant-growth-promoting bacteria and improved plant growth

Community-forming traits (CFts) play an important role in the effective colonization of plant-growth-promoting bacterial communities that influence host plants positively by modulating their adaptive functions. In this study, by considering plant-growth-promoting traits (PGPts) and community-forming traits (CFts), three communities were constructed, viz., SM1 (PGPts), SM2 (CFts), and SM3 (PGPts+CFts). Each category isolates were picked up on the basis of their catabolic diversity of different carbon sources. Results revealed a distinctive pattern in the colonization of the communities possessed with CF traits. It was observed that the community with CFts colonized inside the plant in groups or in large aggregations, whereas the community with only PGPts colonized as separate individual and small colonies inside the plant root and leaf. The effect of SM3 in the microcosm experiment was more significant than the uninoculated control by 22.12%, 27.19%, and 9.11% improvement in germination percentage, chlorophyll content, and plant biomass, respectively. The significant difference shown by the microbial community SM3 clearly demonstrates the integrated effect of CFts and PGPts on effective colonization vis-à-vis positive influence on the host plant. Further detailed characterization of the interaction will take this technology ahead in sustainable agriculture.

Microbial diversity in polyextreme salt flats and their potential applications

Recent geological, hydrochemical, and mineralogical studies performed on hypersaline salt flats have given insights into similar geo-morphologic features on Mars. These salt-encrusted depressions are widely spread across the Earth, where they are characterized by high salt concentrations, intense UV radiation, high evaporation, and low precipitation. Their surfaces are completely dry in summer; intermittent flooding occurs in winter turning them into transitory hypersaline lakes. Thanks to new approaches such as culture-dependent, culture-independent, and metagenomic-based methods, it is important to study microbial life under polyextreme conditions and understand what lives in these dynamic ecosystems and how they function. Regarding these particular features, new halophilic microorganisms have been isolated from some salt flats and identified as excellent producers of primary and secondary metabolites and granules such as halocins, enzymes, carotenoids, polyhydroxyalkanoates, and exopolysaccharides. Additionally, halophilic microorganisms are implemented in heavy metal bioremediation and hypersaline wastewater treatment. As a result, there is a growing interest in the distribution of halophilic microorganisms around the world that can be looked upon as good models to develop sustainable biotechnological processes for all fields. This review provides insights into diversity, ecology, metabolism, and genomics of halophiles in hypersaline salt flats worldwide as well as their potential uses in biotechnology.

Structural elucidation of the exopolysaccharide from Streptococcus thermophilus XJ53 and the effect of its molecular weight on immune activity

EPS53, a homogeneous exopolysaccharide (EPS) was isolated from Streptococcus thermophiles XJ53 fermented in skimmed milk via anion exchange column chromatography. The relative molecular weight of EPS53 was above 6.7 × 10⁵ g/mol; its repeating structural unit of EPS53 consisted of β-T-Galp, β-1,3-Galf, α-1,3-Glcp and β-1,3,6-Glcp residues in a molar ratio of 1:1:1:1, with β-T-Galp attached to the O-6 position of β-1,3,6-Glcp，identical to the EPS produced from S. thermophilus SFi39. EPS53-D, purified under similar conditions as EPS53 except for the deproteinization of trichloroacetic acid (TCA), had a lower molecular weight but the same repeating structural unit. The effects of EPS53 and EPS53-D on proliferation, phagocytosis and nitric oxide (NO) release of macrophage RAW264.7 were compared. EPS53 exhibited stronger immune activity than EPS53-D, suggesting that the molecular weight might have an important effect on the activity of EPS molecules. Treatment with TCA might affect the activities of native EPSs produced by fermentation.

Molecular Characterization and Biocompatibility of Exopolysaccharide Produced by Moderately Halophilic Bacterium Virgibacillus dokdonensis from the Saltern of Kumta Coast

The use of natural polysaccharides as biomaterials is gaining importance in tissue engineering due to their inherent biocompatibility. In this direction, the present study aims to explore the structure and biocompatibility of the EPS produced by Virgibacillus dokdonensis VITP14. This marine bacterium produces 17.3 g/L of EPS at 96 h of fermentation. The EPS was purified using ion exchange and gel permeation chromatographic methods. The porous web-like structure and elemental composition (C, O, Na, Mg, P, S) of the EPS were inferred from SEM and EDX analysis. AFM analysis revealed spike-like lumps with a surface roughness of 84.85 nm. The zeta potential value of −10 mV indicates the anionic nature of the EPS. Initial molecular characterization showed that the EPS is a heteropolysaccharide composed of glucose (25.8%), ribose (18.6%), fructose (31.5%), and xylose (24%), which are the monosaccharide units in the HPLC analysis. The FTIR spectrum indicates the presence of functional groups/bonds typical of EPSs (O-H, C-H, C-O-H, C-O, S=O, and P=O). The polymer has an average molecular weight of 555 kDa. Further, NMR analysis revealed the monomer composition, the existence of two α- and six β-glycosidic linkages, and the branched repeating unit as → 1)[α-D-Xylp-(1 → 2)-α-D-Glcp-(1 → 6)-β-D-Glcp-(1 → 5)]-β-D-Frup-(2 → 2)[β-D-Xylp-(1 → 4)]-β-D-Xylp-(1 → 6)-β-D-Fruf-(2 → 4)-β-D-Ribp-(1 →. The EPS is thermally stable till 251.4 °C. X-ray diffraction analysis confirmed the semicrystalline (54.2%) nature of the EPS. Further, the EPS exhibits significant water solubility (76.5%), water-holding capacity (266.8%), emulsifying index (66.8%), hemocompatibility (erythrocyte protection > 87%), and cytocompatibility (cell viability > 80% on RAW264.7 and keratinocyte HaCaT cells) at higher concentrations and prolongs coagulation time in APTT and PT tests. Our research unveils the significant biocompatibility of VITP14 EPS for synthesizing a variety of biomaterials.

Production of Exopolysaccharides by Cultivation of Halotolerant Bacillus atrophaeus BU4 in Glucose- and Xylose-Based Synthetic Media and in Hydrolysates of Quinoa Stalks

A halotolerant, exopolysaccharide-producing bacterium isolated from the Salar de Uyuni salt flat in Bolivia was identified as Bacillus atrophaeus using next-generation sequencing. Comparisons indicate that the genome most likely (p-value: 0.0024) belongs to a subspecies previously not represented in the database. The growth of the bacterial strain and its ability to produce exopolysaccharides (EPS) in synthetic media with glucose or xylose as carbon sources, and in hydrolysates of quinoa stalks, was investigated. The strain grew well in all synthetic media, but the growth in glucose was better than that in xylose. Sugar consumption was better when initial concentrations were low. The growth was good in enzymatically produced cellulosic hydrolysates but was inhibited in hemicellulosic hydrolysates produced using hydrothermal pretreatment. The EPS yields were up to 0.064 g/g on initial glucose and 0.047 g/g on initial xylose, and was higher in media with relatively low sugar concentrations. The EPS was isolated and purified by a sequential procedure including centrifugation, cold ethanol precipitation, trichloroacetic acid treatment, dialysis, and freeze-drying. Glucose and mannose were the main sugars identified in hydrolyzed EPS. The EPS was characterized by size-exclusion chromatography, Fourier-transform infrared (FTIR) spectroscopy, heteronuclear single-quantum coherence nuclear magnetic resonance (HSQC NMR) spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. No major differences were elucidated between EPS resulting from cultivations in glucose- or-xylose-based synthetic media, while some divergences with regard to molecular-weight averages and FTIR and HSQC NMR spectra were detected for EPS from hydrolysate-based media.

Extraction of the Bacterial Extracellular Polysaccharide FucoPol by Membrane-Based Methods: Efficiency and Impact on Biopolymer Properties

In this study, membrane-based methods were evaluated for the recovery of FucoPol, the fucose-rich exopolysaccharide (EPS) secreted by the bacterium Enterobacter A47, aiming at reducing the total water consumption and extraction time, while keeping a high product recovery, thus making the downstream procedure more sustainable and cost-effective. The optimized method involved ultrafiltration of the cell-free supernatant using a 30 kDa molecular weight cut-off (MWCO) membrane that allowed for a 37% reduction of the total water consumption and a 55% reduction of the extraction time, compared to the previously used method (diafiltration-ultrafiltration with a 100 kDa MWCO membrane). This change in the downstream procedure improved the product’s recovery (around 10% increase) and its purity, evidenced by the lower protein (8.2 wt%) and inorganic salts (4.0 wt%) contents of the samples (compared to 9.3 and 8.6 wt%, respectively, for the previously used method), without impacting FucoPol’s sugar and acyl groups composition, molecular mass distribution or thermal degradation profile. The biopolymer’s emulsion-forming and stabilizing capacity was also not affected (emulsification activity (EA) with olive oil, at a 2:3 ratio, of 98 ± 0% for all samples), while the rheological properties were improved (the zero-shear viscosity increased from 8.89 ± 0.62 Pa·s to 17.40 ± 0.04 Pa·s), which can be assigned to the higher purity degree of the extracted samples. These findings demonstrate a significant improvement in the downstream procedure raising FucoPol’s recovery, while reducing water consumption and operation time, key criteria in terms of process economic and environmental sustainability. Moreover, those changes improved the biopolymer’s rheological properties, known to significantly impact FucoPol’s utilization in cosmetic, pharmaceutical or food products.

Residual Brewing Yeast as Substrate for Co-Production of Cell Biomass and Biofilm Using Candida maltosa SM4

Candida maltosa was cultivated in the liquid phase of residual brewing yeast, a major brewery residue, to produce biomass and biofilm. Using response surface methodology, the effect of two variables at two different levels was investigated. The independent variables were agitation speed (at 100 and 200 rpm), and aeration (at 1 and 3 L min−1). Aeration was identified to be important for the production of both biomass and biofilm, while agitation was the only factor significantly affecting biofilm production. The maximal production of biofilm (2.33 g L−1) was achieved for agitation of 200 rpm and aeration of 1 L min−1, while the maximum for biomass (16.97 g L−1) was reached for 100 rpm agitation and 3 L min−1 air flow. A logistic model applied to predict the growth of C. maltosa in the exponential phase and the biofilm production, showed a high degree of agreement between the prediction and the actual biomass measured experimentally. The produced biofilms were further characterized using Fourier-transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA). FTIR allowed the identification of methyl, carbonyl ester and sulfate groups, and revealed the presence of uronic acid moieties and glycosidic bonds. Water-retention ability up to relatively high temperatures was revealed by TGA, and that makes the produced biofilm suitable for production of hydrogels. SEM also gave indications on the hydrogel-forming potential of the biofilm.