Effect of Different Initial Fermentation pH on Exopolysaccharides Produced by Pseudoalteromonas agarivorans Hao 2018 and Identification of Key Genes Involved in Exopolysaccharide Synthesis via Transcriptome Analysis

Bacterial exopolysaccharides: Characteristics and antioxidant mechanism

Bacterial exopolysaccharides (EPS) are secondary metabolites of microorganisms which play important roles in adhesion, protection, biofilm formation, and as a source of nutrition. Compared with polysaccharides obtained from animal and plant species, bacterial polysaccharides have significant advantages in terms of production cost and large-scale production due to their abundant metabolic pathways and efficient polysaccharide production capacity. Most extracellular polysaccharides are water-soluble, and some are insoluble, such as bacterial cellulose. Some soluble bacterial EPS also have biological activities such as anticancer, antioxidant, antibacterial and immunomodulatory activities. These biological activities are mainly affected by the molecular weight, monosaccharide type, composition and structure of EPS. In recent years, bacterial EPS are considered as novel functional polysaccharides with important application prospects, especially in free radical scavenging and antioxidation. This review focuses on the characteristics of bacterial EPS, their ability to scavenge free radicals and their corresponding antioxidant mechanisms, and summarizes the relationship between different structures (such as monosaccharide composition, functional groups, molecular weight, etc.) and antioxidant activities. It provides a new idea for the development of more bioactive bacterial EPS antioxidants, points out a new direction for the commercial production of natural, safe and economical polysaccharide drugs and health products.

Pseudoalteromonas qingdaonensis sp. nov., isolated from the intestines of Ilyoplax deschampsi

A Gram-stain-negative, aerobic, motile, catalase-positive, oxidase-positive, short rod-shaped marine bacterium, designated as YIC-827T, was isolated from Qingdao, Shandong Province, China. The results showed that cells of strain YIC-827T could grow optimally at 25-35 °C, pH 6.5-7.5 and 2-7% (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequence showed that the strain YIC-827T was a member of the genus Pseudoalteromonas. The closest relative to this strain was Pseudoalteromonas ruthenica KMM 300T, with a similarity of 98.39%. The digital DNA-DNA hybridization value between the new isolate and phylogenetically related species is 19.6%. Strain YIC-827T could decompose sodium alginate, casein and esters (Tween 20, Tween 40, Tween 60 and Tween 80), but could not hydrolyse starch, cellulose and DNA. The fatty acid profile of a strain consists of a large number of C16:0, C18:1 ω7c and C16:1 ω7c/C16:1 ω6c. The G+C content of the DNA of this strain was determined to be 48.93%. Based on phenotypic characteristics, phylogenetic analysis and DNA-DNA correlation data, the strain YIC-827 T represents a novel species of the genus Pseudoalteromonas with the name Pseudoalteromonas qingdaonensis sp. nov. The type strain of P. qingdaonensis sp. is strain YIC-827T (=MCCC 1K08807T=CGMCC 1.62085T=KCTC 8212T).

Enhancement mechanism of xanthan gum production in Xanthomonas campestris induced by atmospheric and room-temperature plasma (ARTP) mutagenesis

Xanthan gum, produced by the aerobic fermentation of carbohydrates by Xanthomonas campestris, is a significant natural and industrial biopolymer known for its exceptional properties. Enhancing the yield of xanthan gum production remains a critical challenge. This study employed atmospheric and room temperature plasma (ARTP) technology to induce mutagenesis in X. campestris, resulting in a high-yielding strain, X20. The X20 mutant exhibited a substantial increase in xanthan gum yield, ranging from 13.3 % to 30.0 % over the starting strain across NaCl concentrations of 0, 6.0, and 8.0 g/L, along with improved viscosity and molecular weight. In the whole genome of X20 mutant, a total of 80 variant sites differing from the reference genome were identified, involving 76 mutated genes. Among these, 19 were missense mutations primarily associated with the two-component system. Transcriptome analysis highlighted their role in enhancing flagellar movement, biofilm formation, and metabolic synthesis, thereby elevating the capability of the mutant strain in xanthan gum production. This study demonstrates the potential of ARTP as an effective tool for microbial mutagenesis breeding, providing theoretical guidance for future studies on the synthesis regulation of xanthan gum and the engineering modification of X. campestris.

The Marine-Origin Exopolysaccharide-Producing Bacteria Micrococcus Antarcticus HZ Inhibits Pb Uptake in Pakchoi (Brassica chinensis L.) and Affects Rhizosphere Microbial Communities

Exopolysaccharides (EPSs) produced by microorganisms play an important role in biotolerance and reducing heavy metal (HM) contamination by limiting the migration of HMs into plants. However, research on the application of EPS-producing marine bacteria for soil heavy metal remediation remains limited, particularly regarding their mechanisms of HM immobilization in soil and impact on plant growth. In this study, the EPS-producing marine bacterium Micrococcus antarcticus HZ was investigated for its ability to immobilize Pb and produce EPSs in soil filtrate. The effects on the growth quality and biomass of pakchoi (Brassica chinensis L.), as well as bacterial communities in inter-root soil contaminated with Pb, were also investigated. The results indicated that HZ could reduce the Pb concentration in the soil filtrate, achieving a removal rate of 43.25-63.5%. The EPS content and pH levels increased in the presence of Pb. Pot experiments showed that adding HZ significantly increased the biomass of pakchoi (9.45-14.69%), vitamin C (Vc) (9.69-12.92%), and soluble protein content (22.58-49.7%). HZ reduced the Pb content in the roots (17.52-47.48%) and leaves (edible tissues) (43.82-52.83%) of pakchoi. HZ increased soil enzyme activities (alkaline phosphatase, dehydrogenase, and urease), and the contents of ammonium nitrogen and nitrate nitrogen. Additionally, HZ also increased the relative abundance of beneficial bacteria (e.g., Proteobacteria, Cyanobacteria, and Chlorobacteria) in the inter-root soil, which have prophylactic and heavy-metal fixation functions. In summary, HZ reduces effective Pb content in edible tissues, roots, and inter-root soil by regulating inter-root soil microbial community structure, increasing soil pH, nitrogen content, and soil enzyme activity, and altering dominant phylum abundance.

Temperature stress improved exopolysaccharide yield from Tetragenococcus halophilus: Structural differences and underlying mechanisms revealed by transcriptomic analysis

This study aimed to enhance exopolysaccharide production by Tetragenococcus halophilus, and results showed that low temperature (20 °C) significantly improved exopolysaccharide production. Based on the analysis of batch fermentation kinetic parameters, a temperature-shift strategy was proposed, and the exopolysaccharide yield was increased by 28 %. Analysis of the structure of exopolysaccharide suggested that low temperature changed the molecular weight and monosaccharide composition. Transcriptomic analysis was performed to reveal mechanisms of low temperature improving exopolysaccharide production. Results suggested that T. halophilus regulated utilization of carbon sources through phosphotransferase system and increased the expression of key genes in exopolysaccharide biosynthesis to improve exopolysaccharide production. Meanwhile, metabolic pathways involved in glycolysis, amino acids synthesis, two-component system and ATP-binding cassette transporters were affected at low temperature. Results presented in this paper provided a theoretical basis for biosynthetic pathway of exopolysaccharide in T. halophilus and aided to strengthen its production and application in many areas.

Taxonomic identification and temperature stress tolerance mechanisms of Aequorivita marisscotiae sp. nov

The deep sea harbours microorganisms with unique life characteristics and activities due to adaptation to particular environmental conditions, but the limited sample collection and pure culture techniques available constrain the study of deep-sea microorganisms. In this study, strain Ant34-E75 was isolated from Antarctic deep-sea sediment samples and showed the highest 16 S rRNA gene sequence similarity (97.18%) with the strain Aequorivita viscosa 8-1bT. Strain Ant34-E75 is psychrotrophic and can effectively increase the cold tolerance of Chlamydomonas reinhardtii (a model organism). Subsequent transcriptome analysis revealed multiple mechanisms involved in the Ant34-E75 response to temperature stress, and weighted gene co-expression network analysis (WGCNA) showed that the peptidoglycan synthesis pathway was the key component. Overall, this study provides insights into the characteristics of a deep-sea microorganism and elucidates mechanisms of temperature adaptation at the molecular level.

Transcriptome analysis of three medicinal plants of the genus Polygonatum: identification of genes involved in polysaccharide and steroidal saponins biosynthesis

Polysaccharides and saponins are the main active components of Polygonati Rhizoma. Studying the molecular mechanism of their synthesis pathway is helpful in improving the content of active components at the molecular level. At present, transcriptome analysis of three Polygonatum species (Polygonatum sibiricum Red., Polygonatum cyrtonema Hua, Polygonatum kingianum Coll. et Hemsl.) has been reported, but no comparative study has been found on the transcriptome data of the three species. Transcriptome sequencing was performed on the rhizomes of three Polygonatum species based on high-throughput sequencing technology, and all transcripts were assembled. A total of 168,108 unigenes were generated after the removal of redundancy, of which 121,642 were annotated in seven databases. Through differential analysis and expression analysis of key enzyme genes in the synthesis pathway of three Polygonatum polysaccharides and steroidal saponins, 135 differentially expressed genes encoding 18 enzymes and 128 differentially expressed genes encoding 28 enzymes were identified, respectively. Numerous transcription factors are involved in the carbohydrate synthesis pathway. Quantitative real-time PCR was used to further verify the gene expression level. In this paper, we present a public transcriptome dataset of three medicinal plants of the genus Polygonatum, and analyze the key enzyme genes of polysaccharide and steroidal saponins synthesis pathway, which lays a foundation for improving the active component content of Polygonati Rhizoma by molecular means.

Effect of fermentation pH on the structure, rheological properties, and antioxidant activities of exopolysaccharides produced by Alteromonas australica QD

The pH value was essential for the growth and metabolism of microorganisms. Acidic pH exopolysaccharide (AC-EPS) and alkaline pH exopolysaccharide (AL-EPS) secreted by A. australica QD mediated by pH were studied in this paper. The total carbohydrate content and molecular weight of AC-EPS (79.59% ± 2.24% (w/w), 8.374 × 10⁵ Da) and AL-EPS (82.48% ± 1.46% (w/w), 6.182 × 10⁵ Da) were estimated and compared. In AC-EPS, mannose (3.78%) and galactose (3.24%) content was more, while the proportion of glucuronic acid was less in comparison to AL-EPS. The scanning electron microscopy revealed the structural differences among the AC-EPS and AL-EPS. Thermogravimetric analysis showed degradation temperatures of 272.8 °C and 244.9 °C for AC-EPS and AL-EPS, respectively. AC-EPS was found to exhibit better rheological properties and emulsifying capabilities, while AL-EPS had superior antioxidant activities. Overall, both AC-EPS and AL-EPS have the potential to be used as emulsifiers and biological antioxidants.

Exopolysaccharide production from Alkalibacillus sp. w3: statistical optimization and biological activity

Microbial exopolysaccharides (EPS) provide a broad range of applications. Thus, there is an increasing interest in the production, characterization, and use of EPS derived from various microorganisms. Extremophile polysaccharides have unique properties and applications due to its unique structures. The importance of exopolysaccharides synthesized by a new bacterial strain, Alkalibacillus sp. w3, was highlighted in this study. Alkalibacillus sp. w3, a haloalkalitolerant firmicute that was recovered from a salt lake, was optimized for EPS production, and its biological activities were studied. Exopolysaccharide synthesis was observed in Horikoshi I broth medium. The optimal culture conditions for achieving the highest exopolysaccharide production were a 7-day incubation period, pH 10, and 250 g/L of NaCl. The most effective carbon and nitrogen sources for EPS production were glucose and a combination of yeast extract and peptone. Additionally, Plackett-statistical Burman’s design showed that all factors tested had a favorable impact, with glucose having the greatest significance on the production of EPS. The model’s best predictions for culture conditions resulted in a two-fold improvement in EPS production compared to the original yield before optimization. The recovered EPS contained 65.13% carbohydrates, 30.89% proteins, and 3.98% lipids. Moreover, EPS produced by Alkalibacillus sp. w3 demonstrated anticancer activity against hepatocellular carcinoma (HepG2) and human colon carcinoma (HCT-116) cell lines, with IC50 values as low as 11.8 and 15.5 µg/mL, respectively, besides antibacterial activity against various Gram-positive, Gram-negative bacteria, and yeast. Based on these results, EPS made by Alkalibacillus sp. w3 has many useful properties, which make it suitable for use in the medical field.

Overexpression of phosphomannomutase increases the production and bioactivities of Ganoderma exopolysaccharides

In this study, we explored a novel approach to enhancing the production and bioactivities of Ganoderma exopolysaccharides. The homologous phosphomannomutase gene (PMM1) was cloned and overexpressed in Ganoderma for the first time. As a result, the maximum production of exopolysaccharides by the PMM1 transformant was 1.53 g/L, which was 1.41-fold higher than of a wild-type (WT) strain in a 5-L bioreactor. The transcription levels of PMM1 and PMM2 increased 40.5- and 2.4-fold, respectively, whereas the value of the GDP-D-mannose pyrophosphorylase gene did not change significantly in this transgenic strain. Furthermore, the major exopolysaccharide fractions from PMM1 transformants contained higher amounts of mannose (56.5 % and 21.1 %) than those from a WT strain (26.7 % and 9.3 %). Moreover, the major fractions from PMM1 transformants exhibited stronger regulation effects on macrophage. In conclusion, this study is helpful for the efficient production and application of Ganoderma exopolysaccharides and facilitates an understanding of polysaccharide biosynthesis regulation.

Isolation, identification, and biochemical characterization of a novel bifunctional phosphomannomutase/phosphoglucomutase from the metagenome of the brown alga Laminaria digitata

Macroalgae host diverse epiphytic bacterial communities with potential symbiotic roles including important roles influencing morphogenesis and growth of the host, nutrient exchange, and protection of the host from pathogens. Macroalgal cell wall structures, exudates, and intra-cellular environments possess numerous complex and valuable carbohydrates such as cellulose, hemi-cellulose, mannans, alginates, fucoidans, and laminarin. Bacterial colonizers of macroalgae are important carbon cyclers, acquiring nutrition from living macroalgae and also from decaying macroalgae. Seaweed epiphytic communities are a rich source of diverse carbohydrate-active enzymes which may have useful applications in industrial bioprocessing. With this in mind, we constructed a large insert fosmid clone library from the metagenome of Laminaria digitata (Ochrophyta) in which decay was induced. Subsequent sequencing of a fosmid clone insert revealed the presence of a gene encoding a bifunctional phosphomannomutase/phosphoglucomutase (PMM/PGM) enzyme 10L6AlgC, closely related to a protein from the halophilic marine bacterium, Cobetia sp. 10L6AlgC was subsequently heterologously expressed in Escherichia coli and biochemically characterized. The enzyme was found to possess both PMM and PGM activity, which had temperature and pH optima of 45°C and 8.0, respectively; for both activities. The PMM activity had a K m of 2.229 mM and V max of 29.35 mM min-1 mg-1, while the PGM activity had a K m of 0.5314 mM and a V max of 644.7 mM min-1 mg-1. Overall characterization of the enzyme including the above parameters as well as the influence of various divalent cations on these activities revealed that 10L6AlgC has a unique biochemical profile when compared to previously characterized PMM/PGM bifunctional enzymes. Thus 10L6AlgC may find utility in enzyme-based production of biochemicals with different potential industrial applications, in which other bacterial PMM/PGMs have previously been used such as in the production of low-calorie sweeteners in the food industry.

Anionic exopolysaccharide from Cryptococcus laurentii 70766 as an alternative for alginate for biomedical hydrogels

Alginates are widely used polysaccharides for biomaterials engineering, which functional properties depend on guluronic and mannuronic acid as the building blocks. In this study, enzymatically crosslinked hydrogels based on sodium alginate (Na-Alg) and the exopolysaccharide (EPS) derived from Cryptococcus laurentii 70766 with glucuronic acid residues were synthesized and characterized as a new potential source of polysaccharide for biomaterials engineering. The EPS was extracted (1.05 ± 0.57 g/L) through ethanol precipitation. Then the EPS and Na-Alg were functionalized with tyramine hydrochloride to produce enzymatically crosslinked hydrogels in the presence of horseradish peroxidase (HRP) and H₂O₂. Major characteristics of the hydrogels such as gelling time, swelling ratio, rheology, cell viability, and biodegradability were studied. The swelling ratio and degradation profile of both hydrogels showed negative values, indicating an increased crosslinking degree and a lower water uptake percentage. The EPS hydrogel showed similar gelation kinetics compared to the Alg hydrogel. The EPS and its hydrogel were found cytocompatible. The results indicate the potential of EPS from C. laurentii 70766 for biomedical engineering due to its biocompatibility and degradability. Further studies are needed to confirm this EPS as an alternative for Alg in tissue engineering applications, particularly in the development of wound dressing products.

Pan-Genomic and Transcriptomic Analyses of Marine Pseudoalteromonas agarivorans Hao 2018 Revealed Its Genomic and Metabolic Features

The genomic and carbohydrate metabolic features of Pseudoalteromonas agarivorans Hao 2018 (P. agarivorans Hao 2018) were investigated through pan-genomic and transcriptomic analyses, and key enzyme genes that may encode the process involved in its extracellular polysaccharide synthesis were screened. The pan-genome of the P. agarivorans strains consists of a core-genome containing 2331 genes, an accessory-genome containing 956 genes, and a unique-genome containing 1519 genes. Clusters of Orthologous Groups analyses showed that P. agarivorans harbors strain-specifically diverse metabolisms, probably representing high evolutionary genome changes. The Kyoto Encyclopedia of Genes and Genomes and reconstructed carbohydrate metabolic pathways displayed that P. agarivorans strains can utilize a variety of carbohydrates, such as d-glucose, d-fructose, and d-lactose. Analyses of differentially expressed genes showed that compared with the stationary phase (24 h), strain P. agarivorans Hao 2018 had upregulated expression of genes related to the synthesis of extracellular polysaccharides in the logarithmic growth phase (2 h), and that the expression of these genes affected extracellular polysaccharide transport, nucleotide sugar synthesis, and glycosyltransferase synthesis. This is the first investigation of the genomic and metabolic features of P. agarivorans through pan-genomic and transcriptomic analyses, and these intriguing discoveries provide the possibility to produce novel marine drug lead compounds with high biological activity.