An overview of functional genomics and relevance of glycosyltransferases in exopolysaccharide production by lactic acid bacteria

Rhizosphere bacterial exopolysaccharides: composition, biosynthesis, and their potential applications

Bacterial exopolysaccharides (EPS) are biopolymers of carbohydrates, often released from cells into the extracellular environment. Due to their distinctive physicochemical properties, biocompatibility, biodegradability, and non-toxicity, EPS finds applications in various industrial sectors. However, the need for alternative EPS has grown over the past few decades as lactic acid bacteria's (LAB) low-yield EPS is unable to meet the demand. In this case, rhizosphere bacteria with the diverse communities in soil leading to variations in composition and structure, are recognized as a potential source of EPS applicable in various industries. In addition, media components and cultivation conditions have an impact on EPS production, which ultimately affects the quantity, structure, and biological functions of the EPS. Therefore, scientists are currently working on manipulating bacterial EPS by developing cultures and applying abiotic and biotic stresses, so that better production of exopolysaccharides can be attained. This review highlights the composition, biosynthesis, and effects of environmental factors on EPS production along with the potential applications in different fields of industry. Ultimately, an overview of potential future paths and tactics for improving EPS implementation and commercialization is pointed out.

Fermentation of Orange Peels by Lactic Acid Bacteria: Impact on Phenolic Composition and Antioxidant Activity

Orange processing generates peel by-products rich in phenolic compounds, particularly flavanones like hesperidin and narirutin, offering potential health benefits. Utilizing these by-products is of significant interest in supporting Spain's circular bioeconomy. Therefore, the aim of this study was to investigate the fermentation of orange peels by different lactic acid bacteria (LAB) strains and its impact on phenolic composition and antioxidant activity. Three different LAB strains, two Lactiplantibacillus plantarum, and one Levilactobacillus brevis were utilized. The phenolic compounds were measured by HPLC-ESI-TOF-MS, and antioxidant activity was assessed using DPPH and ABTS methods. The growth of the LAB strains varied, showing initial increases followed by gradual declines, with strain-specific patterns observed. Medium acidification occurred during fermentation. A phenolic analysis revealed an 11% increase in phenolic acids in peels fermented by La. plantarum CECT 9567-C4 after 24 h, attributed to glycosylation by LAB enzymes. The flavonoid content exhibited diverse trends, with Le. brevis showing an 8% increase. The antioxidant assays demonstrated strain- and time-dependent variations. Positive correlations were found between antioxidant activity and total phenolic compounds. The results underscore the importance of bacterial selection and fermentation time for tailored phenolic composition and antioxidant activity in orange peel extracts. LAB fermentation, particularly with La. plantarum CECT 9567 and Le. brevis, holds promise for enhancing the recovery of phenolic compounds and augmenting antioxidant activity in orange peels, suggesting potential applications in food and beverage processing.

Recent advances in the biosynthesis of fungal glucan structural diversity

Glucans are the most abundant class of macromolecule polymers in fungi, which are commonly found in Ascomycota and Basidiomycota. Fungal glucans are not only essential for cell integrity and function but also crucial for the immense industrial interest in high value applications. They present a variety of structural characteristics at the nanoscale due to the high regulation of genes and the involvement of stochastic processes in synthesis. However, although recent findings have demonstrated the genes of glucans synthesis are relatively conserved across diverse fungi, the formation and organization of diverse glucan structures is still unclear in fungi. Here, we summarize the structural features of fungal glucans and the recent developments in the mechanisms of glucans biosynthesis. Furthermore, we propose the engineering strategies of targeted glucan synthesis and point out the remaining challenges in the synthetic process. Understanding the synthesis process of diverse glucans is necessary for tailoring high value glucan towards specific applications. This engineering strategy contributes to enable the sustainable and efficient production of glucan diversity.

Exopolysaccharide production by salt-tolerant bacteria: Recent advances, current challenges, and future prospects

Natural biopolymers derived from exopolysaccharides (EPSs) are considered eco-friendly and sustainable alternatives to available traditional synthetic counterparts. Salt-tolerant bacteria inhabiting harsh ecological niches have evolved a number of unique adaptation strategies allowing them to maintain cellular integrity and assuring their long-term survival; among these, producing EPSs can be adopted as an effective strategy to thrive under high-salt conditions. A great diversity of EPSs from salt-tolerant bacteria have attracted widespread attention recently. Because of factors such as their unique structural, physicochemical, and functional characteristics, EPSs are commercially valuable for the global market and their application potential in various sectors is promising. However, large-scale production and industrial development of these biopolymers are hindered by their low yields and high costs. Consequently, the research progress and future prospects of salt-tolerant bacterial EPSs must be systematically reviewed to further promote their application and commercialization. In this review, the structure and properties of EPSs produced by a variety of salt-tolerant bacterial strains isolated from different sources are summarized. Further, feasible strategies for solving production bottlenecks are discussed, which provides a scientific basis and direct reference for more scientific and rational EPS development.

Reconstructing the transcriptional regulatory network of probiotic L. reuteri is enabled by transcriptomics and machine learning

Limosilactobacillus reuteri, a probiotic microbe instrumental to human health and sustainable food production, adapts to diverse environmental shifts via dynamic gene expression. We applied the independent component analysis (ICA) to 117 RNA-seq data sets to decode its transcriptional regulatory network (TRN), identifying 35 distinct signals that modulate specific gene sets. Our findings indicate that the ICA provides a qualitative advancement and captures nuanced relationships within gene clusters that other methods may miss. This study uncovers the fundamental properties of L. reuteri's TRN and deepens our understanding of its arginine metabolism and the co-regulation of riboflavin metabolism and fatty acid conversion. It also sheds light on conditions that regulate genes within a specific biosynthetic gene cluster and allows for the speculation of the potential role of isoprenoid biosynthesis in L. reuteri's adaptive response to environmental changes. By integrating transcriptomics and machine learning, we provide a system-level understanding of L. reuteri's response mechanism to environmental fluctuations, thus setting the stage for modeling the probiotic transcriptome for applications in microbial food production.

IMPORTANCE

We have studied Limosilactobacillus reuteri, a beneficial probiotic microbe that plays a significant role in our health and production of sustainable foods, a type of foods that are nutritionally dense and healthier and have low-carbon emissions compared to traditional foods. Similar to how humans adapt their lifestyles to different environments, this microbe adjusts its behavior by modulating the expression of genes. We applied machine learning to analyze large-scale data sets on how these genes behave across diverse conditions. From this, we identified 35 unique patterns demonstrating how L. reuteri adjusts its genes based on 50 unique environmental conditions (such as various sugars, salts, microbial cocultures, human milk, and fruit juice). This research helps us understand better how L. reuteri functions, especially in processes like breaking down certain nutrients and adapting to stressful changes. More importantly, with our findings, we become closer to using this knowledge to improve how we produce more sustainable and healthier foods with the help of microbes.

Leuconostoc mesenteroides and Liquorilactobacillus mali strains, isolated from Algerian food products, are producers of the postbiotic compounds dextran, oligosaccharides and mannitol

Six lactic acid bacteria (LAB) isolated from Algerian sheep's milk, traditional butter, date palm sap and barley, which produce dextran, mannitol, oligosaccharides and vitamin B2 have been characterized. They were identified as Leuconostoc mesenteroides (A4X, Z36P, B12 and O9) and Liquorilactobacillus mali (BR201 and FR123). Their exopolysaccharides synthesized from sucrose by dextransucrase (Dsr) were characterized as dextrans with (1,6)-D-glucopyranose units in the main backbone and branched at positions O-4, O-2 and/or O-3, with D-glucopyranose units in the side chain. A4X was the best dextran producer (4.5 g/L), while the other strains synthesized 2.1-2.7 g/L. Zymograms revealed that L. mali strains have a single Dsr with a molecular weight (Mw) of ~ 145 kDa, while the Lc. mesenteroides possess one or two enzymes with 170-211 kDa Mw. As far as we know, this is the first detection of L. mali Dsr. Analysis of metabolic fluxes from sucrose revealed that the six LAB produced mannitol (~ 12 g/L). The co-addition of maltose-sucrose resulted in the production of panose (up to 37.53 mM), an oligosaccharide known for its prebiotic effect. A4X, Z36P and B12 showed dextranase hydrolytic enzymatic activity and were able to produce another trisaccharide, maltotriose, which is the first instance of a dextranase activity encoded by Lc. mesenteroides strains. Furthermore, B12 and O9 grew in the absence of riboflavin (vitamin B2) and synthesized this vitamin, in a defined medium at the level of ~ 220 μg/L. Therefore, these LAB, especially Lc. mesenteroides B12, are good candidates for the development of new fermented food biofortified with functional compounds.

Exopolysaccharides of lactic acid bacteria: Structure, biological activity, structure-activity relationship, and application in the food industry: A review

Over the past few decades, researchers have discovered that probiotics play an important role in our daily lives. With the further deepening of research, more and more evidence show that bacterial metabolites have an important role in food and human health, which opens up a new direction for the research of lactic acid bacteria (LAB) in the food and pharmaceutical industry. Many LAB have been widely studied because of the ability of exopolysaccharides (EPS). Lactic acid bacteria exopolysaccharides (LAB EPS) not only have great potential in the treatment of human diseases but also can become natural ingredients in the food industry to provide special qualitative structure and flavor. This paper has organized and summarized the biosynthesis, strain selection, production process parameters, structure, and biological activity of LAB EPS, filling in the monotony and incompleteness of previous articles' descriptions of LAB EPS. Therefore, this paper focuses on the general biosynthetic pathway, structural characterization, structure-activity relationship, biological activity of LAB EPS, and their application in the food industry, which will help to deepen people's understanding of LAB EPS and develop new active drugs from LAB EPS. Although the research results are relatively affluent, the low yield, complex structure, and few clinical trials of EPS are still the reasons that hinder its development. Therefore, future knowledge expansion should focus on the regulation of structure, physicochemical properties, function, higher production of EPS, and clinical trial applications, which can further increase the commercial significance and value of EPS. Furthermore, better understanding the structure-function relationship of EPS in food remains a challenge to date.

Draft Genome Sequence and Comparative Genome Analysis Reveal Potential Functional Properties in Lacticaseibacillus paracasei ItalPN16

Nowadays, there is a great interest on rapid and effective methods for initial identification of probiotic bacteria. In this work, potential probiotic features of the lactic acid bacteria strain ItalPN16 isolated from a traditional Brazilian cheese were studied using bioinformatic tools. The complete genome sequence was obtained, and in silico analyses were carried out to identify the strain and its potential probiotic properties. The sequenced genome (3.02 Mb) presented 3126 protein-coding sequences distributed on 244 SEED subsystems, classifying the strain as nomadic lactobacilli. Phylogenetic and ANI analyses allowed to locate the ItalPN16 strain as a member of the Lacticaseibacillus paracasei group, due to the highest number of orthologous genes in common with reference L. paracasei strains (>98%). In silico analyses revealed the presence of CDSs related to microbe-host interactions, such as adhesion proteins and exopolysaccharide biosynthesis genes. The comparative analysis reveals the presence of a strain-specific glycosyl transferases, compared with other three L. paracasei strains and a high level of protein expression (92%) with the probiotic L. paracasei BL29. The results obtained here indicated interesting probiotic features of the strain L. paracasei ItalPN16 that could favor a future application in the food industry.

Nisin controlled homologous Over-expression of an exopolysaccharide biosynthetic glycosyltransferase gene for enhanced EPS production in Lactobacillus plantarum BR2

Glycosyltransferases synthesize a variety of exopolysaccharides (EPS) with different properties by altering the type of glycosidic linkage, degree of branching, length, mass, and conformation of the polymers. The genome analysis of an EPS-producing, Lactobacillus plantarum BR2 (Accession No: MN176402) showed twelve glycosyltransferase genes, and the gene BR2gtf (1116 bp), annotated as an EPS biosynthetic glycosyltransferase was cloned into the pNZ8148 vector. The recombinant pNZ8148 vector along with pNZ9530, a regulatory plasmid, were electroporated to L. plantarum BR2 for the over-expression of gtf gene under a nisin-controlled expression system and the glycosyltransferase activity of the recombinant and the wild-type strains were analysed. The recombinant strain showed 54.4% increase in EPS production with the maximum EPS production of 23.2 ± 0.5 g/L in a 5 L bioreactor study after 72 h of fermentation. This study shows an effective molecular strategy possibly to be adopted in lactic acid bacteria to enhance exopolysaccharide production.

New progress in the identifying regulatory factors of exopolysaccharide synthesis in lactic acid bacteria

The exopolysaccharides (EPSs) of lactic acid bacteria (LAB) have presented various bioactivities and beneficial characteristics, rendering their vast commercial value and attracting a broad interest of researchers. The diversity of EPS structures contributes to the changes of EPS functions. However, the low yield of EPS of LAB has severely limited these biopolymers' comprehensive studies and applications in different areas, such as functional food, health and medicine fields. The clarification of biosynthesis mechanism of EPS will accelerate the synthesis and reconstruction of EPS. In recent years, with the development of new genetic manipulation techniques, there has been significant progress in the EPS biosynthesis mechanisms in LAB. In this review, the structure of LAB-derived EPSs, the EPS biosynthesis basic pathways in LAB, the EPS biosynthetic gene cluster, and the regulation mechanism of EPS biosynthesis will be summarized. It will focus on the latest progress in EPS biosynthesis regulation of LAB and provide prospects for future related developments.

Phenotypic Analysis, Molecular Characterization, and Antibiogram of Caries-Causing Bacteria Isolated from Dental Patients

Dental caries is a biofilm-mediated, sugar-driven, multifactorial, dynamic disease that results in the phasic demineralization and remineralization of dental hard tissues. Despite scientific advances in cariology, dental caries remains a severe global concern. The aim of this study was to determine the optimization of microbial and molecular techniques for the detection of cariogenic pathogens in dental caries patients, the prevalence of cariogenic bacteria on the basis of socioeconomic, climatological, and hygienic factors, and in vitro evaluation of the antimicrobial activity of selected synthetic antibiotics and herbal extracts. In this study, oral samples were collected from 900 patients for bacterial strain screening on a biochemical and molecular basis. Plant extracts, such as ginger, garlic, neem, tulsi, amla, and aloe vera, were used to check the antimicrobial activity against the isolated strains. Synthetic antimicrobial agents, such as penicillin, amoxicillin, erythromycin, clindamycin, metronidazole, doxycycline, ceftazidime, levofloxacin, and ciprofloxacin, were also used to access the antimicrobial activity. Among 900 patients, 63% were males and 37% were females, patients aged between 36 and 58 (45.7%) years were prone to disease, and the most common symptom was toothache (61%). For oral diseases, 21% used herbs, 36% used antibiotics, and 48% were self-medicated, owing to sweets consumption (60.66%) and fizzy drinks and fast food (51.56%). Staphylococcus mutans (29.11%) and Streptococcus sobrinus (28.11%) were found as the most abundant strains. Seven bacterial strains were successfully screened and predicted to be closely related to genera S. sobrinus, S. mutans, Actinomyces naeslundii, Lactobacillus acidophilus, Eubacterium nodatum, Propionibacterium acidifaciens, and Treponema Pallidum. Among plant extracts, the maximum zone of inhibition was recorded by ginger (22.36 mm) and amla (20.01 mm), while among synthetic antibiotics, ciprofloxacin and levofloxacin were most effective against all microbes. This study concluded that phyto extracts of ginger and amla were considered suitable alternatives to synthetic antibiotics to treat dental diseases.

Rhizoctonia solani AG1 IA extracellular polysaccharides: Structural characterization and induced resistance to rice sheath blight

Sheath blight, caused by Rhizoctonia solani (R. solani), is one of the most serious diseases of rice. Extracellular polysaccharides (EPS) are complex polysaccharides secreted by microbes that have a pivotal role in the plant-microbe interaction. At present, many studies have been carried out on R. solani, but it is not very clear whether the EPS is secreted by R. solani exists. Therefore, we isolated and extracted the EPS from R. solani, two kinds of EPS (EW-I and ES-I) were obtained by DEAE-cellulose 52 and Sephacryl S-300HR column further purification, and their structures were characterized by FT-IR, UV, GC, and NMR analysis. The results showed that EW-I and ES-I had similar monosaccharide composition but different molar ratio, they were composed of fucose, arabinose, galactose, glucose, and mannose with a ratio of 7.49: 27.72: 2.98: 6.66: 55.15 and 3.81: 12.98: 6.15: 10.83: 66.23, and their backbone may be composed of →2)-α-Manp-(1→ residues, beside ES-I was highly branched compared to EW-I. The exogenous application of EW-I and ES-I had no effect on the growth of R. solani AG1 IA itself, but their pretreatment of rice induced plant defense through activation of the salicylic acid pathway, resulting in enhanced resistance to sheath blight.

Direct Utilization and Conversion of raw Starch to Exopolysaccharides by a newly isolated Amylolytic Streptococcus sp

A newly isolated culture is identified as Streptococcus lutetiensis with significant starch saccharifying activity. Along with considerable amylolytic property (~ 2.71U/mL), the culture exhibited significant production of exopolysaccharide (EPS) in starch medium. Interestingly, the glycosyl transferase activity which is essential in the biosynthesis of polysaccharide is also detected in the culture and after screening and process optimization, a maximum EPS titre of 19.92 ± 0.5g/L was obtained from cassava starch. The crude EPS, after purification and characterization (monosaccharide analysis, FT-IR, TGA, GPC, NMR, and SEM) was found to be of dextran nature with a Mw of 1275.36kDa. Dextran type exopolysaccharide are synthesized by dextransucrase enzyme by the transfer of glucosyl residues from sucrose to dextran polymer. Iinterestingly, the glycosyl transferase enzyme activity which is essential in the biosynthesis of EPS is also detected in the culture. The particle size (447.8 dnm) and the zeta potential (-33.4) analysis of the purified EPS showed that the EPS produced is a stable molecule and has a random coil confirmation when exposed to alkaline condition with shear thinning property. One step conversion of sustainable low-cost starchy raw materials without adding external enzymes for hydrolysis, improved the economic viability of EPS production.

Relationship of Gene-Structure-Antioxidant Ability of Exopolysaccharides Derived from Lactic Acid Bacteria: A Review

Polysaccharides derived from lactic acid bacteria (LAB) have widespread industrial applications owing to their excellent safety profile and numerous biological properties. The antioxidant activity of exopolysaccharides (EPS) offers defense against disease conditions caused by oxidative stress. Several genes and gene clusters are involved in the biosynthesis of EPS and the determination of their structures, which play an important role in modulating their antioxidant ability. Under conditions of oxidative stress, EPS are involved in the activation of the nonenzyme (Keap1-Nrf2-ARE) response pathway and enzyme antioxidant system. The antioxidant activity of EPS is further enhanced by the targeted alteration of their structures, as well as by chemical methods. Enzymatic modification is the most commonly used method, though physical and biomolecular methods are also frequently used. A detailed summary of the biosynthetic processes, antioxidant mechanisms, and modifications of LAB-derived EPS is presented in this paper, and their gene-structure-function relationship has also been explored.

Whole-Genome Sequence of Lactococcus lactis Subsp. lactis LL16 Confirms Safety, Probiotic Potential, and Reveals Functional Traits

Safety is the most important criteria of any substance or microorganism applied in the food industry. The whole-genome sequencing (WGS) of an indigenous dairy isolate LL16 confirmed it to be Lactococcus lactis subsp. lactis with genome size 2,589,406 bp, 35.4% GC content, 246 subsystems, and 1 plasmid (repUS4). The Nextera XT library preparation kit was used to generate the DNA libraries, and the sequencing was carried out on an Illumina MiSeq platform. In silico analysis of L. lactis LL16 strain revealed non-pathogenicity and the absence of genes involved in transferable antimicrobial resistances, virulence, and formation of biogenic amines. One region in the L. lactis LL16 genome was identified as type III polyketide synthases (T3PKS) to produce putative bacteriocins lactococcin B, and enterolysin A. The probiotic and functional potential of L. lactis LL16 was investigated by the presence of genes involved in adhesion and colonization of the host's intestines and tolerance to acid and bile, production of enzymes, amino acids, and B-group vitamins. Genes encoding the production of neurotransmitters serotonin and gamma-aminobutyric acid (GABA) were detected; however, L. lactis LL16 was able to produce only GABA during milk fermentation. These findings demonstrate a variety of positive features that support the use of L. lactis LL16 in the dairy sector as a functional strain with probiotic and GABA-producing properties.

Diverse Repertoire and Relationship of Exopolysaccharide Genes in Cold-Adapted Acinetobacter sp. CUI-P1 Revealed by Comparative Genome Analysis

This study focused on the exploration of microbial communities inhabiting extreme cold environments, such as the Passu and Pisan glaciers of Pakistan, and their potential utilization in industrial applications. Among the 25 initially screened strains, five were found to be suitable candidates for exopolysaccharide (EPS) production, with strain CUI-P1 displaying the highest yield of 7230.5 mg/L compared to the other four strains. The purified EPS from CUI-P1 was tested for its ability to protect probiotic bacteria and E. coli expressing green fluorescence protein (HriGFP) against extreme cold temperatures, and it exhibited excellent cryoprotectant and emulsification activity, highlighting its potential use in the biotechnological industry. Furthermore, the genome of Acinetobacter sp., CUI-P1 comprised 199 contigs, with a genome size of 10,493,143bp and a G + C content of 42%, and showed 98.197% nucleotide identity to the type genome of Acinetobacter baumannii ATCC 17978. These findings offer promising avenues for the application of EPS as a cryoprotectant, an essential tool in modern biotechnology.

Exopolysaccharides produced by Enterococcus genus - An overview

Exopolysaccharide (EPS) biomolecules produced by lactic acid bacteria (LAB) are of prodigious interest due to their unique structural, physico-chemical, and functional characteristics. Several genera of LAB including Enterococcus spp. have been studied for EPS production by various research groups worldwide. EPS produced by various strains from Enterococcus spp. have shown a wide range of functional and technological properties with potential commercial applications. Numerous techniques are used in the characterization of Enterococcus EPS to reveal their structure, linkage, monosaccharide units, functional groups, morphology, and thermal properties. Bioactive potentials of Enterococcus EPS include antioxidant, antibacterial, antibiofilm, anticancer, immunological, prebiotic, and antidiabetic potentials which have been widely reported. These functional and biological properties make Enterococcus EPS a candidate of great importance for multiple applications in the area of food, pharmaceuticals, biomedical and environmental. This review is focused on EPS produced by various strains of the Enterococcus genus isolated from different sources. Several procedures and parameters involved in the production and purification of Enterococcus EPS are also deliberated along with the functional aspects and potential applications.

AepG is a glucuronosyltransferase involved in acidic exopolysaccharide synthesis and contributes to environmental adaptation of Haloarcula hispanica

The attachment of a sugar to a hydrophobic lipid carrier is the first step in the biosynthesis of many glycoconjugates. In the halophilic archaeon Haloarcula hispanica, HAH_1206, renamed AepG, is a predicted glycosyltransferase belonging to the CAZy Group 2 family that shares a conserved amino acid sequence with dolichol phosphate mannose synthases. In this study, the function of AepG was investigated by genetic and biochemical approaches. We found that aepG deletion led to the disappearance of dolichol phosphate-glucuronic acid. Our biochemical assays revealed that recombinant cellulose-binding, domain-tagged AepG could catalyze the formation of dolichol phosphate-glucuronic acid in time- and dose-dependent manners. Based on the in vivo and in vitro analyses, AepG was confirmed to be a dolichol phosphate glucuronosyltransferase involved in the synthesis of the acidic exopolysaccharide produced by H. hispanica. Furthermore, lack of aepG resulted in hindered growth and cell aggregation in high salt medium, indicating that AepG is vital for the adaptation of H. hispanica to a high salt environment. In conclusion, AepG is the first dolichol phosphate glucuronosyltransferase identified in any of the three domains of life and, moreover, offers a starting point for further investigation into the diverse pathways used for extracellular polysaccharide biosynthesis in archaea.

Whole genome sequence of Lactiplantibacillus plantarum MC5 and comparative analysis of eps gene clusters

Introduction

Probiotic Lactiplantibacillus plantarum MC5 produces large amounts of exopolysaccharides (EPS), and its use as a compound fermentor can greatly improve the quality of fermented milk.

Methods

To gain insight into the genomic characteristics of probiotic MC5 and reveal the relationship between its EPS biosynthetic phenotype and genotype, we analyzed the carbohydrate metabolic capacity, nucleotide sugar formation pathways, and EPS biosynthesis-related gene clusters of strain MC5 based on its whole genome sequence. Finally, we performed validation tests on the monosaccharides and disaccharides that strain MC5 may metabolize.

Results

Genomic analysis showed that MC5 has seven nucleotide sugar biosynthesis pathways and 11 sugar-specific phosphate transport systems, suggesting that the strain can metabolize mannose, fructose, sucrose, cellobiose, glucose, lactose, and galactose. Validation results showed that strain MC5 can metabolize these seven sugars and produce significant amounts of EPS (> 250 mg/L). In addition, strain MC5 possesses two typical eps biosynthesis gene clusters, which include the conserved genes epsABCDE, wzx, and wzy, six key genes for polysaccharide biosynthesis, and one MC5-specific epsG gene.

Discussion

These insights into the mechanism of EPS-MC5 biosynthesis can be used to promote the production of EPS through genetic engineering.

Insight into biofilm-forming patterns: biofilm-forming conditions and dynamic changes in extracellular polymer substances

The microbial biofilm adheres to the surface of the carrier, which protects the pollutant-degrading bacteria and resists harsh environments; thus, research on biofilm-forming patterns will help promote the application of biofilms in wastewater treatment. Herein, univariate analysis and response surface methodology (RSM) confirmed that glucose and mannose at 3-5 g/L promoted biofilm formation. Notably, the microplate method demonstrated that compared to trivalent cations, divalent cations could more greatly enhance the activity (especially magnesium) of the biofilm matrix, and the period of biofilm formation in the three strains was divided into the following stages: initial attachment (0-10 h), microcolony (10-24 h), maturation (24-48 h), and dispersion (36-72 h). During maturation, large amounts of extracellular polysaccharides (EPs) and extracellular DNA (eDNA) were distributed in the extracellular and intracellular spaces, respectively, as observed by super-resolution structured illumination microscopy (SR-SIM). This study enhances the understanding of the characteristics and patterns of biofilm formation and can facilitate the application of biofilms in wastewater treatment.

Effects of galactosyltransferase on EPS biosynthesis and freeze-drying resistance of Lactobacillus acidophilus NCFM

Galactosyltransferase (GalT) is an important enzyme in synthesizing exopolysaccharide (EPS), the major polymer of biofilms protecting cells from severe conditions. However, the contribution to, and regulatory mechanism of GalT, in stressor resistance are still unclear. Herein, we successfully overexpressed GalT in Lactobacillus acidophilus NCFM by genetic engineering. The GalT activity and freeze-drying survival rate of the recombinant strain were significantly enhanced. The EPS yield also increased by 17.8%, indicating a positive relationship between freeze-drying resistance and EPS. RNA-Seq revealed that GalT could regulate the flux of the membrane transport system, pivotal sugar-related metabolic pathways, and promote quorum sensing to facilitate EPS biosynthesis, which enhanced freeze-drying resistance. The findings concretely prove that the mechanism of GalT regulating EPS biosynthesis plays an important role in protecting lactic acid bacteria from freeze-drying stress.

Structural insight into a glucomannan-type extracellular polysaccharide produced by a marine Bacillus altitudinis SORB11 from Southern Ocean

Extracellular polysaccharide (EPS) produced by a deep-sea, psychrotolerant Bacillus altitudinis SORB11 was evaluated by considering physiochemical nature and structural constituents. The productivity of crude EPS was measured ~ 13.17 g L^-1. The surface topography of the crude EPS showed a porous, webbed structure along with a branched coil-like configuration. The crystalline crude EPS contained a high amount of sulfur. Further, the crude EPS was subjected for purification. The molecular weight of purified EPS was determined ~ 9.8 × 10⁴ Da. The purified EPS was appeared to show glucomannan-like configuration that is composed of → 4)-β-Manp-(1 → and → 4)-β-Glcp-(1 → residues. So, this polysaccharide was comparable to the structure of plant-derived glucomannan. Subsequently, EPS biosynthesis protein clusters like EpsC, EpsD, EpsE, and glycosyltransferase family proteins were predicted from the genome of strain SORB11, which may provide an insight into the production of glucomannan-type of polysaccharide. This low molecular weight linear form of glucomannan-type EPS might be involved to form a network-like unattached aggregation, and helps in cell-to-cell interaction in deep-sea microbial species.

Comparative genomics reveals the organic acid biosynthesis metabolic pathways among five lactic acid bacterial species isolated from fermented vegetables

Lactic acid bacteria (LAB) comprise a widespread bacterial group, inhabiting the niches of fermented vegetables and capable of producing beneficial organic acids. In the present study, several bioinformatics approaches were used to perform whole-genome sequencing and comparative genomics of five LAB species, Lactobacillus plantarum PC1-1, Pediococcus pentosaceus PC2-1(F2), Weissella hellenica PC1A, Lactobacillus buchneri PC-C1, and Enterococcus sp. YC2-6, to enhance understanding of their different genetic functionalities and organic acid biosynthesis. The results revealed major carbohydrate-active enzymes, putative operons and unique mobile genetic elements, including plasmids, resistance genes, insertion sequences and composite transposons involved in organic acid biosynthesis. The metabolic pathways of organic acid biosynthesis emphasize the key genes encoding specific enzymes required for organic acid metabolism. The five genomes were found to contain various regions of secondary metabolite biosynthetic gene clusters, including the type III polyketide synthases (T3PKS) enriched with unique genes encoding a hydroxymethylglutaryl-CoA synthase, capable of exhibiting specific antimicrobial activity with biopreservative potential, and a cyclic AMP receptor protein (CPR) transcription factor acting as a glucose sensor in organic acid biosynthesis. This could enable the organisms to prevail in the fermentation process, suggesting potential industrial applications.

Investigating the Functional Role of Hypothetical Proteins From an Antarctic Bacterium Pseudomonas sp. Lz4W: Emphasis on Identifying Proteins Involved in Cold Adaptation

Exploring the molecular mechanisms behind bacterial adaptation to extreme temperatures has potential biotechnological applications. In the present study, Pseudomonas sp. Lz4W, a Gram-negative psychrophilic bacterium adapted to survive in Antarctica, was selected to decipher the molecular mechanism underlying the cold adaptation. Proteome analysis of the isolates grown at 4°C was performed to identify the proteins and pathways that are responsible for the adaptation. However, many proteins from the expressed proteome were found to be hypothetical proteins (HPs), whose function is unknown. Investigating the functional roles of these proteins may provide additional information in the biological understanding of the bacterial cold adaptation. Thus, our study aimed to assign functions to these HPs and understand their role at the molecular level. We used a structured insilico workflow combining different bioinformatics tools and databases for functional annotation. Pseudomonas sp. Lz4W genome (CP017432, version 1) contains 4493 genes and 4412 coding sequences (CDS), of which 743 CDS were annotated as HPs. Of these, from the proteome analysis, 61 HPs were found to be expressed consistently at the protein level. The amino acid sequences of these 61 HPs were submitted to our workflow and we could successfully assign a function to 18 HPs. Most of these proteins were predicted to be involved in biological mechanisms of cold adaptations such as peptidoglycan metabolism, cell wall organization, ATP hydrolysis, outer membrane fluidity, catalysis, and others. This study provided a better understanding of the functional significance of HPs in cold adaptation of Pseudomonas sp. Lz4W. Our approach emphasizes the importance of addressing the “hypothetical protein problem” for a thorough understanding of mechanisms at the cellular level, as well as, provided the assessment of integrating proteomics methods with various annotation and curation approaches to characterize hypothetical or uncharacterized protein data. The MS proteomics data generated from this study has been deposited to the ProteomeXchange through PRIDE with the dataset identifier–PXD029741.

Exopolysaccharides synthesized by lactic acid bacteria: biosynthesis pathway, structure-function relationship, structural modification and applicability

Probiotics and their fermentation products are increasingly been focused on due to their health-boosting effects. Exopolysaccharides (EPS) synthetized by lactic acid bacteria (LAB) are widely applied as texture modifiers in dairy, meat and bakery products owning to their improved properties. Moreover, LAB-derived EPS have been confirmed to possess diverse physiological bioactivities including antioxidant, anti-biofilm, antiviral, immune-regulatory or antitumor. However, the low production and high acquisition cost hinder their development. Even though LAB-derived EPS have been extensively studied for their production-improving, there are only few reports on the systematic elucidation and summary of the relationship among biosynthesis pathway, strain selection, production parameter, structure-function relationship. Therefore, a detailed summary on biosynthesis pathway, production parameter and structure-function relationship of LAB-derived EPS is provided in this review, the structural modifications together with the current and potential applications are also discussed in this paper.

Recent Advancements in Microbial Polysaccharides: Synthesis and Applications

Polysaccharide materials are widely applied in different applications including food, food packaging, drug delivery, tissue engineering, wound dressing, wastewater treatment, and bioremediation sectors. They were used in these domains due to their efficient, cost-effective, non-toxicity, biocompatibility, and biodegradability. As is known, polysaccharides can be synthesized by different simple, facile, and effective methods. Of these polysaccharides are cellulose, Arabic gum, sodium alginate, chitosan, chitin, curdlan, dextran, pectin, xanthan, pullulan, and so on. In this current article review, we focused on discussing the synthesis and potential applications of microbial polysaccharides. The biosynthesis of polysaccharides from microbial sources has been considered. Moreover, the utilization of molecular biology tools to modify the structure of polysaccharides has been covered. Such polysaccharides provide potential characteristics to transfer toxic compounds and decrease their resilience to the soil. Genetically modified microorganisms not only improve yield of polysaccharides, but also allow economically efficient production. With the rapid advancement of science and medicine, biosynthesis of polysaccharides research has become increasingly important. Synthetic biology approaches can play a critical role in developing polysaccharides in simple and facile ways. In addition, potential applications of microbial polysaccharides in different fields with a particular focus on food applications have been assessed.