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A strain Leuconostoc citreum B-2 was isolated from homemade fermentation product of pineapple and its polysaccharide yield was 28.3 g/L after cultivating the strain in Man-Rogosa-Sharpe (MRS) medium with 75 g/L sucrose. The exopolysaccharide (EPS) was characterized by gas chromatography (GC), Fourier-transform infrared (FT-IR) spectra, high-performance size-exclusion chromatography (HPSEC), nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscope (SEM) analysis in present study. The monosaccharide composition of EPS was glucose and molecular weight was 3.77 × 10 6 Da. FT-IR and NMR spectra revealed that the B-2 EPS was composed of 75% α-(1 → 6) linked d -glucopyranose units existing in the main chain with 19% α-(1 → 3) branching and only a few α-(1 → 2) branching. The SEM of the dried EPS appeared irregular sheets with glittering surface and compact structure. Water solubility index and water holding capacity of B-2 EPS were 80% and 450%, respectively. All the mentioned characteristics suggested that the EPS has a potential application in the food, cosmetic and pharmaceuticals industry. [ABSTRACT FROM AUTHOR]

Carbon dioxide sequestering bacterial strains were previously isolated from free air CO 2 enriched (FACE) soil. In the present study, these strains were screened for PHA accumulation and Bacillus cereus SS105 was found to be the most prominent PHA accumulating strain on sodium bicarbonate and molasses as carbon source. This strain was further characterized by Spectrofluorometric method and Confocal microscopy after staining with Nile red. PHA granules in inclusion bodies were visualized by Transmission Electron Microscopy. The PHA and its monomer composition were characterized by GC–MS followed by FTIR and NMR. The genetic basis of PHA production was confirmed by the amplification, cloning and analysis of PHA biosynthesis genes phaR, phaB and phaC from B. cereus with the degenerate primers . The PHA production was further optimized by Response Surface Methodology and the percent increase observed after optimization was 55.16% (w/v). [ABSTRACT FROM AUTHOR]

A novel exopolysaccharide (EPS), promisingly served as natural alternatives of commercial additives, was obtained from a culture of Lactobacillus plantarum KX041 , a specie of lactic acid bacteria (LAB) regarded as Generally Recognized as Safe Foods (GRAS). However, the low yield severely hindered further study and application of the EPS. The influences of medium components and culture conditions were investigated and the optimal conditions of the EPS production were successfully obtained by response surface methodology (RSM). Maximum EPS production 599.52 mg/mL (about 3 folds than the original production) was obtained at optimal conditions of soybean peptone (20 g/L), fermentation temperature (35 °C) and initial pH (6.38). The EPS had a molecular weight of 38.67 KDa and it consisted of arabinose, mannose, glucose and galactose in a molar ratio of 0.95:12.94:7.26:3.31. A specific spectrogram of neutral polysaccharide was obtained by FT-IR analysis, and the EPS also exhibited higher thermal stability with a degradation temperature of 289.01 °C in DSC analysis. A comprehensive investigation of antioxidant activity in vitro indicated that the EPS possessed superior antioxidant activity with the EC 50 value of ABTS, DPPH, hydroxyl and superoxide free radical scavenging were 0.2, 1.4, 1.7 and 5.6 mg/mL, respectively. Furthermore, combined with reducing power analysis, it suggested that the EPS not only acted as electrons donor to directly react with free radicals, but also exerted antioxidant activity with other mechanisms which need to be studied further. All these results collectively shown that as a natural compound, the EPS produced by Lactobacillus plantarum KX041 had a great potential to be developed as natural antioxidants or functional additive in food industry. [ABSTRACT FROM AUTHOR]

The exopolysaccharide succinoglycan is produced mainly by a large number of soil microbes of Agrobacterium, Rhizobium or Pseudomonas genera etc. Structural properties of succinoglycan are unique in terms of its thermal stability and superior viscosifying property. Unlike the other highly commercialized bacterial exopolysaccharides like dextran or xanthan, mass scale application of succinoglycan has not been that much broadly explored yet. Bacterial succinoglycan is found suitable as a viscosifying and emulsifying agent in food industry, in gravel packing or fluid-loss control agent etc. In this present review, the key aspects of succinoglycan study, in particular, developments in structural characterizations, exo/ exs operon system involved in biosynthesis pathway, commercial applications in food and other industries and patenting trends have been discussed. [ABSTRACT FROM AUTHOR]

Exopolysaccharides play an important role in the physiology of a bacterial cell. Ensifer meliloti is capable of producing at least two types of exopolysaccharides (EPS): succinoglycan and galactoglucan. In E. meliloti, EPS are best known for their role in mediating interaction with its symbiotic hosts. It was previously shown that high concentrations of Mg2+ or K+ were capable of suppressing the mucoid phenotype associated with galactoglucan production in an expR+ derivative of Rm1021. In an attempt to determine how Mg2+ regulates galactoglucan production, SRmD363 was mutagenised and screened for mutants which were visibly mucoid at high concentrations of magnesium. Tn5 mutations in genes exoX, emmB, phoC and SMc00722 were isolated. SMc00722 is annotated as a hypothetical transmembrane protein that is conserved in the α-proteobacteria. Characterisation of SMc00722 in Rm1021 showed that the increased mucoidy was due to succinoglycan. Strains carrying mutations in SMc00722 showed increased biofilm production, and were more sensitive to high Mg2+ concentrations and deoxycholate. In addition, we show that strains carrying a mutation in SMc00722 have elevated intracellular Mg2+ concentrations. Taken together, the data are consistent with the hypothesis that SMc0722 may play a role in maintaining intracellular magnesium concentration, and we suggest that this gene be tentatively annotated as mhrA (magnesium homeostasis related). [ABSTRACT FROM AUTHOR]

An exopolysaccharide (EPS) producing strain CAS grown in a Bushnell Haas medium was isolated from curd sample and identified as Rhizobium radiobacter CAS. The biopolymer was duly characterized by FT-IR and NMR spectroscopy and was found to be composed of glucose and galactose in a molar ratio of 6.99:1 as confirmed by HPAEC; thus depicting it to be succinoglycan type exopolysaccharide. In addition, conceivable presence of one succinate and two acetate groups of succinoglycan was estimated using 1 H NMR analysis by specific signal integration. Furthermore, as a documented fact, the insights into the rheological behaviors portray phenomenal influences in food, cosmetics and pharmaceutical industries as thickening, gelling, stabilizing and emulsifying agent. However, this piece of information has remained unnoticed from the existing literature. Thus, in the present study the rheological properties of succinoglycan type biopolymer in aqueous solution were systematically investigated. The flow behaviour testing in an aqueous solution verified its pseudoplastic character and higher apparent viscosity. Furthermore, study on its potential strength and tolerance in various thermal conditions, cation salts, and pH has been studied in depth. Such a study can provide a thorough guidance on the rheological behaviour of the biomaterial and thus impart significant insights into postulating its application spectrum into food, cosmetics and pharmaceutical industrial sectors. The present study is thus, one of its kinds which decipher the complete rheological behavioural portrait. [ABSTRACT FROM AUTHOR]

Agrobacterium is a genus of gram-negative bacteria that can produce several typical exopolysaccharides with commercial uses in the food and pharmaceutical fields. In particular, succinoglycan and curdlan, due to their good quality in high yield, have been employed on an industrial scale comparatively early. Exopolysaccharide biosynthesis is a multiple-step process controlled by different functional genes, and various environmental factors cause changes in exopolysaccharide biosynthesis through regulatory mechanisms. In this mini-review, we focus on the genetic control and regulatory mechanisms of succinoglycan and curdlan produced by Agrobacterium. Some key functional genes and regulatory mechanisms for exopolysaccharide biosynthesis are described, possessing a high potential for application in metabolic engineering to modify exopolysaccharide production and physicochemical properties. This review may contribute to the understanding of exopolysaccharide biosynthesis and exopolysaccharide modification by metabolic engineering methods in Agrobacterium. [ABSTRACT FROM AUTHOR]

Bacterial surface components and extracellular compounds, particularly flagella, lipopolysaccharides (LPSs), and exopolysaccharides (EPSs), in combination with environmental signals and quorum-sensing signals, play crucial roles in bacterial autoaggregation, biofilm development, survival, and host colonization. The nitrogen-fixing species Sinorhizobium meliloti (S. meliloti) produces two symbiosis-promoting EPSs: succinoglycan (or EPS I) and galactoglucan (or EPS II). Studies of the S. meliloti/alfalfa symbiosis model system have revealed numerous biological functions of EPSs, including host specificity, participation in early stages of host plant infection, signaling molecule during plant development, and (most importantly) protection from environmental stresses. We evaluated functions of EPSs in bacterial resistance to heavy metals and metalloids, which are known to affect various biological processes. Heavy metal resistance, biofilm production, and co-culture were tested in the context of previous studies by our group. A range of mercury (Hg II) and arsenic (As III) concentrations were applied to S. meliloti wild type strain and to mutant strains defective in EPS I and EPS II. The EPS production mutants were generally most sensitive to the metals. Our findings suggest that EPSs are necessary for the protection of bacteria from either Hg (II) or As (III) stress. Previous studies have described a pump in S. meliloti that causes efflux of arsenic from cells to surrounding culture medium, thereby protecting them from this type of chemical stress. The presence of heavy metals or metalloids in culture medium had no apparent effect on formation of biofilm, in contrast to previous reports that biofilm formation helps protect various microorganism species from adverse environmental conditions. In co-culture experiments, EPS-producing heavy metal resistant strains exerted a protective effect on AEPS-non-producing, heavy metal-sensitive strains; a phenomenon termed "rescuing" of the non-resistant strain. [ABSTRACT FROM AUTHOR]

The aim of the work was to optimize the combination of two strains of Streptococcus thermophilus used as a starter culture to develop a reduced-fat soft cheese with improved texture and added bio-value. Two strains, St 907 and St 399, were selected for the ability to produce exopolysaccharides (EPS) in milk. Biochemical characterization of EPS showed that the two biopolymers were similar in monosaccharide composition (glucose, galactose, rhamnose and mannose) but different in the relative molar ratio of the monomers and in molecular weight. St 907 produced a long chain and stringy EPS with very high water holding capacity, whereas St 399 produced a smaller-sized EPS, acting as texture enhancer. The strain St 399 was also selected as a major folic acid producer. The cheese obtained had 69.3% of moisture, 18.1% of proteins and 11.5% of fat. Despite the high level of hydration, the structure of the cheese was preserved and the low fat content was successfully compensated by EPS, which gave a positive effect on mouthfeel and cheese yield. The optimized formulation of the starter culture significantly increased the content of folates by up to 67% compared to control cheeses obtained using a commercial starter culture for soft cheeses. [ABSTRACT FROM AUTHOR]

Both bacterial symbionts and pathogens rely on their host-sensing mechanisms to activate the biosynthetic pathways necessary for their invasion into host cells. The Gram-negative bacterium Sinorhizobium meliloti relies on its RSI (ExoR-ExoS-ChvI) Invasion Switch to turn on the production of succinoglycan, an exopolysaccharide required for its host invasion. Recent whole-genome sequencing efforts have uncovered putative components of RSI-like invasion switches in many other symbiotic and pathogenic bacteria. To explore the possibility of the existence of a common invasion switch, we have conducted a phylogenomic survey of orthologous ExoR, ExoS, and ChvI tripartite sets in more than ninety proteobacterial genomes. Our analyses suggest that functional orthologs of the RSI invasion switch co-exist in Rhizobiales, an order characterized by numerous invasive species, but not in the order’s close relatives. Phylogenomic analyses and reconstruction of orthologous sets of the three proteins in Alphaproteobacteria confirm Rhizobiales-specific gene synteny and congruent RSI evolutionary histories. Evolutionary analyses further revealed site-specific substitutions correlated specifically to either animal-bacteria or plant-bacteria associations. Lineage restricted conservation of any one specialized gene is in itself an indication of species adaptation. However, the orthologous phylogenetic co-occurrence of all interacting partners within this single signaling pathway strongly suggests that the development of the RSI switch was a key adaptive mechanism. The RSI invasion switch, originally found in S. meliloti, is a characteristic of the Rhizobiales, and potentially a conserved crucial activation step that may be targeted to control host invasion by pathogenic bacterial species. [ABSTRACT FROM AUTHOR]

Sinorhizobium meliloti requires exopolysaccharides in order to form a successful nitrogen-fixing symbiosis with Medicago species. Additionally, during early stages of symbiosis, S. meliloti is presented with an oxidative burst that must be overcome. Levels of production of the exopolysaccharides succinoglycan (EPS-I) and galactoglucan (EPS-II) were found to correlate positively with survival in hydrogen peroxide (H2O2). H2O2 damage is dependent on the presence of iron and is mitigated when EPS-I and EPS-II mutants are cocultured with cells expressing either exopolysaccharide. Purified EPS-I is able to decrease in vitro levels of H2O2, and this activity is specific to the symbiotically active low-molecular-weight form of EPS-I. This suggests a potential protective function of exopolysaccharides against H2O2 during early symbiosis. [ABSTRACT FROM AUTHOR]

Rhizobia establish a symbiotic relationship with their host legumes to induce the formation of nitrogen-fixing nodules. This process is regulated by many rhizobium regulators, including some two-component regulatory systems (TCSs). NtrY/NtrX, a TCS that was first identified in Azorhizobium caulinodans, is required for free-living nitrogen metabolism and symbiotic nodulation on Sesbania rostrata. However, its functions in a typical rhizobium such as Sinorhizobium meliloti remain unclear. Here we found that the S. meliloti response regulator NtrX but not the histidine kinase NtrY is involved in the regulation of exopolysaccharide production, motility, and symbiosis with alfalfa. A plasmid insertion mutant of ntrX formed mucous colonies, which overproduced succinoglycan, an exopolysaccharide, by upregulating its biosynthesis genes. This mutant also exhibited motility defects due to reduced flagella and decreased expression of flagellins and regulatory genes. The regulation is independent of the known regulatory systems of ExoR/ExoS/ChvI, EmmABC, and ExpR. Alfalfa plants inoculated with the ntrX mutant were small and displayed symptoms of nitrogen starvation. Interestingly, the deletion mutant of ntrY showed a phenotype similar to that of the parent strain. These findings demonstrate that the S. meliloti NtrX is a new regulator of succinoglycan production and motility that is not genetically coupled with NtrY. [ABSTRACT FROM AUTHOR]

The article discusses a study which demonstrated that increased exopolysaccharide succinoglycan production is not detrimental to symbiotic development but enhances the symbiotic productivity of Sinorhizobium meliloti 1021 with the host plant Medicago truncatula cv. ]emalong A17. The study showed that increased succinoglycan production was engineered by overexpression of the exoYgene. It also proposed several possible roles for succinoglycan in infection thread initiation and development.

Swarming is a mode of translocation dependent on flagellar activity that allows bacteria to move rapidly across surfaces. In several bacteria, swarming is a phenotype regulated by quorum sensing. It has been reported that the swarming ability of the soil bacterium Sinorhizobium meliloti Rm2011 requires a functional ExpR/Sin quorum-sensing system. However, our previous published results demonstrate that strains Rm 1021 and Rm2011, both known to have a disrupted copy of expR, are able to swarm on semisolid minimal medium. In order to clarify these contradictory results, the role played by the LuxR-type regulator ExpR has been reexamined. Results obtained in this work revealed that S. meliloti can move over semisolid surfaces using at least two different types of motility. One type is flagellum-independent surface spreading or sliding, which is positively influenced by a functional expR gene mainly through the production of exopolysaccharide II (EPS II). To a lesser extent, EPS II-deficient strains can also slide on surfaces by a mechanism that is at least dependent on the siderophore rhizobactin 1021. The second type of surface translocation shown by S. meliloti is swarming, which is greatly dependent on flagella and rhizobactin 1021 but does not require ExpR. We have extended our study to demonstrate that the production of normal amounts of succinoglycan (EPS I) does not play a relevant role in surface translocation but that its overproduction facilitates both swarming and sliding motilities. [ABSTRACT FROM AUTHOR]

In Sinorhizobium meliloti, the production of exopolysaccharides such as succinoglycan and exopolysaccharide II (EPS II) enables the bacterium to invade root nodules on Medicago sativa and establish a nitrogen-fixing symbiosis. While extensive research has focused on succinoglycan, less is known concerning the regulation of EPS II or the mechanism by which it mediates entrance into the host plant. Previously, we reported that the ExpR/Sin quorum-sensing system is required to produce the symbiotically active low-molecular-weight fraction of this exopolysaccharide. Here, we show that this system induces EPS II production by increasing expression of the expG-expC operon, encoding both a transcriptional regulator (ExpG) and a glycosyl transferase (ExpC). ExpG derepresses EPS II production at the transcriptional level from MucR, a RosR homolog, while concurrently elevating expression of expC, resulting in the synthesis of the low-molecular-weight form. While the ExpR/Sin system abolishes the role of MucR on EPS II production, it preserves a multitude of other quorum-sensing-independent regulatory functions which promote the establishment of symbiosis. In planktonic 5. meliloti, MucR properly coordinates a diverse set of bacterial behaviors by repressing a variety of genes intended for expression during symbiosis and enhancing the bacterial ability to induce root nodule formation. Quorum sensing precisely modulates the functions of MucR to take advantage of both the production of symbiotically active EPS II as well as the proper coordination of bacterial behavior required to promote symbiosis. [ABSTRACT FROM AUTHOR]

The article focuses on a research study related to anti-biofilm activity of an exopolysaccharide from a sponge-associated strain of Bacillus licheniformis. During the course of the study, polysaccharide was extracted from a Bacillus licheniformis strain associated with the marine organism Spongia officinalis. The polysaccharide isolated from sponge-associated B. licheniformis has several features that provide a tool for better exploration of novel anti-biofilm compounds.

Sinorhizobium meliloti is a soil bacterium that elicits the formation of root organs called nodules on its host plant, Medicago sativa. Inside these structures, the bacteria are able to convert atmospheric nitrogen into ammonia, which is then used by the plant as a nitrogen source. The synthesis by S. meliloti of at least one exopolysaccharide, succinoglycan or EPS II, is essential for a successful symbiosis. While exopolysaccharide-deficient mutants induce the formation of nodules, they fail to invade them, and as a result, no nitrogen fixation occurs. Interestingly, the low-molecular-weight fractions of these exopolysaccharides are the symbiotically active forms, and it has been suggested that they act as signals to the host plant to initiate infection thread formation. In this work, we explored the role of these rhizobial exopolysaccharides in biofilm formation and their importance in the symbiotic relationship with the host. We showed that the ExpR/Sin quorum-sensing system controls biofilm formation in S. meliloti through the production of EPS II, which provides the matrix for the development of structured and highly organized biofilms. Moreover, the presence of the low-molecular-weight fraction of EPS II is vital for biofilm formation, both in vitro and in vivo. This is the first report where the symbiotically active fraction of EPS II is shown to be a critical factor for biofilm formation and root colonization. Thus, the ability of S. meliloti to properly attach to root surfaces and form biofilms conferred by the synthesis of exopolysaccharides may embody the main function of these symbiotically essential molecules. [ABSTRACT FROM AUTHOR]

Exopolysaccharides, either succinoglycan or galactoglucan, are essential for the establishment of the symbiosis between Sinorhizobium meliloti and Medicago sativa (alfalfa). The ExoS/ChvI two-component regulatory system is known as a regulator of succinoglycan production but the genes that are directly regulated by ChvI have not been determined. Difficulty isolating exoS and chvI null mutants has prompted the suggestion that these genes are essential for S. meliloti viability. We have successfully isolated exoS and chvI null mutants using a merodiploid-facilitated strategy. We present evidence that the S. meliloti ExoS/ChvI two-component regulatory system is essential for symbiosis with alfalfa. Phenotypic analyses of exoS and chvI null mutant strains demonstrate that ExoS/ChvI controls both succinoglycan and galactoglucan production and is required for growth on over 21 different carbon sources. These new findings suggest that the ExoS/ChvI regulatory targets might not be the exo genes that are specific for succinoglycan biosynthesis but rather genes that have common influence on both succinoglycan and galactoglucan production. Other studied alpha-proteobacteria ExoS/ChvI orthologues are required for the bacteria to invade or persist in host cells and thus we present more evidence that this two-component regulatory system is essential for alpha-proteobacterial host interaction. [ABSTRACT FROM AUTHOR]