Microbial polysaccharides from Gram-negative bacteria

Cold adaptation in the marine bacterium, Sphingopyxis alaskensis, assessed using quantitative proteomics

The cold marine environment constitutes a large proportion of the Earth's biosphere. Sphingopyxis alaskensis was isolated as a numerically abundant bacterium from several cold marine locations, and has been extensively studied as a model marine bacterium. Recently, a metabolic labelling platform was developed to comprehensively identify and quantify proteins from S. alaskensis. The approach incorporated data normalization and statistical validation for the purpose of generating highly confident quantitative proteomics data. Using this approach, we determined quantitative differences between cells grown at 10°C (low temperature) and 30°C (high temperature). Cold adaptation was linked to specific aspects of gene expression: a dedicated protein-folding system using GroESL, DnaK, DnaJ, GrpE, SecB, ClpB and PPIase; polyhydroxyalkanoate-associated storage materials; a link between enzymes in fatty acid metabolism and energy generation; de novo synthesis of polyunsaturated fatty acids in the membrane and cell wall; inorganic phosphate ion transport by a phosphate import PstB homologue; TonB-dependent receptor and bacterioferritin in iron homeostasis; histidine, tryptophan and proline amino acid metabolism; and a large number of proteins without annotated functions. This study provides a new level of understanding on how important marine bacteria can adapt to compete effectively in cold marine environments. This study is also a benchmark for comparative proteomic analyses with other important marine bacteria and other cold-adapted organisms.

Bacterial exopolysaccharides from extreme marine habitats: production, characterization and biological activities

Many marine bacteria produce exopolysaccharides (EPS) as a strategy for growth, adhering to solid surfaces, and to survive adverse conditions. There is growing interest in isolating new EPS producing bacteria from marine environments, particularly from extreme marine environments such as deep-sea hydrothermal vents characterized by high pressure and temperature and heavy metal presence. Marine EPS-producing microorganisms have been also isolated from several extreme niches such as the cold marine environments typically of Arctic and Antarctic sea ice, characterized by low temperature and low nutrient concentration, and the hypersaline marine environment found in a wide variety of aquatic and terrestrial ecosystems such as salt lakes and salterns. Most of their EPSs are heteropolysaccharides containing three or four different monosaccharides arranged in groups of 10 or less to form the repeating units. These polymers are often linear with an average molecular weight ranging from 1 × 10⁵ to 3 × 10⁵ Da. Some EPS are neutral macromolecules, but the majority of them are polyanionic for the presence of uronic acids or ketal-linked pyruvate or inorganic residues such as phosphate or sulfate. EPSs, forming a layer surrounding the cell, provide an effective protection against high or low temperature and salinity, or against possible predators. By examining their structure and chemical-physical characteristics it is possible to gain insight into their commercial application, and they are employed in several industries. Indeed EPSs produced by microorganisms from extreme habitats show biotechnological promise ranging from pharmaceutical industries, for their immunomodulatory and antiviral effects, bone regeneration and cicatrizing capacity, to food-processing industries for their peculiar gelling and thickening properties. Moreover, some EPSs are employed as biosurfactants and in detoxification mechanisms of petrochemical oil-polluted areas. The aim of this paper is to give an overview of current knowledge on EPSs produced by marine bacteria including symbiotic marine EPS-producing bacteria isolated from some marine annelid worms that live in extreme niches.

Modification of exopolysaccharide composition and production by three cyanobacterial isolates under salt stress

BACKGROUND, AIM, AND SCOPE

Polysaccharides are renewable resources representing an important class of polymeric materials of biotechnological interest, offering a wide variety of potentially useful products to mankind. Exopolysaccharides (EPSs) of microbial origin with a novel functionality, reproducible physico-chemical properties, stable cost and supply, became a better alternative to polysaccharides of algal origin. EPSs are believed to protect bacterial cells from desiccation, heavy metals or other environmental stresses, including hostimmune responses, and to produce biofilms, thus enhancing the cells chances of colonising special ecological niches. One of the most important stress factor is salt stress for microorganisms. The present investigation is aimed to determine correlation between salt resistance and EPS production by three cyanobacterial isolates (Synechocystis sp. BASO444, Synechocystis sp. BASO507 and Synechocystis sp. BASO511). It is also aimed to investigate the effect of salt concentrations on EPS production by cyanobacteria and effect of salt on monosaccharide composition of EPS.

MATERIALS AND METHODS

Cyanobacterial isolates were identified by 16 S rRNA analysis. Its salt (NaCl) tolerance and association with exopolysaccharides (EPSs) production in three cyanobacterial isolates were investigated. Also, EPS was analysed by HPLC for monomer characterization.

RESULTS

Increased EPS production was associated with NaCl tolerance. The most tolerant isolate, Synechocystis sp. BASO444, secreted the most EPS (500 mg/L). EPS production by Synechocystis sp. BASO444, Synechocystis sp. BASO507 and Synechocystis sp. BASO511 was investigated following exposure to 0.2 and 0.4 M NaCl. Also, flasks containing medium without NaCl were inoculated in the same manner to serve as controls. The monosaccharide compositions of EPS produced by the three isolates following exposure to 0.2 M NaCl were analysed by HPLC. Control EPS of BASO444 was composed of glucose (97%) and galacturonic acid (3%). The composition of BASO511 (control) was glucose (95%), xylose (4.80%), arabinose (0.13%), glucuronic acid (0.03%) and galacturonic acid (0.04%). However, the composition of BASO507 (control) was glucose (0.98%), xylose (98.00%), arabinose (1.00%), glucuronic acid (0.01%) and galacturonic acid (0.01%). In the presence of 0.2 M NaCl, EPS compositions and ratios of three cyanobacterial isolates changed.

DISCUSSION

Although hyperproduction of EPS in response to starvation, antiviral activity, thickening agent and cosmetic industry for product formulations has been reported for cyanobacteria, the effect of NaCl on EPS production in cyanobacteria is not a popular area of study. There are no clear reports correlating EPS production and NaCl tolerance. The gap in the data about the effect of NaCl on cyanobacterial EPS production was filled by this investigation, and the results of our study have important implications in both the industrial and environmental arenas.

CONCLUSIONS

Our results indicate that 1) exposure to elevated concentrations of NaCl affects the composition of EPS produced by Synechocystis sp. BASO444, Synechocystis sp. BASO507 and Synechocystis sp. BASO511, and 2) there is a correlation between NaCl tolerance and EPS production in some cyanobacteria.

RECOMMENDATIONS AND PERSPECTIVES

Differences in the monosaccharide composition and ratios of EPS may promote NaCl tolerance in these microorganisms. As well, these alternative composition polysaccharides may be important for industrial applications.

Transcriptional profile of the Shigella flexneri response to an alkaloid: berberine

Berberine, a natural isoquinoline alkaloid found in many medicinal herbs, has been shown to be active against a variety of microbial infections. To examine the potential effects of berberine on Shigella flexneri, a whole-genome DNA microarray was constructed and a transcriptome analysis of the cellular responses of S. flexneri when exposed to berberine chloride (BC) was performed. Our data revealed that BC upregulated a group of genes involved in DNA replication, repair and division. Intriguingly, the expression of many genes related to cell envelope biogenesis was increased. In addition, many genes involved in cell secretion, nucleotide metabolism, translation, fatty acid metabolism and the virulence system were also induced by the drug. However, more genes from the functional classes of carbohydrate metabolism, energy production and conversion as well as amino acid metabolism were significantly repressed than were induced. These results provide a comprehensive view of the changes in gene expression when S. flexneri was exposed to BC, and shed light on its complicated effects on this pathogen.

Evaluation of chromium(VI) removal behaviour by two isolates of Synechocystis sp. in terms of exopolysaccharide (EPS) production and monomer composition

Chromium(VI) removal and its association with exopolysaccharide (EPS) production in cyanobacteria were investigated. Synechocystis sp. BASO670 produced higher EPS (548 mg L(-1)) than Synechocystis sp. BASO672 (356 mg L(-1)). While the EC(50) of the Cr(VI) for Synechocystis sp. BASO670 and Synechocystis sp. BASO672 were determined as 11.5 mg L(-1), and 2.0 mg L(-1), respectively, there was no relation between Cr(VI) removal and EPS production. Synechocystis sp. BASO672, which has higher EPS value, removed (33%) more Cr(VI) than Synechocystis sp. BASO670. Monomer compositions of EPS of each of the isolates were determined differently. Synechocystis sp. BASO672 which removed higher Cr(VI), had higher values of uronic acid and glucuronic acid (192 microg/mg and 89%, respectively). Our results showed that EPS might play a role in Cr(VI) tolerance. Monomer composition, especially uronic acid and glucuronic acid content of EPS may have enhanced Cr(VI) removal.

Bacterial extracellular polysaccharides involved in biofilm formation

Extracellular polymeric substances (EPS) produced by microorganisms are a complex mixture of biopolymers primarily consisting of polysaccharides, as well as proteins, nucleic acids, lipids and humic substances. EPS make up the intercellular space of microbial aggregates and form the structure and architecture of the biofilm matrix. The key functions of EPS comprise the mediation of the initial attachment of cells to different substrata and protection against environmental stress and dehydration. The aim of this review is to present a summary of the current status of the research into the role of EPS in bacterial attachment followed by biofilm formation. The latter has a profound impact on an array of biomedical, biotechnology and industrial fields including pharmaceutical and surgical applications, food engineering, bioremediation and biohydrometallurgy. The diverse structural variations of EPS produced by bacteria of different taxonomic lineages, together with examples of biotechnological applications, are discussed. Finally, a range of novel techniques that can be used in studies involving biofilm-specific polysaccharides is discussed.

Application of bioemulsifiers in soil oil bioremediation processes. Future prospects

Biodegradation is one of the primary mechanisms for elimination of petroleum and other hydrocarbon pollutants from the environment. It is considered an environmentally acceptable way of eliminating oils and fuel because the majority of hydrocarbons in crude oils and refined products are biodegradable. Petroleum hydrocarbon compounds bind to soil components and are difficult to remove and degrade. Bioemulsifiers can emulsify hydrocarbons enhancing their water solubility and increasing the displacement of oily substances from soil particles. For these reasons, inclusion of bioemulsifiers in a bioremediation treatment of a hydrocarbon polluted environment could be really advantageous. There is a useful diversity of bioemulsifiers due to the wide variety of producer microorganisms. Also their chemical compositions and functional properties can be strongly influenced by environmental conditions. The effectiveness of the bioemulsifiers as biostimulating agent in oil bioremediation processes has been demonstrated by several authors in different experimental assays. For example, they have shown to be really efficient in combination with other products frequently used in oil bioremediation such as they are inorganic fertilizer (NPK) and oleophilic fertilizer (i.e. S200C). On the other hand, the bioemulsifiers have shown to be more efficient in the treatment of soil with high percentage of clay. Finally, it has been proved their efficacy in other biotechnological processes such as in situ treatment and biopiles. This paper reviews literature concerning the application of bioemulsifiers in the bioremediation of soil polluted with hydrocarbons, and summarizes aspects of the current knowledge about their industrial application in bioremediation processes.

Characterization and transcriptional analysis of an ECF sigma factor from Xanthomonas campestris pv. campestris

The genomic DNA segment encoding the rpoE gene and its flanking region was cloned from Xanthomonas campestris pv. campestris strain 11 (Xc11). The transcriptional start site of rpoE was located at nucleotide G, which is 33 nucleotides preceding the putative translation initiation codon of rpoE, and a extracytoplasmic function sigma factors (sigma(E))-dependent promoter was identified with -35 (5'-GAACTT-3') and -10 (5'-TCTCA-3') consensus sequences. The protein encoded by rpoE gene acted as a sigma (sigma) factor and was sufficient to direct core RNA polymerase to the rpoE promoter and to stimulate initiation of transcription in vitro. The specific binding of the reconstituted Esigma(E) holoenzyme with the Xc11 rpoE promoter was demonstrated by gel retardation assay and DNAse I footprint analysis. This study clearly demonstrated that the rpoE-rseA-mucD genomic organization of X. campestris is similar to that found in Xylella fastidiosa; however, expression of rpoE in X. campestris is autoregulated by its own sigma(E)-dependent promoter.

Characterization of an extracellular polysaccharide produced by a Pseudomonas strain grown on glycerol

A new extracellular charged polysaccharide composed mainly by galactose, with lower amounts of mannose, glucose and rhamnose, was produced by the cultivation of Pseudomonas oleovorans NRRL B-14682 using glycerol as the sole carbon source. Thermal and solid-state NMR analysis showed that this polymer is essentially amorphous, with a glass transition temperature of 155.7 degrees C. The exopolysaccharide aqueous solutions have viscoelastic properties similar to that of Guar gum, but with affinity to salts as a result of its polyelectrolyte character. In addition, the exopolysaccharide has demonstrated good flocculating and emulsifying properties and film-forming capacity. These properties make this polymer a good alternative to more expensive natural polysaccharides, such as Guar gum, in several applications in the food, pharmaceutical, cosmetic, textile, paper and petroleum industries.

Production of bioemulsifier by Bacillus subtilis, Alcaligenes faecalis and Enterobacter species in liquid culture

Three bacterial strains isolated from waste crude oil were selected due to their capacity of growing in the presence of hydrocarbons and production of bioemulsifier. The genetic identification (PCR of the 16S rDNA gene using fD1 and rD1 primers) of these strains showed their affiliation to Bacillus subtilis, Alcaligenes faecalis and Enterobacter sp. These strains were able to emulsify n-octane, toluene, xylene, mineral oils and crude oil, look promising for bioremediation application. Finally, chemical composition, emulsifying activity and surfactant activity of the biopolymers produced by the selected strains were studies under different culture conditions. Our results showed that chemical and functional properties of the bioemulsifiers were affected by the carbon source added to the growth media.

Heterologous expression of a position 2-substituted (1-->3)-beta-D-glucan in Lactococcus lactis

Exopolysaccharides play an important role in the rheology and texture of fermented foods, and among these beta-glucans have immunomodulating properties. We show that the overproduction of the Pediococcus parvulus GTF glycosyltransferase in an uncapsulated Lactococcus lactis strain results in synthesis and secretion (300 mg liter(-1)) of a position 2-substituted (1-->3)-beta-D-glucan that has potential use as a food additive.

Characteristics of bioemulsifier V2-7 synthesized in culture media added of hydrocarbons: chemical composition, emulsifying activity and rheological properties

The bioemulsifier V2-7 is an exopolysaccharide (EPS) synthesized by strain F2-7 of Halomonas eurihalina and it has the property of emulsifying a wide range of hydrocarbons i.e. n-tetradecane, n-hexadecane, n-octane, xylene mineral light and heavy oils, petrol and crude oil. Characteristics of exopolysaccharide V2-7 produced in media supplemented with various hydrocarbons (n-tetradecane, n-hexadecane, n-octane, xylene, mineral light oil, mineral heavy oil, petrol or crude oil) were studied. Yield production varied from 0.54 to 1.45 g L(-1) according to the hydrocarbon added, in the same way chemical composition, viscosity and emulsifying activity of EPS varied with the culture conditions. Respect to chemical composition, percentage of uronic acids found in exopolymers produced in hydrocarbon media was always higher than that described for V2-7 EPS (1.32%) obtained with glucose. This large amount of uronic acid present could be useful in biodetoxification and waste water treatment. On the other hand, the highest amount of biopolymer was synthesized with mineral light oil, while the most active emulsifiers were those obtained from media added with petrol and n-octane. Furthermore, all EPS were capable of emulsifying crude oil more efficiently than the three chemical surfactants tested as control (Tween 20, Tween 80 and Triton X-100). The capacity of strain F2-7 to grow and produce bioemulsifier in presence of oil hydrocarbons together with the high emulsifying activity and low viscosity power of the biopolymers synthesized in hydrocarbons media could be considered highly beneficial for application of both bioemulsifier and producing strain in bioremediation of oil pollutants.

Bacterial exopolysaccharides – a perception

Microbial polysaccharides are multifunctional and can be divided into intracellular polysaccharides, structural polysaccharides and extracellular polysaccharides or exopolysaccharides (EPS). Extracellular polymeric substances (EPS), produced by both prokaryotes (eubacteria and archaebacteria) and eukaryotes (phytoplankton, fungi, and algae), have been of topical research interest. Newer approaches are carried out today to replace the traditionally used plant gums by their bacterial counterparts. The bacterial exopolysaccharides represent a wide range of chemical structures, but have not yet acquired appreciable significance. Chemically, EPS are rich in high molecular weight polysaccharides (10 to 30 kDa) and have heteropolymeric composition. They have new-fangled applications due to the unique properties they possess. Owing to this, exopolysaccharides have found multifarious applications in the food, pharmaceutical and other industries. Hence, the present article converges on bacterial exopolysaccharides.

Surgarcane biopolymer patch in femoral artery angioplasty on dogs

PURPOSE: The objective of this study was to evaluate the use of the sugarcane biopolymer membrane in femoral artery patch angioplasty on dogs. METHODS: Eight dogs were submitted to bilateral femoral artery patch angioplasty with a sugarcane biopolymer membrane patch on one side and e-PTFE patch on the contralateral side. This research was performed at Experimental Surgical Research Laboratory of the Centro de Ciências da Saúde at Universidade Federal de Pernambuco. The dogs were submitted to a new surgery at 180 days after the patch angioplasty in order to harvest the femoral artery. All the animals were evaluated by: clinical examination, measure of femoral artery diameter, arteriogram and Doppler fluxometry. Yet the material harvested was sent to histological study. Each animal served as its own control. RESULTS: In all vessels of both groups there were no cases of infection, aneurysm formation, rupture or pseudoaneurysm formation and thrombosis. In both groups it was observed a chronic inflammatory reaction with lymphocytes, neutrophils and fibrosis in the outer surface of the patches. It was observed fibrosis in the inner surfaces of all the patches. In e-PTFE patches occurred invasion by fibroblasts. CONCLUSION: The sugarcane biopolymer membrane can be used as a patch in femoral artery angioplasty on dogs.

Production, composition and Pb2+ adsorption characteristics of capsular polysaccharides extracted from a cyanobacterium Gloeocapsa gelatinosa

Pb2+ adsorption by the living cells of the cyanobacterium Gloeocapsa gelatinosa was studied. Cyanobacterial cells with intact capsular polysaccharide (CPS) showed 5.7 times higher Pb adsorption capacity than that of cells without CPS. The adsorbed Pb was desorbed by EDTA, indicating that Pb2+ adsorption occurred mainly on cell surface. Production, sugar content and ability of CPS to remove Pb2+ were then studied in details. CPS production by G. gelatinosa increased when culture time was prolonged. The maximum CPS production was 35.43 mg g(-1) dry weight after 30-day cultivation. Xylose, arabinose, ribose, rhamnose, galactose, glucose, mannose and fructose were the neutral sugars presented in CPS of G. gelatinosa. Acidic sugars including galacturonic and glucuronic acids were also found in CPS. The amount and composition of G. gelatinosa's CPS varied according to its growth phase and culture conditions. The highest amount of acidic sugars was produced when cultured under low light intensity. The extracted CPS rapidly removed Pb2+ from the solution (82.22+/-4.82 mg Pb2+ per g CPS), directly demonstrating its roles in binding Pb2+ ions. Its ability to remove Pb2+ rapidly and efficiently, to grow under sub-optimal conditions (such as low pH and low light intensity), and to produce high amount of CPS with acidic sugars, leads us to conclude that G. gelatinosa is a potential viable bioadsorber for mildly acidic water contaminated with Pb2+.

Polymeric and compositional properties of novel extracellular microbial polyglucosamine biopolymer from new strain of citrobacter sp. BL-4

A novel polyglucosamine polymer, PGB-2, was produced extracellularly from a new strain Citrobacter sp. BL-4 using pH-stat fed batch cultivation. It was composed of 97.3% glucosamine and 2.7% rhamnose; its average molecular weight, solubility in 2% acetic acid and viscosity were 20 kDa, 5 g l(-1) and 2.9 cps, respectively. FT-IR and 1H NMR spectra of PGB-2 revealed a close identity with chitosan from crab shells.

Partial characterization of extracellular polysaccharides from cyanobacteria

Four cyanobacterial strains, Cyanothece sp., Oscillatoria sp., Nostoc sp. and Nostoc carneum were studied for physico-chemical characterization of extracellular polysaccharide (EPS) secreted during the controlled growth condition. Hydrolyzed EPSs showed the compositional involvement of four sugar moieties viz. mannose, glucose, xylose and ribose in varying combinations. Infrared spectra of EPSs showed a specific absorbance of O-H stretching at 3448-3400 cm(-1), asymmetrical-symmetrical C-H stretching at 2924 and 2854 cm(-1) and a bending vibration of C-H at 1400-1380 cm(-1). Absorbance at 1259 and 1140 cm(-1) with Cyanothece sp. EPS, indicated the presence of sulfur containing functional group. Thermal gravimetric analysis and differential scanning calorimetric analysis confirmed the polysaccharides thermal stability as high as around 250 degrees C. In the presence of 0.1 M NaCl aqueous solution, the intrinsic viscosity of polysaccharides from Oscillatoria sp. and Nostoc sp. decreased 1.6 fold, whereas, 3-5 fold reduction in intrinsic viscosity was observed with commercially available guar and xanthan gum.

Effects of exopolysaccharide-producing probiotic strains on experimental colitis in rats

PURPOSE

Inflammatory bowel disease is suggested to result from a dysregulated immune response toward intestinal microflora, which may be restored by probiotic therapy based on the concept of healthy microflora. Ideal probiotic bacteria may be beneficial in inflammatory bowel disease; however, the mechanism of action and the clinical efficacy of probiotic usage are still unclear. In the present study, the effect of exopolysaccharide producing probiotics was evaluated on an experimental colitis model in rats.

METHODS

Colitis was induced by intracolonic administration of acetic acid. Then, rats were treated daily with two probiotic strains, Lactobacillus delbrueckii subsp. bulgaricus B3 strain (exopolysaccharide of 211 mg/l: high-EPS group) or Lactobacillus delbrueckii subsp. bulgaricus A13 strain (EPS of 27 mg/l: low-EPS group), which were given into the stomach. The non-colitis-fed control group was only treated with high-exopolysaccharide strain. The model-control and control groups were treated only with tap water. Rats were killed after a seven-day treatment period. Disease activity was quantified by use of histologic scores and colonic myeloperoxidase activity, which is a marker of neutrophil infiltration during inflammation.

RESULTS

The enhanced inflammatory response was accompanied by a higher level of myeloperoxidase activity in the colitis group. Histologic scores of colonic damage and myeloperoxidase activity were lower in both probiotic-treated groups compared with those of the colitis control group (P<0.001), although the mentioned scores improved significantly more in the high-EPS group than in the low-EPS group (P<0.001).

CONCLUSIONS

Exopolysaccharide-producing probiotics significantly attenuate experimental colitis, which may be mediated by exopolysaccharide in a dose-dependent manner. Therefore, exopolysaccharide-producing probiotics may be a promising therapeutic role in inflammatory bowel disease.

epsABCJ genes are involved in the biosynthesis of the exopolysaccharide mauran produced by Halomonas maura

The moderately halophilic strainHalomonas mauraS-30 produces a high-molecular-mass acidic polymer (4·7×106 Da) composed of repeating units of mannose, galactose, glucose and glucuronic acid. This exopolysaccharide (EPS), known as mauran, has interesting functional properties that make it suitable for use in many industrial fields. Analysis of the flanking regions of a mini-Tn5insertion site in an EPS-deficient mutant ofH. maura, strain TK71, led to the identification of five ORFs (epsABCDJ), which form part of a gene cluster (eps) with the same structural organization as others involved in the biosynthesis of group 1 capsules and some EPSs. Conserved genetic features were found such as JUMPstart andopselements, which are characteristically located preceding the gene clusters for bacterial polysaccharides. On the basis of their amino-acid-sequence homologies, their putative hydropathy profiles and the effect of their mutations, it is predicted that EpsA (an exporter-protein homologue belonging to the OMA family) and EpsC (a chain-length-regulator homologue belonging to the PCP family) play a role in the assembly, polymerization and translocation of mauran. The possibility that mauran might be synthesized via a Wzy-like biosynthesis system, just as it is for many other polysaccharides, is also discussed. This hypothesis is supported by the fact that EpsJ is homologous with some members of the PST-exporter-protein family, which seems to function together with each OMA–PCP pair in polysaccharide transport in Gram-negative bacteria, transferring the assembled lipid-linked repeating units from the cytoplasmic membrane to the periplasmic space. Maximum induction of theepsgenes is reached during stationary phase in the presence of 5 % (w/v) marine salts.

Structure of the exopolysaccharide produced by Enterobacter amnigenus

The bacterial species Enterobacter amnigenus was isolated from sugar beets harvested in Finland. It produced an exopolysaccharide rich in l-fucose, which gave viscous water solutions. Its primary structure was determined mainly by NMR spectroscopy and ESIMS of oligosaccharides and a polysaccharide with decreased molecular weight, obtained by Smith degradation of the O-deacetylated native polymer [carbohydrate structure: see text]

Curdlan and other bacterial (1→3)-β-d-glucans

Three structural classes of (1-->3)-beta-D-glucans are encountered in some important soil-dwelling, plant-associated or human pathogenic bacteria. Linear (1-->3)-beta-glucans and side-chain-branched (1-->3,1-->2)-beta-glucans are major constituents of capsular materials, with roles in bacterial aggregation, virulence and carbohydrate storage. Cyclic (1-->3,1-->6)-beta-glucans are predominantly periplasmic, serving in osmotic adaptation. Curdlan, the linear (1-->3)-beta-glucan from Agrobacterium, has unique rheological and thermal gelling properties, with applications in the food industry and other sectors. This review includes information on the structure, properties and molecular genetics of the bacterial (1-->3)-beta-glucans, together with an overview of the physiology and biotechnology of curdlan production and applications of this biopolymer and its derivatives.

Biodiversity of exopolysaccharides produced by Streptococcus thermophilus strains is reflected in their production and their molecular and functional characteristics

Twenty-six lactic acid bacterium strains isolated from European dairy products were identified as Streptococcus thermophilus and characterized by bacterial growth and exopolysaccharide (EPS)-producing capacity in milk and enriched milk medium. In addition, the acidification rates of the different strains were compared with their milk clotting behaviors. The majority of the strains grew better when yeast extract and peptone were added to the milk medium, although the presence of interfering glucomannans was shown, making this medium unsuitable for EPS screening. EPS production was found to be strain dependent, with the majority of the strains producing between 20 and 100 mg of polymer dry mass per liter of fermented milk medium. Furthermore, no straightforward relationship between the apparent viscosity and EPS production could be detected in fermented milk medium. An analysis of the molecular masses of the isolated EPS by gel permeation chromatography revealed a large variety, ranging from 10 to >2,000 kDa. A distinction could be made between high-molecular-mass EPS (>1,000 kDa) and low-molecular-mass EPS (<1,000 kDa). Based on the molecular size of the EPS, three groups of EPS-producing strains were distinguished. Monomer analysis of the EPS by high-performance anion-exchange chromatography with amperometric detection was demonstrated to be a fast and simple method. All of the EPS from the S. thermophilus strains tested were classified into six groups according to their monomer compositions. Apart from galactose and glucose, other monomers, such as (N-acetyl)galactosamine, (N-acetyl)glucosamine, and rhamnose, were also found as repeating unit constituents. Three strains were found to produce EPS containing (N-acetyl)glucosamine, which to our knowledge was never found before in an EPS from S. thermophilus. Furthermore, within each group, differences in monomer ratios were observed, indicating possible novel EPS structures. Finally, large differences between the consistencies of EPS solutions from five different strains were assigned to differences in their molecular masses and structures.

Chemical structure of aeromonas gum––extracellular polysaccharide from Aeromonas nichidenii 5797

Aeromonas (A) gum, an extracellular heteropolysaccharide produced by the bacterium Aeromonas nichidenii strain 5797, was studied by 1H and 13C NMR spectroscopy including 2D COSY, TOCSY, 1H, 13C HMQC, HMBC and ROESY experiments after O-deacetylation and Smith degradation. These investigations revealed the presence of an O-acetylated pentasaccharide repeating unit composed of mannose, glucose, xylose and glucuronic acid, and it has the following structure: [Image: see text]

Biochemistry, genetics, and applications of exopolysaccharide production in Streptococcus thermophilus: a review

Many strains of Streptococcus thermophilus synthesize extracellular polysaccharides. These molecules may be produced as capsules that are tightly associated with the cell, or they may be liberated into the medium as a loose slime (i.e., "ropy" polysaccharide). Although the presence of exopolysaccharide does not confer any obvious advantage to growth or survival of S. thermophilus in milk, in situ production by this species or other dairy lactic acid bacteria typically imparts a desirable "ropy" or viscous texture to fermented milk products. Recent work has also shown that exopolysaccharide-producing S. thermophilus can enhance the functional properties of Mozzarella cheese, but they are not phage-proof. As our understanding of the genetics, physiology, and functionality of bacterial exopolysaccharides continues to improve, novel applications for polysaccharides and polysaccharide-producing cultures are likely to emerge inside and outside the dairy industry. This article provides an overview of biochemistry, genetics, and applications of exopolysaccharide production in S. thermophilus.

Structural characterisation of a perdeuteriomethylated exopolysaccharide by NMR spectroscopy: characterisation of the novel exopolysaccharide produced by Lactobacillus delbrueckii subsp. bulgaricus EU23

The exopolysaccharide (EPS) from Lactobacillus delbrueckii subsp. bulgaricus EU23 was perdeuteriomethylated and the perdeuteriomethylated EPS (pdm-EPS) purified by elution from a C(18) Sep-Pak cartridge. Both 1D and 2D NMR spectra were recorded for the pdm-EPS and these were interpreted to provide assignments for the individual 1H and 13C resonances of the sugar residues of the repeating unit. Using a combination of the results from monomer analysis and linkage analysis of the native EPS and the ROESY and HMBC NMR spectra of the pdm-EPS the following structure has been determined for the repeating unit:A process for characterising polysaccharides having low solubility in aqueous solution is reported.