Characterization of a Sinorhizobium isolate and its extracellular polymer implicated in pollutant transport in soil.

A bacterium isolated from soil (designated 9702-M4) synthesizes an extracellular polymer that facilitates the transport of such hydrophobic pollutants as polynuclear aromatic hydrocarbons, as well as the toxic metals lead and cadmium in soil. Biolog analysis, growth rate determinations, and percent G+C content identify 9702-M4 as a strain of Sinorhizobium meliloti. Sequence analysis of a 16S rDNA fragment gives 9702-M4 a phylogenetic designation most closely related to Sinorhizobium fredii. The extracellular polymer of isolate 9702-M4 is composed of both an extracellular polysaccharide (EPS) and a rough lipopolysaccharide. The EPS component is composed mainly of 4-glucose linkages with monomers of galactose, mannose, and glucuronic acid and has pyruval and acetyl constituents. The lipid fraction and the negative charge associated with carbonyl groups of the exopolymer are thought to account for the binding of polynuclear aromatic hydrocarbons and cationic metals.     

Methanotrophic Bacteria and Facilitated Transport of Pollutants in Aquifer Material

In situ stimulation of methanotrophic bacteria has been considered as a methodology for aquifer remediation. Chlorinated aliphatic hydrocarbons such as trichloroethylene are fortuitously oxidized by the methane monooxygenase produced by methanotrophic bacteria. Experimental results are presented that indicate that both colloidal suspensions containing methanotrophic cells and the soluble extracellular polymers produced by methanotrophic cells have the potential to enhance the transport and removal of other environmental contaminants such as polynuclear aromatic hydrocarbons and transition metals in aquifer material. Three well-characterized methanotrophic bacteria were used in the experiments: Methylomonas albus BG8 (a type I methanotroph), Methylosinus trichosporium OB3b (a type II methanotroph), and Methylocystis parvus OBBP (a type II methanotroph). Isotherms were obtained for sorption of two radiolabeled pollutants, [¹⁴C] phenanthrene and ¹⁰⁹Cd, onto an aquifer sand in the presence and absence of washed cells and their extracellular polymer. Column transport experiments were performed with the washed methanotrophic cells and phenanthrene. The distribution coefficients for Cd with extracellular polymers were of the same order as that obtained with the aquifer sand, indicating that polymers from the methanotrophic bacteria could act to increase the transport of Cd in a porous medium. Polymer from BG8 significantly reduced the apparent distribution coefficient for Cd with an aquifer sand. [¹⁴C] phenanthrene also sorbed to extracellular polymer and to washed, suspended methanotrophic cells. The exopolymer of BG8 and OBBP significantly reduced the apparent distribution coefficient (K_d) for phenanthrene with aquifer sand. The distribution coefficients for phenanthrene with the methanotrophic cells were an order of magnitude greater than those previously reported for other heterotrophic bacteria. Cells of the methanotrophs also significantly reduced the apparent K_d for phenanthrene with an aquifer sand. The three strains of methanotrophs tested displayed mobility in a column of packed sand, and strain OBBP reduced the retardation coefficient of phenanthrene with an aquifer sand by 27%. These data indicate that both extracellular polymer and mobile cells of methanotrophic bacteria display a capacity to facilitate the mobility of pollutant metals and polynuclear aromatic hydrocarbons in aquifer material.     

Enhanced production and partial characterization of an extracellular polysaccharide from newly isolated Azotobacter sp. SSB81

A strain was selected by its highest extracellular polysaccharide (EPS) production ability compare to other isolates from the same rhizospheric soil. The selected strain was identified by 16S rDNA sequencing and designated as SSB81. Phylogenetic analysis of the gene sequence showed its close relatedness with Azotobacter vinelandii and Azotobacter salinestris. Maximum EPS (2.52 g l⁻¹) was recovered when the basal medium was supplemented with glucose (2.0%), riboflavin (1 mg l⁻¹) and casamino acid (0.2%). The EPS showed a stable viscosity level at acidic pH (3.0–6.5) and the pyrolysis temperature was found to be at 116.73 °C with an enthalpy (ΔH) of 1330.72 Jg⁻¹. MALDI TOF mass spectrometric result suggests that polymer contained Hex₅Pent₃ as oligomeric building subunit. SEM studies revealed that the polymer had a porous structure with small pore size distribution indicating the compactness of the polymer. This novel EPS may find possible application as a polymer for environmental bioremediation and biotechnological processes.     

Assessment of occupational exposure to PAHs in an Estonian coke oven plant- correlation of total external exposure to internal dose measured as 1-hydroxypyrene concentration

The exposure of cokery workers to polynuclear aromatic hydrocarbons at an Estonian oil shale processing plant was assessed by using occupational hygiene and biomonitoring measurements which were carried out twice, in midwinter and in the autumn. To assess the external dose of polynuclear aromatic hydrocarbons, pyrene and benzo[a]pyrene concentrations were measured from the breathing zone of workers during a workshift. Skin contamination with pyrene and benzo[a]pyrene was assessed by skin wipe sampling before and after the workshift. As a biomarker of overall exposure to polynuclear aromatic hydrocarbons, and as an integral of all absorption routes of pyrene, 1-hydroxypyrene concentration was measured from post shift urine samples. Of the personal air samples, 18% exceeded the Finnish threshold limit value of benzo[a]pyrene (10 μg m^-3). Mean value (two separate measurements together) for benzo[a]pyrene was 5.7 μg m^-3 and for pyrene, 8.1 μg m^-3. Based on skin wipe sample analyses, the skin contamination was also obvious. The mean value of benzo[a]pyrene in the samples collected after the shift was 1.2 ng cm^-2. Benzo[a]pyrene was not found in control samples. The mean value of urinary 1-hydroxypyrene concentration was 6.0 μmol mol^-1 creatinine for the exposed workers and 0.5 μmol mol^-1 creatinine for the controls. This study undoubtedly shows the usefulness of 1-hydroxypyrene as an indicator of internal dose of polynuclear aromatic hydrocarbons. It can be concluded that the cokery workers at the Kohtla-Järve plant are exposed to high concentrations of polynuclear aromatic compounds, and the exposure level is considerably higher during the winter measurements.     

Synthesis of a Low-Molecular-Weight Form of Exopolysaccharide by Bradyrhizobium japonicum USDA 110

A novel extracellular low-molecular-weight polysaccharide was detected as a contaminant within extracellular cyclic β-1,6-β-1,3-glucan preparations from Bradyrhizobium japonicum USDA 110 cultures. Compositional analysis, methylation analysis, and nuclear magnetic resonance analysis revealed that this low-molecular-weight polysaccharide was composed of the same pentasaccharide repeating unit previously described for the high-molecular-weight form of the exopolysaccharide (EPS) synthesized by B. japonicum strains. Mass spectrometry analysis indicated that the size of this low-molecular-weight form of EPS was consistent with a dimeric form of the pentasaccharide repeating unit.     

High level synthesis of levan by a novel Halomonas species growing on defined media

A novel halophilic isolate from soil samples taken from Çamalt? Saltern area in Turkey, Halomonas sp. AAD6 (JCM 15723) strain, was found to produce high levels of exopolysaccharides (EPS), in the presence of sucrose in defined media, by flasks and bioreactor condition yielded 1.073 g L^?1 and 1.844 g L^?1, respectively. Sugar analysis, methylation studies and NMR analysis of EPS indicated the repeating unit of this polysaccharide was composed of β-(2,6)-d-fructofuranosyl residues. Hence with this work, Halomonas sp. has been described as a levan producer microorganism for the first time. Biocompatibility studies showed this EPS did not affect cellular viability and proliferation of osteoblasts and murine macrophages. The protective effect of the polymer against the toxic activity of avarol implied its additional use as an anti-cytotoxic agent. Halomonas sp. AAD6 could represent an alternative cheap source of levan polymer when grown on defined media hypothesizing its larger employment in industrial application being non pathogenic microorganism.     

Role of Bacterial Exopolysaccharides (EPS) in the Fate of the Oil Released during the Deepwater Horizon Oil Spill

Halomonas species are recognized for producing exopolysaccharides (EPS) exhibiting amphiphilic properties that allow these macromolecules to interface with hydrophobic substrates, such as hydrocarbons. There remains a paucity of knowledge, however, on the potential of Halomonas EPS to influence the biodegradation of hydrocarbons. In this study, the well-characterized amphiphilic EPS produced by Halomonas species strain TG39 was shown to effectively increase the solubilization of aromatic hydrocarbons and enhance their biodegradation by an indigenous microbial community from oil-contaminated surface waters collected during the active phase of the Deepwater Horizon oil spill. Three Halomonas strains were isolated from the Deepwater Horizon site, all of which produced EPS with excellent emulsifying qualities and shared high (97-100%) 16S rRNA sequence identity with strain TG39 and other EPS-producing Halomonas strains. Analysis of pyrosequence data from surface water samples collected during the spill revealed several distinct Halomonas phylotypes, of which some shared a high sequence identity (≥97%) to strain TG39 and the Gulf spill isolates. Other bacterial groups comprising members with well-characterized EPS-producing qualities, such as Alteromonas , Colwellia and Pseudoalteromonas , were also found enriched in surface waters, suggesting that the total pool of EPS in the Gulf during the spill may have been supplemented by these organisms. Roller bottle incubations with one of the Halomonas isolates from the Deepwater Horizon spill site demonstrated its ability to effectively produce oil aggregates and emulsify the oil. The enrichment of EPS-producing bacteria during the spill coupled with their capacity to produce amphiphilic EPS is likely to have contributed to the ultimate removal of the oil and to the formation of oil aggregates, which were a dominant feature observed in contaminated surface waters.     

Relationship between Desiccation and Exopolysaccharide Production in a Soil Pseudomonas sp

The relationship between desiccation and the production of extracellular polysaccharides (EPS) by soil bacteria was investigated by using a Pseudomonas species isolated from soil. Cultures subjected to desiccation while growing in a sand matrix contained more EPS and less protein than those growing at high water potential, suggesting that resources were allocated to EPS production in response to desiccation. Desiccation did not have a significant effect on activity as measured by reduction of iodonitrotetrazolium. Purified EPS produced by the Pseudomonas culture contained several times its weight in water at low water potential. Sand amended with EPS held significantly more water and dried significantly more slowly than unamended sand, implying that an EPS matrix may buffer bacterial colonies from some effects of desiccation. We conclude that bacteria may use EPS production to alter their microenvironment to enhance survival of desiccation.     

Biodegradation of Aromatic Hydrocarbons in an Extremely Acidic Environment

The potential for biodegradation of aromatic hydrocarbons was evaluated in soil samples recovered along gradients of both contaminant levels and pH values existing downstream of a long-term coal pile storage basin. pH values for areas greatly impacted by runoff from the storage basin were 2.0. Even at such a reduced pH, the indigenous microbial community was metabolically active, showing the ability to oxidize more than 40% of the parent hydrocarbons, naphthalene and toluene, to carbon dioxide and water. Treatment of the soil samples with cycloheximide inhibited mineralization of the aromatic substrates. DNA hybridization analysis indicated that whole-community nucleic acids recovered from these samples did not hybridize with genes, such as nahA, nahG, nahH, todC1C2, and tomA, that encode common enzymes from neutrophilic bacteria. Since these data suggested that the degradation of aromatic compounds may involve a microbial consortium instead of individual acidophilic bacteria, experiments using microorganisms isolated from these samples were initiated. While no defined mixed cultures were able to evolve ¹⁴CO₂ from labeled substrates in these mineralization experiments, an undefined mixed culture including a fungus, a yeast, and several bacteria successfully metabolized approximately 27% of supplied naphthalene after 1 week. This study shows that biodegradation of aromatic hydrocarbons can occur in environments with extremely low pH values.     

Coriolopsis rigida,a potential model of white-rot fungi that produce extracellular laccases

In the last two decades, a significant amount of work aimed at studying the ability of the white-rot fungus Coriolopsis rigida strain LPSC no. 232 to degrade lignin, sterols, as well as several hazardous pollutants like dyes and aliphatic and aromatic fractions of crude oil, including polycyclic aromatic hydrocarbons, has been performed. Additionally, C. rigida in association with arbuscular mycorrhizal fungi appears to enhance plant growth, albeit the physiological and molecular bases of this effect remain to be elucidated. C. rigida's ability to degrade lignin and lignin-related compounds and the capacity to transform the aromatic fraction of crude oil in the soil might be partially ascribed to its ligninolytic enzyme system. Two extracellular laccases are the only enzymatic components of its lignin-degrading system. We reviewed the most relevant findings regarding the activity and role of C. rigida LPSC no. 232 and its laccases and discussed the work that remains to be done in order to assess, more precisely, the potential use of this fungus and its extracellular enzymes as a model in several applied processes.     

Rhizobial exopolysaccharides: genetic control and symbiotic functions

Specific complex interactions between soil bacteria belonging to Rhizobium, Sinorhizobium, Mesorhizobium, Phylorhizobium, Bradyrhizobium and Azorhizobium commonly known as rhizobia, and their host leguminous plants result in development of root nodules. Nodules are new organs that consist mainly of plant cells infected with bacteroids that provide the host plant with fixed nitrogen. Proper nodule development requires the synthesis and perception of signal molecules such as lipochitooligosaccharides, called Nod factors that are important for induction of nodule development. Bacterial surface polysaccharides are also crucial for establishment of successful symbiosis with legumes. Sugar polymers of rhizobia are composed of a number of different polysaccharides, such as lipopolysaccharides (LPS), capsular polysaccharides (CPS or K-antigens), neutral β-1, 2-glucans and acidic extracellular polysaccharides (EPS). Despite extensive research, the molecular function of the surface polysaccharides in symbiosis remains unclear.     

Nostoc cyanobacterial inoculation in South African agricultural soils enhances soil structure, fertility, and maize growth

Many soils in South Africa have low nutrient supply, poor structural stability and are prone to soil erosion due to susceptibility to surface sealing and crusting. Two crusting soils from the Eastern Cape Province, South Africa were used to evaluate the effects of inoculation with a strain of Nostoc on soil structure, fertility and maize growth. The Nostoc suspension was uniformly applied over potted soils at a rate of 6g (dry weight) per square meter soon after maize germination. Nostoc inoculation increased soil N by 17% and 40% in Hertzog and Guquka soils, respectively. Soil C was also increased significantly and this increase was strongly associated with that of soil N (R ² = 0.838). The highest contents of soil C, soil N and mineral N, however, were found in non-cropped Nostoc inoculated soils. Nostoc inoculation increased maize dry matter yields by 49% and 40% in Hertzog and Guquka soils, respectively. Corresponding increases in maize tissue N were 23% and 14%, respectively. Scanning electron microscopy (SEM) revealed that soil particles and fragments of non-cropped inoculated soils had coatings of extracellular polymeric substances (EPS) with other particles enmeshed in networks of filaments, whilst by contrast little or no EPS and/or filaments were observed on cropped and/or non-inoculated soils. This was consistent with chemical analysis which showed that Nostoc caused significant increases in the EPS and soil C contents of non-cropped soils. The proportion of very stable aggregates was increased by inoculation with Nostoc possibly due to the greater quantities of soil C and EPS observed in inoculated soils. Inoculated soils cropped with maize had a lower proportion of stable aggregates presumably due to their low soil C and EPS contents compared to non-cropped soils. The results suggested that Nostoc could improve the fertility and structural stability of the studied degraded soils.     

Exopolysaccharide (EPS) synthesis in Bradyrhizobium japonicum : sequence, operon structure and mutational analysis of an exo gene cluster

The nucleotide sequence of a 8330-bp DNA fragment from Bradyrhizobium japonicum 110spc4 was determined. Sequence analysis revealed that six ORFs were present and the deduced amino acid sequences were homologous to enzymes involved in exopolysaccharide (EPS) biosynthesis. The genes appear to be organized into at least four different operons. One gene was found to be homologous to exoB, which encodes a UDP-galactose 4′-epimerase. Other ORFs were homologous to UDP-hexose transferases and one ORF showed similarity to Sinorhizobium (Rhizobium) meliloti ExoP, which has been suggested to be involved in EPS chain-length determination. A set of deletion and insertion mutants was constructed and the resulting B. japonicum strains were tested for their symbiotic traits. Deletion mutant ΔP22, which lacks the C-terminal part of ExoP, the UDP-hexose transferase ExoT and the N-terminal part of ExoB, shows a delayed nodulation phenotype and induces symptoms of plant defense reactions; its EPS does not contain galactose and no high molecular weight fraction is synthesized. In contrast, insertion mutant EH3, which expresses an exoP gene product that is truncated in its putative periplasmic domain, produced an EPS containing both HMW and LMW fractions. However, the interaction of EH3 with soybeans was severely perturbed. As a rule, only the initial steps of nodule formation were observed.     

New procedure of high-voltage electrophoresis in polyacrylamide gel and its application to the sequencing of nucleic acids.

Addition of primary organic amines, such as n-butylamine, to the mobile phase altered the capacity factors and selectivity of benzo[a]pyrene metabolites obtained with reverse-phase high pressure liquid chromatography on an ODS column. Separation of benzo[a]pyrene phenols in particular was improved with 8 of the 10 available metabolites resolved, including those known to be biologically produced. The method offers sufficiently improved resolution or convenience that it should prove useful in comparative studies of metabolism of benzo[a]-pyrene and other polynuclear aromatic hydrocarbons. Applying the method to analysis of benzo[a]pyrene metabolites produced in vitro by hepatic microsomes from the marine fish Stenotomus versicolor indicated the principal phenolic derivatives produced by this fish were 1-hydroxy-, 3-hydroxy-, 7-hydroxy-, and 9-hydroxybenzo[a]pyrene.     

Metal-Induced Production of a Novel Bioadsorbent Exopolysaccharide in a Native Rhodotorula mucilaginosa from the Mexican Northeastern Region

There is a current need to develop low-cost strategies to degrade and eliminate industrially used colorants discharged into the environment. Colorants discharged into natural water streams pose various threats, including: toxicity, degradation of aesthetics and inhibiting sunlight penetration into aquatic ecosystems. Dyes and colorants usually have complex aromatic molecular structures, which make them very stable and difficult to degrade and eliminate by conventional water treatment systems. The results in this work demonstrated that heavy metal-resistant Rhodotorula mucilaginosa strain UANL-001L isolated from the northeast region of Mexico produce an exopolysaccharide (EPS), during growth, which has colorant adsorption potential. The EPS produced was purified by precipitation and dialysis and was then physically and chemically characterized by Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, and chemical elemental analysis. Here, the ability of the purified EPS produced to adsorb methylene blue (MB), which served as a model colorant, is studied. MB adsorption by the EPS is found to follow Langmuir Adsorption Isotherm kinetics at 25°C. Further, by calculating the Langmuir constant the adsorption capabilities of the EPS produced by the Rhodotorula mucilaginosa strain UANL-001L is compared to that of other adsorbents, both, microbially produced and from agroindustrial waste. The total adsorption capacity of the EPS, from the Rhodotorula mucilaginosa strain UANL-001L, was found to be two-fold greater than the best bioadsorbents reported in the literature. Finally, apart from determining which heavy metals stimulated EPS production in the strain, the optimal conditions of pH, heavy metal concentration, and rate of agitation of the growing culture for EPS production, was determined. The EPS reported here has the potential of aiding in the efficient removal of colorants both in water treatment plants and in situ in natural water streams.     

Role of extracellular polymeric substance (EPS) in toxicity response of soil bacteria Bacillus sp. S3 to multiple heavy metals

Heavy metal resistant bacteria are of great interest because of their potential use in bioremediation. Understanding the survival and adaptive strategies of these bacteria under heavy metal stress is important for better utilization of these bacteria in remediation. The objective of this study was to investigate the role of bacterial extracellular polymeric substance (EPS) in detoxifying against different heavy metals in Bacillus sp. S3, a new hyper antimony-oxidizing bacterium previously isolated from contaminated mine soils. The results showed that Bacillus sp. S3 is a multi-metal resistant bacterial strain, especially to Sb(III), Cu(II) and Cr(VI). Toxic Cd(II), Cr(VI) and Cu(II) could stimulate the secretion of EPS in Bacillus sp. S3, significantly enhancing the adsorption and detoxification capacity of heavy metals. Both Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation–emission matrix (3D-EEM) analysis further confirmed that proteins were the main compounds of EPS for metal binding. In contrast, the EPS production was not induced under Sb(III) stress. Furthermore, the TEM–EDX micrograph showed that Bacillus sp. S3 strain preferentially transported the Sb(III) to the inside of the cell rather than adsorbed it on the extracellular surface, indicating intracellular detoxification rather than extracellular EPS precipitation played an important role in microbial resistance towards Sb(III). Together, our study suggests that the toxicity response of EPS to heavy metals is associated with difference in EPS properties, metal types and corresponding environmental conditions, which is likely to contribute to microbial-mediated remediation.

     

Influence of ε-caprolactam on growth and physiology of environmental bacteria

ε-Caprolactam was found to have an effect on ecologically important soil bacteria. It inhibited the growth of several Bacillus sp. and Rhizobium sp. but cells of Arthrobacter sp. were able to grow in the presence of caprolactam. Sphingomonas sp. lost its inherent capacity to produce extracellular polymer (EPS) if grown in medium containing caprolactam. In the case of raw domestic sewage, the diversity of native bacteria was diminished in presence of caprolactam. Polluted sea water yielded predominantly one type of caprolactam-degrading bacteria of the genus Achromobacter. These cells efficiently utilized up to 10 g caprolactam/L as the sole source of carbon and nitrogen in synthetic medium even in the presence of 20 g NaCl/L. Compared to cells of Arthrobacter sp., cells of Achromobacter sp. accumulated high amount of 6-aminocaproic acid due to degradation of caprolactam. When using caprolactam as sole source of carbon and nitrogen, Achromobacter cells showed unique physiological ability to produce EPS upon prolonged incubation in solid medium and in broth with low phosphate (C:N:P ratio 100:20:0.05). Hydrolyzed cell-free EPS had glucose as its major component though the only substrate provided in the medium for growth was caprolactam.     

Culture Conditions Determine the Balance between Two Different Exopolysaccharides Produced by Lactobacillus pentosus LPS26

Lactobacillus pentosus LPS26, isolated from a natural fermentation of green olives, produces a capsular polymer constituted of two exopolysaccharides (EPS): EPS A, a high-molecular-weight (high-M_w) polysaccharide (1.9 × 10⁶ Da) composed of glucose and rhamnose (3:1), and EPS B, a low-M_w polysaccharide (3.3 × 10⁴ Da) composed of glucose and mannose (3:1). Fermentation experiments in a chemically semidefined medium with different carbon sources (glucose, fructose, mannitol, and lactose) showed that all of them except fructose supported EPS A production rather than EPS B production. The influence of temperature and pH was further analyzed. As the temperature dropped, increased synthesis of both EPS was detected. The control of pH especially enhanced EPS B production. With regard to this, the maximum total EPS production (514 mg liter⁻¹) was achieved at a suboptimal growth temperature (20°C) and pH 6.0. Continuous cultures showed that EPS A, synthesized mainly at low dilution rates, is clearly dependent on the growth rate, whereas EPS B synthesis was hardly affected. EPS production was also detected in supplemented skimmed milk, but no increase on the viscosity of the fermented milk was recorded. This could be linked to the high proportion of the low-M_w polysaccharide produced in these conditions in contrast to that observed in culture media. Overall, the present study shows that culture conditions have a clear impact on the type and concentration of EPS produced by strain LPS26, and consequently, these conditions should be carefully selected for optimization and application studies. Finally, it should be noted that this is, to our knowledge, the first report on EPS production by L. pentosus.     

Coprecipitation of Th<Superscript>4+</Superscript> and the purified extracellular polysaccharide produced by bacterium <Emphasis Type="Italic">Bradyrhizobium</Emphasis> (<Emphasis Type="Italic">Chamaecytisus</Emphasis>) BGA-1

The soil bacterium Bradyrhizobium (Chamaecytisus) strain BGA-1 produces an extracellular polymeric substance (EPS) that, in the presence of Fe³⁺, Al³⁺ or Th⁴⁺ solutions, forms a gel-like precipitate composed of polysaccharide, protein, lipopolysaccharide and the metal. Precipitation of the main component of the EPS, the extracellular polysaccharide, and thorium was studied. The precipitate was stable, but redissolved at pH values below 3.0 or in the presence of 10 mM EDTA. In the precipitate, the ratio thorium/basic repeating unit of the polysaccharide ranged from 0.4 to 0.8 mol/mol. Soluble polysaccharide–thorium complexes were not found, and larger polysaccharide molecules were precipitated in preference to smaller ones. Kinetic studies showed a non-linear dependence of the precipitate on the concentrations of both thorium and polysaccharide. The behaviors of the purified polysaccharide and of whole EPS with the thorium-containing precipitate were compared. The results suggested that EPS components other than polysaccharide are able to modify the precipitating ability of the polysaccharide. Thus, whole EPS is a better substrate than the purified polysaccharide for the removal of thorium from its solutions.     

Production and composition of extracellular polysaccharide synthesized by a Rhizobium isolate of Vigna mungo (L.) Hepper

An extracellular polysaccharide (EPS) was produced by a Rhizobium sp. isolated from the root nodules of Vigna mungo (L.) Hepper. Maximum EPS production (346 mg l⁻¹) was when the yeast extract basal medium was supplemented with mannitol (1%), biotin (1.5 mg l⁻¹) and asparagine (0.3%). Ribose (53%) and mannose (47%) were the principle monomers of the EPS. Chemical, chromatographic and spectroscopic analysis showed that this polymer, which has Man₄Rib₁ as an oligomeric subunit, has an apparent molecular mass of 750 kDa.