Evaluation of Arthrospira platensis extracellular polymeric substances production in photoautotrophic, heterotrophic and mixotrophic conditions

The kinetic study of Arthrospira platensis extracellular polymeric substances (EPS) production under different trophic modes??photoautotrophy (100???mol photons m^?2?s^?1), heterotrophy (1.5?g/L glucose), and mixotrophy (100???mol photons m^?2?s^?1 and 1.5?g/L glucose)??was investigated. Under photoautotrophic and heterotrophic conditions, the maximum EPS production 219.61?±?4.73 and 30.30?±?1.97?mg/L, respectively, occurred during the stationary phase. Under a mixotrophic condition, the maximum EPS production (290.50?±?2.21?mg/L) was observed during the early stationary phase. The highest specific EPS productivity (433.62?mg/g per day) was obtained under a photoautotrophic culture. The lowest specific EPS productivity (38.33?mg/g per day) was observed for the heterotrophic culture. The effects of glucose concentration, light intensity, and their interaction in mixotrophic culture on A. platensis EPS production were evaluated by means of 32 factorial design and response surface methodology. This design was carried out with a glucose concentration of 0.5, 1.5, and 2.5?g/L and at light levels of 50, 100, and 150???mol photons m^?2?s^?1. Statistical analysis of the model demonstrated that EPS concentration and EPS yield were mainly influenced by glucose concentration and that conditions optimizing EPS concentration were dissimilar from those optimizing EPS yield. The highest maximum predicted EPS concentration (369.3?mg/L) was found at 150???mol photons m^?2?s^?1 light intensity and 2.4?g/L glucose concentration, while the highest maximum predicted EPS yield (364.3?mg/g) was recorded at 115???mol photons m^?2?s^?1 light intensity and 1.8?g/L glucose concentration.     

Combined effect of temperature and light intensity on growth and extracellular polymeric substance production by the cyanobacterium Arthrospira platensis

The effects of light intensity and temperature on Arthrospira platensis growth and production of extracellular polymeric substances (EPS) in batch culture were evaluated using a three-level, full-factorial design and response surface methodology. Three levels were tested for each parameter (temperature: 30, 35, 40°C; light intensity: 50, 115, 180 μmol photons m⁻² s⁻¹). Both growth and EPS production are influenced mainly by the temperature factor but the interaction term temperature*light intensity also had a significant effect. In addition, conditions optimising EPS production are different from those optimising growth. The highest growth rate (0.414 ± 0.003 day⁻¹) was found at the lowest temperature (30°C) and highest light intensity (180 μmol photons m⁻² s⁻¹) tested, no optima were detectable within the given test range. Obviously, optima for growth must be at a temperature lower than 30°C and a light intensity higher than 180 μmol photons m⁻² s⁻¹. For EPS production, light intensity had a positive linear effect (optimum obviously higher than 180 μmol photons m⁻² s⁻¹), but for the temperature parameter a maximum effect was detectable at 35°C.     

Enhanced Exopolysaccharide Production by Metabolic Engineering of Streptococcus thermophilus

It is possible that the low levels of production of exopolysaccharides (EPSs) by lactic acid bacteria could be improved by altering the levels of enzymes in the central metabolism that influence the production of precursor nucleotide sugars. To test this hypothesis, we identified and cloned the galU gene, which codes for UDP glucose pyrophosphorylase (GalU) in Streptococcus thermophilus LY03. Homologous overexpression of the gene led to a 10-fold increase in GalU activity but did not have any effect on the EPS yield when lactose was the carbon source. However, when galU was overexpressed in combination with pgmA, which encodes phosphoglucomutase (PGM), the EPS yield increased from 0.17 to 0.31 g/mol of carbon from lactose. A galactose-fermenting LY03 mutant (Gal⁺) with increased activities of the Leloir enzymes was also found to have a higher EPS yield (0.24 g/mol of carbon) than the parent strain. The EPS yield was further improved to 0.27 g/mol of carbon by overexpressing galU in this strain. However, the highest EPS yield, 0.36 g/mol of carbon, was obtained when pgmA was knocked out in the Gal⁺ strain. Measurements of the levels of intracellular metabolites in the cultures revealed that the Gal⁺ strains had considerably higher glucose 1-phosphate levels than the other strains, and the strain lacking PGM activity had threefold-higher levels of glucose 1-phosphate than the other Gal⁺ strains. These results show that it is possible to increase EPS production by altering the levels of enzymes in the central carbohydrate metabolism.     

Structure of bacterial extracellular polymeric substances at different pH values as determined by SAXS

Extracellular polymeric substances (EPS) play an important role in cell aggregation, cell adhesion, and biofilm formation, and protect cells from a hostile environment. The EPS was isolated by trichloroacetic acid/ethanol extraction from broth culture of a marine bacterium isolate. The EPS was composed of glucose and galactose as determined by HPLC and TLC; the protein content was on average 15 ± 5% of EPS dry mass. The solution structure of EPS at different values of pH was revealed by small-angle x-ray scattering. Scattering curves of EPS solutions (0.4%, w/v) consistently showed two nearly linear log-log regions with slopes a and b in the q-ranges from 0.06 nm⁻¹ to 0.26 nm⁻¹, and from 0.27 nm⁻¹ to 0.88 nm⁻¹, respectively. Slope a was sensitive to pH changes whereas slope b was not. The observed sensitivity to pH was not a consequence of ionic strength variation with pH, as checked by salt addition. The pH variation causes major rearrangements of EPS structure mainly at length scales above 24 nm. To get a better understanding of the pH effect on EPS structure, the original model proposed by Geissler was refined into a mathematical model that enabled fitting of the experimental scattering curves in the pH range from 0.7 to 11.0. The model describes EPS structure as a network of randomly coiled polymeric chains with denser domains of polymeric chains. The results obtained from the model indicate that dense domains increase in average size from 19 nm at pH 11.0 to 52 nm at pH 0.7. The average distance between the polysaccharide chains at pH 0.7 was 2.3 nm, which indicates a compact EPS structure. Swelling was found to be at a maximum around pH = 8.8, where the average distance between the chains was 4.8 nm.     

Composition and immunochemical characteristics of exopolysaccharides from the rhizobacterium <Emphasis Type="Italic">Paenibacillus polymyxa</Emphasis> 1465

Exopolysaccharides (EPS) synthesized by Paenibacillus polymyxa 1465 in the course of batch cultivation were proven to contain neutral and acidic fractions. EPS are heterogeneous polysaccharides, represented by a complex of macromolecules with molecular mass of 7 × 10⁴ to 2 × 10⁶ Da. The acidic component was shown to be predominant in EPS preparations isolated from bacteria cultivated on glucose, which corresponds to a higher viscosity of EPS water solutions. The exoglycans were shown to contain glucose, mannose, galactose, and uronic acids. Polyclonal rabbit antibodies against the isolated P. polymyxa 1465 EPS preparations were used in a comparative immunodiffusion analysis of a number of P. polymyxa strains.     

Light History Influences the Response of Fluvial Biofilms to Zn Exposure

Fluvial biofilms are subject to multistress situations in natural ecosystems, such as the co‐occurrence of light intensity changes and metal toxicity. However, studies simultaneously addressing both factors are rare. This study evaluated in microcosm conditions the relationship between short‐term light intensity changes and Zn toxicity on fluvial biofilms with long‐term photoacclimation to different light conditions. Biofilms that had long‐term photoacclimation to 25 μmol photons · m^?2 · s^?1 (low light [LL] biofilms), 100 μmol photons · m^?2 · s^?1 (medium light [ML] biofilms), and 500 μmol photons · m^?2 · s^?1 (high light [HL] biofilms) were characterized by different structural (Chlorophyll‐a [Chl‐a], total biomass‐AFDW, EPS, algal groups, and diatom taxonomy) and physiological attributes (ETR‐I curves and photosynthetic pigments). HL biofilms showed higher light saturation intensity and a higher production of xanthophylls than LL biofilms. In contrast, LL biofilms had many structural differences; a higher proportion of diatoms and lower AFDW and EPS contents than ML and HL biofilms. A clear effect of light intensity changes on Zn toxicity was also demonstrated. Zn toxicity was enhanced when a sudden increase in light intensity also occurred, mainly with LL biofilms, causing higher inhibition of both the Φ′_PSII and the Φ_PSII. A decoupling of NPQ from de‐epoxidation reaction (DR) processes was also observed, indicating substantial damage to photoprotective mechanisms functioning in biofilms (i.e., xanthophyll cycle of diatoms) due to Zn toxicity. This study highlights the need to take into account environmental stress (e.g., light intensity changes) to better assess the environmental risks of chemicals (e.g., metals).     

Production and characterization of the exopolysaccharide produced by <Emphasis Type="Italic">Paenibacillus jamilae</Emphasis> grown on olive mill-waste waters

Paenibacillus jamilae, a strain isolated from compost prepared with olive-mill wastewaters, produced an extracellular polysaccharide (EPS) when it was grown in a culture containing olive-mill waste waters (OMWW) as sole carbon and energy sources. Maximal EPS production in 100 mL batch-culture experiments (5.1 g L⁻¹) was reached with a concentration of 80% of OMWW as fermentation substrate (v/v). Although an inhibitory effect was observed on growth and EPS production when OMWW concentration was increased, an appreciable amount of EPS (2.7 g L⁻¹) was produced with undiluted OMWW. Sepharose CL-2B chromatography showed that the EPS presented two fractions, EPS I (>2000 kDa) and EPS II (500 kDa). Both fractions were characterized by GC-MS as two different acidic heteropolysaccharides containing glucose, galactose and mannose as the major components. The performed study made evident the possibility of using OMWW as substrate for the production of EPS by P. jamilae with a satisfactory yield.     

Production of exopolysaccharides from a thermophilic microorganism isolated from a marine hot spring in flegrean areas

A thermophilic strain isolated from sea sand at Maronti, near Sant' Angelo (Ischia), is described. The organism grows well at an optimal temperature of 60 °C at pH 7.0. The thermophilic bacterium, named strain 4004, produces an exocellular polysaccharide (EPS) in yields of 90 mg/l. The EPS fraction was produced with all substrates tested, although a higher yield was obtained with sucrose or trehalose as sole carbon source. During growth, the EPS content was proportional to the biomass. Three fractions (EPS1, EPS2, EPS3) were obtained after purification. Quantitative monosaccharide analysis of the EPSs revealed the presence of mannose:glucose:galactose in a relative ratio of 0.5:1.0:0.3 in EPS1, mannose:glucose:galactose in a relative ratio of 1.0:0.3:trace in EPS2, and galactose:mannose:glucosamine:arabinose in a relative ratio of 1.0:0.8:0.4:0.2 in EPS3. The average molecular mass of EPS3 was determined to be 1×10⁶ Da. From comparison of the chemical shift values in ¹H and ¹³C spectra, we conclude that EPS3 presents a pentasaccharide repeating unit. Electronic Publication     

DAILY FLUCTUATIONS OF EXOPOLYMERS IN CULTURES OF THE BENTHIC DIATOMS CYLINDROTHECA CLOSTERIUM AND NITZSCHIA SP. (BACILLARIOPHYCEAE)1

Dynamics in the production of extracellular polymeric substances (EPS) were investigated for the benthic diatoms Cylindrotheca closterium (Ehrenberg) and Nitzschia sp. The effect of growth phase and light:dark conditions were examined using axenic cultures. Two EPS fractions were distinguished. Soluble EPS was recovered from the culture supernatant and represented polysaccharides that were only loosely associated with the cells. Bound EPS was extracted from the cells using warm (30° C) water and was more closely associated with the diatom aggregates. Concentrations of EPS exceeded internal concentrations of sugar throughout growth, indicating that EPS production is important in these organisms. Soluble and bound EPS revealed distinct differences in daily dynamics during the course of growth. Soluble EPS was produced continuously once cultures entered the stationary phase. During the stationary phase, chl a‐normalized EPS production rates equaled 6.4 and 3.4 d ^{? 1} for C. closterium and Nitzschia sp., respectively. In contrast, production of bound EPS occurred only in the light and was highest during the exponential phase. Up to 90% of the attached EPS that was produced in the light was degraded during the subsequent dark period. The monosaccharide distribution of EPS was constant during the course of the experiment. The soluble EPS consisted of high amounts of galactose and glucuronic acid, relative to rhamnose, glucose, xylose/mannose, and galacturonic acid. In contrast, glucose was the dominant monosaccharide present in the bound EPS. These differences suggest that the production of the two distinct EPS fractions is under different metabolic controls and probably serves different cellular functions.     

Exopolysaccharide production by cyanobacteria grown in closed photobioreactors and immobilized using white cotton towelling

Two exopolysaccharide (EPS) – producing cyanobacteria, Croococcus minutus and Nostoc insulare, were grown as batch cultures in closed cultivation systems (8-L flasks or 12-L and 250-L photobioreactorswith internal illumination) at light intensities ranging between 25 and 150μmol photon m^-2 s^-1. Another batch of each organism was immobilized on white cotton towelling and grown in 470-ml and17-L flat upright transparent chambers made of polycarbonate at light intensities of 0.5–1.5 μmol photon m^-2s^-1. Both cultivation systems were compared with regard to EPS productivity and technological feasibility. The EPS excreted by both cyanobacteria was separated into fractions which had different molecular weights (540–1600 kD) and analyzed for their sugar composition. Both organisms produced acidic EPS, which contained, respectively, 4.2 and 25.3% uronic acids. This revised version was published online in August 2006 with corrections to the Cover Date.     

Subfractionation of rat liver plasma membrane: Uneven distribution of plasma membrane-bound enzymes on the liver cell surface

Plasma membranes were islotaed from rat liver mainly under isotonic conditions. As marker enzymes for the plasma membrane, 5′-nucleotidase and (Na⁺+K⁺)-ATPase were used. The yield of plasma membrane was 0.6–0.9 mg protein per g wet weight of liver. The recovery of 5′-nucleotidase and (Na⁺+K⁺)-ATPase activity was 18 and 48% of the total activity of the whole-liver homogenate, respectively. Judged from the acitvity of glucose-6 phosphatase and succinate dehydrogenase in the plasma membrane, and from the electron microscopic observation of it, the contamination by microsomes and mitochondria was very low. A further homogenization of the plasma membrane yielded two fractions, the light and heavy fractions, in a discontinuous sucrose gradient centrifugation. The light fraction showed higher specific activities of 5′-nucleotidase, alkaline phosphatase, (Na⁺+K⁺)-ATPase and Mg²⁺-ATPase, whereas the heavy one showed a higher specific activity of adenylate cyclase. Ligation of the bile duct for 48 h decreased the specific activities of (Na⁺+K⁺)-ATPase and Mg²⁺-ATPase in the light fraction, whereas it had no significant influence on the activities of these enzymes in the heavy fraction. The specific activity of alkaline phosphatase was elevated in both fractions by the obstruction of the bile flow. Electron microscopy on sections of the plasma membrane subfractions showed that the light fraction consisted of vesicles of various sizes and that the heavy fractions contained membrane sheets and paired membrane strips connected by junctional complexes, as well as vesicles. The origin of these two fractions is discussed and it is suggested that the light fraction was derived from the bile front of the liver cell surface and the heavy one contained the blood front and the lateral surface of it.     

Effects of paclitaxel-producing fungal endophytes on growth and paclitaxel formation of <Emphasis Type="Italic">Taxus cuspidata</Emphasis> cells

Effects of a fungal endophyte, Fusarium mairei, on growth and paclitaxel formation of Taxus cuspidata cells were investigated by adding fungal endophyte culture supernatant (FECS) to suspension cultures of T. cuspidata cells. The main effective chemical responsible for paclitaxel formation in FECS was an exopolysaccharide (EPS) of molecular weight ~2 kDa. FECS fractions except EPS stimulated growth of Taxus cells but had no effects on paclitaxel accumulation. Additionally, elicitation efficiency of FECS based on different culture conditions was studied. EPS content in FECS was related to FECS culture conditions. FECS with long cultivation and high-aeration cultivation contained higher EPS content and resulted in higher paclitaxel yield than that with short cultivation and low-aeration cultivation. The maximum yield of paclitaxel from Taxus cultures, elicited by FECS with 9-day cultivation, was 4.7-fold that of the control cultures.     

Medium optimization, molecular characterization, and bioactivity of exopolysaccharides from Pleurotus eryngii

An optimal medium for exopolysaccharides (EPS) production was obtained through one-factor-at-a-time method and response surface methodology. Under optimal culture medium, the maximum EPS concentration in shake flask was 5.16 g/l. Two groups of EPSs (designated as Fr-I and Fr-II) were obtained from the culture filtrates by size exclusion chromatography/multiangle laser light scattering, and the weight average molar masses (M _w) of Fr-I and Fr-II were determined to be 4.098 × 10⁴ and 1.114 × 10⁴ g/mol, respectively. The molecular confirmation of Fr-I was revealed to be a rigid rod form in aqueous solution. Moreover, monosaccharide composition and characteristic groups were investigated by GC and Fourier transform infrared, respectively. Finally, pharmacology experiment in vitro indicated EPS Fr-II of Pleurotus eryngii exhibited higher antioxidant and antitumor abilities than Fr-I, which might be attributed to the different molecular weights and chemical compositions in the EPS fraction.     

Effects of illumination and nitrogen starvation on accumulation of arachidonic acid by the microalga Parietochloris incisa

Parietochloris incisa is a unicellular freshwater green alga capable of accumulating high amounts of the valuable long-chain polyunsaturated arachidonic acid (AA) in triacylglycerols (TAG) of cytoplasmic oil bodies. To find the cultivation conditions providing maximum AA yield, the effects of illumination and N-availability on the dry weight (DW), chlorophyll, carotenoid, and AA content were studied. Under nitrogen starvation, TAG accounted for over 30% of dry weight (DW) and the AA content became as high as about 55% of total fatty acids. For biomass accumulation, light intensity of ca 400 μE m^?2 s^?1 was found to be optimal for growing P. incisa on a complete medium. Lower light intensities (or a higher cell density of inoculum) resulted in a higher AA yield when the alga was cultivated on nitrogen-free media. In the absence of nitrogen, algal cells were unable to cope with high illumination and suffered from photooxidative damage, whereas the nutrientsufficient culture survived under such illumination conditions, probably due to accumulation of carotenoids. Nitrogen-deprived P. incisa cells displayed elevated sensitivity to light.     

Characterization and antioxidant activity for exopolysaccharide from submerged culture of Boletus aereus

Three polysaccharide fractions (designated as Fr-I, Fr-II and Fr-III) were successfully purified from the crude exopolysaccharide (EPS) produced from submerged culture of Boletus aereus by gel filtration chromatography on Sepharose CL-6B. The size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS) system showed that the average molecular weights (Mws) of these three fractions were 1.365 × 10⁶, 1.048 × 10⁵ and 2.471 × 10⁴ g/mol, respectively. The SEC/MALLS also revealed that the molecular conformation of the Fr-I was a random coil, with Fr-II being a rigid rod in aqueous solution. Moreover, monosaccharide composition analysis indicated that Fr-I was mainly composed of glucose, while both of Fr-II and Fr-III were mainly composed of mannose and glucose. Then, FT-IR spectral analysis of the purified EPS revealed prominent characteristic groups. Furthermore, thermo gravimetric analysis (TGA) indicated the degradation temperature of the Fr-I (170 °C) was higher than those of Fr-II (156 °C) and Fr-III (155 °C). Finally, on the basis of the antioxidant activity test in vitro, Fr-I exhibited the highest antioxidant ability among these samples, which might be attributed to the monosaccharide composition and molecular weight in the EPS fraction.     

Effects of carbon sources on growth and extracellular polysaccharide production of Nostoc flagelliforme under heterotrophic high-cell-density fed-batch cultures

Dissociated cells separated from a natural colony of Nostoc flagelliforme were cultivated heterotrophically in the darkness on glucose under fed-batch culture conditions. The effects of carbon sources (glucose, fructose, xylose, and sucrose) and concentrations on cell growth and extracellular polysaccharide (EPS) production were investigated. At harvest, the culture contained 1.325 g L^?1 of biomass and 117.2 mg L^?1 of EPS, respectively. The gravimetric EPS production rate was 16.7 mg g^?1 cell dry weight day^?1, which was 2.1 times higher than previously reported. Using sigmoid model, batch fermentation of N. flagelliforme was kinetically simulated to obtain equations including substrate consumption, biomass growth, and EPS accumulation. Results from a simulation correlated well with the experimental ones, indicating that this method could be useful in studying EPS production from batch and fed-batch cultures.     

Physicochemical Properties of the Microbial Exopolysaccharide Ethapolan Synthesized on a Mixture of Growth Substrates

Some physicochemical properties of the microbial exopolysaccharide (EPS) ethapolan synthesized by Acinetobacter sp. 12S depended on whether the producer was grown on a mixture of ethanol and glucose or on a single substrate. Irrespective of the carbon source in the nutrient medium, the contents of carbohydrates, pyruvic acid, uronic acids, and mineral components in the EPS remained unchanged. The EPS were also identical in their monosaccharide composition: the molar ratio of glucose, mannose, galactose, and rhamnose was 3 : 2 : 1 : 1. EPS with a higher content of fatty acids was synthesized during growth on the mixture of ethanol and glucose. The average molecular mass and the content of high-molecular (M > 2 MDa) fractions were greater in ethapolan produced on the substrate mixture. In the presence of 0.1 M KCl, after transformation into the H⁺ form, and in the Cu²⁺–glycine system, solutions of these EPS showed higher viscosity than solutions of EPS synthesized on single substrates. The reasons for the improved rheological properties of the EPS produced on the substrate mixture are discussed.     

Molecular sieve chromatography of biosynthetic cell (14C)glucomannan chains

Radioactive d-glucomannan chains, prepared using Phaseolus aureus enzymes, were acetylated and subjected to molecular sieve chromatography. A comparison with dextran acetates, of known molecular weight range, provided approximate molecular weight data. The [¹⁴C]glucomannan chains were not uniformly dispersed, but were separated into two major fractions. These fractions may be collections of polysaccharide chains incompletely resolved. The two fractions had a mobility similar to that of dextrans with molecular weights of 200,000–300,000 and 60,000–90,000. The molecular weight of the largest [¹⁴C]-glucomannan fragment is, consequently, around 200,000 at the minimum. Preliminary results suggest that the lower molecular weight components may be precursors of the higher molecular weight components. Mild acid and alkaline treatment cause the production of materials of much lower molecular size.     

Growth of Spirulina platensis enhanced under intermittent illumination

The growth characteristics of microalgae under different light conditions (continuous or intermittent) are essential information for photobioreactor design and operation. In this study, we constructed a thin-layer (10 mm) flat plate photobioreactor device with a light/dark (L/D) alternation system to investigate the growth of Spirulina platensis under two different light regimes: (1) continuous illumination in a wide range of light intensities (1.00-77.16 mW cm⁻²); (2) intermittent illumination in medium frequency (0.01-20 Hz). Specific growth rate and light efficiency based on biomass production were determined for each round of experiment. Four regions (light limited region, intermediate region, light saturated region and light inhibition region) were recognized according to the results under continuous illumination. Under intermittent illumination, when L/D frequency increased from 0.01 Hz to 20 Hz, specific growth rate and light efficiency were enhanced. However, the enhancement was different, depending on the applied light intensity and light fraction. The higher the light intensity, the greater the enhancement would be when L/D frequency increased from 0.01 Hz to 20 Hz; and the higher the light intensity, the lower the light fractions is needed to maintain light efficiency as high as that under continuous illumination in light limited region.     

Metabolism associated with raised metabolic flux to sugar nucleotide precursors of exopolysaccharides in Lactobacillus delbrueckii subsp. bulgaricus

Exopolysaccharide (EPS) metabolism was studied in a galactose-negative strain of Lactobacillus delbrueckii subsp. bulgaricus, using two different approaches. Firstly, using both the parent strain and a chemically induced mutant with higher yield and specific productivity of EPS than the parent, comparative information was obtained relating to enzyme activities and metabolite levels associated with EPS formation when grown on lactose. Under continuous culture conditions (D=0.10 h⁻¹), the higher metabolic flux towards EPS formation in the mutant strain relative to the parent appeared to be mediated by raised levels of UDP-glucose pyrophosphorylase (UGP). Marginally raised UDP-galactose 4-epimerase (UGE) activity in the mutant strain suggested that this enzyme could also play a role in EPS overproduction. The second approach involved investigating the effect of growth rate on sugar nucleotide metabolism in the parent, as it is known that EPS production is growth-associated in this strain. UGE activity in the parent strain appeared to increase when the growth rate was elevated from 0.05 to 0.10 h⁻¹, and further to 0.35 h⁻¹, conditions that can be associated with higher levels of metabolic flux to EPS formation. Concurrent with these increments, intracellular ATP levels in the cell were raised. In both investigations glucose-6-phosphate accumulated pointing to a constriction at this branch-point, and a limitation in the flow of carbon towards fructose-6-phosphate or glucose-1-phosphate. The changes in metabolism associated with enhanced flux to EPS provide guidance as to how the yield of Lactobacillus delbrueckii subsp. bulgaricus EPS can be improved.