Xanthan gum: production, recovery, and properties

Xanthan gum is a microbial polysaccharide of great commercial significance. This review focuses on various aspects of xanthan production, including the producing organism Xanthomonas campestris, the kinetics of growth and production, the downstream recovery of the polysaccharide, and the solution properties of xanthan.     

Xanthan gum production by wild-type isolates of Xanthomonas campestris

Five newly-isolated strains of Xanthomonas campestris when compared with the standard strain, NRRL B-1459, showed higher broth viscosity and xanthan gum production. Evaluation of polysaccharide rheology is a very important determinant for selecting new xanthan-producing isolates.     

Xanthan gum production by altered pathogenicity variants of Xanthomonas campestris

Summary Several morphologically different isolates of Xanthomonas campestris pv. campestris were obtained by treatment with N-methyl-N-nitro-N-nitrosoguanidine. These variants were used to infect Brassica plants where several degrees of virulence were found. The strains were cultured in order to produce polysaccharide, which was recovered by precipitation and subjected to physical and chemical characterization. A relationship was noted between virulence and parameters such as the final viscosity of the culture, the viscosifying capacity of the polymer and the amount of acetyl substituents in the gum. Infrared spectral analysis revealed that intramolecular interaction of gum constituents could play a significant role in virulence. It is suggested that the degree of virulence could be used as a criterion for selecting and isolating producers of high quality xanthan gum.     

Xanthan gum production and rheological behavior using different strains of Xanthomonas sp.

The proposal of the present study was to select and carry out the molecular characterization of strains of Xanthomonas sp. in order to correlate with gum production and determine possible genetic alterations during the study. The gums produced were also evaluated rheologically. Ten strains of Xanthomonas were used in the screening and the best ones in terms of productivity were Xanthomonas campestris pv. mangiferaeindicae 1230 (8.93 g/L), X. campestris pv. campestris 254 (9.49 g/L) and X. campestris pv. campestris 1078 (9.67 g/L). The gum produced by X. campestris pv. mangiferaeindicae presented the best apparent viscosity. The results for the profiles of the bands produced by RAPD showed considerable genetic variability amongst the evaluated strains, making not possible to neither group the strains according to pathovar or species, nor correlate the band profile with the productivity obtained. According to the RAPD analysis, no detectable mutations occurred in these bacteria during the study.     

Xanthan gum production under several operational conditions: molecular structure and rheological properties*

Xanthan gum production under several operational conditions has been studied. Temperature, initial nitrogen concentration and oxygen mass transfer rate have been changed and average molecular weight, pyruvilation and acetylation degree of xanthan produced have been measured in order to know the influence of these variables on the synthesised xanthan molecular structure. Also, xanthan gum solution viscosity has been measured, and rheological properties of the solutions have been related to molecular structure and operational conditions. The Casson model has been employed to describe the rheological behaviour. The parameter values of the Casson model, tau(0) and K(c), have been obtained for each polysaccharide synthesised under different operational conditions. Both pyruvilation and acetylation degrees and average molecular weight of xanthan increase with fermentation time at any operating conditions. Xanthan molecules with the highest average molecular weight have been obtained at 25 degrees C. Nevertheless, at this temperature acetate and pyruvate radical concentration are lowest. Nitrogen concentration in broth does not show any clear influence over xanthan average molecular weight, although with high nitrogen source concentration xanthan with low pyruvilation degree is produced.     

Xanthan gum and ethanol production by Xanthomonas campestris and Zymomonas mobilis from peach pulp

The wild type of Xanthomonas campestris and a mutant strain of Zymomonas mobilis CP4, tolerant to sucrose up to 40% (w/v), were used to produce either xanthan gum or ethanol, respectively, from peach pulp supplemented with different salts. Both bacteria grew well (2.7 mg/ml for X. campestris and 1.45 mg/ml for Z. mobilis) in fine peach pulp and the production of xanthan gum or ethanol was 0.1–0.2 g/l or 110 g/l, respectively.     

Xanthan production from olive-mill wastewaters

Olive mill wastewaters (OMW) are a by-product from olive oil manufacture that cause environmental pollution. These wastes have been used as substrate for the production of the extracellular polysaccharide xanthan by Xanthomonas campestris NRRL B1459-S4L41. Growth and xanthan production on dilute OMW as a sole source of nutrients were obtained at OMW concentrations below 60%, yielding a maximal xanthan production of 4.4gl⁻¹ at 30–40% OMW concentration. Addition of nitrogen and/or salts led to significantly increased xanthan yields with a maximum of 7.7gl⁻¹. The N/salts supplements also allowed an increase in the optimal OMW concentration. Inocula pre-grown on OMW can be used. Results suggest that an improved xanthan yield could be obtained with adequate balance between waste concentration and nitrogen or salt supplementation. OMW is proposed as a low-cost substrate for xanthan production with the additional environmental benefit of this use.     

Xanthan gum biosynthesis and application: a biochemical /genetic perspective

Xanthan gum is a complex exopolysaccharide produced by the plant-pathogenic bacterium Xanthomonas campestris pv. campestris. It consists of D-glucosyl, D-mannosyl, and D-glucuronyl acid residues in a molar ratio of 2:2:1 and variable proportions of O-acetyl and pyruvyl residues. Because of its physical properties, it is widely used as a thickener or viscosifier in both food and non-food industries. Xanthan gum is also used as a stabilizer for a wide variety of suspensions, emulsions, and foams. This article outlines aspects of the biochemical assembly and genetic loci involved in its biosynthesis, including the synthesis of the sugar nucleotide substrates, the building and decoration of the pentasaccharide subunit, and the polymerization and secretion of the polymer. An overview of the applications and industrial production of xanthan is also covered. Received: 18 March 1998 / Received revision: 29 April 1998 / Accepted: 30 April 1998     

Xanthan gum produced from whey by a mutant strain ofxanthomonas campestris

Exopolymer gum of xanthan type was produced from whey by a mutant strian ofXanthomonas campestris lac ⁺ In 75-L and 300-L fermentatin tanks the cultivation and production conditions were studied. After optimization a maximum yield of 20 g/L polymer production in a nutritive medium was reached.     

蜡状芽孢杆菌活菌制剂(促菌生)大罐深层培养的研究

本试验就蜡状芽孢杆菌大罐深层培养法进行了初步研究,基本解决了蜡状芽孢杆菌大罐液体深层培养条件下芽孢生成、适宜培养基的选择、培养方法的建立以及菌体的收集方法等技术问题,大罐深层培养生产工艺的建立较固体培养法产量大为增加,污染耗损降至最低,减少劳动强度和繁琐的操作,而且产品质量得到保证和提高.     

Xanthan production by some Xanthomonas isolates

An electroporation-induced transformation system was developed for two raw sausage starter organisms: Lactobacillus curvatus Lc2-c and Lact. sake Ls2. Several plasmids of different origin (pAMβ1, pIL253, pNZ12 and pLP825) were tested for transformation and expression of their resistance determinants. Transfer rates were strongly dependent on growth phase and voltage. Several parameters were studied with possible influence on trasformation efficiencies.     

Xanthan production in a plunging jet reactor

Summary A plunging jet reactor (0.04–0.08 m³) was used for the production of the exopolysaccharide xanthan with Xanthomonas campestris. The microorganism was not affected by the pump shear force. Similar specific growth rates and xanthan space-time yields to those in other reactor types were achieved at much lower specific power input. The better oxygen sorption efficiency in the jet reactor overcompensated for the effect of poor mixing in the wall region at high xanthan concentrations. Offprint requests to: A. Schumpe     

Xanthan production byXanthomonas campestris in continuous fermentation

Summary Xanthan production by a strain ofX. campestris was maintained longer under glucose—limited than nitrogen—limited conditions in continuous culture. The turnover Q was 12 at lower pH(5.0–6.0) and 6.5 at neutral pH; xanthan productivity was comparable at both pH in nitrogen—limited continuous cultures. In the Fe—rich continuous fermentation cell degeneration did not occur for 65 turnovers whereas in the Fe—deficient fermentation it occurred in 12 turnovers. The culture stability for xanthan formation is higher under conditions which are favorable for cell growth with limited xanthan production.     

Xanthan gum: an economical substitute for agar in plant tissue culture media

Xanthan gum, a microbial desiccation-resistant polysaccharide prepared commercially by aerobic submerged fermentation from Xanthomonas campestris, has been successfully used as a solidifying agent for plant tissue culture media. Its suitability as a substitute to agar was demonstrated for in vitro seed germination, caulogenesis and rhizogenesis of Albizzia lebbeck, androgenesis in anther cultures of Datura innoxia, and somatic embryogenesis in callus cultures of Calliandra tweedii. Culture media used for eliciting these morphogenic responses were gelled with either 1% xanthan gum or 0.9% agar. Xanthan gum, like agar, supported all these responses.     

Xanthan production in bubble column and air-lift reactors

A bubble column (0.05 m(3)) and an air-lift fermentor (1.2 m(3)) were used for the production of the exocellular microbial polysaccharide xanthan with Xanthomonas campestris in a synthetic medium. Upon oxygen depletion in the liquid, the xanthan production rate dropped sharply and then became a linear function of the oxygen transfer rate. The volumetric mass transfer coefficients for oxygen conformed to the correlation of Suh et al. Using this correlation in combination with the model for xanthan batch fermentation suggested by Peters et al., the xanthan fermentations in the bubble column were well described. The model also correctly predicted the time course of the molecular weight of the polysaccharide even when a complex medium was used. In the air-lift fermentor, however, the xanthan production rate and the xanthan yields with respect to oxygen and glucose were lower than expected at the overall oxygen transfer rate. The poor performance of the air lift was traced back to the lack of any oxygen supply in the downcomer.     

Xanthan production by Xanthomonas albilineans infecting sugarcane stalks

Xanthomonas albilineans is the causal organism of leaf scald, a bacterial vascular disease of sugarcane. Xanthomonas may invade the parenchyma between the bundles and cause reddened pockets of gum, identified as a xanthan-like polysaccharide. Since xanthan contains glucuronic acid, the ability of Xanthomonas to produce an active UDP glucose dehydrogenase is often seen as a virulence factor. X. albilineans axenically cultured did not secrete xanthans to Willbrink liquid media, but the use of inoculated sugarcane tissues for producing and characterizing xanthans has been required. A hypothesis about the role of sugarcane polysaccharides to assure the production of bacterial xanthan is discussed.     

Growth of Human Lymphoid Cells (Raji Strain) in a Five-Liter Fermentor

Procedures used to produce an established line of mammalian cells (L cell) in a New Brunswick fermentor were adapted to propagate human lymphoid cells in suspended culture. Control of pH within defined limits was more effective for regulation of cell metabolism than control of oxidation-reduction potential. An unusually high rate of agitation was required.     

Xanthomonas campestris pv. campestris gum Mutants: Effects on Xanthan Biosynthesis and Plant Virulence

Xanthan is an industrially important exopolysaccharide produced by the phytopathogenic, gram-negative bacterium Xanthomonas campestris pv. campestris. It is composed of polymerized pentasaccharide repeating units which are assembled by the sequential addition of glucose-1-phosphate, glucose, mannose, glucuronic acid, and mannose on a polyprenol phosphate carrier (L. Ielpi, R. O. Couso, and M. A. Dankert, J. Bacteriol. 175:2490–2500, 1993). A cluster of 12 genes in a region designated xpsI or gum has been suggested to encode proteins involved in the synthesis and polymerization of the lipid intermediate. However, no experimental evidence supporting this suggestion has been published. In this work, from the biochemical analysis of a defined set of X. campestris gum mutants, we report experimental data for assigning functions to the products of the gum genes. We also show that the first step in the assembly of the lipid-linked intermediate is severely affected by the combination of certain gum and non-gum mutations. In addition, we provide evidence that the C-terminal domain of the gumD gene product is sufficient for its glucosyl-1-phosphate transferase activity. Finally, we found that alterations in the later stages of xanthan biosynthesis reduce the aggressiveness of X. campestris against the plant.     

Macromolecular distribution of Acacia senegal gum (gum arabic) by size-exclusion chromatography

Fractionation of Acacia senegal gum has been carried out on Sephacryl gels S-400 and S-500. The shape and relative height of the chromatograms are sample dependent.Physicochemical data including circular dichroism and the weight-average molecular weights distribution show that about 70% of the material is composed of homogeneous polysaccharide chains with a very low nitrogen content. The remaining material is a combination of polysaccharide and nitrogen moieties (probably an arabinogalactan-protein complex).Our data are consistent with the new and simplified structural models proposed recently for this polysaccharide.     

Solution properties of conventional gum arabic and a matured gum arabic (Acacia (sen) SUPER GUM)

Dilute solution properties of two specially matured gum arabic samples (EM1 and EM2) were compared to the conventional gum (EM0) using static light scattering. The apparent molar mass (M(w,app) and radius of gyration (R(g,app)) for the three samples showed unusual concentration dependence. These data were satisfactorily interpreted by a simple association model that takes into account the repulsive interaction among clusters, which allowed us to obtain the true molar mass (Mw(0)) and radius of gyration (Rg(0)). A common power law relation was observed between Mw(0) and Rg(0) , giving a somewhat higher exponent than expected for linear and branched polymers in a good solvent. Mw(0) and Rg(0) obtained for the three gums do not differ significantly from each other. However, the data showed clearly a constant increase of the association from EM0 to EM2 with increasing concentration. This is in accordance with the previously observed improved functional properties for the matured products.