Stability of xanthan in aqueous sodium chloride at elevated temperature

Aqueous NaCl solutions of dimerized Na xanthan with salt concentrations of 0.005, 0.01 and 0.1 were exposed to 80°C for different time periods t, and their viscosities were determined as a function of t. The measured relative viscosities decreased markedly with t, suggesting that Na xanthan denatured at 80°C undergoes some conformation changes or degradation. The molecular weights of the test samples recovered at different t were estimated by viscometry in cadoxen, a single-coil solvent for xanthan, and were found to decrease monotonically with t. Thus, it was concluded that the observed decreases in relative viscosity are due primarily to degradation of Na xanthan.     

Response time and electrorheology of semidiluted gellan, xanthan and cellulose suspensions

Response times with electrical fields of gellan and xanthan dry powder suspensions of 25, 32 and 53 μm average diameter and concentrations of 1.0, 1.5 and 2.0% (w/w) dispersed in commercial corn oil were optically measured through a specifically designed set up. In all cases, the delay time was proportional to 1/E^a, where E is the applied field and a is an adjustable parameter. The values of parameter a were very different from the typical value of some known electrorheolgical fluids. Response time of gellan suspensions was shorter than the one obtained for xanthan and it is comparable to the time found by using silica particles in silicon oil. Response times for cellulose were very large and the fibrillation phenomenon was negligible for E<1.0 kv/mm.

Viscosity measurements of semidiluted xanthan, gellan and cellulose suspensions (1.0 and 1.5% w/w) under the influence of electrical fields, were performed in a parallel plates rheometer. Results in the range of stress <70 Pa showed that viscosity values of gellan suspensions were larger than those obtained with xanthan or cellulose under the same applied electric field at shear rates higher than 10 s⁻¹. However, cellulose suspensions showed larger viscosity values compared with the ones measured with xanthan and gellan suspensions at very low shear rates. Dielectric measurements of cellulose, xanthan and gellan 1.5% w/w suspensions were performed in the range 10⁰–8×10⁴ Hz. Results agree with a Maxwell–Wagner type relaxation model.     

Xanthan Lyase of Bacillus sp. Strain GL1 Liberates Pyruvylated Mannose from Xanthan Side Chains

When the bacterium Bacillus sp. strain GL1 was grown in a medium containing xanthan as the carbon source, the viscosity of the medium decreased in association with growth, showing that the bacterium had xanthan-depolymerizing enzymes. One of the xanthan-depolymerizing enzymes (xanthan lyase) was present in the medium and was found to be induced by xanthan. The xanthan lyase purified from the culture fluid was a monomer with a molecular mass of 75 kDa, and was most active at pH 5.5 and 50°C. The enzyme was highly specific for xanthan and produced pyruvylated mannose. The result indicates that the enzyme cleaved the linkage between the terminal pyruvylated mannosyl and glucuronyl residues in the side chain of xanthan.     

Xanthan–galactomannan interactions as related to xanthan conformations

The influence of xanthan conformation on the physicochemical behaviour of their mixtures with galactomannan from Schizolobium parahybae mannose:galactose ratio (M/G=3), was studied by viscoelastic measurements, differential scanning calorimetry (DSC) and chiroptical (circular dichroism) methods. The results suggested a more effective interaction of the galactomannan with disordered xanthan segments, which are more abundant in low salt concentrations but are still present in lower proportion at temperatures lower than the temperature of xanthan conformational transition (T_m). The dependence of ellipticity with temperature in a circular dichroism (CD) spectra suggested an ordering of the xanthan chains induced by galactomannan at the temperature of gel formation (T_g≈25°C), under conditions where xanthan alone exhibits a disordered conformation. The lower T_g value found (≈25°C) compared with that (60°C) usually described in the literature is certainly related to the M/G ratio and the galactosyl unit distribution along the mannan main chain.     

Polysaccharide Lyase: Molecular Cloning, Sequencing, and Overexpression of the Xanthan Lyase Gene of Bacillus sp. Strain GL1

When grown on xanthan as a carbon source, the bacterium Bacillus sp. strain GL1 produces extracellular xanthan lyase (75 kDa), catalyzing the first step of xanthan depolymerization (H. Nankai, W. Hashimoto, H. Miki, S. Kawai, and K. Murata, Appl. Environ. Microbiol. 65:2520–2526, 1999). A gene for the lyase was cloned, and its nucleotide sequence was determined. The gene contained an open reading frame consisting of 2,793 bp coding for a polypeptide with a molecular weight of 99,308. The polypeptide had a signal peptide (2 kDa) consisting of 25 amino acid residues preceding the N-terminal amino acid sequence of the enzyme and exhibited significant homology with hyaluronidase of Streptomyces griseus (identity score, 37.7%). Escherichia coli transformed with the gene without the signal peptide sequence showed a xanthan lyase activity and produced intracellularly a large amount of the enzyme (400 mg/liter of culture) with a molecular mass of 97 kDa. During storage at 4°C, the purified enzyme (97 kDa) from E. coli was converted to a low-molecular-mass (75-kDa) enzyme with properties closely similar to those of the enzyme (75 kDa) from Bacillus sp. strain GL1, specifically in optimum pH and temperature for activity, substrate specificity, and mode of action. Logarithmically growing cells of Bacillus sp. strain GL1 on the medium with xanthan were also found to secrete not only xanthan lyase (75 kDa) but also a 97-kDa protein with the same N-terminal amino acid sequence as that of xanthan lyase (75 kDa). These results suggest that, in Bacillus sp. strain GL1, xanthan lyase is first synthesized as a preproform (99 kDa), secreted as a precursor (97 kDa) by a signal peptide-dependent mechanism, and then processed into a mature form (75 kDa) through excision of a C-terminal protein fragment with a molecular mass of 22 kDa.     

新分离菌Streptomyces产小分子CMC液化酶的研究

新分离纤维素分解菌经鉴定为链霉菌属中的新种,暂定名为ＳｔｒｅｐｔｏｍｙｃｅｓｓｐＬＸ,革兰氏阳性,产气生孢子,好氧生长,最适生长温度和ＰＨ为３０℃和７．２。该菌能够完全降解纤维素且不产生还原糖,并分泌一种分子量为９．２ｋｕ的液化性质的内切纤维素液化酶,亦即ＣＭＣ液化酶,该酶在裂解滤纸为短纤维的过程中既没有还原糖生成,也没有失重现象发生,而且纤维素的聚合度也几乎没有明显变化,推测可能是一种能打开氢键的小分子解链酶。     

Polysaccharide lyase: molecular cloning, sequencing, and overexpression of the xanthan lyase gene of Bacillus sp. strain GL1

When grown on xanthan as a carbon source, the bacterium Bacillus sp. strain GL1 produces extracellular xanthan lyase (75 kDa), catalyzing the first step of xanthan depolymerization (H. Nankai, W. Hashimoto, H. Miki, S. Kawai, and K. Murata, Appl. Environ. Microbiol. 65:2520-2526, 1999). A gene for the lyase was cloned, and its nucleotide sequence was determined. The gene contained an open reading frame consisting of 2,793 bp coding for a polypeptide with a molecular weight of 99,308. The polypeptide had a signal peptide (2 kDa) consisting of 25 amino acid residues preceding the N-terminal amino acid sequence of the enzyme and exhibited significant homology with hyaluronidase of Streptomyces griseus (identity score, 37.7%). Escherichia coli transformed with the gene without the signal peptide sequence showed a xanthan lyase activity and produced intracellularly a large amount of the enzyme (400 mg/liter of culture) with a molecular mass of 97 kDa. During storage at 4 degrees C, the purified enzyme (97 kDa) from E. coli was converted to a low-molecular-mass (75-kDa) enzyme with properties closely similar to those of the enzyme (75 kDa) from Bacillus sp. strain GL1, specifically in optimum pH and temperature for activity, substrate specificity, and mode of action. Logarithmically growing cells of Bacillus sp. strain GL1 on the medium with xanthan were also found to secrete not only xanthan lyase (75 kDa) but also a 97-kDa protein with the same N-terminal amino acid sequence as that of xanthan lyase (75 kDa). These results suggest that, in Bacillus sp. strain GL1, xanthan lyase is first synthesized as a preproform (99 kDa), secreted as a precursor (97 kDa) by a signal peptide-dependent mechanism, and then processed into a mature form (75 kDa) through excision of a C-terminal protein fragment with a molecular mass of 22 kDa.     

Viscosity of locust bean, guar and xanthan gum solutions in the Newtonian domain: a critical examination of the log (ηsp)o-log c[η]o master curves

The viscosity in the low shear rate Newtonian domain of three biopolymers, locust bean gum, guar gum and xanthan gum was studied as a function of temperature and of polymer concentration in various aqueous solvents. The intrinsic viscosities [η]_o of both galactomannans are not modified in the presence of 10 or 40% sucrose. In this case, a master curve relating the Newtonian specific viscosity (η_sp)_o, to the reduced concentration c[η]_o is obtained and allows (in good agreement with theoretical conjectures), two critical concentrations C* and C** to be defined, from which the value of the expansion coefficient may be estimated. For xanthan, as expected for a polyelectrolyte, [η]_o depends strongly on salt concentration and on added sucrose and the results did not obey the above-mentioned master curve. However, it is shown that (η_sp)_o depends only on xanthan concentration whenC > C**, and then it is assumed that chain dimensions have attained their unperturbed values whatever the solvent. Considering that both types of chains, random coils (galactomannans) and semi-rigid (xanthan) should give the same (η_sp)_o-C[η]_o master curve for C > C** when [η]_o is replaced by its unperturbed counterpart [η]_θ, a method for estimating [η]_θ for the xanthan sample is proposed. In conclusion, the numerous exceptions to the widely accepted (η_sp)_o vs C[η]_o “universal” behaviour are mainly ascribed to significant differences in expansion coefficient values which depend on both the polymer and the solvent.     

Power consumption of three impeller combinations in mixing Xanthan fermentation broths

Xanthan gum fermentation represents a good model for the study of the mixing of rheologically complex culture broths. Most of the previous work on power consumption dealt with ‘standard’, single impellers and used model fluids to simulate xanthan broths. This work describes the characterization of three dual-impeller combinations (D/T = 0·53) for the mixing of dehydrated—reconstituted fermentation broths of Xanthomonas campestris that had matched rheology to the actual broths. The bottom impeller was a Rushton turbine (RT) and the top impeller was another RT, a 45° pitched blade turbine (PT) or an A-310 Lightnin mixer (A310). The experiments were carried out in a tank of 0·0094 m³ working volume equipped with an air bearing dynamometer. The power was measured in a wide range of xanthan concentrations (5–40 kg m⁻³) in aerated (0·25, 0·5 and 1·0 vvm) and unaerated conditions. Unaerated power number (Po) vs. Reynolds number (Re) curves showed similar trends for the three combinations. Exponents close to −1 were obtained in the laminar region. A minimum in Po (Po_min) occurred at Re = 30–40, then increasing to a plateau value which was evident at Re> 200. In the transition region Po_min values were 4·3 (RT and RT), 3·6 (RT and PT) and 2·4 (RT and A310). The aerated power data for (RT and PT) and (RT and A-310) showed higher torque instabilities than the dual RT combinations at higher xanthan concentrations. The higher the xanthan concentrations, the higher the drop in power and the less important the effect of the aeration rate. Among the combinations tested, when using Rushton turbines, the well-mixed ‘cavern’ reached the tank wall (i.e., fluid motion was observed) at the lowest volumetric power input. High     

Cochliopodium barki n. sp. (Rhizopoda, Himatismenida) re-isolated from soil 30 years after its initial description

A strain of Cochliopodium isolated from grassland soil at Sourhope Research Station (Scotland, UK) was found to be identical to the strain “Cochliopodium sp.2” studied by Bark in 1973. We name it Cochliopodium barki. It belongs to a group of species (comprising also C. minus and Cochliopodium sp. “NYS strain”) with very similar scale pattern.     

Loss of Symbiodinium from bleached soft corals Sarcophyton ehrenbergi, Sinularia sp. and Xenia sp.

The deleterious effects of temperature-induced coral bleaching, a process by which corals lose their endosymbiotic algae (zooxanthellae; genus Symbiodinium) primarily at temperatures above mean yearly maximums, has not been well described for alcyonacean soft corals (Coelenterata, Octocorallia). The study of Symbiodinium cells lost from Sarcophyton ehrenbergi, Sinularia sp., and Xenia sp., which have not been compared in bleaching studies, indicate that the soft coral S. ehrenbergi released the greatest number of symbiont cells, however, it was less susceptible to heat stress surviving temperatures of 34 °C for >39 h. Sinularia sp. showed intermediate levels of bleaching tolerance to elevated temperatures, surviving prolonged exposures at 32 °C, but dying within 24 h at 34 °C. Xenia sp., however, was the most vulnerable to high heat stress maximally releasing Symbiodinium at temperatures ≤30 °C. This evidence indicates that Xenia sp. is even more susceptible to elevated temperatures than Acropora spp., previously reported to be the most vulnerable coral species to elevated temperature-induced bleaching.

Molecular analysis showed that the more resistant soft coral species (S. ehrenbergi) had the same type of Symbiodinium (clade C) as less resistant soft corals (Xenia sp.). In comparison to scleractinian corals collected from the same region that show similar bleaching resistance to high temperatures (e.g. Porities solida—more robust; Favites complanata—moderate resistance; Acropora hyacinthus—less robust), all scleractinian corals were symbiotic with Symbiodinium from clade C. A. hyacinthus, however, was found to possess multiple symbionts (clades B and C), and this represents a first report of Clade B in any Acropora species.     

基于差异基因表达谱的Microbacterium sp. XT11降解黄原胶潜能挖掘

为挖掘微杆菌(Microbacterium sp.)XT11在黄原胶降解过程中起关键作用的功能基因,预测黄原胶降解通路,利用转录组测序技术对该菌株在不同碳源培养条件下的转录本进行测序,对差异基因进行功能富集分析。结果表明,菌株XT11以葡萄糖为对照组,以黄原胶为碳源时可获得上调差异基因213个。显著上调的基因主要富集在聚糖降解、淀粉和蔗糖代谢途径、ABC转运、苯丙氨酸代谢、丙酮酸代谢五个KEGG途径。碳水化合物活性酶(Carbohydrate-active enzymes, CAZymes)功能注释表明,位于同一基因簇上的4个CAZymes基因和黄原胶降解直接相关,其余的CAZymes基因具有潜在的黄原胶降解活性。此外,预测到磷酸转移酶系统(phosphotransferase system, PTS)和ABC转运途径(ABC transporters)参与了胞外黄原胶降解中间产物的跨膜转运。挖掘了菌株XT11中黄原胶降解过程中的功能基因,并阐述了菌株XT11的黄原胶降解通路。     

The Distribution of Tardigrades Upwind and Downwindof a Missouri Coal-Burning Power Plant

Significant differences occurred in the density of tardigrades, rotifers, and nematodes and the diversity of tardigrades between collecting sites located upwind and downwind from a coal-burning power plant in Missouri. The oak tree species and lichen genera also varied in the two areas. Tardigrade and rotifer densities were greater in upwind sites, whereas nematode density was higher in downwind samples. One tardigrade species (Ramazzottius sp.) was found only at the upwind sites, and one species (Echiniscus sp.) was only in the downwind samples. In contrast, three species (Macrobiotus sp., Minibiotus sp., and Milnesium tardigradum) were found both upwind and downwind but in different densities in the two areas. The study presents baseline data for long-term monitoring of the effects of environmental factors on nematode and rotifer densities as well as tardigrade density and diversity.     

Biodegradation of corrosion inhibitors and their influence on petroleum product pipeline

The present study enlightens the role of Bacillus cereus ACE4 on biodegradation of commercial corrosion inhibitors (CCI) and the corrosion process on API 5LX steel. Bacillus cereus ACE4, a dominant facultative aerobic species was identified by 16S rDNA sequence analysis, which was isolated from the corrosion products of refined diesel-transporting pipeline in North West India. The effect of CCI on the growth of bacterium and its corrosion inhibition efficiency were investigated. Corrosion inhibition efficiency was studied by rotating cage test and the nature of biodegradation of corrosion inhibitors was also analyzed. This isolate has the capacity to degrade the aromatic and aliphatic hydrocarbon present in the corrosion inhibitors. The degraded products of corrosion inhibitors and bacterial activity determine the electrochemical behavior of API 5LX steel.     

Exopolysaccharide production by free and immobilized microbial cultures

The batch production of different exopolysaccharides (alginate, xanthan, pullulan, dextran) by free and immobilized microbial cultures was investigated. First, conventional free-cell cultures were performed to obtain control fermentation parameters and macromolecular characteristics of exopolysaccharides. Then microbial cultures were immobilized in composite agar layer/microporous membrane structures and tested for polysaccharide production. The immobilized-cell system proved unsuitable for xanthan and pullulan production. Owing to the fouling of the microporous membrane by the polysaccharide, dextran production by immobilized Leuconostoc mesenteroides also was inefficient. More promising results have been obtained with immobilized Azotobacter vinelandii cultures. The amount of alginate produced by immobilized A. vinelandii represented about 60% of that recovered from a free-cell culture, whereas the polysaccharide yield reached 35% instead of 9% for the free counterpart. These results are compared to the macromolecular characteristics of exopolysaccharides.     

A retrospective study of the microbiological and parasitological status of laboratory rodents in France

Between 1988 and 1997, 72 mouse colonies and 38 rat colonies were examined for the presence of bacteria parasite infections. Among mouse and rat bacteria, high positive rates were observed with Proteus species (sp.), Pasteurella pneumotropica, Mycoplasma sp. and Pseudomonas aeruginosa. Concerning murine colonies, parasites frequently detected were Tritrichomonas sp., Syphacia sp., Aspiculuris tetraptera, Entamoeba muris, Spironucleus muris, Myobia musculi, Chilomastix sp. and Myocoptes musculinus. In rats, high rates were obtained with Syphacia sp., Tritrichomonas sp., Spironucleus muris, Entamoeba muris and Chilomastix sp. During the first part of the last decade, some agents such as Clostridium piliforme, Citrobacter sp., Mycoplasma sp., Pseudomonas aeruginosa, Myobia musculi, Radfordia ensifera, Spironucleus muris and Giardia muris were often found among rodents, and most of them were still present in 1997. At the time of our study, results point out that some agents are still persistent, even increasing during the same period. It is particularly the case for parasites such as Entamoeba muris and the oxyurids, but also for bacteria like Proteus sp. and Klebsiella pneumoniae. We can thus conclude that only very limited success has been achieved in preventing microbial and parasitic infections in mice and rats colonies.     

Field application of an insect virus in the Mekong Delta: Effects of a Vietnamese nucleopolyhedrovirus on Spodoptera litura (Lepidoptera: Noctuidae) and its parasitic natural enemies

A new Vietnamese isolate of Spodoptera litura nucleopolyhedrovirus (NPV) was applied in local soybean fields, and the effect of its application on S. litura larvae was examined. The virus was propagated in vivo and a crude extract was prepared for spraying at high and low doses (1.7×10⁸ and 3.3×10⁷ occlusion bodies/m², respectively). The percentage of larvae infected with NPV increased from 22.2% on the day before NPV application (Day 0) to 50.8% (Day 6) in the high dose treatment plot, and from 7.9% (Day 0) to 35.7% (Day 6) in the low-dose plot. Microsporidium sp. was observed as another major pathogen of S. litura larvae. Three dominant parasitic natural enemies were found in S. litura larvae: Microplitis manilae (Braconidae), Chelonus sp. (Braconidae), and Peribaea orbata (Tachinidae). The fate of parasitoids developing within virus- and Microsporidium- infected hosts differed between these three parasitoids; more Chelonus sp. emerging from infected hosts died during their larval stage before spinning cocoons, or failed to reach adult eclosion, than did P. orbata. This suggests that the impact of virus application on the survival of parasitoids varies from species to species.     

Distribution and habitat preferences of species within the genus Elaphoidella Chappuis, 1929 (Crustacea: Copepoda: Harpacticoida) in Slovenia

Twelve species of the harpacticoid genus Elaphoidella, most of them exclusively groundwater species, have been recorded in Slovenia (SE Europe). Their distribution and ecology are reviewed with the aim of evaluating distribution patterns, species preferences for groundwater habitats, ecological preferences and interactions with other copepod species at regional scale. Data on Elaphoidella species were obtained partly from the existing literature and partly from the author's (AB) own sampling campaigns carried out together with his co-workers. During the rich history of collecting copepods in Slovenia (from the 1920s to present), Elaphoidella species were recorded at 78 sampling sites altogether. The majority of collecting was conducted in the southern (Dinaric region) and north-western (Alpine region) Slovenia. The most intensively sampled habitats were porous aquifers of alluvial plains, springs in the karstic unsaturated zone and percolation water in caves. The highest species richness of Elaphoidella was recorded in the southern Slovenia, where 10 species were found. The strictly “Dinaric” species are E. charon, E. franci, E. karstica, E. stammeri, E. sp. 1 and E. sp. 2, while E. phreatica and E. bidens were found exclusively in the north-western Slovenia. From the latest data on the copepod distributions (2002–2004), where the environmental characteristics of sampling sites were also measured, the relationship between selected environmental characteristics of the habitats and the presence of Elaphoidella species was analysed. The distribution of Elaphoidella species in Slovenia was found to be related with the region, habitat type, altitude, conductivity and pH of the water.     

Substrate induction of isomaltulose synthase in a newly isolated Klebsiella sp. LX3

AIMS: Production of isomaltulose by newly isolated Klebsiella sp. LX3. METHODS AND RESULTS: The bacterial isolate LX3, which transforms sucrose to isomaltulose and trehalulose, has been isolated from a soil sample in Singapore. Morphological and biochemical analysis, as well as 16s rRNA sequence demonstrated that the isolate could represent a new member of genus Klebsiella. The strain has several interesting features. The immobilized cells of Klebsiella sp. LX3 convert more than 99% of sucrose to products that consist of more than 87% of isomaltulose, 11.6% of trehalulose, and <1% of glucose. CONCLUSIONS: The production of isomaltulose synthase in isolate LX3 is inducible by its substrate sucrose and the sugars containing a fructofuranosyl group. SIGNIFICANCE AND IMPACT OF STUDY: It would be useful for future biotechnological applications to understand the structural features or motifs of the isomaltulose synthases that determine the sucrose conversion efficiency and the ratio of the conversion products.