Two extracellular endoxylanases from alkaliphilic Bacillus firmus differ in their synthesis

To investigate the synthesis of two extracellular endoxylanases, xylan-binding and unbound xylanases from an alkaliphilic Bacillus firmus, washed cells were incubated in alkaline mineral salt media containing various carbon sources. The 23 kDa xylan-binding endoxylanase (XBE), which hydrolyses insoluble xylan, was produced before the 45 kDa, unbound endoxylanase. All the carbon sources tested at 5 mg ml^–1, including glucose, induced production of XBE but the unbound xylanase was totally repressed by glucose. The production of XBE increased when glucose concentration increased but was not synthesized until the glucose in the medium was less than 1 mg ml^–1.     

Subsite mapping of purified glucoamylase I, II, III produced by Arthrobotrys amerospora ATCC 34468

Arthrobotrys amerospora ATCC 34468 produced glucoamylase in a medium containing maize starch as carbon source. On native PAGE, crude glucoamylase showed three isoenzymes which were designated as Glu I, Glu II, Glu III according to their electrophoretic mobility. These were purified by column chromatography techniques. The energy of binding for each glucoamylase was calculated using Hiromi's kinetic based calculation. At subsite 1, the binding energies for Glu I, II and III were found to be negative.     

Biochemical properties of xylanases from a thermophilic fungus,Melanocarpus albomyces, and their action on plant cell walls

Melanocarpus albomyces, a thermophilic fungus isolated from compost by enrichment culture in a liquid medium containing sugarcane bagasse, produced cellulase-free xylanase in culture medium. The fungus was unusual in that xylanase activity was inducible not only by hemicellulosic material but also by the monomeric pentosan unit of xylan but not by glucose. Concentration of bagasse-grown culture filtrate protein followed by size-exclusion and anion-exchange chromatography separated four xylanase activities. Under identical conditions of protein purification, xylanase I was absent in the xylose-grown culture filtrate. Two xylanase activities, a minor xylanase IA and a major xylanase IIIA, were purified to apparent homogeneity from bagasse-grown cultures. Both xylanases were specific forβ-1,4 xylose-rich polymer, optimally active, respectively, at pH 6.6 and 5.6, and at 65°C. The xylanases were stable between pH 5 to 10 at 50°C for 24 h. Xylanases released xylobiose, xylotriose and higher oligomers from xylans from different sources. Xylanase IA had a M_r of 38 kDa and contained 7% carbohydrate whereas xylanase IIIA had a M_r of 24 kDa and no detectable carbohydrate. The K_m for larchwood xylan (mg ml⁻¹) and V_max (μmol xylose min⁻¹ mg⁻¹ protein) of xylanase IA were 0.33 and 311, and of xylanase IIIA 1.69 and 500, respectively. Xylanases IA, II and IIIA showed no synergism in the hydrolysis of larchwood glucuronoxylan or oat spelt and sugarcane bagasse arabinoxylans. They had different reactivity on untreated and delignified bagasse. The xylanases were more reactive than cellulase on delignified bagasse. Simultaneous treatment of delignified bagasse by xylanase and cellulase released more sugar than individual enzyme treatments. By contrast, the primary cell walls of a plant, particularly from the region of elongation, were more susceptible to the action of cellulase than xylanase. The effects of xylanase and cellulase on plant cell walls were consistent with the view that hemicellulose surrounds cellulose in plant cell walls.     

Bacterial volatiles and their action potential

During the past few years, an increasing awareness concerning the emission of an unexpected high number of bacterial volatiles has been registered. Humans sense, intensively and continuously, microbial volatiles that are released during food transformation and fermentation, e.g., the aroma of wine and cheese. Recent investigations have clearly demonstrated that bacteria also employ their volatiles during interactions with other organisms in order to influence populations and communities. This review summarizes the presently known bioactive compounds and lists the wide panoply of effects possessed by organisms such as fungi, plants, animals, and bacteria. Because bacteria often emit highly complex volatile mixtures, the determination of biologically relevant volatiles remains in its infancy. Part of the future goal is to unravel the structure of these volatiles and their biosynthesis. Nevertheless, bacterial volatiles represent a source for new natural compounds that are interesting for man, since they can be used, for example, to improve human health or to increase the productivity of agricultural products.     

Cellulolytic enzymes of a thermotolerantAspergillus terreus strain and their action on cellulosic substrates

A thermotolerant fungal strainAspergillus terreus produced high activities of cellulolytic enzymes when grown in shake flasks for 8 days at 40°C or 14 days at 28°C in medium containing 2.5% (w/v) cellulose powder and 1% (w/v) wheat bran. There was little difference between the final activities of endo-(1,4)--glucanase (ca. 14.4 U/ml); filter paper activity (ca. 1.3 U/ml) and -glucosidase (ca. 10 U/ml). Endoglucanase had maximum activity at 60°C and pH 3.8; the other two enzymes were optimal at 60°C and pH 4.8. The maximum hydrolysis of different cellulosic substrates (about 50%) was obtained within 48 h when 1.1 U/ml of filter paper cellulase activity were employed to saccharify 100 mg alkali-treated cotton, filter paper, bagasse, and rice straw at 50°C and pH 4.8. The major end-product, glucose, was produced from all substrates, with traces of cellobiose and other larger oligosaccharides being present in rice straw hydrolysates.     

Production and properties of xylanases from thermophilic actinomycetes

30 strains of xylanolytic thermophilic actinomycetes were isolated from composted grass and cattle manure and identified as members of the generaThermomonospora, Saccharomonospora, Microbispora, Streptomyces andActinomadura. Screening of these strains for extracellular xylanase indicated that strains ofSaccharomonospora andMicrobispora generally were poor xylanase producers (0.5–1.5 U/ml) whereas relatively high activities were observed in cultures ofStreptomyces andActionomadura (4–12 U/ml).A preliminary characterization of the enzymes of strains of the latter genera suggested that xylanases of all the strains ofActinomadura exhibited higher thermostabilities than those ofStreptomyces. To evaluate the potential of thermophilicActinomadura for industrial applications, xylanases of three strains were studied in more detail. The highest activity levels for xylanases were observed in cultures grown on xylan and wheat bran. The optimal pH and temperature for xylanase activities ranged from 6.0 to 7.0 and 70 to 80°C. The enzymes exhibited considerable thermostability at their optimum temperature. The half-lives at 75°C were in the range from 6.5 to 17h. Hydrolysis of xylan by extracellular xylanases yielded xylobiose, xylose and arabinose as principal products. Estimated by the amount of reducing sugars liberated the degree of hydrolysis was 55 to 65%. Complete utilization of xylan is presumably achieved by -xylosidase activities which could be shown to be largely cell-associated in the 3Actinomadura strains.     

Octopamine receptor subtypes and their modes of action

Octopamine receptor subclasses were first proposed to explain differences in the pharmacological profiles of a range of physiological responses to octopamine obtained in the extensor-tibiae neuromuscular preparation of the locust. Thus, OCTOPAMINE₁ receptors which inhibit an endogenous myogenic rhythm, increase intracellular calcium levels. Also OCTOPAMINE₂ receptors which modulate neuromuscular transmission in this preparation, increase the level of adenylate cyclase activity. The current status of this classification is reviewed by examining the pharmacology of responses to octopamine in a range of preparations. It is concluded that the distinction between OCTOPAMINE₁ and OCTOPAMINE₂ receptor types is still valid, but that OCTOPAMINE₂ receptors exhibit some tissue specific variations. Studies on a clonedDrosophila octopamine/tyramine (phenolamine) receptor are discussed and illustrate many of the difficulties presently encountered in making a definitive classification of octopamine receptors. These include the possibilities that single receptors may activate multiple second messenger systems and that different agonists may differentially couple the same receptor to different second messenger systems.     

Production of xylanases byAspergillus fumigatus andAspergillus oryzae on xylan-based media

Aspergillus fumigatus andA. oryzae were cultivated in laboratory fermenters on media containing xylan as the main carbon source.A. fumigatus produced xylanase on unsubstituted, insoluble beech xylan but growth and enzyme production on soluble xylo-oligosaccharides from the steaming of hardwood were poor due to the presence of inhibitors. An essential prerequisite for good xylanase production byA. fumigatus was decrease in the pH of the cultivation below 3.0 At higher pH values, the production of proteolytic enzymes caused degradation of the xylanase activity already produced.A. oryzae produced rather less xylanase activity thanA. fumigatus on the beech xylan medium but, after adaptation, was capable of efficient enzyme production on the steamed substrate.M.J. Bailey and L. Viikari are with the VTT, Biotechnical Laboratory, PO Box 202, SF-02151 Espoo, Finland     

Substrate hydrolysis by combinations of Trichoderma xylanases

The hydrolysis of five xylan substrates was examined using combinations of two pairs of xylanases from two species of Trichoderma. Antisynergy was observed in acetylated xylan isolated from aspen when the maximum hydrolysis achieved by certain xylanase combinations was significantly lower than that achieved by the most effective enzyme in the combination. Cooperative interactions among xylanases were observed in pine holocellulose where xylanase combinations were more effective than single xylanases.     

Production,isolation and partial purification of xylanases from anAspergillus sp.

AnAspergillus sp., isolated from a rubbish dump, produced 10.6 IU ml^-1 xylanase activity. Two xylanases were recognized and each was purified to homogeneity by two-stage chromatography on DEAE-and CM-Sepharose. Xylanase I had a pI of 7.2 and anM _r of 26 kDa whereas xylanase II had a pI of 4.7 and anM _r of 21 kDa. At 50°C, xylanase I was stable for 2.5 h but xylanase II was only stable for 1 h.P. Khanna is with the National Environmental Engineering Research Institute, Nehru Marg, Nagpur 440 020, India. S. Sivakami Sundari and N. Jothi Kumar are with the National Environmental Engineering Research Institute, Madras Zonal Laboratory, CSIR Madras Complex, Taramani 600 113, India.     

Multiple mode of action of the feeding deterrent,toosendanin, on the sense of taste in Pieris brassicae larvae

Toosendanin, a tetranortriterpenoid isolated from the bark of Melia toosendan, is a feeding deterrent for larvae of Pieris brassicae. By using electrophysiological techniques, it was found that toosendanin stimulates a deterrent receptor cell located in the medial maxillary sensillum styloconicum. Toosendanin also inhibits responses of both the sugar and glucosinolate receptor cell, which are localized in the lateral sensillum styloconicum. The degree of inhibition of the sugar receptor increases with increasing sucrose concentration. The glucosinolate receptor cell shows a reversed reaction: inhibition by toosendanin decreases with increasing sinigrin concentration. Inhibitory effects occur at a toosendanin concentration as low as 10^–9 M and are dose dependent. The taste neurons that respond to amino acids or deterrents in the lateral sensillum, however, are not affected by toosendanin. It is concluded that the sensory code underlying feeding behaviour is modulated by toosendanin via several different peripheral sensory mechanisms.     

Expression of the cloned xylanases from an alkalophilic,thermophilic Bacillus in Bacillus subtilis

A recombinant plasmid construct, pLPX6.5, harbouring a 6.5 kb Hind III fragment of genomic DNA, from an alkalophilic, thermophilic Bacillus NCIM 59 and coding for xylanase activity, was electroporatically transformed into Bacillus subtilis MI 111. The expression of the recombinant xylanases was confirmed by cross-reactivity with antibodies raised against purified xylanase II (M _r 15,800) from NCIM 59. However, as there were different xylan hydrolysis products from NCIM 59 and the host B. subtilis, the two xylanases appear to have different modes of action. Xylanase expression in the transformants was 6-fold higher than in the host. There was no significant enhancement in the expression of recombinant xylanases by adding xylan to the growth medium.The authors are with the Division of Biochemical Sciences, National Chemical Laboratory, Pune-411008, India     

硬化地表对不同树种土壤微生物群落结构和功能的影响

城市硬化地表可减少土壤有机物输入,并改变土壤理化性质,由此可能影响土壤微生物群落结构和功能,但目前国内外相关研究较少。为研究不同树种下土壤微生物群落对硬化地表的响应,设置透水硬化地表(Pervious pavement, P)、不透水硬化地表(Impervious pavement, IP)和自然地表(Control, C)3个处理水平的地表类型,并栽种北方常见的常绿针叶树油松(pine,Pinus tabulaeformis)和落叶阔叶树白蜡(ash,Fraxinus chinensis)。采用氯仿熏蒸浸提法、磷脂脂肪酸法(PLFA)及BIOLOG培养法分别测定了土壤微生物量、群落结构和功能多样性。结果表明:(1)与自然地表(C)相比,硬化地表下土壤微生物生物量碳、氮含量显著降低(P0.05),土壤微生物群落组成和群落功能多样性发生了改变。透水和不透水硬化地表下土壤微生物细菌、真菌数量降低,真菌/细菌(fungi/bacteria, F/B)、cy/pre(环丙基脂肪酸/前体结构cyclopropyl fatty acid/monoenoic precursors)和sat/mono(一般饱和脂肪酸/单不饱和脂肪酸normal saturated fatty acid/monounsaturated fatty acid)等环境压力指标均显著升高(P0.05),且土壤微生物cy/pre值在不透水硬化地表下显著高于透水硬化地表下,表明不透水硬化地表下土壤环境压力更大;不透水硬化地表下土壤微生物对糖类、氨基酸类、羧酸类、胺类和聚合物的利用显著降低(P0.05),微生物群落功能丰富度及多样性指数显著降低(P0.05)。(2)土壤微生物群落结构和功能多样性在不同树种间存在一定差异。油松树下土壤微生物真菌、丛枝菌根真菌(arbuscular mycorrhizal fungi, AMF)和F/B值在透水和不透水硬化地表下均显著降低(P0.05),而白蜡树下只在透水硬化地表下显著降低(P0.05);硬化地表使土壤微生物对糖类、氨基酸类和聚合物的利用强度在油松和白蜡树下表现出显著差异。硬化地表对土壤微生物的影响将进一步影响城市绿地的养分循环、树木生境和生态系统服务功能。     

Antifungal activity and mode of action of silver nano-particles on Candida albicans

In this study, the antifungal effects of silver nano-particles (nano-Ag) and their mode of action were investigated. Nano-Ag showed antifungal effects on fungi tested with low hemolytic effects against human erythrocytes. To elucidate the antifungal mode of action of nano-Ag, flow cytometry analysis, a glucose-release test, transmission electron microscopy (TEM) and the change in membrane dynamics using 1,6-diphenyl-1,3,5-hexatriene (DPH), as a plasma membrane probe, were performed with Candida albicans. The results suggest nano-Ag may exert an antifungal activity by disrupting the structure of the cell membrane and inhibiting the normal budding process due to the destruction of the membrane integrity. The present study indicates nano-Ag has considerable antifungal activity, deserving further investigation for clinical applications. K.-J. Kim and W. S. Sung contributed equally to this work and should be considered co-first authors.     

A review of zoanthid nematocyst types and their population structure

Hydrobiologia - Seven different types of nematocyst are detailed and illustrated from the Zoanthidea. We studied the size population structure of nematocyst capsules: how they are affected by...     

Production and characterization of xylanases of a Bacillus strain isolated from soil

Xylanase production was performed by growing a Bacillus isolate on agricultural by-products, wheat straw, wheat bran, corn cobs and cotton bagasse. A maximum xylanase activity of 180 U/ml was obtained together with a cellulase activity of 0.03 U/ml on 4 (w/v) corn cobs. Electrophoretic analysis showed the presence of three endo--1, 4-xylanases having molecular weights of about 22, 23 and 40 kDa. Xylanolytic activity was stable up to 50 °C in the pH range of 4.5–10 and the highest activity was observed at 70 °C and pH 6.5.     

Amino acids and sugars in nectar,and their putative evolutionary significance

Individual amino acids and sugars from flower nectar of 32 plant species with different pollination systems were quantified and compared. Data show that there is no correlation between sugar and amino acid concentration. Furthermore there is no correlation between composition and concentration of amino acids and evolutionary advancement, nor any direct relation with pollination systems. However, higher sugar concentrations are often linked with more advanced morphological characters. Nectars from pierced or damaged flowers or nectars contaminated with pollen exhibit modifications and increases in amino acid composition. The presence of proline probably indicates such pollen contamination. Most pollinating animals depend on flower nectar in their energetic requirements, yet innumerable alternative amino acid and protein sources exist. Future research has to consider the relationship between nutritional requirements of pollinating animals and dependence on flower nectars.Dedicated to Prof. Dr.L. van der Pijl, Den Haag, in honour of his 80th birthday.     

Purification and characterization of two different xylanases from the thermophilic actinomycete Microtetraspora flexuosa SIIX

Two endoxylanases were isolated from the xylanolytic enzyme system of the thermophilic actinomycete Microtetraspora flexuosa SIIX, and purified by ammonium sulfate fractionation, DEAE-Sepharose chromatography, gel filtration on Sephacryl S 200 and fast protein liquid chromatography on Q-Sepharose. The molecular masses of xylanase I and II were 26.3 and 16.8 kDa, and isoelectric points were 8.4 and 9.45, respectively. optimal enzyme activities were obtained at 80° C and pH 6.0. The thermostability of both xylanases was greatly diminished during purification but could be restored by preincubation of the purified enzymes in the presence of xylan. The half-lives at 80° C were approximately 25 min. The kinetic constants of xylanases I and II determined with Remazol-brilliant-blue xylan were V_max of 1537 and 353 mol·min^-1·mg protein^-1 and K _m values of 2.44 and 1.07 mg·ml^-1, respectively. Purified xylanases utilized xylan as well as small oligosaccharides such as xylotriose as substrate. They did not exhibit xylobiase or debranching activities. The predominant products of arabinoxylan hydrolysis were xylobiose and xylotriose, the latter being hydrolysed to xylobiose and xylose upon further incubation. In addition, fragments containing arabinose side chains accumulated. The xylanases did not act on crystalline or amorphous cellulose indicating a possible application in biobleaching processes.     

Loud calls ofGalago crassicaudatus andG. garnettii and their relation to habitat structure

Long distance vocalizations have been shown to be good indicators of genetic species in primates. Here the loud calls of two recently identified greater galago taxa —Galago crassicaudatus andG. garnettii — are compared and analyzed statistically. Observed differences in call structures are investigated further as potential indicators of differences in the structures of habitats frequented by the two species. Although the calls share a repetitive structure, and show similar dominant frequency bands (1,000 – 1,500 Hz), they differ significantly in the number of units per call, unit duration, inter-unit interval, highest frequency, lowest frequency, dominant frequency band, first harmonic, and call duration. The duration of theG. crassicaudatus call is more than twice that ofG. garnettii. Strong intraspecific consistency is seen in the most energetic frequency bands (dominant frequency band and first harmonic), and durations of the individual units and inter-unit intervals. Information important to species recognition is thus most likely to be contained in these features. Individual recognition may be encoded in the relative emphasis of higher level harmonics. The frequency structures of the calls will reflect requirements for acoustical transmission in a forest environment, as well as structural constraints imposed by body size. Higher frequencies detected in theG. garnettii call (up to 8,500 Hz) may have a functional significance related to distance estimation, or may simply be a reflection of smaller body size. The greater modulation of theG. garnettii call suggests that its habitat constitutes a denser or more turbulent medium for sound transmission than does the habitat ofG. crassicaudatus.