Multiple, novel biologically active endophytic actinomycetes isolated from upper Amazonian rainforests

Microbial biodiversity provides an increasingly important source of medically and industrially useful compounds. We have isolated 14 actinomycete species from a collection of approximately 300 plant stem samples from the upper Amazonian rainforest in Peru. All of the cultured isolates produce substances with inhibitory activity directed at a range of potential fungal and bacterial pathogens. For some organisms, this activity is very broad in spectrum while other organisms show specific activity against a limited number of organisms. Two of these organisms preferentially inhibit bacterial test organisms over eukaryotic organisms. rDNA sequence analysis indicates that these organisms are not equivalent to any other cultured deposits in GenBank. Our results provide evidence of the untapped biodiversity in the form of biologically active microbes present within the tissues of higher plants.

Synergism among volatile organic compounds resulting in increased antibiosis in Oidium sp

Oidium sp. has been recovered as an endophyte in Terminalia catappa (tropical chestnut) in Costa Rica. The volatile organic compounds (VOCs) of this organism uniquely and primarily consist of esters of propanoic acid, 2-methyl-, butanoic acid, 2-methyl-, and butanoic acid, 3-methyl-. The VOCs of Oidium sp. are slightly inhibitory to many plant pathogenic fungi. Previous work on the VOCs of Muscodor albus demonstrated that besides esters of small organic acids, a small organic acid and a naphthalene derivative were needed to obtain maximum antibiotic activity. Thus, the addition of exogenous volatile compounds such as isobutyric acid and naphthalene, 1,1'-oxybis caused a dramatic synergistic increase in the antibiotic activity of the VOCs of Oidium sp. against Pythium ultimum. In fact, at elevated concentrations, there was not only 100% inhibition of P. ultimum but killing as well. In addition, a coculture of Muscodor vitigenus (making only naphthalene) and Oidium sp. plus isobutyric acid produced an additive antibiosis effect against P. ultimum. The biological implications of multiple volatile compounds acting to bring about antibiosis in nature are discussed.

Bioactive endophytic streptomycetes from the Malay Peninsula

Three novel endophytic streptomycetes have been isolated and characterized from plants with ethnobotanical uses on the Malay Peninsula including: Thottea grandiflora (family -Aristolochiaceae), Polyalthia spp. (family -Annonaceae), and Mapania sp. (family -Cyperaceae). Each isolate, as studied by scanning electron microscopy, has small hyphae, and produces typical barrel-shaped spores arising by hyphal fragmentation. Interestingly, although none has any detectable antibacterial killing properties, each has demonstrable killing activity against one or more pathogenic fungi including organisms such as Phytophthora erythroseptica, Pythium ultimum, Sclerotinia sclerotiorum, Mycosphaerella fijiensis and Rhizoctonia solani. Molecular biological studies on the rRNA gene sequence of each isolate revealed that it is distinct from all other genetic accessions of streptomyectes in GenBank, and each bears some genetic similarity to other streptomycetes. The bioactivity of each microbe was extractable in various organic solvents.

Biologically active endophytic streptomycetes from Nothofagus spp. and other plants in Patagonia

Endophytic streptomycetes have been isolated and characterized from several species of Nothofagus and other plants growing in the southern reaches of Patagonia. No endophytic streptomycete was obtained from any plant species studied in Northern Patagonia. However, from Southern Patagonia, biologically active Streptomyces spp. from several plant species were isolated. Each isolate, as studied by scanning electron microscopy (SEM), has small hyphae, some produce typical barrel-shaped spores in culture and each has some unique hyphal surface structures. Interestingly, although none has any detectable antibacterial killing properties, each has demonstrable killing activity against one or more pathogenic fungi including representative plant pathogenic organisms such as Phytophthora erythroseptica, Pythium ultimum, Sclerotinia sclerotiorum, Mycosphaerella fijiensis, and Rhizoctonia solani. The 16S rDNA sequences of the isolates were distinct from all other genetic accessions of Streptomyces in GenBank. However, isolate C-2 from Chiliotrichum diffusum (Compositae) is identical, in all respects, to isolate C-4 obtained from Misodendrum punctulatum (Loranthaceae). These results confirm that endophytic streptomycetes represent a novel source of biologically active microorganisms.

Scanning electron microscopy of some endophytic streptomycetes in snakevine--Kennedia nigricans

Soils of all types and locations have generally served as the major sources of streptomycetous bacteria. These organisms are the source of nearly 80% of the world's antibiotics. Now, it is realized that Streptomyces spp. (within the group of prokaryotic filamentous bacteria known as actinomycetes) can exist as endophytes within the interstices of some higher plants. While it is sometimes possible to isolate one or two different streptomycetes from certain plants, most plants are free of these organisms. However, the snakevine (Kennedia nigricans) of the Northern Territory of Australia has yielded at least 39 different endophytic actinomycetes (95% of them being Streptomyces spp.) Most of these isolates possessed no detectable antibiotic properties, while at least seven had antibacterial and antifungal activities. Examination of eight selected cultures by scanning electron microscopy (SEM) as well as environmental scanning electron microcopy (FEI ESEM FEG) (FEI Company, Hillsobro, Ore., USA) revealed unusual patterns, structures, and features of the spores and hyphae of these microorganisms. For instance, as revealed by ESEM FEG for the first time, it has become obvious that extremely fine hair-like structures (average 25-49 nm with gold-coated specimens) exist on the spores and hyphae of some endophytic streptomycetes. The biological purpose of these hair-like protrusions is unknown. Both SEM and ESEM FEG can be effectively used as tools in identification and elucidation of the biology of these organisms. In addition, unusual colony morphology, observed with the unaided eye can very easily be used to distinguish some of these isolates since characteristic donut and pseudo-horn shaped colonies appeared in culture.

New endophytic isolates of Muscodor albus, a volatile-antibiotic-producing fungus

Muscodor albus, an endophytic fungus originally isolated from Cinnamomum zeylanicum, produces a mixture of volatile organic compounds (VOCs) in culture and its spectrum of antimicrobial activity is broad. Using the original isolate of M. albus as a selection tool, it has been possible to find other culturally and biochemically unique wild-type isolates of this organism existing as endophytes in a variety of other plant species, including Grevillea pterifolia (fern-leafed grevillea), Kennedia nigriscans (snake vine) and Terminalia prostrata (nanka bakarra) growing in the northern reaches of the Northern Territory of Australia. Interestingly, none of the new isolates had a culture morphology that was identical to the original isolate, nevertheless each possessed hyphal characteristics that resembled that isolate. Furthermore, their ITS-5.8S rDNA sequences were 96-99 % identical to that of M. albus and the isolates were considered M. albus on the basis of the DNA sequence data. However, the VOCs produced by these new isolates greatly differed in quality from the original strain by virtue of the production of naphthalene, naphthalene, 1,1'-oxybis-, and one or more other compounds. In bioassays with a range of test micro-organisms, including fungi and bacteria, each isolate possessed biological activity but the range of activity was great. Artificial mixtures of some of the VOCs mimicked the effects of the VOCs of the fungus. The value of these observations to the biology and practical uses of M. albus in agriculture and other applications is discussed.

Ambuic acid, a highly functionalized cyclohexenone with antifungal activity from Pestalotiopsis spp. and Monochaetia sp

Ambuic acid, a highly functionalized cyclohexenone, was isolated and characterized from Pestalotiopsis spp. and Monochaetia sp. these being biologically related endophytic fungi associated with many tropical plant species. This compound was found in representative isolates of these fungal species obtained from rainforest plants located on several continents. The relevance of ambuic acid to the biology of the association of these fungi to their host plants is also discussed.

Induction of the sexual stage of Pestalotiopsis microspora, a taxol-producing fungus

Pestalotiopsis microspora, isolate NE-32, is an endophyte of the Himalayan yew (Taxus wallichiana) that produces taxol, an important chemotherapeutic drug used in the treatment of breast and ovarian cancers. Conditions were determined to induce the perfect stage (teleomorph) of this organism in the laboratory as a critical first step to study inheritance of taxol biosynthetic genes. The perfect stage of Pestalotiopsis microspora NE-32 forms in a period of 3-6 weeks on water agarose with dried yew needles at 16-20 degrees C with 12 h of light per day. Morphological analysis of the teleomorph and sequencing of the 18S rDNA indicates that Pestalosphaeria hansenii is the perfect stage of Pestalotiopsis microspora. Only certain plants (e.g. yews, some pines, pecan, oat and some barley cultivars) allow the production of perithecia. Exhaustive methylene chloride extraction of yew (Taxus cuspidata) needles removes their capacity to induce production of perithecia. The methylene chloride extract is able to induce formation of perithecia by strain NE-32 in a bioassay system utilizing the sterilized sheaths of the Cholla cactus (Opuntia bigelovii) spine, indicating that a chemical compound(s) in yew stimulates the formation of the perfect stage. This hydrophobic plant compound(s) has been designated the perithecial-stimulating factor (PSF). The data suggest that plant products may play a role in regulating the biology of endophytic microbes.

Oocydin A, a chlorinated macrocyclic lactone with potent anti-oomycete activity from Serratia marcescens

A unique chlorinated macrocyclic lactone, termed oocydin A, was isolated from a strain of Serratia marcescens growing as an epiphyte on Rhyncholacis pedicillata, an aquatic plant native to the Carrao river of the Venezuelan-Guyanan region of South America. The lactone has a molecular mass of 470 Da, and contains one atom of chlorine, a carboxyl group and a tetrahydrofuran ring internal to a larger macrocyclic ring. MICs of approximately 0.03 microg ml(-1) were noted for oocydin A against such phytopathogenic oomycetes as Pythium ultimum, Phytophthora parasitica, Phytophthora cinnamomi and Phytophthora citrophora. With regard to the true fungi, oocydin A had either minimal or no effect against certain Fungi Imperfecti (including several pathogens of humans), two ascomycetes and a basidiomycete. Oocydin A may have potential as an antimycotic in agricultural applications and especially for crop protection.

Seimatoantlerium tepuiense gen. nov., a unique epiphytic fungus producing taxol from the Venezuelan Guyana

Seimatoantlerium gen. nov., type species, S. tepuiense sp. nov. is proposed for an acervular fungus producing 4-septate, holoblastic conidia with 6-8 unbranched, apical appendages that dehisce as an appendage apparatus and also commonly possessing one or two exogenous basal appendages as well as a pedicel. It is compared with Seimatosporium, Seimatosporiopsis, and other genera. It is epiphytic on Maguireothamnus speciosus, a rubiaceous plant endemic to the tepuis of southeastern Venezuela. It produces the anti-oomycetous anticancer compound, taxol, as shown by immunological and spectroscopic methods. Taxol production is discussed relative to the ability of this fungus to exist in an extremely moist ecosystem, as well as to its relationship to other plant associated fungi.

Cryptocandin, a potent antimycotic from the endophytic fungus Cryptosporiopsis cf. quercina

A unique lipopeptide antimycotic, termed cryptocandin, is described from Cryptosporiopsis cf. quercina, an endophytic fungus. Cryptocandin, with a molecular mass of 1079 Da, contains equimolar amounts of 3,4-dihydroxyhomotyrosine, 4-hydroxyproline, threonine, glutamine, 3-hydroxy-4-hydroxymethylproline, 4,5-dihydroxyornithine and palmitic acid. Cryptocandin is chemically related to well-known antimycotics, the echinocandins and pneumocandins, which are produced by such fungi as Zalerion arboricola, Pezicula spp. and Aspergillus spp. Cryptocandin has minimal inhibitory concentration values of 0.03-0.07 microgram ml-1 against isolates of Candida albicans, Trichophyton mentagrophytes and Trichophyton rubrum. Cryptocandin is also active against a number of plant-pathogenic fungi including Sclerotinia sclerotiorum and Botrytis cinerea.

A scanning electron microscopy study of Taxus leaves as related to taxonomy

Scanning electron microscopy, when applied to the surfaces of the needles of Taxus spp. (yew) revealed features that appear useful in the taxonomy of this tree species which yields the important anticancer drug, taxol. For instance, all of the four North American species have 3-5 rows of stomata on one-half of the abaxial leaf surface, whereas all of the others, including those from Europe and Asia, have 7-10 rows of stomata. The appearance of individual or fused papilliform epidermal cells and their arrangement on the leaf surface also is a feature that varies between species. Patterns of wax formation appeared on all species of yew examined but none could characteristically be assigned to a given species. Wax pattern variation was dependent upon age, environment, and probably to some extent, species differences. This study may provide some additional useful and reliable indicators in Taxus taxonomy.

Glucosylation of the peptide leucinostatin A, produced by an endophytic fungus of European yew, may protect the host from leucinostatin toxicity

BACKGROUND

Yew species (Taxus spp.) throughout the world are hosts to hundreds, or perhaps thousands, of endophytic organisms. Most commonly, these organisms are fungi, living in a commensal or a symbiotic relationship with their host plant, so the plants exhibit little or no outward evidence that they are supporting these microorganisms. Little is known about any of the biochemical mechanisms that mediate the interactions between the yew host and its associated microbes. We feel that such information may not only contribute to our understanding of endophyte-tree biology, but also may provide novel pharmaceutical leads, because some of the compounds produced by these endophytes have demonstrated pharmacological activities.

RESULTS

Acremonium sp. was isolated as an endophytic fungus of the European yew, Taxus baccata. Entry of Acremonium sp. into the plant may proceed via invasion of natural openings such as stomata. The relationship between Acremonium sp. and T. baccata may be a symbiotic one, because no symptoms are seen when Taxus media p.v. Hicksii is inoculated with this fungus. In culture, the fungus makes leucinostatin A, a peptide with phytotoxic, anticancer and antifungal properties. Although this peptide causes necrotic symptoms in many non-host plants and other cell types, it causes no visible symptoms in the host plant. T. baccata and several other plants have a UDP glucose; leucinostatin A glucosyl transferase that catalyzes the production of leucinostatin A beta di-O-glucoside from leucinostatin A. This glucoside, also made by the fungus, has a lower bioactivity against plants, fungi and a breast cancer cell line, BT-20, than leucinostatin A.

CONCLUSIONS

Leucinostatin A may be one of several potentially toxic peptides produced by Acremonium sp. that contribute to the defense of the host, thereby preserving the fungus' own biological niche. The host plant is relatively immune to leucinostatin A because it has an enzyme which transfers two glycosyl residues to leucinostatin A, markedly reducing the peptide's bioactivity. Our results suggest that glucosylation reactions may play a more general role in plant defenses, especially against toxin-mediated disease development.

Endophytic taxol-producing fungi from bald cypress, Taxodium distichum

Pestalotiopsis microspora occurs as a range of strains in bald cypress, Taxodium distichum. The organisms live as endophytes in the bark, phloem and xylem, and isolates show differences in cultural and microscopic characteristics on common laboratory media. Many of these fungi make taxol as determined by the reactivity of partially purified culture extracts with specific monoclonal antibodies against taxol. In the case of one strain of P. microspora (CP-4), taxol was isolated from culture medium and was shown to be identical to authentic taxol by chromatographic and spectroscopic means.

Taxol from Pestalotiopsis microspora, an endophytic fungus of Taxus wallachiana

Pestalotiopsis microspora was isolated from the inner bark of a small limb of Himalayan yew, Taxus wallachiana, and was shown to produce taxol in mycelial culture. Taxol was identified by spectroscopic and chromatographic comparisons with authentic taxol. Optimal taxol production occurred after 2-3 weeks in still culture at 23 degrees C. [14C]Acetate and [14C]phenylalanine served as precursors for fungal [14C]taxol. These observations on P. microspora are discussed in relation to the biological importance of taxol production by fungi in general.

Carbon-Black-Elastomer Interaction II: Effects of Carbon Black Surface Activity and Loading

Carbon black morphology, surface activity and loading have been varied systematically to study the effects on an SBR formulation. The surface activity of five commercial grades of carbon black was varied by heat treating the standard grade samples at 1100°C and 1500°C in an inert atmosphere. Measurements on carbon black-elastomer interaction were based on a parameter I, defined elsewhere. The parameter I exhibited the previously reported correlation with known indicators of the surface activity of carbon blacks. The heats of adsorption by inverse gas chromatography at infinite dilution have been found useful as a measure of the carbon-black surface energy related to rubber interaction. These measurements have been employed in conjunction with carbon-black morphology and loading to develop a surface-area-modified and a surface energy-modified effective volume fraction V′ and ψ, respectively. The parameter V′ was utilized to explain the variation of the dynamic elastic modulus E′ at 1 % double strain amplitude (DSA) for all rubber compounds. The parameter ψ was used to explain the variation of E′ at 25% DSA and the factor σ in the calculation of I. The parameters V′ and ψ provide a model for the estimation of I from fundamental carbon-black morphological properties and surface energy.

Characterization of Immiscible Elastomer Blends

Considerable improvements have been made in the analysis of elastomer blends for composition, morphology and filler inter-phase distribution. GC, IR, NMR and thermal analysis (DTG, DSC, TG) techniques can provide quantitative information on composition. The latter three methods, along with SAXS, SANS, DMTA and microscopy (LM phase contrast, TEM, SEM, AFM) are also useful for resolving differences in blend homogeneity. The microscopical techniques are the most useful for characterizing morphology. TEM, in conjunction with cryosectioning and staining techniques, has provided the best means of resolving filler distribution to date. However, new AFM scanning modes may provide improved analyses in the future. Carbon black inter-phase distribution in blends of NR, SBR and BR can be controlled reasonably well by blending Banbury mixed masterbatches containing the desired carbon black loading in each polymer. Transfer of carbon black from one elastomer to another is favored by low unsaturation for the polymer originally containing the black, or a low heat history (e.g. solution and latex mixing) during preparation of the masterbatch. The overall polymer interaction with carbon black increases in the order: IIR, EPDM, NR, BR, SBR, the latter two being fairly close. Commercial carbon blacks will transfer extensively from an IIR Banbury masterbatch to NR, but not from EPDM to NR. Significant transfer to SBR occurs from both IIR and EPDM. Inert (partially graphitized) carbon blacks tend to distribute more evenly between the blend components regardless of which polymer contained them initially. Carbon black phase distributional variations can cause significant changes in unvulcanized and vulcanized rubber properties. For NR/BR and NR/SBR blends, reduced hysteresis generally occurs with a higher carbon black loading in the NR phase. Tear strength and cut growth tend to be maximized with higher carbon black in the continuous polymer phase, particularly when that phase is the higher strength polymer. The smaller the carbon black particle size, the greater the improvement in tear strength as a function of phase distribution. NR/BR fatigue life was maximized with about an equal distribution of carbon black in each polymer. This type of carbon black distribution also produced the greatest resistance to ozone cracking for NR/EPDM blends, which were further improved with very small domain size for the EPDM (disperse) phase. The abrasion resistance of NR/BR blends has indicated some improvement in the direction of higher carbon black in the BR. These results have been variable, however, and further study is needed for clarification.

Characterization of Dispersions

The methods of pigment dispersion analysis have been reviewed in regard to their application to rubber, plastics, and other vehicle systems. The characteristics of dispersions have been divided into three categories: (1) agglomeration (2) microdispersion (networking) and (3) polymer-phase distribution. Stylus roughness measurements on cut surfaces offer the combination of simplicity and speed of operation with high accuracy and precision for measuring pigment agglomeration in elastomer systems of known composition. This method may also be applied to the surface of thin plastic extrudates. However, optical analyses of thin cryosections are preferred for most plastics or unknown rubber compounds containing high loadings of carbon black. X-radiography is generally preferable for the analysis of inorganic agglomeration in most polymeric vehicle systems. The scanning electron microscope is also applicable for this type of analysis and has the added capability of identifying unknown agglomerates by energy dispersive x-ray analysis. Automated image-analysis techniques may also be utilized in conjunction with microscopical methods for quantifying the agglomeration of most types of pigments. For carbon blacks, the most suitable materials for on-line image analyses with transmitted light are plastics, paints, and inks which contain low black loadings. Higher carbon-black loadings in rubber can be analyzed by incident light using metallographic polishing of sulfur-hardened specimens. The microdispersion of carbon blacks at the primary aggregate level can be measured by means of electrical conductivity. This method is not applicable to inorganic pigments, large-particle-size carbon blacks, or blacks at very high or low loadings. Pigment microdispersion in different vehicle systems may also be assessed by means of scanning electron microscopy of thick cross sections (plasma etched to enhance contrast) or by transmission electron microscopy of thin cryosections. The tendency for the finer pigments to form 3-dimensional network structures in elastomers may also be measured as a function of the augmentation of dynamic modulus from high to low strain amplitudes. Pigment phase distribution in elastomer blends may be studied by scanning electron microscopy or transmission electron microscopy of thin cryosections, in conjunction with a staining or etching procedure to produce contrast between the separate polymer components. Selective staining is applicable to blends of polymers which differ significantly in their relative levels of unsaturation (e.g., NR/CIIR). Pyrolytic etching (under vacuum) may be used to produce interzone contrast in blends of polymers which differ significantly in their resistance to thermal degradation (e.g., NR/BR, NR/SBR). Pyrolysis GC may be utilized to determine the amount of carbon black in the separate phases of certain elastomer blends. This method is based on the relative intensity of the primary GC peaks for the individual polymers. The chromatographs are obtained from the bound rubber (carbon-polymer gel) that is developed during the mixing of the compound.

Carbon-Black-Elastomer Interaction

A number of different techniques were applied to measure carbon-black-surface reactivity and the level of black-polymer interaction in four different elastomer systems (SBR, IIR, NR, and NBR) representing differences in unsaturation, crystallinity and polarity. Known within-grade surface activity variations were based on partial graphitization of an N121-type carbon black. The surface activity of different black grades was studied as a function of variations in both surface area and DBPA. Direct measurements of carbon-black-surface reactivity were based on hydrogen analysis, SIMS, IGC, and moisture adsorption. In-rubber measurements included bound rubber, SIMS of cut surfaces, and an interaction parameter, σ/η, which is derived from the slope (σ) of the stress-strain curve at low elongations, and (η), the ratio of dynamic modulus (E′) at 1% and 25% DSA. The following trends were observed: 1. The σ/η values provided a good measure of black-polymer interaction in all four polymer systems for either the within-grade or across-grade comparisons. 2. Higher σ/η values were indicated for SBR and NBR, followed by NR and IIR in that order. 3. SBR indicated the greatest sensitivity for bound-rubber measurements in terms of distinguishing within-grade variations in black-polymer interaction, followed by IIR, NR, and NBR in that order. 4. Positive SIMS on dry carbon black indicates the presence of complex hydrocarbon structures suitable for chemical reactivity at the carbon-black surface. 5. SIMS analyses on the dry carbon blacks exhibited intensity variations in the negative hydrocarbon fragments which were in line with the within-grade variations in hydrogen content. 6. SIMS analyses on the cut-rubber compound surfaces showed overall variations in intensity which were proportional to the range and level of the bound-rubber measurements. The most meaningful variations were recorded for SBR and IIR. 7. Heats of adsorption derived from IGC measurements with different adsorbates showed an excellent correlation with black-polymer interaction for the within-grade studies. Measurements across grades did not correlate as well with the in-rubber measurements, but the best results were obtained using styrene as the adsorbate. 8. The within-grade moisture adsorption measurements showed excellent agreement with IGC and the other techniques for the N121 series of heat-treated carbon blacks.

New Studies on the Surface Properties of Carbon Blacks

A series of carbon blacks of widely varying morphology and microstructure were analyzed for surface compositional properties employing SIMS, XPS/ESCA, and GC-MS. These studies were supported by bulk analyses for hydrogen and oxygen content. Surface reactivity was assessed by means of inverse gas chromatography, moisture adsorption, and oxidation in an oxygen plasma. To directly assess carbon-black-polymer interaction, the carbon blacks were evaluated in SBR and IIR compounds for stress-strain and dynamic properties as well as bound rubber. The major findings of these studies are: 1. The combined results of hydrogen content, SIMS, and pyrolysis-GC-MS suggest a complex hydrogen functionality at the carbon-black surface, which governs the level of interaction with elastomers. 2. SIMS analyses have shown that the hydrogen functionality at the carbon-black surface is preserved after an 1173 K heat treatment in an inert atmosphere. 3. Gas-solid chromatography results indicate that this technique may be very useful to determine the degree of heterogeneity of a carbon-black surface. It also provides a tool to characterize the nature of the surface sites which are responsible for such a heterogeneity. 4. Moisture-adsorption rates provides a means to explore the reactivity of carbon-black-surface sites. Initial rates of adsorption can be well explained by a second-order-rate mechanism. 5. Bound-rubber development (SBR) and oxygen content per square meter of carbon-black-surface area were directly proportional to the hydrogen content of the black. The hydrogen content is considered to be the primary compositional factor relating to carbon-black-surface activity, while bound rubber and oxygen levels are specific measures of surface reactivity. 6. The slope of the stress-strain curves (or the modulus value) in the λ=1 to 3 region divided by the black networking factor, η (E′ at 2% ptp ÷ at 25% ptp), is sensitive to changes in black-polymer interaction. This ratio (σ/η or M/η) shows an excellent correlation with black hydrogen content and bound rubber (SBR). 7. The σ/η values for SBR and IIR are highly correlated, although the values for SBR are two to three times higher, and there was no measurable bound rubber for any of the IIR compounds. 8. The σ/η values for IIR (λ=2−3) and the oxygen/m2 values were found to be the best discriminators for black-polymer interaction in explaining within-grade treadwear variations in SBR/BR multisection radial-passenger treads.

Human hair morphology: a scanning electron microscopy study on a male Caucasoid and a computerized classification of regional differences

The present study was performed to provide a better understanding of the morphological variations of mammalian hair. Terminal hair samples were obtained from different regions of the body of the same Caucasian male. All hair samples were either cleaned or treated before being examined with scanning electron microscopy. As human scalp hair grew it appeared small like lanugo hair, but the increase in diameter appeared to have been relatively rapid. As hair increased in diameter the appearance of the scales changed. Neck hair was slightly smaller in diameter than scalp hair, and axillary hair was slightly smaller in diameter than neck hair. Nostril hair was larger than scalp or axillary hair. Eyelash hair was much smaller and much shorter than eyebrow hair. Neck hair, forearm hair, and shin hair were smaller than hair from most other regions of the body. Chest hair was similar in size to scalp hair, and pubic and sideburn hair were larger than scalp hair. A morphological feature called "steak-boning" was more characteristically present in whiskers of Caucasoids than Orientals or Blacks. "Steak-boning" occurred most frequently in hair of the mustache, followed by that of the chin, sideburn, cheek and under the chin. Cut surfaces of whiskers were different for electric as compared with straightedge razors. Hair morphology varied relative to the body region. Computer analysis of resin-embedded hair made it possible to classify arm, mustache, cheek, chin, head, shin, and pubic hair, and to quantify cross-sectioned differences.

Growth and sporulation of the dikaryons of the dwarf bunt fungus in wheat plants and in culture

In the wheat plants infected with dwarf bunt, sporulation occurs only in developing kernels. The dikaryon was isolated from infected kernels and from the rachis of infected spikes. The development of pathogenic hyphae and teliosporogenesis in vivo and in vitro is described. Ultrastructural studies indicated that in vivo teliospore primordia detach from sporogenous hyphae in the hymenium layer and develop into mature teliospores. Teliospores were borne terminally on sporogenous hyphae in vitro. Substances that stimulate hyphal branching and inhibit teliospore formation of the dikaryon were isolated from vegetative wheat tissues but not from bunt-infected spikes containing the sporulating dikaryon. The dikaryon resumed sporulation only when transferred to rich nutrient media without extracts. Extracts from infected wheat spikes containing the sporulating dikaryon induced the vegetative dikaryon to sporulate. The bioregulators involved in these phenomena were not identified. Bioactive extracts had no apparent effect on the growth of the monokaryon. A fluorochrome, mithramycin, was used to detect nuclei in monokaryotic and dikaryotic hyphae. New approaches to bunt control are discussed. Key words: Tilletia caries, Tilletia controversa, monokaryon, teliospores, bioregulators.

Carbon Black in NR/BR Blends for Truck Tires

A series of ten commercial tread-grade carbon blacks were evaluated in a 60/40 NR/BR truck tire tread formulation. A number of important physical properties and performance criteria were assessed in terms of carbon black surface area and DBPA. Significant response equations were obtained for viscosity, bound rubber, resilience, heat buildup, tear strength, and dynamic properties. Dynamic modulus showed a much greater dependence on DBPA in comparison to previous studies on SBR/BR compounds. In a second designed experiment, a single carbon black (N299) was studied as a function of the NR/BR ratio and the amount of carbon black added to the BR phase. The BR black loading was varied at 30, 60, and 90 phr using separate masterbatches which were blended with NR-black masterbatches to give the same final composition for all of the compounds. Properties such as resilience, heat buildup, fatigue life, and tear strength were all improved in the direction of higher loadings of carbon black in the NR phase. A high loading of black in the BR phase caused low bound-rubber development and poor dispersion. This was found to be related to the viscosity ratio of the separate masterbatches. NR to BR viscosity ratios of about 1 to 3 produced good dispersion and high bound rubber. When the BR masterbatch viscosity was two to three times higher than the NR masterbatch, however, dispersion and bound-rubber development dropped sharply at the same total mixing energy. Low hysteresis properties were found to be most dependent on high bound-rubber development, with polymer phase distribution having a relatively minor influence. In contrast, tear strength and fatigue life reached their maximum levels when the NR was the more continuous polymer phase. High bound rubber also appears to enhance tear strength and fatigue life by improving the microdispersion of the carbon black.

The Influence of Carbon Black, Mixing, and Compounding Variables on Dispersion

A series of response equations relating dispersion and rubber properties to mixing and compounding variables have been developed for formulations based on SBR and EPDM. These provide insight on the relationship of dispersion to rubber performance as carbon black type and loading are widely varied. Optimum conditions have been defined for minimizing Banbury mixing time and power consumption to achieve acceptable dispersion for different grades of carbon black. The different blacks can be classified in terms of their relative tendency to be shear-stress or shear-strain sensitive. The finer, low-DBPA carbon blacks such as N326 are shear-stress sensitive. To achieve high dispersion levels, this type of black requires initially high compound viscosities, i.e., by means of high loadings, withholding all or part of the extender oil until after black incorporation, or by high black/oil ratios. The coarser, high-DBPA carbon blacks such as N650 are more shear-strain dependent and will reach high dispersion levels if enough energy (usually relatively low) is imparted to the batch during Banbury mixing. N650 consistently gave high dispersion levels over a wide range of black/oil levels, regardless of the polymer type or mixing variables. Carbon black dispersibility in SBR-1500 was improved in the direction of increasing DBPA and decreasing surface area. The surface area response was most pronounced when loose oil was added with the black. High oil with the carbon black tends to form harder, more persistent agglomerates which have a greater depressing effect on rubber strength properties such as tensile and fatigue. The effect of carbon black surface area on dispersion was considerably less in SBR-1712 with no loose oil addition. In EPDM, upside-down mixes of different grades of black at varied black/oil loadings produced some notable changes in the dispersion response to carbon black DBPA. At some of the high black/oil ratios, low DBPA was actually beneficial to dispersion. The finer, higher-DBPA blacks such as N351 showed a tendency to form more persistent agglomerates analogous to conventional SBR-1500 mixes in which high amounts of loose oil are added with low-DBPA blacks. These persistent agglomerates are most prone to form in an EPDM upside-down mix when the oil loading is close to the absorptive capacity of the carbon black. The Banbury power profiles of such compounds indicated a high initial peak and a depressed or missing second peak. A normal power profile and a high level of dispersion were achieved with these problem mixes when 25 to 50% of the oil was withheld until after black incorporation. N650 gave excellent dispersion in EPDM at all black/oil loadings and only minimal variations in vulcanizate properties were observed at mixing times ranging from 1 to 5 min.

Role of pit membranes in macromolecule-induced wilt of plants

Macromolecules present in low concentrations in xylem fluid of Medicago sativa L. var DuPuits will increase the resistance to xylem liquid flow. This increase in resistance was found to be reversible by backflushing the xylem. Autoradiography showed that very large molecules do not pass through pit membrane pores. A comparison of pit membrane pore sizes to molecule sizes suggests that increased resistance to xylem flow is a result of plugging pit membrane pores. It was also found that pit membranes located in two parts of the plant differ in the apparent diameter of their pores and, thus, in their susceptibility to plugging by macromolecules. Macromolecules in xylem fluid may result from hostparasite interactions and may play a significant role in the outcome of the interaction.

Improved Particle Size Measurements on Pigments for Rubber

High shear mixes of carbon black and many other pigments in a cellulose acetate butyrate paint chip formulation have provided superior specimens for analysis by automated electron microscope image analysis. Specimens prepared from these mixes exhibit reduced aggregation and improved dispersion. Testing accuracy, precision, and sampling are significantly improved in comparison to previous techniques. The CAB method is applicable to carbon blacks, silica, precipitated calcium carbonate, red iron oxide, titanium dioxide, and any rubber grade pigment that is composed of stable particles that are reasonably isotropic in nature. Certain ground pigments or those containing highly anisotropic particles may give erroneous results due to breakage (e.g., clay, acicular zinc oxide). An improved particle size analysis program for automated electron microscope image analysis was developed. This utilizes a self-determining factor to correct for particle aggregation. The method provided good grade classification for a broad range of carbon blacks in CAB and is also suitable for screening blacks in the dry state or extracted from rubber.

The Effects of Carbon Black and Other Compounding Variables on Tire Rolling Resistance and Traction

The rolling resistance of SBR/BR radial passenger tire treads was varied as a function of carbon black type and loading, as well as other compounding variables, such as oil content, high-viscosity oil and resin addition, and NR substitution. In all instances, the rolling loss variations showed a good correlation with either tan δ or resilience. The tan δ response was valid for a wide range of test temperatures, frequencies, and strain amplitudes. Wet (32 km/h) and dry (64 km/h) traction indicated a high positive correlation with loss compliance (D″). Here, the best correlations were obtained at lower dynamic testing temperatures (0–25°C.) and higher strain amplitudes. High-speed wet traction (97 km/h) appeared to be relatively independent of the tread compounding variables but did show a slight correlation with tan δ measured at ™25°C. The following patterns were observed relative to tread rolling resistance, traction, and wear as a function of compounding variables: 1. Black loading.—Reduced black loading lowers rolling resistance without much effect on traction. About 4% less black in the tread compound lowers rolling resistance by about 5–6% in the formulations which were evaluated. 2. Oil loading.—At a fixed black level, increased oil raises both rolling resistance and traction. About 2% higher rolling resistance was found for a 10 phr increase in oil loading, but the effect on wet traction appeared to be much greater (7–8%). 3. Black type.—Increasing black fineness raises both rolling resistance and traction, the latter effect being considerably less. Increased DBPA has very little effect on rolling resistance but reduces traction. At reduced black loadings, the finer and higher DBPA blacks show the least loss in treadwear resistance. Blacks with broad aggregate size distribution give lower rolling resistance at the same surface area and DBPA. For extreme blends (carcass and tread grades), however, the loss in treadwear resistance is quite severe (∼30%). 4. Curatives.—Increased sulfur and accelerator levels produced a significant reduction in tan δ, with a similar but lesser drop in D″. The same reduction in tan δ with increased accelerator (OBTS) level produced less effect on D″ than the sulfur increase. 5. Natural rubber substitution.—Compounds in which 30 phr of NR were substituted for 25 phr of SBR and 5 phr of BR indicated slightly better performance in terms of both rolling resistance and traction. 6. High-viscosity oil or resin substitution.—Replacing conventional extender oil with high-viscosity oil or resin appears to improve traction but has a greater adverse effect on rolling resistance. 7. Compound optimization.—N299 black gives the best overall balance of performance in terms of rolling resistance, traction, and treadwear at reduced black loadings. N121 confers about 10% better treadwear and equal traction in the same compound, but at about 4% higher rolling resistance.

Development and nature of the partition layer in Tilletia caries teliospore walls

Developing Tilletia caries teliospores were studied with thin sectioning procedures. After the W1 and W2 spore walls are formed, lamellar material begins to form adjacent to the W2 wall layer. The patches of lamellar material become continuous, and additional layers are added. After the W3 wall starts to form, the lamellar material is difficult to see without special staining. The lamellar material makes it difficult to get resins to penetrate the partition layer of teliospore walls.

Surface rodlets of Tilletia indica teliospores

Tilletia indica teliospores were studied by use of thin sections and freeze-etch replicas. Surfaces of these spores have rodlet patterns which differ from those previously reported for spores of other fungi. The rodlets on T. indica teliospores average 240 nm in length and are not grouped into fascicles.

Measurement of Carbon Black Dispersion in Rubber by Surface Analysis

A stylus-type surface roughness tester has been applied to the study of carbon black dispersion in a number of different rubber systems. The method is based on a freshly cut rubber surface which is tracked by the stylus to provide a roughness trace on a strip chart. Carbon black agglomerates deflect the cut path because of their higher hardness relative to the surrounding matrix. Thus, surface roughness diminishes at increasing levels of dispersion. A quantitative index of dispersion quality may be derived from the frequency and average height of the roughness peaks. The method offers a distinct advantage over previous methods in its ability to provide precise dispersion ratings over a very wide range of rubber processing levels from the masterbatch to the final product. The technique is applicable to the analysis of unvulcanized rubber compounds and could be utilized as a factory quality control procedure. Direct interfacing of the surface analyzer to a programmable calculator would provide quantitative dispersion ratings within five minutes of the receipt of a sample. Studies of varied carbon black dispersions in SBR and SBR/BR passenger tread formulations have confirmed the work of previous authors. Tensile strength, fatigue life, resilience, elongation, and extrusion shrinkage increased at higher dispersion levels, while Mooney viscosity, Shore hardness and heat buildup exhibited a progressive decrease. The properties of a 50/50 NR/BR truck tread formulation showed a more varied response to black dispersion. Tensile strength and resilience showed considerably less dispersion dependence than SBR and SBR/BR. However, the tensile response increases with increasing black fineness and decreasing structure, while resilience showed the opposite trend. Fatigue life and heat buildup showed the same trends observed for SBR and SBR/BR. However, NR/BR treadwear (radial tires) showed considerably less dependence on dispersion above the 70% level, in comparison to those other polymers (bias ply tires). NR/BR with N220 at a dispersion index of 68 gave treadwear resistance that was equivalent to the same compound at a dispersion index of 89. However, dispersion indices of 50 or lower caused severely depressed treadwear resistance for the different blacks that were tested. The milling of NR/BR masterbatches cooled overnight produced significantly higher dispersion levels in comparison to hot batches at the same total mixing energy. This procedure can be employed to optimize treadwear and other properties at lower levels of energy consumption.

Carbon Black Morphology in Rubber

Electron microscope image analysis of carbon blacks in specific rubber compounds has greatly expanded the range of useful applications for studies of this type. This dispersed carbon-gel procedure has improved the sampling and test precision at operating speeds that are now reasonably comparable to the simple colloidal procedures for characterizing carbon black. Improved models have been developed for deriving black surface area and intraunit occlusion capacity. The EM image analysis approach has been useful in applying certain principles of reinforcement theory, as well as in explaining rubber property differences that are attributable to carbon black variables. Studies on hysteresis at constant strain (E″) have indicated that the important black variables, in diminishing order of significance, are loading, structure (intraunit occlusion and anisometry), unit size, unit size distribution, and surface activity. For hysteresis at constant energy (resilience), the most important black variables appear to be black loading, unit size, unit size distribution, surface activity, and structure. In terms of tread wear resistance (moderate wear rates with SBR-BR), a somewhat different pattern of carbon black variables is apparent. At constant loading, the most important black properties appear to be specific surface area, surface activity, structure, and unit size distribution. At any given tread wear-surface area level, hysteresis can be lowered by broadening the unit size distribution and increasing the surface activity of the black.