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1.
Two strains of X. campestris from a collection and a wild strain isolated from infected cabbage were cultured in a defined medium in a 25 dm3 fermenter. The rheological characteristics of the broth were measured using a Weissenberg rheogoniometer. The rheological behaviour over a wide range of shear rates could be described with the power law model and a yield stress was obtained using the Herschel-Bulkley equation. As expected, the broth's flow behaviour is highly influenced by gum concentration. In general, the rheological parameters during the fermentations varied within the following ranges: K (2–210 dyn-sn/cm2), n (0.2–0.9), τ y (0.02–50 dyn/ cm2), with strain 1459 reaching the maximum values as well as the highest gum concentration. Differences in flow behaviour could be associated with different molecular configurations of the polymers produced by the different strains. Heat treatment of the broths change the rheological characteristics, increasing K and decreasing n. Reconstituted solutions of all sterilized gums exhibited similar rheological characteristics and, at low concentrations, also similar to those of a commercial xanthan. 相似文献
2.
The invasion kinetics ofhobo transposable element in theDrosophila melanogaster genome was studied byin situ hybridization on the polytene chromosomes. Six independent lines ofDrosophila melanogaster flies that had been previously transformed by microinjection of the pHFL1 plasmid containing a completehobo element were followed over 50 generations. We observed thathobo elements were scattered on each of the chromosome arms, with more insertion sites on the 3R arm. The total number of insertion sites remains quite small, between four and six, at generation 52. On the 2R arm, a short inversion appeared once at generation 52. Most of the integration sites reported here were already described for several transposons but some of them appear to be hotspots forhobo elements. 相似文献
3.
For several species of lepidoptera, most of the approximately 350-bp
mitochondrial control-region sequences were determined. Six of these
species are in one genus, Jalmenus; are closely related; and are believed
to have undergone recent rapid speciation. Recent speciation was supported
by the observation of low interspecific sequence divergence. Thus, no
useful phylogeny could be constructed for the genus. Despite a surprising
conservation of control-region length, there was little conservation of
primary sequences either among the three lepidopteran genera or between
lepidoptera and Drosophila. Analysis of secondary structure indicated only
one possible feature in common--inferred stem loops with higher-than-random
folding energies-- although the positions of the structures in different
species were unrelated to regions of primary sequence similarity. We
suggest that the conserved, short length of control regions is related to
the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In
addition, determination of flanking sequences for one Jalmenus species
indicated (i) only weak support for the available model of insect 12S rRNA
structure and (ii) that tRNA translocation is a frequent event in the
evolution of insect mitochondrial genomes.
相似文献
4.
Sa´nchez A. Rami´rez M.E. Torres L.G. Galindo E. 《World journal of microbiology & biotechnology》1997,13(4):443-451
Seventeen wild-type Xanthomonas isolates were screened in terms of broth viscosity in shake-flasks. As culture conditions affect polymer characteristics, a fair comparison among isolates required their cultivation in a fermenter under controlled dissolved oxygen tension. Three isolates and a reference strain were studied. The mean molecular weights and molecular weight distributions of their xanthans were determined. Products showed different pyruvate (0.2–7%), acetate (5–10%) and proteinaceous nitrogen (1–3%) contents. The selected isolates exhibit properties which could improve xanthan gum production and some could be used to produce polymers with specific characteristics. 相似文献
5.
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 (Pomin) occurred at Re = 30–40, then increasing to a plateau value which was evident at Re> 200. In the transition region Pomin 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 相似文献
6.
7.
C. Flores C. Vidal M.R. Trejo-Hernández E. Galindo L. Serrano-Carreón 《Journal of applied microbiology》2009,106(1):249-257
Aims: To select Trichoderma strains for enhanced laccase production in Pleurotus ostreatus or Agaricus bisporus cultures.
Methods and Results: Laccase production by P. ostreatus and A. bisporus was evaluated in liquid (axenic) and solid (dual cultures) malt extract medium. Oxidation of ABTS, DMP and syringaldazine was evaluated in order to assess the potential of Trichoderma strains to enhance laccase production by basidiomycetes. Selected Pleurotus–Trichoderma interactions yielded higher increases in laccase volumetric activity and an additional laccase isoform was produced. By contrast, Agaricus–Trichoderma interactions lead to smaller increases on laccase volumetric activity, probably as result of repression (or degradation) towards one of the laccases isoforms.
Conclusions: The strains of P. ostreatus and A. bisporus assessed in this work showed good potential as laccase producers. The Trichoderma -mediated biological stimulation of laccase production by P. ostreatus and A. bisporus is relevant in order to develop highly productive processes.
Significance and Impact of the Study: Extracellular laccases from basidiomycetes are produced only in small amounts. It is therefore important to increase process productivity for potential industrial applications. The results from this study enable the selection Trichoderma strains capable of increasing laccase production by P. ostreatus or A. bisporus in dual cultures. 相似文献
Methods and Results: Laccase production by P. ostreatus and A. bisporus was evaluated in liquid (axenic) and solid (dual cultures) malt extract medium. Oxidation of ABTS, DMP and syringaldazine was evaluated in order to assess the potential of Trichoderma strains to enhance laccase production by basidiomycetes. Selected Pleurotus–Trichoderma interactions yielded higher increases in laccase volumetric activity and an additional laccase isoform was produced. By contrast, Agaricus–Trichoderma interactions lead to smaller increases on laccase volumetric activity, probably as result of repression (or degradation) towards one of the laccases isoforms.
Conclusions: The strains of P. ostreatus and A. bisporus assessed in this work showed good potential as laccase producers. The Trichoderma -mediated biological stimulation of laccase production by P. ostreatus and A. bisporus is relevant in order to develop highly productive processes.
Significance and Impact of the Study: Extracellular laccases from basidiomycetes are produced only in small amounts. It is therefore important to increase process productivity for potential industrial applications. The results from this study enable the selection Trichoderma strains capable of increasing laccase production by P. ostreatus or A. bisporus in dual cultures. 相似文献
8.
David M. Alba Salvador Moyà‐Solà Assumpció Malgosa Isaac Casanovas‐Vilar Josep M. Robles Sergio Almécija Jordi Galindo Cheyenn Rotgers Juan Vicente Bertó Mengual 《American journal of physical anthropology》2010,141(1):52-75
Pliopithecus (Pliopithecus) canmatensis sp. nov. is described from several Late Aragonian localities from Abocador de Can Mata (ACM) in els Hostalets de Pierola (Vallès‐Penedès Basin, Catalonia, Spain), spanning from ~11.7 to 11.6 Ma (C5r.3r subchron), and being correlated to the MN8 (reference locality La Grive L3). The ACM remains display a pliopithecine dental morphology with well‐developed pliopithecine triangles on M/2 and M/3. This, together with other occlusal details, negates an attribution to the subgenus Epipliopithecus. Although slightly smaller, the ACM remains are most similar in size to comparable elements of P. piveteaui and P. antiquus. Several occlusal details (such as the greater development of the buccal cingulid in lower molars) and dental proportions (M/3 much longer than M/2), however, indicate greater similarities with P. antiquus from Sansan and La Grive. The ACM remains, however, differ from P. antiquus in dental proportions as well as occlusal morphology of the lower molars (including the less peripheral position of the protoconid and more medial position of the hypoconulid, the more mesial position of the buccal cuspids as compared to the lingual ones, the narrower but distinct mesial fovea, the higher trigonid, and the more extensive buccal cingulid, among others). These differences justify a taxonomic distinction at the species level of the ACM pliopithecid remains with respect to P. antiquus. Previous pliopithecid findings from the Vallès‐Penedès Basin, previously attributed to P. antiquus, are neither attributable to the latter species nor to the newly erected one. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc. 相似文献
9.
In the southwestern United States (US), the Rio Grande chub (Gila pandora) is state-listed as a fish species of greatest conservation need and federally listed as sensitive due to habitat alterations and competition with non-native fishes. Characterizing genetic diversity, genetic population structure, and effective number of breeders will assist with conservation efforts by providing a baseline of genetic metrics. Genetic relatedness within and among G. pandora populations throughout New Mexico was characterized using 11 microsatellite loci among 15 populations in three drainage basins (Rio Grande, Pecos, Canadian). Observed heterozygosity (HO) ranged from 0.71–0.87 and was similar to expected heterozygosity (0.75–0.87). Rio Ojo Caliente (Rio Grande) had the highest allelic richness (AR = 15.09), while Upper Rio Bonito (Pecos) had the lowest allelic richness (AR = 6.75). Genetic differentiation existed among all populations with the lowest genetic variation occurring within the Pecos drainage. STRUCTURE analysis revealed seven genetic clusters. Populations of G. pandora within the upper Rio Grande drainage (Rio Ojo Caliente, Rio Vallecitos, Rio Pueblo de Taos) had high levels of admixture with Q-values ranging from 0.30–0.50. In contrast, populations within the Pecos drainage (Pecos River and Upper Rio Bonito) had low levels of admixture (Q = 0.94 and 0.87, respectively). Estimates of effective number of breeders (N b ) varied from 6.1 (Pecos: Upper Rio Bonito) to 109.7 (Rio Grande: Rio Peñasco) indicating that populations in the Pecos drainage are at risk of extirpation. In the event that management actions are deemed necessary to preserve or increase genetic diversity of G. pandora, consideration must be given as to which populations are selected for translocation. 相似文献
10.
Germano Siqueira Adriane MF Milagres Walter Carvalho Gerald Koch André Ferraz 《Biotechnology for biofuels》2011,4(1):7