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51.
Pirkko L. Suominen Arja L. Mäntylä Taina Karhunen Satu Hakola Helena Nevalainen 《Molecular genetics and genomics : MGG》1993,241(5-6):523-530
Four cellulase genes of Trichoderma reesei, cbh1, cbh2, egl1 and egl2, have been replaced by the amdS marker gene. When linear DNA fragments and flanking regions of the corresponding cellulase locus of more than 1 kb were used, the replacement frequencies were high, ranging from 32 to 52%. Deletion of the major cellobiohydrolase 1 gene led to a 2-fold increase in the production of cellobiohydrolase II; however, replacement of the cbh2 gene did not affect the final cellulase levels and deletion of egl1 or egl2, slightly increased production of both cellobiohydrolases. Based on our results, endoglucanase II accounts for most of the endoglucanase activity produced by the hypercellulolytic host strain. Furthermore, loss of the egl2, gene causes a significant drop in the filter paper-hydrolysing activity, indicating that endoglucanase II has an important role in the total hydrolysis of cellulose. 相似文献
52.
Green-tree retention is a forest management method in which some living trees are left on a logged area. The aim is to offer ‘lifeboats’ to support species immediately after logging and to provide microhabitats during and after forest re-establishment. Several studies have shown immediate decline in bryophyte diversity after retention logging and thus questioned the effectiveness of this method, but longer term studies are lacking. Here we studied the epiphytic bryophytes on European aspen (Populus tremula L.) retention trees along a 30-year chronosequence. We compared the bryophyte flora of 102 ‘retention aspens’ on 14 differently aged retention sites with 102 ‘conservation aspens’ on 14 differently aged conservation sites. We used a Bayesian community-level modelling approach to estimate the changes in bryophyte species richness, abundance (area covered) and community structure during 30 years after logging. Using the fitted model, we estimated that two years after logging both species richness and abundance of bryophytes declined, but during the following 20–30 years both recovered to the level of conservation aspens. However, logging-induced changes in bryophyte community structure did not fully recover over the same time period. Liverwort species showed some or low potential to benefit from lifeboating and high potential to re-colonise as time since logging increases. Most moss species responded similarly, but two cushion-forming mosses benefited from the logging disturbance while several weft- or mat-forming mosses declined and did not re-colonise in 20–30 years. We conclude that retention trees do not function as equally effective lifeboats for all bryophyte species but are successful in providing suitable habitats for many species in the long-term. To be most effective, retention cuts should be located adjacent to conservation sites, which may function as sources of re-colonisation and support the populations of species that require old-growth forests. 相似文献
53.
Ooi T Shibata T Sato R Ohno H Kinoshita S Thuoc TL Taguchi S 《Applied microbiology and biotechnology》2007,76(2):377-386
Three endoxylanase genes were cloned from the thermophilic fungus Chaetomium thermophilum CBS 730.95. All genes contained the typical consensus sequence of family 11 glycoside hydrolases. Genomic copies of Ct xyn11A, Ct xyn11B, and Ct xyn11C were expressed in the filamentous fungus T. reesei under the control of the strong T. reesei cel7A (cellobiohydrolase 1, cbh1) promoter. The molecular masses of the Ct Xyn11A, Ct Xyn11B, and Ct Xyn11C proteins on sodium dodecyl sulfate polyacrylamide
gel electrophoresis (SDS-PAGE) were 27, 23, and 22 kDa, respectively. Ct Xyn11A was produced almost as efficiently as the
homologous xylanase II from a corresponding single-copy transformant strain. Ct Xyn11B production level was approximately
half of that of Ct Xyn11A. The amount of Ct Xyn11C was remarkably lower. Ct Xyn11A had the highest temperature optimum and
stability of the recombinant xylanases and the highest activity at acid-neutral pH (pH 5–7). It was the most suitable for
industrial bleaching of kraft pulp at high temperature. 相似文献
54.
Spatially structured populations in patchy habitats show much variation in migration rate, from patchy populations in which individuals move repeatedly among habitat patches to classic metapopulations with infrequent migration among discrete populations. To establish a common framework for population dynamics in patchy habitats, we describe an individual-based model (IBM) involving a diffusion approximation of correlated random walk of individual movements. As an example, we apply the model to the Glanville fritillary butterfly (Melitaea cinxia) inhabiting a highly fragmented landscape. We derive stochastic patch occupancy model (SPOM) approximations for the IBMs assuming pure demographic stochasticity, uncorrelated environmental stochasticity, or completely correlated environmental stochasticity in local dynamics. Using realistic parameter values for the Glanville fritillary, we show that the SPOMs mimic the behavior of the IBMs well. The SPOMs derived from IBMs have parameters that relate directly to the life history and behavior of individuals, which is an advantage for model interpretation and parameter estimation. The modeling approach that we describe here provides a unified framework for patchy populations with much movements among habitat patches and classic metapopulations with infrequent movements. 相似文献
55.
Ovaskainen O 《Mathematical biosciences》2003,181(2):165-176
According to metapopulation theory, the capacity of a habitat patch network to support the persistence of a species is measured by the metapopulation capacity of the patch network. Mathematically, metapopulation capacity is given by the leading eigenvalue lambda(M) of an appropriately constructed non-negative n x n matrix M, where n is the number of habitat patches. Both habitat destruction (in the sense of destruction of entire patches) and habitat deterioration (in the sense of partial destruction of patches) lower the metapopulation capacity of the patch network. The effect of gradual habitat deterioration is given by the derivative of lambda(M) with respect to patch attributes and may be straightforwardly evaluated by sensitivity analysis. In contrast, destruction of entire patches leads to a rank modification of matrix M, the effect of which on lambda(M) may be derived from eigenvector-eigenvalue relations. Eigenvector-eigenvalue relations have previously been analyzed only for symmetric matrices, which restricts their use in biological applications. In this paper I generalize some of the previous results by deriving eigenvector-eigenvalue relations for general non-symmetric matrices. In addition to the exact eigenvector-eigenvalue relations, I also derive eigenvalue perturbation formulae for rank-one modifications. These results lead to simple and intuitive approximation formulae, which may be used e.g. to assess the contribution of particular habitat patches to the metapopulation capacity of the landscape. The mathematical results presented are not restricted to the metapopulation context, but they should find a number of useful applications in biology, engineering and other applied sciences, where the removal (or addition) of matrix rows and columns often corresponds in a natural manner to decreasing (or increasing) the degrees of freedom of the focal system. 相似文献
56.
Ovaskainen O 《The American naturalist》2002,160(5):612-628
I analyze stochastic patch occupancy models (SPOMs), which record habitat patches as empty or occupied. A problem with SPOMs has been that if the spatial structure of a heterogeneous habitat patch network is taken into account, the computational effort needed to analyze a SPOM grows as a power of 2n, where n is the number of habitat patches. I propose a computationally feasible approximation method, which approximates the behavior of a heterogeneous SPOM by an "ideal" metapopulation inhabiting a network of identical and equally connected habitat patches. The transformation to the ideal metapopulation is based on weighting the individual patch occupancies by the dynamic values of the habitat patches, which may be calculated from the deterministic mean-field approximation of the original SPOM. Conceptually, the method resembles the calculation of the effective size of a population in the context of population genetics. I demonstrate how the method may be applied to SPOMs with flexible structural assumptions and with spatially correlated and temporally varying parameter values. I apply the method to a real habitat patch network inhabited by the Glanville fritillary butterfly, illustrating that the metapopulation dynamics of this species are essentially driven by temporal variability in the environmental conditions. 相似文献
57.
Pirkko L. Suominen Arja L. Mäntylä Taina Karhunen Satu Hakola Helena Nevalainen 《Molecular & general genetics : MGG》1993,241(5-6):523-530
Four cellulase genes of Trichoderma reesei, cbh1, cbh2, egl1 and egl2, have been replaced by the amdS marker gene. When linear DNA fragments and flanking regions of the corresponding cellulase locus of more than 1 kb were used, the replacement frequencies were high, ranging from 32 to 52%. Deletion of the major cellobiohydrolase 1 gene led to a 2-fold increase in the production of cellobiohydrolase II; however, replacement of the cbh2 gene did not affect the final cellulase levels and deletion of egl1 or egl2, slightly increased production of both cellobiohydrolases. Based on our results, endoglucanase II accounts for most of the endoglucanase activity produced by the hypercellulolytic host strain. Furthermore, loss of the egl2, gene causes a significant drop in the filter paper-hydrolysing activity, indicating that endoglucanase II has an important role in the total hydrolysis of cellulose. 相似文献
58.
Predator-induced synchrony in population oscillations of coexisting small mammal species 总被引:5,自引:0,他引:5
Korpimäki E Norrdahl K Huitu O Klemola T 《Proceedings. Biological sciences / The Royal Society》2005,272(1559):193-202
Comprehensive analyses of long-term (1977-2003) small-mammal abundance data from western Finland showed that populations of Microtus voles (field voles M. agrestis and sibling voles M. rossiaemeridionalis) voles, bank (Clethrionomys glareolus) and common shrews (Sorex araneus) fluctuated synchronously in 3 year population cycles. Time-series analyses indicated that interspecific synchrony is influenced strongly by density-dependent processes. Synchrony among Microtus and bank voles appeared additionally to be influenced by density-independent processes. To test whether interspecific synchronization through density-dependent processes is caused by predation, we experimentally reduced the densities of the main predators of small mammals in four large agricultural areas, and compared small mammal abundances in these to those in four control areas (2.5-3 km(2)) through a 3 year small-mammal population cycle. Predator reduction increased densities of the main prey species, Microtus voles, in all phases of the population cycle, while bank voles, the most important alternative prey of predators, responded positively only in the low and the increase phase. Manipulation also increased the autumn densities of water voles (Arvicola terrestris) in the increase phase of the cycle. No treatment effects were detected for common shrews or mice. Our results are in accordance with the alternative prey hypothesis, by which predators successively reduce the densities of both main and alternative prey species after the peak phase of small-mammal population cycles, thus inducing a synchronous low phase. 相似文献
59.
60.
Otso Arponent Mazen Sudah Amro Masarwah Mikko Taina Suvi Rautiainen Mervi K?n?nen Reijo Sironen Veli-Matti Kosma Anna Sutela Juhana Hakum?ki Ritva Vanninen 《PloS one》2015,10(10)