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81.
Brucella abortus INTA2, a novel mutant strain, was constructed by inactivation of two B. abortus S19 genes: bp26 and bmp18, with the objective of obtaining a mutant strain that could be compatible with a diagnostic test and have less residual virulence than strain 19. The double mutant was constructed by replacing a large section of the bp26 coding region with the luciferase (luc) coding gene, resulting in mutant strain B. abortus M1luc, followed by partial deletion of bmp18 coding sequence. Both genes were inactivated by allelic replacement assisted by sacB counter-selection. Luciferase expression was evaluated and confirmed that it is a valid marker in the construction of mutant strains. When B. abortus INTA2 was inoculated in BALB/c mice, significantly fewer colony forming units (CFUs) were recovered from mice spleens during initial phase of infection. No splenomegaly was observed in strain INTA2-immunized mice at any time suggesting that strain INTA2 has lost some residual virulence of the parental strain. Nevertheless, similar protection levels against virulent challenge were observed in mice immunized with strains INTA2 or S19. Although strain INTA2 would still induce O-side antibodies, it does not express BP26. This would allow differentiation of INTA2-vaccinated animals from animals infected with field strains by measuring anti-BP26 antibodies, either by an agglutination test or ELISA using BP26 as antigen. Altogether these results indicate that B. abortus INTA2 might be a promising vaccine strain against brucellosis.  相似文献   
82.
At present, Trichinella spiralis is the only species of this genus reported from South America. Herein, we detail a molecular analysis of a new encapsulated isolate of muscle larvae of Trichinella, found in a mountain lion (Puma concolor) coming from the Patagonia, Argentina. We studied three DNA regions previously probed to be useful for the identification of all eleven recognized Trichinella genotypes: expansion segment 5 (ES5), cytochrome c-oxidase subunit I (COI) and 5S ribosomal DNA intergenic spacer region (5S ISR). BLAST searches with these DNA sequences showed that the mitochondrial and nuclear ribosomal regions most closely resemble other Trichinella sequences available in GenBank. However, they did not exactly match any of the eleven recognized genotypes. The phylogenetic analysis from COI and 5S ISR sequences showed that the mountain lion isolate is grouped with encapsulated members, in concordance with morphological data. Furthermore, this new isolate was located at the base of the encapsulated genotypes, signifying that it is an old genotype that could have emerged earliest in this group. These data strongly suggest that this isolate from the Patagonia represents the twelfth genotype (T12) described in the genus Trichinella. Nevertheless, further studies are necessary to adequately establish this isolate as a unique genotype.  相似文献   
83.

Context

Land use change and forest degradation have myriad effects on tropical ecosystems. Yet their consequences for low-order streams remain very poorly understood, including in the world´s largest freshwater basin, the Amazon.

Objectives

Determine the degree to which physical and chemical characteristics of the instream habitat of low-order Amazonian streams change in response to past local- and catchment-level anthropogenic disturbances.

Methods

To do so, we collected field instream habitat (i.e., physical habitat and water quality) and landscape data from 99 stream sites in two eastern Brazilian Amazon regions. We used random forest regression trees to assess the relative importance of different predictor variables in determining changes in instream habitat response variables.

Results

Multiple drivers, operating at multiple spatial scales, were important in determining changes in the physical habitat and water quality of the sites. Although we found few similarities in modelled relationships between the two regions, we observed non-linear responses of specific instream characteristics to landscape change; for example 20 % of catchment deforestation resulted in consistently warmer streams.

Conclusions

Our results highlight the importance of local riparian and catchment-scale forest cover in shaping instream physical environments, but also underscore the importance of other land use changes and activities, such as road crossings and upstream agriculture intensification. In contrast to the property-scale focus of the Brazilian Forest code, which governs environmental regulations on private land, our results reinforce the importance of catchment-wide management strategies to protect stream ecosystem integrity.
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84.
The effect of the addition of Bacillus probiotic during larvae and postlarvae culture of the white shrimp Litopenaeus vannamei was examined in three separate experiments: (I) Nauplius4‐5 to Zoea3, which were exposed to probiotic in the water (Pw), only in the microalgae (Pm), in the water and microalgae (Pwm) and a control with no probiotic (C); (II) Mysis1 to Mysis3, which were exposed to probiotic in the water (Pw), only in Artemia (Pa), in the water and Artemia (Pwa) and a control (C); (III) PL1 to PL10, which were exposed to similar treatments for mysis experiment. The use of probiotic Bacillus spp. resulted in an increase in the survival and growth of zoea and mysis phases, especially when the probiotic was added only in the water. For postlarvae, the use of the probiotic had no influence on the zootechnical parameters, however, there was a reduction in the count of presumptive Vibrio both for water and shrimp.  相似文献   
85.
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86.
Changes in soil properties related to natural regeneration of silver fir (Abies alba, Mill.) in small (185 m2) and medium (410 m2) gaps, in the Calabria Apennines (Southern Italy), were studied 2 years after gap creation. The organic matter within the medium gaps decayed more rapidly than those in the small gaps. Among the microenvironmental variables and soil properties, soil temperature was most strongly positively related to organic matter decomposition rates. Medium gaps had high soil temperature and photosynthetically active radiation (PAR) transmittance, and low soil moisture. Within medium gaps, we found a great amount of phenolic compounds and a low content of organic matter and humic acids. These results indicate that in the medium gaps mineralization of organic matter was more important than humification. In contrast, in small gaps, the great amount of organic matter, the high content of humic acid and the values of humification index suggested that in these gaps the humification process of organic matter prevailed. Within small gaps, we observed more silver fir regeneration than medium gaps. Difference in organic matter content, particularly in the amount of phenolic compounds, may account for differences observed in natural regeneration of silver fir between small and medium gaps.  相似文献   
87.

Purpose

Forests play a key role in providing protection against soil erosion. Particularly, the role of vertical forest structure in increasing rainfall interception capacity is crucial for mitigating raindrop impact and reducing splash and rill erosion. For this reason, studies on the relationships between forest structures, the past management, and the observed rates of soil loss are needed. In the last few decades, importance was given to the use of cesium-137 (137Cs) as radioactive tracer to estimate soil erosion rates. The 137Cs technique is linked to the global fallout of bomb-derived radiocesium which occurred during a period extending from the mid 1950s to the late 1970s.

Materials and methods

The 137Cs technique, providing long-term retrospective estimates, could be related to forest treatments applied during the last decades in different sites, also considering the tree species composition. This approach could be useful to compare the effect of different canopy cover and biomass on soil erosion rates related to different tree species. In the work proposed here, a study area dominated by pine and beech high forests located in the Aspromonte Mountains (Calabria, Italy) was selected. The measurements, related to forest structural traits, focusing on canopy cover and biomass, and also on management approaches and forest types, are compared with rates of soil erosion provided by 137Cs.

Results and discussion

The overall results suggest that the minimum values of soil loss are documented in areas with higher canopy cover and biomass evidencing the protective effect provided by forests against soil erosion. Also, techniques based on the use of tracers like 137Cs proved to be helpful to select the best forest management options useful to optimize the protective role of forests, with the aim to reduce erosion processes in a long-term perspective.

Conclusions

The experiment indicates that care must be taken when new silviculture treatments are planned. These findings are in agreement with what documented by other authors in similar environments but need further studies to confirm the effectiveness of using 137Cs in different forest ecosystems.
  相似文献   
88.
Casearia sylvestris methanolic extract (MCE) was screened at doses of 125–500 mg/kg for its antihyperlipidemic activity. The antihyperlipidemic effect was evaluated in olive oil-loaded mice. Acute treatment caused inhibition in the triglyceride (TG) and serum lipase elevation-induced by 5 ml/kg of olive oil.  相似文献   
89.
The present study evaluated the effects of feeding frequency during the grow‐out phase of Litopenaeus vannameiin biofloc system. The experiment comprised of four treatments with three replicates each, corresponding to the following feeding frequencies: one (8:00 a.m.), two (8:00 a.m. and 4:00 p.m.), three (8:00 a.m., 12:00 p.m. and 4:00 p.m.) and four times a day (8:00 a.m., 10:00 a.m., 12:00 p.m. and 4:00 p.m.). Zootechnical performance and digestive enzyme activity were monitored for 63 days. At the end of the experiment, the highest survival rates were found for the individuals fed three and four times a day. Wet weight gain (6.63 g) and specific growth rate (3.46% per day) of the individuals fed three times a day were significantly higher compared to animals fed one and four times a day, but did not differ significantly to the group fed twice a day (6.15 g and 3.46% per day, respectively). The digestive enzyme activities were not affected by the feeding frequency, but negative correlations were found between these activities and shrimp weight. It is recommended that L. vannamei should be fed three times a day during the grow‐out phase in a biofloc system under the conditions used in this study.  相似文献   
90.
An outbreak of acute encephalopathy occurred in pregnant ewes and their newborn lambs associated with consumption of Talisia esculenta fruits and bark. Clinical signs in 5 adult pregnant ewes included drooling, bloat, tachypnea, depression, ataxia, body shaking, difficulty in rising, and recumbency. Three neonatal lambs born to some of those ewes had similar clinical signs. No significant gross abnormalities were observed on autopsy. Histologically, neuronal necrosis, axonal and dendritic swelling, and loss of Purkinje neurons were observed in the cerebellum. The observation of similar neurologic clinical signs and lesions in pregnant ewes and their neonatal lambs suggests that the toxic principle of T. esculenta crosses the placenta and reaches the fetus.  相似文献   
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