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- Diaz-Ravina, M, et al.
(författare)
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Development of metal tolerance in soil bacterial communities exposed to experimentally increased metal levels
- 1996
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 62:8, s. 2970-2977
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Tidskriftsartikel (refereegranskat)abstract
- The development of metal tolerance in soil bacterial communities exposed to different heavy metals was examined under laboratory conditions. An agricultural soil amended with different Zn concentrations was studied most intensively, and measurements were made over a 28-month incubation period by means of the thymidine incorporation technique. Tolerance levels were not affected by metal concentrations lower than 2 mmol of Zn kg (dry weight) of soil(sup-1), but above this value, the level of Zn tolerance increased exponentially with the logarithm of the soil Zn concentration. An increased metal tolerance was detected after only 2 days of Zn exposure. Thereafter, stable tolerance values were observed at different sampling times for bacterial communities exposed to up to 8 mmol of Zn kg (dry weight)(sup-1), indicating no changes in tolerance with time. The tolerance of bacterial communities exposed to 32 mmol of Zn kg (dry weight)(sup-1) increased rapidly within the second week of incubation, but then the values remained unchanged until the end of the experiment. Bacterial communities from soil contaminated with 16 mmol of Zn kg (dry weight)(sup-1) showed an increase of the same magnitude, but the increase started later, after 4 months of incubation, and took place for a much longer period (more than 1 year). Cd, Cu, and Ni addition also resulted in metal-tolerant communities, and the level of tolerance increased with prolonged incubations of the soils. The bacterial community at the end of the incubation period also exhibited a lower pH optimum and an increased tolerance to low osmotic potential. The results suggest that the increase in metal tolerance of the community after adding metals can be attributed to an immediate effect due to the death of sensitive species and a later effect due to different competitive abilities and adaptation of surviving bacteria.
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- Liu, B, et al.
(författare)
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Quantitative determination of antiinflammatory principles in some Polypodium species as a basis for standardization
- 1998
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Ingår i: Phytomedicine. - 0944-7113 .- 1618-095X. ; 5:3, s. 187-194
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Tidskriftsartikel (refereegranskat)abstract
- Recently, several, compounds including polyunsaturated fatty acids (linoleic, linolenic, arachidonic), the triflavonoid selligueain and a sulfonoglycolipid (SQDG) have been isolated from the South American fern, Polypodium decumanum using bioactivity directed fractionation. The present study describes the quantitative analysis using HPLC methods of these three classes of compounds in the leaves and rhizomes of the five Polypodium species. Furthermore, extracts of the five ferns are studied in three in vitro bioassays using platelet activating factor (PAF) and leukotriene B-4 (LTB4). The models are the same that previously have led to the isolation of the active principles in Polypodium decumanum. The objective of this study was to investigate if the identified active compounds could be used for standardization of the extracts. Since the SQDG was found to be present in pharmacologically detectable amounts in the crude extracts and since it presents a specific mode of action it is recommended that quantitative analysis of this constituent should be used for future standardization of the extracts.
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