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41.
Inhibition of atrazine degradation by cyanazine and exogenous nitrogen in bacterial isolate M91-3 总被引:7,自引:0,他引:7
A variety of s-triazine herbicides and nitrogen fertilizers frequently occur as co-contaminants at pesticide manufacturing and distribution
facilities. The degradation of atrazine and cyanazine by the bacterial isolate M91-3 was investigated in washed-cell suspensions
and crude cellular extracts. Cyanazine competitively inhibited atrazine degradation. The maximum atrazine degradation rate
(V
max) was 41 times higher and the half-saturation constant for the inhibitor (K
i) was 1.3 times higher in the crude cellular extract than in the washed-cell suspension, suggesting that cellular uptake influenced
degradation of the s-triazines. Cultures that had received prior exposure to atrazine and simazine exhibited comparable atrazine degradation rates,
while cells exposed to cyanazine, propazine, ametryne, cyanuric acid, 2-hydroxyatrazine, biuret, and urea exhibited a lack
of atrazine-degradative activity. Growth in the presence of exogenous inorganic nitrogen inhibited subsequent atrazine-degradative
activity in washed-cell suspensions, suggesting that regulation of s-triazine and nitrogen metabolism are linked in this bacterial isolate. These findings have significant implications for the
environmental fate of s-triazines in agricultural settings since these herbicides are frequently applied to soils receiving N fertilizers. Furthermore,
these results suggest that bioremediation of s-triazine-contaminated sites (common at pesticide distribution facilities in the cornbelt) may be inhibited by the presence
of N fertilizers that occur as co-contaminants.
Received: 3 March 1998 / Received revision: 24 September 1998 / Accepted: 11 October 1998 相似文献
42.
Rhizomes and attached leaves of Phyllospadix scouleri Hook, were collected in the intertidal zone along the central California coast and exposed to a solution of NaH14CO3 in seawater under controlled laboratory conditions. Over a 90-min period roots and rhizomes absorbed very little 14C compared to leaves. Translocation during that time was minor. Plants pretreated with the photosynthetic inhibitor DCMU showed no 14C uptake, indicating that under normal circumstances the carbon which is absorbed by leaves is fixed and accumulates as photosynthate. The rate of gross photosynthesis was about 13 mg CO2 g dry wt−1 hr−1. Gross photosynthesis of wet leaves exposed to 14CO2 in air was significantly less than leaves exposed to NaH14CO3. The effect of a leaf-grazing limpet (Notoacmea paleacea) on leaf anatomy and 14C uptake is discussed. 相似文献
43.
The murid rodent subfamily Sigmodontinae contains 79 genera which are
distributed throughout the New World. The time of arrival of the first
sigmodontines in South America and the estimated divergence time(s) of the
different lineages of South American sigmodontines have been controversial
due to the lack of a good fossil record and the immense number of extant
species. The "early-arrival hypothesis" states that the sigmodontines must
have arrived in South America no later than the early Miocene, at least 20
MYA, in order to account for their vast present-day diversity, whereas the
"late-arrival hypothesis" includes the sigmodontines as part of the
Plio-Pleistocene Great American Interchange, which occurred approximately
3.5 MYA. The phylogenetic relationships among 33 of these genera were
reconstructed using mitochondrial DNA (mtDNA) sequence data from the ND3,
ND4L, arginine tRNA, and ND4 genes, which we show to be evolving at the
same rate. A molecular clock was calibrated for these genes using published
fossil dates, and the genetic distances were estimated from the DNA
sequences in this study. The molecular clock was used to estimate the dates
of the South American sigmodontine origin and the main sigmodontine
radiation in order to evaluate the "early-" and "late-arrival" scenarios.
We estimate the time of the sigmodontine invasion of South America as
between approximately 5 and 9 MYA, supporting neither of the scenarios but
suggesting two possible models in which the invading lineage was either (1)
ancestral to the oryzomyines, akodonts, and phyllotines or (2) ancestral to
the akodonts and phyllotines and accompanied by the oryzomyines. The
sigmodontine invasion of South America provides an example of the advantage
afforded to a lineage by the fortuitous invasion of a previously
unexploited habitat, in this case an entire continent.
相似文献
44.
45.
Phytochrome-mediated phototropism in de-etiolated seedlings : occurrence and ecological significance 总被引:5,自引:1,他引:4
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Phototropic responses to broadband far red (FR) radiation were investigated in fully de-etiolated seedlings of a long-hypocotyl mutant (lh) of cucumber (Cucumis sativus L.), which is deficient in phytochrome-B, and its near isogenic wild type (WT). Continuous unilateral FR light provided against a background of white light induced negative curvatures (i.e. bending away from the FR light source) in hypocotyls of WT seedlings. This response was fluence-rate dependent and was absent in the lh mutant, even at very high fluence rates of FR. The phototropic effect of FR light on WT seedlings was triggered in the hypocotyls and occurred over a range of fluence rates in which FR was very effective in promoting hypocotyl elongation. FR light had no effect on elongation of lh-mutant hypocotyls. Seedlings grown in the field showed negative phototropic responses to the proximity of neighboring plants that absorbed blue (B) and red light and back-reflected FR radiation. The bending response was significantly larger in WT than in lh seedlings. Responses of WT and lh seedlings to lateral B light were very similar; however, elimination of the lateral B light gradients created by the proximity of plant neighbors abolished the negative curvature only in the case of lh seedlings. More than 40% of the total hypocotyl curvature induced in WT seedlings by the presence of neighboring plants was present after equilibrating the fluence rates of B light received by opposite sides of the hypocotyl. These results suggest that: (a) phytochrome functions as a phototropic sensor in de-etiolated plants, and (b) in patchy canopy environments, young seedlings actively project new leaves into light gaps via stem bending responses elicited by the B-absorbing photoreceptor(s) and phytochrome. 相似文献
46.
47.
Five controlled burns (ca. 2 ha each) were conducted in the Coast Range of northern California near Hopland, California, between November 18, 1975 and September 15, 1976 to determine the effect of shrub phenology on the sprouting response of chamise (Adenostoma fasciculatum H&A) following fire. The time of burn had little effect on the amount of shoot growth that occurred after fire, although the pattern of growth was altered. Shrubs burned on June 22 or August 2, 1976 grew continually until August 1977, while unburned shrubs or those burned at other times ceased seasonal growth during the first summer after fire. Neither the amount nor the pattern of shoot growth was influenced by the shrub water status before the fire occurred. The relationship between chamise shoot growth after fire, 14CO2 fixation, xylem sap tension, and air temperature was also studied. The growth rate of regrowing shrubs was highly correlated with 14CO2 fixation prior to the growth measurement. Water status (pre-dawn xylem sap tension) had a negative correlation with 14CO2 fixation. The abundance of carbohydrate at the shoot apex is believed to influence the seasonal pattern and rate of chamise shoot growth following fire. 相似文献
48.
Jennifer M. DeBruyn Lauren T. Nixon Mariam N. Fawaz Amy M. Johnson Mark Radosevich 《Applied and environmental microbiology》2011,77(17):6295-6300
Bacteria belonging to phylum Gemmatimonadetes comprise approximately 2% of soil bacterial communities. However, little is known of their ecology due to a lack of cultured representation. Here we present evidence from biogeographical analyses and seasonal quantification of Gemmatimonadetes in soils, which suggests an adaptation to low soil moisture. 相似文献
49.
Background
Living tissues contain a range of intrinsic fluorophores and sources of second harmonic generation which provide contrast that can be exploited for fresh tissue imaging. Microscopic imaging of fresh tissue samples can circumvent the cost and time associated with conventional histology. Further, intrinsic contrast can provide rich information about a tissue''s composition, structure and function, and opens the potential for in-vivo imaging without the need for contrast agents.Methodology/Principal Findings
In this study, we used hyperspectral two-photon microscopy to explore the characteristics of both normal and diseased gastrointestinal (GI) tissues, relying only on their endogenous fluorescence and second harmonic generation to provide contrast. We obtained hyperspectral data at subcellular resolution by acquiring images over a range of two-photon excitation wavelengths, and found excitation spectral signatures of specific tissue types based on our ability to clearly visualize morphology. We present the two-photon excitation spectral properties of four major tissue types that are present throughout the GI tract: epithelium, lamina propria, collagen, and lymphatic tissue. Using these four excitation signatures as basis spectra, linear unmixing strategies were applied to hyperspectral data sets of both normal and neoplastic tissue acquired in the colon and small intestine. Our results show that hyperspectral unmixing with excitation spectra allows segmentation, showing promise for blind identification of tissue types within a field of view, analogous to specific staining in conventional histology. The intrinsic spectral signatures of these tissue types provide information relating to their biochemical composition.Conclusions/Significance
These results suggest hyperspectral two-photon microscopy could provide an alternative to conventional histology either for in-situ imaging, or intraoperative ‘instant histology’ of fresh tissue biopsies. 相似文献50.
Xiaolong Liang Jie Zhuang Frank E. Löffler Yingyue Zhang Jennifer M. DeBruyn Steven W. Wilhelm Sean M. Schaeffer Mark Radosevich 《Environmental microbiology》2019,21(6):2043-2055
The delivery of fermentable substrate(s) to subsurface environments stimulates Fe(III)-bioreduction and achieves detoxification of organic/inorganic contaminants. Although, much research has been conducted on the microbiology of such engineered systems at lab and field scales, little attention has been given to the phage-host interactions and virus community dynamics in these environments. The objective was to determine the responses of soil bacterial communities and viral assemblages to stimulated anaerobic Fe(III)-bioreduction following electron donor (e.g. acetate) addition. Microbial communities, including viral assemblages, were investigated after 60 days of Fe(III)-bioreduction in laboratory-scale columns continuously fed with acetate-amended artificial groundwater. Viral abundances were greatest in the influent section and decreased along the flow path. Acetate availability was important in influencing bacterial diversity, microbial interactions and viral abundance and community composition. The impact of acetate addition was most evident in the influent section of the columns. The increased relative abundance of Fe(III)-reducing bacteria coincided with an increase in viral abundance in areas of the columns exhibiting the most Fe(III) reduction. The genetic composition of viruses in these column sections also differed from the control column and distal sections of acetate-treated columns suggesting viral communities responded to biostimulated Fe(III)-bioreduction. 相似文献