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31.
Bias of some commonly-used time series estimates 总被引:3,自引:0,他引:3
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Transcription of the Bacillus subtilis spoIIA locus 总被引:15,自引:0,他引:15
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Philippe Margot Michael Wahlen Ahmad Gholamhuseinian Patrick Piggot Dimitri Karamata 《Journal of bacteriology》1998,180(3):749-752
Bacillus subtilis cell wall-bound protein CWBP33 is encoded by lytE, a gene expressed during the exponential growth phase. Sequence analysis of LytE, a 33-kDa protein, reveals two domains. The N-terminal domain contains a threefold-repeated motif common to several peptidoglycan binding proteins, while the C-terminal domain, probably carrying the catalytic activity, has homology with certain exoproteins. Zymographs unambiguously reveal that the absence of CWBP33, due to inactivation of lytE, is accompanied by the loss of a lytic activity. In lytE mutants, the cell autolysis rate is significantly decreased, although autolysis of corresponding, purified cell walls does not seem to be affected. 相似文献
38.
Piggot AM Klaus JS Johnson S Phillips MC Solo-Gabriele HM 《Applied and environmental microbiology》2012,78(17):5973-5982
Enterococci, recommended at the U.S. federal level for monitoring water quality at marine recreational beaches, have been found to reside and grow within beach sands. However, the environmental and ecological factors affecting enterococcal persistence remain poorly understood, making it difficult to determine levels of fecal pollution and assess human health risks. Here we document the presence of enterococci associated with beach sediment biofilms at eight south Florida recreational beaches. Enterococcal levels were highest in supratidal sands, where they displayed a nonlinear, unimodal relationship with extracellular polymeric secretions (EPS), the primary component of biofilms. Enterococcal levels peaked at intermediate levels of EPS, suggesting that biofilms may promote the survival of enterococci but also inhibit enterococci as the biofilm develops within beach sands. Analysis of bacterial community profiles determined by terminal restriction fragment length polymorphisms showed the bacterial communities of supratidal sediments to be significantly different from intertidal and subtidal communities; however, no differences were observed in bacterial community compositions associated with different EPS concentrations. Our results suggest that supratidal sands are a microbiologically unique environment favorable for the incorporation and persistence of enterococci within beach sediment biofilms. 相似文献
39.
Reini W Bretveld Chris MG Thomas Paul TJ Scheepers Gerhard A Zielhuis Nel Roeleveld 《Reproductive biology and endocrinology : RB&E》2006,4(1):30
Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system
through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference
with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide
exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function
of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation:
1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition
and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms
are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation
of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies,
exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy,
spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal
function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity,
it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining
the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive
effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in
this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both
in toxicological and epidemiological settings. 相似文献
40.
R S English J S Lampel TJ Vanden Boom 《Journal of industrial microbiology & biotechnology》1998,21(4-5):219-224
The introduction of plasmid DNA into germinating spores of an industrially improved strain of Saccharopolyspora erythraea was accomplished by electroporation. Various parameters affecting the efficiency of electroporation were examined. The most
critical factor was the extent of spore germination. Electrocompetence was limited to a 4-h period following the initial emergence
of the germ tube. Electroporation efficiencies as high as 2 × 105 CFU μg−1 of plasmid DNA were obtained using electrocompetent germlings. The optimal field strength was 12–14 kV cm−1 with a pulse duration of 15–20 ms. Electrocompetent germlings were stored at −80°C without a significant decrease in transformation
efficiency. The utility of this protocol was demonstrated by isolating a propionyl-CoA carboxylase mutant through targeted
gene disruption and replacement.
Received 3 April 1998/ Accepted in revised form 28 September 1998 相似文献