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951.
Jean-Christophe Giard Axel Hartke Sigrid Flahaut Abdellah Benachour Philippe Boutibonnes Yanick Auffray 《Current microbiology》1996,32(5):264-271
Compared with growing bacteria, carbohydrate-starved cells of Enterococcus faecalis show development of a multiresistance state against heat, H2O2, acid, and ethanol, but not against UV irradiation. The kinetics of acquisition of resistance is different according to the
stress. Three hours of starvation provide maximal resistance against ethanol, while the tolerance to heat, H2O2, and acid increases progressively with the duration of starvation. Chloramphenicol treatment does not abolish the ethanol
tolerance. Protein synthesis inhibition during the transitional growth phase and the first hours of starvation partially inhibit
the acquisition of heat and oxidative resistances. Antibiotic treatment after 3 h of starvation does not affect the increase
of these resistances. We suggest that synthesis of specific proteins revealed by 2-D gel analysis in the first 3 h of starvation,
followed by a second mechanism related to protein degradation or alteration, is necessary for acquisition of maximal resistance
towards heat and oxidative stresses. 相似文献
952.
Laïla Rhazi Patrick Grillas Mouhssine Rhazi Jean-Christophe Aznar 《Hydrobiologia》2009,634(1):185-194
The aim of this work was to test the hypotheses that the species composition of the vegetation of one pool in Morocco change
continuously along with rainfall fluctuations, that among the vegetation can be recognized Pool species and Opportunistic
species with distinct dynamics in time. We expected the Pool species to show lower inter-annual variation than the Opportunistic
species. This hypothesis was tested in a 10-year study of the species composition of the vegetation along two permanent transects.
The results showed high cumulative species richness (95 species) with large differences between years and a predominance of
annual species (77). The proportion of Pool species during these 10 years was low (39%) when compared to opportunists (61%).
In dry years the Opportunistic species were dominant and declined during wet years. The number of Pool species was correlated
with the amount of rainfall. A large number of these species revealed a preference for wet years. No negative interaction
between annuals/perennials and pools/non-pools species was found, suggesting that competition was not a major process during
the survey. The intensity of the drought and flood stress, related to climate fluctuations, seems to be the main factors controlling
the species composition of the vegetation of this unstable habitat. However, beyond the inter-annual fluctuation of the species
composition of the vegetation a directional change was noticed. This directional change could result from a recovery process
of the vegetation during the first years of the study after a severe flood which extirpated most of the Opportunistic species
of the pool. In the last years this directional change of the species composition of the vegetation is less clear and random
recruitment of the Opportunistic species from the surrounding forested habitats could contribute to explain inter-annual changes.
The data collected over these 10 years led to the speculation of hypotheses on the consequences of climate change. The expected
reduction of humid years and of rainfall regionally may lead to important changes in the species composition of the vegetation
of the temporary pools in Morocco.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle
Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16
May 2008 相似文献
953.
Aphids are among the few organisms capable of reproducing either sexually or asexually. This plasticity in reproductive mode is viewed as an adaptive response to cope with seasonal changes. Clonal reproduction occurs during the growing season allowing rapid population increase, while sexual reproduction occurs during late summer and leads to frost-resistant eggs that can survive winter conditions. This shift between these two extreme reproductive modes is achieved by using the same genotype, i.e. within the same genetic clone, and is triggered by photoperiodic changes perceived by the aphid brain or visual system. Advances have been made recently to depict genetic programs that relate to the regulation of reproductive modes in aphids. These studies have benefited from the rapid development of genomic and post-genomic resources obtained through the International Aphid Genomics Consortium. Here, we underline the importance of several candidate genes in the switch from clonal to sexual reproduction in aphids and whose roles await full validation. Besides reproductive mode variation expressed at the genotypic level, aphid species also frequently encompass lineages which have lost the sexual phase and hence the alternating clonal and sexual reproductive phases of the life cycle. This coexistence of sex and asexual reproduction within the same species raises questions on its evolutionary and ecological significance. We summarize the knowledge accumulated to date on the maintenance of sex as well as on the origin and evolution of asexuality in aphids. By combining functional genomics, genetic and ecological approaches on reproductive plasticity and polymorphism, we hope to obtain an integrative view of the evolutionary forces shaping aphid reproductive strategies, from gene to population and species levels. 相似文献
954.
955.
956.
Axel Hartke Sandrine Bouché Jean-Christophe Giard Abdellah Benachour Philippe Boutibonnes Yanick Auffray 《Current microbiology》1996,33(3):194-199
The lactic acid tolerance response (LATR) of the lactic acid bacterium Lactococcus lactis subsp. lactis has been studied. A dramatic increase in survival to a severe acid stress (pH 3.9) was obtained by preexposing the cells
for 30 min to a mildly acid shock at pH 5.5. Whole-cell protein extract analysis revealed that during the acid tolerance response
33 polypeptides are induced over the level of naive cells. Among these are the major heat shock proteins DnaK and GroEL. In
conjunction with a previous report (Hartke et al. 1994), the results establish that L. lactis can adapt to lactic acid exposure in two different ways: a logarithmic phase LATR, which may be activated by protons, and
a stationary-phase LATR, which needs no activation by protons. Both systems are independent of de novo protein synthesis.
Received: 8 February 1996 / Accepted: 11 March 1996 相似文献