ABSTRACTHorizontal gene transfer by integrative and conjugative elements (ICEs) is a very important mechanism for spreading antibiotic resistance in various bacterial species. In environmental and ...clinical settings, most bacteria form biofilms as a way to protect themselves against extracellular stress. However, much remains to be known about ICE transfer in biofilms. Using ICEBs1 from Bacillus subtilis, we show that the natural conjugation efficiency of this ICE is greatly affected by the ability of the donor and recipient to form a biofilm. ICEBs1 transfer considerably increases in biofilm, even at low donor/recipient ratios. Also, while there is a clear temporal correlation between biofilm formation and ICEBs1 transfer, biofilms do not alter the level of ICEBs1 excision in donor cells. Conjugative transfer appears to be favored by the biophysical context of biofilms. Indeed, extracellular matrix production, particularly from the recipient cells, is essential for biofilms to promote ICEBs1 transfer. Our study provides basic new knowledge on the high rate of conjugative transfer of ICEs in biofilms, a widely preponderant bacterial lifestyle in the environment, which could have a major impact on our understanding of horizontal gene transfer in natural and clinical environments.IMPORTANCE Transfer of mobile genetic elements from one bacterium to another is the principal cause of the spread of antibiotic resistance. However, the dissemination of these elements in environmental contexts is poorly understood. In clinical and environmental settings, bacteria are often found living in multicellular communities encased in a matrix, a structure known as a biofilm. In this study, we examined how forming a biofilm influences the transmission of an integrative and conjugative element (ICE). Using the model Gram-positive bacterium B. subtilis, we observed that biofilm formation highly favors ICE transfer. This increase in conjugative transfer is due to the production of extracellular matrix, which creates an ideal biophysical context. Our study provides important insights into the role of the biofilm structure in driving conjugative transfer, which is of major importance since biofilm is a widely preponderant bacterial lifestyle for clinically relevant bacterial strains.
Colonization of plant roots by Bacillus subtilis is mutually beneficial to plants and bacteria. Plants can secrete up to 30% of their fixed carbon via root exudates, thereby feeding the bacteria, and ...in return the associated B. subtilis bacteria provide the plant with many growth-promoting traits. Formation of a biofilm on the root by matrix-producing B. subtilis is a well-established requirement for long-term colonization. However, we observed that cells start forming a biofilm only several hours after motile cells first settle on the plant. We also found that intact chemotaxis machinery is required for early root colonization by B. subtilis and for plant protection. Arabidopsis thaliana root exudates attract B. subtilis in vitro, an activity mediated by the two characterized chemoreceptors, McpB and McpC, as well as by the orphan receptor TlpC. Nonetheless, bacteria lacking these chemoreceptors are still able to colonize the root, suggesting that other chemoreceptors might also play a role in this process. These observations suggest that A. thaliana actively recruits B. subtilis through root-secreted molecules, and our results stress the important roles of B. subtilis chemoreceptors for efficient colonization of plants in natural environments. These results demonstrate a remarkable strategy adapted by beneficial rhizobacteria to utilize carbon-rich root exudates, which may facilitate rhizobacterial colonization and a mutualistic association with the host.
Bacillus subtilis is a plant growth-promoting rhizobacterium that establishes robust interactions with roots. Many studies have now demonstrated that biofilm formation is required for long-term colonization. However, we observed that motile B. subtilis mediates the first contact with the roots. These cells differentiate into biofilm-producing cells only several hours after the bacteria first contact the root. Our study reveals that intact chemotaxis machinery is required for the bacteria to reach the root. Many, if not all, of the B. subtilis 10 chemoreceptors are involved in the interaction with the plant. These observations stress the importance of root-bacterium interactions in the B. subtilis lifestyle.
ABSTRACT Horizontal gene transfer by integrative and conjugative elements (ICEs) is a very important mechanism for spreading antibiotic resistance in various bacterial species. In environmental and ...clinical settings, most bacteria form biofilms as a way to protect themselves against extracellular stress. However, much remains to be known about ICE transfer in biofilms. Using ICEBs1 from Bacillus subtilis, we show that the natural conjugation efficiency of this ICE is greatly affected by the ability of the donor and recipient to form a biofilm. ICEBs1 transfer considerably increases in biofilm, even at low donor/recipient ratios. Also, while there is a clear temporal correlation between biofilm formation and ICEBs1 transfer, biofilms do not alter the level of ICEBs1 excision in donor cells. Conjugative transfer appears to be favored by the biophysical context of biofilms. Indeed, extracellular matrix production, particularly from the recipient cells, is essential for biofilms to promote ICEBs1 transfer. Our study provides basic new knowledge on the high rate of conjugative transfer of ICEs in biofilms, a widely preponderant bacterial lifestyle in the environment, which could have a major impact on our understanding of horizontal gene transfer in natural and clinical environments. IMPORTANCE Transfer of mobile genetic elements from one bacterium to another is the principal cause of the spread of antibiotic resistance. However, the dissemination of these elements in environmental contexts is poorly understood. In clinical and environmental settings, bacteria are often found living in multicellular communities encased in a matrix, a structure known as a biofilm. In this study, we examined how forming a biofilm influences the transmission of an integrative and conjugative element (ICE). Using the model Gram-positive bacterium B. subtilis, we observed that biofilm formation highly favors ICE transfer. This increase in conjugative transfer is due to the production of extracellular matrix, which creates an ideal biophysical context. Our study provides important insights into the role of the biofilm structure in driving conjugative transfer, which is of major importance since biofilm is a widely preponderant bacterial lifestyle for clinically relevant bacterial strains.
Horizontal gene transfer by integrative and conjugative elements (ICEs) is a very important mechanism for spreading antibiotic resistance in various bacterial species. In environmental and clinical ...settings, most bacteria form biofilms as a way to protect themselves against extracellular stress. However, much remains to be known about ICE transfer in biofilms. Using ICE
from
, we show that the natural conjugation efficiency of this ICE is greatly affected by the ability of the donor and recipient to form a biofilm. ICE
transfer considerably increases in biofilm, even at low donor/recipient ratios. Also, while there is a clear temporal correlation between biofilm formation and ICE
transfer, biofilms do not alter the level of ICE
excision in donor cells. Conjugative transfer appears to be favored by the biophysical context of biofilms. Indeed, extracellular matrix production, particularly from the recipient cells, is essential for biofilms to promote ICE
transfer. Our study provides basic new knowledge on the high rate of conjugative transfer of ICEs in biofilms, a widely preponderant bacterial lifestyle in the environment, which could have a major impact on our understanding of horizontal gene transfer in natural and clinical environments.
Transfer of mobile genetic elements from one bacterium to another is the principal cause of the spread of antibiotic resistance. However, the dissemination of these elements in environmental contexts is poorly understood. In clinical and environmental settings, bacteria are often found living in multicellular communities encased in a matrix, a structure known as a biofilm. In this study, we examined how forming a biofilm influences the transmission of an integrative and conjugative element (ICE). Using the model Gram-positive bacterium
, we observed that biofilm formation highly favors ICE transfer. This increase in conjugative transfer is due to the production of extracellular matrix, which creates an ideal biophysical context. Our study provides important insights into the role of the biofilm structure in driving conjugative transfer, which is of major importance since biofilm is a widely preponderant bacterial lifestyle for clinically relevant bacterial strains.
We report a simple theory for the reduction of substrate modes in quasi-optical power-combining arrays. This qualitative theory predicts that detrimental substrate-mode effects can be greatly reduced ...through a judicious choice of the array unit cell size. Experimental evidence from quasi-optical tripler grids is presented to confirm the theory. Measured results show a dramatic improvement in the radiation pattern and effective radiated power of arrays with both grounded and ungrounded substrates.
L'analyse des images SPOT et de documents topographiques couvrant le Nord-Est du bras nord de Sulawesi, couplée à une étude de terrain, nous a permis de montrer que cette région est caractérisée par ...un régime tectonique en décrochement sénestre, qui produit une déformation distribuée d'orientation ENE-WSW. Cette déformation accommode le mouvement nord-sud de la mer de Célèbes, tout en constituant une zone de transfert entre la terminaison de la subduetion de la mer de Célèbes et la zone de subduetion de la mer des Moluques. Dans ce contexte, la caldeira de Tondano s'est mise en place dans une zone de relais guidée par des segments de faille décrochants, actuellement partiellement inactifs.
Field study and SPOT image analyses on the Tondano caldera region permit us to show a distributed active sinistral strike-slip fault zone which trends ENE- WSW This faulting accommodates the N-S movement of the Celebes Sea plate and represents a transfer fault zone between the Celebes sea subduetion end and the Moluccas sea subduetion zone. Furthermore, this study permits us to provide evidence for a tectonic control of the Tondano caldera collapse and evolution.
A high-linearity 100-element diode grid mixer Oliveira, M.; Dart-Mao Cheung, C.; Al-Zayed, A. ...
IEEE transactions on antennas and propagation,
05/2002, Letnik:
50, Številka:
5
Journal Article
Recenzirano
Grid-mixer arrays can achieve high linearity and dynamic range through quasi-optical power combining. We present a 100-element single-ended diode grid mixer operating at 2.45 GHz. Each element ...incorporates two diodes in series. We measure an input third-order intercept of 11 W (40.5 dBm), and output third-order intercept of 3.4 W (35.4 dBm), and an associated conversion loss of 5.1 dB. The power-handling capability of the array is 100 times larger than that of a microstrip mixer using a single element. The local oscillator (LO) drive requirement for the entire array is 1.4 W (31.6 dBm). The angular dependence of the array's IF power is also presented and is in agreement with theory.
Active quasi-optics has offered an elegant solution to the current power combining schemes. A two-dimensional array of phase-locked solid-state devices combines the output powers in free-space, ...eliminating conductor losses. Until the present time, only grids using a transmission architecture have been successfully tested. However, because of the heat dissipation issues associated with the transmission architecture, alternative solutions were in demand for high-power applications.In this thesis, the enhanced modeling and first successful operation of a reflection amplifier grid is presented. Because the reflection architecture is not well suited for the use of external polarizers, external tuning of the grid is much less flexible than for its transmissive cousin. Therefore, an extensive electromagnetic simulation of the grid’s passive structure was performed using a High Frequency Structure Simulator (HFSS) software package. Upon successful modeling, a hybrid X-band 16-element grid amplifier was built. The grid uses custom-made differential-pair chips with TRW InP Heterojunction Bipolar Transistors (HBTs) as the active devices. A peak gain of 15 dB at 10.2 GHz was measured. The 3-dB bandwidth is 530 MHz or 5%. If a 3-dB gain reduction can be tolerated, 70° can spatially separate the input and output beams. All measurements were consistent with the theoretical predictions.
We present a 16-element hybrid grid amplifier with improved heat sinking. This is a higher-power version of a previously reported reflection grid amplifier. The grid uses custom-made ...differential-pair chips with TRW InP Heterojunction Bipolar Transistors (HBTs) as the active devices. We measure a peak gain of 15 dB at 8.4 GHz. Measured gain is consistent with theoretical predictions. The grid was able to dissipate up to 4 W of dc bias power without any apparent thermal damage. Measurements on passive resistor arrays demonstrate this architecture's superior thermal performance.
We present a 16-element hybrid grid amplifier. This is the first successful grid amplifier to use a reflection architecture, which should provide thermal performance superior to transmission grids. ...The grid uses custom-made differential-pair chips with TRW InP heterojunction bipolar transistors (HBTs) as the active devices. We measure a peak gain of 15 dB at 10.2 GHz. Gain, tuning, and angular measurements are consistent with theoretical predictions.
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