We report the experimental studies on interaction of two vesicles trapped in a microfluidic four-roll mill, where a plane linear flow is realized. We found that the dynamics of a vesicle in ...tank-treading motion is significantly altered by the presence of another vesicle at separation distances up to 3.2-3.7 times of the vesicle effective radius. This result is supported by measurement of a single vesicle back-reaction on the velocity field. Thus the experiment provides the upper bound for the volume fraction φ = 0.08-0.13 of noninteracting vesicle suspensions.
Integrative conjugative elements (ICEs) are chromosomal elements that are widely distributed in bacterial genomes, hence contributing to genome plasticity, adaptation, and evolution of bacteria. ...Conjugation requires a contact between both the donor and the recipient cells and thus likely depends on the composition of the cell surface envelope. In this work, we investigated the impact of different cell surface molecules, including cell surface proteins, wall teichoic acids, lipoteichoic acids, and exopolysaccharides, on the transfer and acquisition of ICESt3 from Streptococcus thermophilus. The transfer of ICESt3 from wild-type (WT) donor cells to mutated recipient cells increased 5- to 400-fold when recipient cells were affected in lipoproteins, teichoic acids, or exopolysaccharides compared to when the recipient cells were WT. These mutants displayed an increased biofilm-forming ability compared to the WT, suggesting better cell interactions that could contribute to the increase of ICESt3 acquisition. Microscopic observations of S. thermophilus cell surface mutants showed different phenotypes (aggregation in particular) that can also have an impact on conjugation. In contrast, the same mutations did not have the same impact when the donor cells, instead of recipient cells, were mutated. In that case, the transfer frequency of ICESt3 decreased compared to that with the WT. The same observation was made when both donor and recipient cells were mutated. The dominant effect of mutations in donor cells suggests that modifications of the cell envelope could impair the establishment or activity of the conjugation machinery required for DNA transport.
Integrative conjugative elements (ICEs) are chromosomal elements that are widely distributed in bacterial genomes, hence contributing to genome plasticity, adaptation, and evolution of bacteria. ...Conjugation requires a contact between both the donor and the recipient cells and thus likely depends on the composition of the cell surface envelope. In this work, we investigated the impact of different cell surface molecules, including cell surface proteins, wall teichoic acids, lipoteichoic acids, and exopolysaccharides, on the transfer and acquisition of ICE
from
The transfer of ICE
from wild-type (WT) donor cells to mutated recipient cells increased 5- to 400-fold when recipient cells were affected in lipoproteins, teichoic acids, or exopolysaccharides compared to when the recipient cells were WT. These mutants displayed an increased biofilm-forming ability compared to the WT, suggesting better cell interactions that could contribute to the increase of ICE
acquisition. Microscopic observations of
cell surface mutants showed different phenotypes (aggregation in particular) that can also have an impact on conjugation. In contrast, the same mutations did not have the same impact when the donor cells, instead of recipient cells, were mutated. In that case, the transfer frequency of ICE
decreased compared to that with the WT. The same observation was made when both donor and recipient cells were mutated. The dominant effect of mutations in donor cells suggests that modifications of the cell envelope could impair the establishment or activity of the conjugation machinery required for DNA transport.
ICEs contribute to horizontal gene transfer of adaptive traits (for example, virulence, antibiotic resistance, or biofilm formation) and play a considerable role in bacterial genome evolution, thus underlining the need of a better understanding of their conjugative mechanism of transfer. While most studies focus on the different functions encoded by ICEs, little is known about the effect of host factors on their conjugative transfer. Using ICE
of
as a model, we demonstrated the impact of lipoproteins, teichoic acids, and exopolysaccharides on ICE transfer and acquisition. This opens up new avenues to control gene transfer mediated by ICEs.
Brochothrix thermosphacta is considered as a major spoiler of meat and seafood products. This study explores the biofilm formation ability and the biofilm structural diversity of 30 multi-origin B. ...thermosphacta strains using a set of complementary biofilm assays (biofilm ring test, crystal violet staining, and confocal laser scanning microscopy). Two major groups corresponding to low and high biofilm producers were identified. High biofilm producers presented flat architectures characterized by high surface coverage, high cell biovolume, and high surface area.
Nanohybrids based on maghemite iron oxide nanoparticles (IONPs) and carbon dots (CDs), with different linkers between the two components, are synthesized, with the idea of combining several ...properties (magnetic and optical) in one nanomaterial in order to eradicate bacterial biofilm. The photothermal capacities of these materials are expressed by two parameters: the specific absorption rate (SAR) and the photothermal light-to-heat conversion constant (η). They show that the IONP/CD combination is more effective in photothermia (PT) than either of the components, but depends on the linkage (amide > ester > electrostatic). The antibacterial properties of the nanohybrids are first determined for the exponential and stationary growth phases of planktonic S. aureus and B. subtilis with and without PT. In the absence of PT, no nanohybrid has any significant bactericidal effect, but with PT the nanohybrids have different activities, with the IONP-amide-CD pattern the most effective. Combining magnetic actuation and PT on B. subtilis biofilms shows a synergistic effect and reveals the advantages of using such nanohybrid materials for killing bacteria and eradicating biofilm.
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•Synthesis of magnetic iron oxide nanoparticle/carbon dot (IONP/CD) hybrids.•Photothermal properties of hybrids are structure-dependent.•Photothermia of selected nanohybrid is very effective for killing planktonic bacteria.•Combination of photothermia and magnetic actuation of hybrid destructs biofilms efficiently.
We consider a non-interacting bipartite quantum system $\mathcal H_S^A\otimes\mathcal H_S^B$ undergoing repeated quantum interactions with an environment modeled by a chain of independant quantum ...systems interacting one after the other with the bipartite system. The interactions are made so that the pieces of environment interact first with $\mathcal H_S^A$ and then with $\mathcal H_S^B$. Even though the bipartite systems are not interacting, the interactions with the environment create an entanglement. We show that, in the limit of short interaction times, the environment creates an effective interaction Hamiltonian between the two systems. This interaction Hamiltonian is explicitly computed and we show that it keeps track of the order of the successive interactions with $\mathcal H_S^A$ and $\mathcal H_S^B$. Particular physical models are studied, where the evolution of the entanglement can be explicitly computed. We also show the property of return of equilibrium and thermalization for a family of examples.
Listeria monocytogenes has a dichotomous lifestyle, existing as an ubiquitous saprophytic species and as an opportunistic intracellular pathogen. Besides its capacity to grow in a wide range of ...environmental and stressful conditions, L. monocytogenes has the ability to adhere to and colonize surfaces. Morphotype variation to elongated cells forming rough colonies has been reported for different clinical and environmental isolates, including biofilms. This cell differentiation is mainly attributed to the reduced secretion of two SecA2‐dependent cell‐wall hydrolases, CwhA and MurA. SecA2 is a non‐essential SecA paralogue forming an alternative translocase with the primary Sec translocon. Following investigation at temperatures relevant to its ecological niches, i.e. infection (37°C) and environmental (20°C) conditions, inactivation of this SecA2‐only protein export pathway led, despite reduced adhesion, to the formation of filamentous biofilm with aerial structures. Compared to the wild type strain, inactivation of the SecA2 pathway promoted extensive cell aggregation and sedimentation. At ambient temperature, this effect was combined with the abrogation of cell motility resulting in elongated sedimented cells, which got knotted and entangled together in the course of filamentous‐biofilm development. Such a cell differentiation provides a decisive advantage for listerial surface colonization under environmental condition. As further discussed, this morphotypic conversion has strong implication on listerial physiology and is also of potential significance for asymptomatic human/animal carriage.
Summary
Bacteria of the genus Thiomonas are found ubiquitously in arsenic contaminated waters such as acid mine drainage (AMD), where they contribute to the precipitation and the natural ...bioremediation of arsenic. In these environments, these bacteria have developed a large range of resistance strategies among which the capacity to form particular biofilm structures. The biofilm formation is one of the most ubiquitous adaptive response observed in prokaryotes to various stresses, such as those induced in the presence of toxic compounds. This study focused on the process of biofilm formation in three Thiomonas strains (CB1, CB2 and CB3) isolated from the same AMD. The results obtained here show that these bacteria are all capable of forming biofilms, but the architecture and the kinetics of formation of these biofilms differ depending on whether arsenite is present in the environment and from one strain to another. Indeed, two strains favoured biofilm formation, whereas one favoured motility in the presence of arsenite. To identify the underlying mechanisms, the patterns of expression of some genes possibly involved in the process of biofilm formation were investigated in Thiomonas sp. CB2 in the presence and absence of arsenite, using a transcriptomic approach (RNA‐seq). The findings obtained here shed interesting light on how the formation of biofilms, and the motility processes contribute to the adaptation of Thiomonas strains to extreme environments.
This study shows that Thiomonas strains (CB1, CB2 and CB3) isolated from the same Acid Mine Drainage are all capable of forming biofilms, but the architecture and the kinetics of formation of these biofilms differ depending on whether arsenite is present in the environment and from one strain to another. The findings obtained here shed interesting light on how the formation of biofilms and the motility processes contribute to the adaptation of Thiomonas strains to extreme environments.
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