Regulatory linkages between flagella and surfactant during swarming behavior: lubricating the flagellar propeller?

Synergistic Antibacterial Effect of Ethyl Acetate Fraction of Vernonia amygdalina Delile Leaves with Tetracycline against Clinical Isolate Methicillin-Resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa

Multidrug-resistant bacteria have raised global concern about the inability to fight deadly infectious diseases. Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa are the most common resistant bacteria that are causing hospital infections. The present study was undertaken to investigate the synergistic antibacterial effect of the ethyl acetate fraction of Vernonia amygdalina Delile leaves (EAFVA) with tetracycline against the clinical isolates MRSA and P. aeruginosa. Microdilution was used to establish the minimum inhibitory concentration (MIC). A checkerboard assay was conducted for the interaction effect. Bacteriolysis, staphyloxanthin, and a swarming motility assay were also investigated. EAFVA exhibited antibacterial activity against MRSA and P. aeruginosa with a MIC value of 125 μg/mL. Tetracycline showed antibacterial activity against MRSA and P. aeruginosa with MIC values of 15.62 and 31.25 μg/mL, respectively. The interaction between EAFVA and tetracycline showed a synergistic effect against MRSA and P. aeruginosa with a Fractional Inhibitory Concentration Index (FICI) of 0.375 and 0.31, respectively. The combination of EAFVA and tetracycline induced the alteration of MRSA and P. aeruginosa, leading to cell death. Moreover, EAFVA also inhibited the quorum sensing system in MRSA and P. aeruginosa. The results revealed that EAFVA enhanced the antibacterial activity of tetracycline against MRSA and P. aeruginosa. This extract also regulated the quorum sensing system in the tested bacteria.

Biosurfactants: Potential Agents for Controlling Cellular Communication, Motility, and Antagonism

Biosurfactants are surface-active molecules produced by microorganisms, either on the cell surface or secreted extracellularly. They form a thin film on the surface of microorganisms and help in their detachment or attachment to other cell surfaces. They are involved in regulating the motility of bacteria and quorum sensing. Here, we describe the various types of biosurfactants produced by microorganisms and their role in controlling motility, antagonism, virulence, and cellular communication.

Bioinspired, Recyclable, Stretchable Hydrogel with Boundary Ultralubrication

Although hydrogels exhibit excellent low frictional behavior, their friction coefficients cannot meet the requirements for biology, especially at low sliding velocities. Inspired by the natural lubrication mechanism from animals, plants, or even microorganisms, a nonionic surfactant, Tween 80, was introduced into a biofriendly poly(vinyl alcohol) (PVA) hydrogel to construct a composite hydrogel with ultralubrication. Such a combination endows PVA hydrogels with an ultralow coefficient of friction (10^-3 to 10^-4) under an extremely low sliding velocity (0.01 mm/s). Tween 80 micelles and aggregates, together with hydrophobic molds, induce rough surfaces and high carbon contents on the surface of the hydrogel, promoting excellent lubrication behavior of the composite hydrogel. In addition to the desirable lubrication, this environmentally friendly composite hydrogel also exhibited excellent flexibility at subzero temperatures, tensile properties, and good recyclability. Additionally, the method of introducing Tween 80 into hydrogels to reduce friction is also effective in chemically crosslinked double-network hydrogels.

Oral seeding and niche-adaptation of middle ear biofilms in health

The entrenched dogma of a sterile middle ear mucosa in health is incongruent with its periodic aeration and seeding with saliva aerosols. To test this, we sequenced 16S rRNA-V4 amplicons from otic secretions collected at the nasopharyngeal orifice of the tympanic tube and, as controls, oropharyngeal and buccal samples. The otic samples harbored a rich diversity of oral keystone genera and similar functional traits but were enriched in anaerobic genera in the Bacteroidetes (Prevotella and Alloprevotella), Fusobacteria (Fusobacterium and Leptotrichia) and Firmicutes (Veillonella) phyla. Facultative anaerobes in the Streptococcus genus were also abundant in the otic and oral samples but corresponded to distinct, and sometimes novel, cultivars, consistent with the ecological diversification of the oral migrants once in the middle ear microenvironment. Neutral community models also predicted a large contribution of oral dispersal to the otic communities and the positive selection of taxa better adapted to growth and reproduction under limited aeration. These results challenge the traditional view of a sterile middle ear in health and highlight hitherto unknown roles for oral dispersal and episodic ventilation in seeding and diversifying otic biofilms.

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The middle ear mucosa harbors a rich bacterial community in health.

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Oral migration is the primary mechanism for seeding otic biofilms.

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Periodic aeration of the middle ear enriches for anaerobic taxa and promotes the ecological diversification of oral migrants.

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Our study challenges the entrenched dogma of a sterile middle ear in health.

Pseudomonas syringae pv. tomato exploits light signals to optimize virulence and colonization of leaves

Light is pervasive in the leaf environment, creating opportunities for both plants and pathogens to cue into light as a signal to regulate plant-microbe interactions. Light enhances plant defences and regulates opening of stomata, an entry point for foliar bacterial pathogens such as Pseudomonas syringae pv. tomato DC3000 (PsPto). The effect of light perception on gene expression and virulence was investigated in PsPto. Light induced genetic reprogramming in PsPto that entailed significant changes in stress tolerance and virulence. Blue light-mediated up-regulation of type three secretion system genes and red light-mediated down-regulation of coronatine biosynthesis genes. Cells exposed to white light, blue light or darkness before inoculation were more virulent when inoculated at dawn than dusk probably due to an enhanced entry through open stomata. Exposure to red light repressed coronatine biosynthesis genes which could lead to a reduced stomatal re-opening and PsPto entry. Photoreceptor were required for the greater virulence of light-treated and dark-treated PsPto inoculated at dawn as compared to dusk, indicating that these proteins sense the absence of light and contribute to priming of virulence in the dark. These results support a model in which PsPto exploits light changes to maximize survival, entry and virulence on plants.

Cyclic Lipodepsipeptides From Pseudomonas spp. - Biological Swiss-Army Knives

Cyclic lipodepsipeptides produced by Pseudomonas spp. (Ps-CLPs) are biosurfactants that constitute a diverse class of versatile bioactive natural compounds with promising application potential. While chemically diverse, they obey a common structural blue-print, allowing the definition of 14 distinct groups with multiple structurally homologous members. In addition to antibacterial and antifungal properties the reported activity profile of Ps-CLPs includes their effect on bacterial motility, biofilm formation, induced defense responses in plants, their insecticidal activity and anti-proliferation effects on human cancer cell-lines. To further validate their status of potential bioactive substances, we assessed the results of 775 biological tests on 51 Ps-CLPs available from literature. From this, a fragmented view emerges. Taken as a group, Ps-CLPs present a broad activity profile. However, reports on individual Ps-CLPs are often much more limited in the scope of organisms that are challenged or activities that are explored. As a result, our analysis shows that the available data is currently too sparse to allow biological function to be correlated to a particular group of Ps-CLPs. Consequently, certain generalizations that appear in literature with respect to the biological activities of Ps-CLPs should be nuanced. This notwithstanding, the data for the two most extensively studied Ps-CLPs does indicate they can display activities against various biological targets. As the discovery of novel Ps-CLPs accelerates, current challenges to complete and maintain a useful overview of biological activity are discussed.

Sequencing and Analysis of the Pseudomonas fluorescens GcM5-1A Genome: A Pathogen Living in the Surface Coat of Bursaphelenchus xylophilus

It is known that several bacteria are adherent to the surface coat of pine wood nematode (Bursaphelenchus xylophilus), but their function and role in the pathogenesis of pine wilt disease remains debatable. The Pseudomonas fluorescens GcM5-1A is a bacterium isolated from the surface coat of pine wood nematodes. In previous studies, GcM5-1A was evident in connection with the pathogenicity of pine wilt disease. In this study, we report the de novo sequencing of the GcM5-1A genome. A 600-Mb collection of high-quality reads was obtained and assembled into sequence contigs spanning a 6.01-Mb length. Sequence annotation predicted 5,413 open reading frames, of which 2,988 were homologous to genes in the other four sequenced P. fluorescens isolates (SBW25, WH6, Pf0-1 and Pf-5) and 1,137 were unique to GcM5-1A. Phylogenetic studies and genome comparison revealed that GcM5-1A is more closely related to SBW25 and WH6 isolates than to Pf0-1 and Pf-5 isolates. Towards study of pathogenesis, we identified 79 candidate virulence factors in the genome of GcM5-1A, including the Alg, Fl, Waa gene families, and genes coding the major pathogenic protein fliC. In addition, genes for a complete T3SS system were identified in the genome of GcM5-1A. Such systems have proved to play a critical role in subverting and colonizing the host organisms of many gram-negative pathogenic bacteria. Although the functions of the candidate virulence factors need yet to be deciphered experimentally, the availability of this genome provides a basic platform to obtain informative clues to be addressed in future studies by the pine wilt disease research community.