Bacteria have evolved a variety of signal transduction mechanisms that generate different outputs in response to external stimuli. Chemosensory pathways are widespread in bacteria and are among the most complex signaling mechanisms, requiring the participation of at least six proteins. These pathways mediate flagellar chemotaxis, in addition to controlling alternative functions such as second messenger levels or twitching motility. The human pathogen Pseudomonas aeruginosa has four different chemosensory pathways that carry out different functions and are stimulated by signal binding to 26 chemoreceptors. Recent research employing a diverse range of experimental approaches has advanced enormously our knowledge on these four pathways, establishing P. aeruginosa as a primary model organism in this field. In the first part of this article, we review data on the function and physiological relevance of chemosensory pathways as well as their involvement in virulence, whereas the different transcriptional and posttranscriptional regulatory mechanisms that govern pathway function are summarized in the second part. The information presented will be of help to advance the understanding of pathway function in other organisms.

Pseudomonas aeruginosa as a Model To Study Chemosensory Pathway Signaling.

Bacterial exopolysaccharides (EPS) are essential natural biopolymers used in different areas including biomedicine, food, cosmetic, petroleum, and pharmaceuticals and also in environmental remediation. The interest in them is primarily due to their unique structure and properties such as biocompatibility, biodegradability, higher purity, hydrophilic nature, anti-inflammatory, antioxidant, anti-cancer, antibacterial, and immune-modulating and prebiotic activities. The present review summarizes the current research progress on bacterial EPSs including their properties, biological functions, and promising applications in the various fields of science, industry, medicine, and technology, as well as characteristics and the isolation sources of EPSs-producing bacterial strains. This review provides an overview of the latest advances in the study of such important industrial exopolysaccharides as xanthan, bacterial cellulose, and levan. Finally, current study limitations and future directions are discussed.

Exopolysaccharides Producing Bacteria: A Review

The formation of biofilms results from a multicellular mode of growth, in which bacteria remain enwrapped by an extracellular matrix of their own production. Many different bacteria form biofilms, but among the most studied species are those that belong to the Pseudomonas genus due to the metabolic versatility, ubiquity, and ecological significance of members of this group of microorganisms. Within the Pseudomonas genus, biofilm studies have mainly focused on the opportunistic human pathogen Pseudomonas aeruginosa due to its clinical importance. The extracellular matrix of P. aeruginosa is mainly composed of exopolysaccharides, which have been shown to be important for the biofilm architecture and pathogenic features of this bacterium. Notably, some of the exopolysaccharides recurrently used by P. aeruginosa during biofilm formation, such as the alginate and polysaccharide synthesis loci (Psl) polysaccharides, are also used by pathogenic and beneficial plant-associated Pseudomonas during their interaction with plants. Interestingly, their functions are multifaceted and seem to be highly dependent on the bacterial lifestyle and genetic context of production. This paper reviews the functions and significance of the exopolysaccharides produced by plant-associated Pseudomonas, particularly the alginate, Psl, and cellulose polysaccharides, focusing on their equivalents produced in P. aeruginosa within the context of pathogenic and beneficial interactions.

https://www.mdpi.com/2076-2607/9/2/445/pdf

Beyond the Wall: Exopolysaccharides in the Biofilm Lifestyle of Pathogenic and Beneficial Plant-Associated Pseudomonas.

Cellulose is one of the most abundant renewable biopolymer in nature and is present as major constituent in both plant cell walls as well as synthesized by some microorganisms as extracellular products. In both the systems, cellulose self-assembles into a hierarchical ordered architecture to form micro to nano-fibrillated structures, on basis of which it is classified into various forms. Nanocellulose (NCs) exist as rod-shaped highly crystalline cellulose nanocrystals to high aspect ratio cellulose nanofibers, micro-fibrillated cellulose and bacterial cellulose (BC), depending upon the origin, structural and morphological properties. Moreover, NCs have been processed into diversified products ranging from composite films, coatings, hydrogels, aerogels, xerogels, organogels, rheological modifiers, optically active birefringent colored films using traditional-to-advanced manufacturing techniques. With such versatility in structure-property, NCs have profound application in areas of healthcare, packaging, cosmetics, energy, food, electronics, bioremediation, and biomedicine with promising commercial potential. Herein this review, we highlight the recent advancements in synthesis, fabrication, processing of NCs, with strategic chemical modification routes to tailor its properties for targeted biomedical applications. We also study the basic mechanism and models for biosynthesis of cellulose in both plant and microbial systems and understand the structural insights of NC polymorphism. The kinetics study for both enzymatic/chemical modifications of NCs and microbial growth behavior of BC under various reactor configurations are studied. The challenges associated with the commercial aspects as well as industrial scale production of pristine and functionalized NCs to meet the growing demands of market are discussed and prospective strategies to mitigate them are described. Finally, post chemical modification evaluation of biological and inherent properties of NC are important to determine their efficacy for development of various products and technologies directed for biomedical applications.

Biomedical engineering aspects of nanocellulose: a review

Water and soil contain a multiplicity of particulate material coated with bacterial populations and communities. Microbiotic particles are any type of small particle (measuring less than 2 mm) to which bacteria and other microbes attach, resulting in medium to long-term colonization. This study reviews the interactions of ecologically distant bacterial organisms on microbiotic particles in soil and water as a method for explaining the evolution and spread of antibiotic resistance traits. These particles include bacteria-bacteria aggregates, which can merge with particles from fungi, protozoa, phytoplankton, zooplankton, and biodetritus resulting from animal and vegetal decomposition, humus, mineral particles (clay, carbonates, silicates), and anthropogenic particles (including wastewater particles and microplastics). In turn, these complex particles can interact and coalesce. Natural phenomena (waterflow, tides, tsunamis, currents, and strong winds) and anthropogenic activity (agriculture, waste-water management, mining, excavation/construction) favor the interaction and merging of microbiotic particles in soil and water, resulting in enhanced recombinant communities capable of exchanging genetic material, including antimicrobial resistance genes, particularly in antimicrobial-polluted environments. In this review, we propose that the worldwide spread of antimicrobial resistance might be related to the environmental dynamics of microbiotic particles, and we discuss possible methods for reducing this problem that threatens One Health and Planetary Health.

https://www.frontiersin.org/articles/10.3389/fenvs.2022.824963/pdf

The Influence of Coalescent Microbiotic Particles From Water and Soil on the Evolution and Spread of Antimicrobial Resistance

Cellulose-overproducing wrinkly spreader mutants of Pseudomonas fluorescens SBW25 have been the focus of much investigation, but conditions promoting the production of cellulose in ancestral strain SBW25 and its effects and consequences have escaped in-depth investigation through lack of an in vitro phenotype. Here, using a custom-built device, we reveal that in static broth microcosms, ancestral SBW25 encounters environmental signals at the air-liquid interface that activate, via three diguanylate cyclase-encoding pathways (Wsp, Aws, and Mws), production of cellulose. Secretion of the polymer at the meniscus leads to modification of the environment and growth of numerous microcolonies that extend from the surface. Accumulation of cellulose and associated microbial growth leads to Rayleigh-Taylor instability resulting in bioconvection and rapid transport of water-soluble products over tens of millimeters. Drawing upon data, we built a mathematical model that recapitulates experimental results and captures the interactions between biological, chemical and physical processes.IMPORTANCE This work reveals a hitherto unrecognized behavior that manifests at the air-liquid interface that depends on production of cellulose and hints at undiscovered dimensions to bacterial life at surfaces. Additionally, the study links activation of known diguanylate cyclase-encoding pathways to cellulose expression and to signals encountered at the meniscus. Further significance stems from recognition of the consequences of fluid instabilities arising from surface production of cellulose for transport of water-soluble products over large distances.

/pdf/causes-and-biophysical-consequences-of-cellulose-production-2pvvs1yg1a.pdf

Causes and Biophysical Consequences of Cellulose Production by Pseudomonas fluorescens SBW25 at the Air-Liquid Interface.

Cellulose over-producing wrinkly spreader mutants of Pseudomonas fluorescens SBW25 have been the focus of much investigation, but conditions promoting the production of cellulose in ancestral SBW25, its effects and consequences have escaped investigation through lack of in vitro phenotype. Here, using a custom built device, we reveal that in static broth microcosms ancestral SBW25 encounters environmental signals at the air-liquid interface that activate, via three diguanylate cyclase-encoding pathways (Wsp, Aws and Mws), production of cellulose. Secretion of the polymer at the meniscus leads to modification of the environment and growth of numerous micro-colonies that extend out from the surface. Accumulation of cellulose and associated microbial growth leads to Rayleigh-Taylor instability resulting in bioconvection and rapid transport of water-soluble products over tens of millimetres. Drawing upon data we build a mathematical model that recapitulates experimental results and captures the interactions between biological, chemical and physical processes. IMPORTANCE This work reveals a new bacterial behaviour that manifests at the air-liquid interface, which depends on production of cellulose, and hints to hitherto unrecognised dimensions to bacterial life at surfaces. Additionally, the study links activation of known diguanylate cyclase-encoding pathways to cellulose expression and to signals encountered at the air-liquid interface. Further significance stems from recognition of the consequences of fluid instabilities arising from surface production of cellulose for transport of water-soluble products over large distances.

https://www.biorxiv.org/content/biorxiv/early/2019/02/01/538561.full.pdf

Causes and consequences of cellulose production by Pseudomonas fluorescens SBW25 at the air-liquid interface

Pyoverdin is a water-soluble metal-chelator synthesized by members of the genus Pseudomonas and used for the acquisition of insoluble ferric iron. Although freely diffusible in aqueous environments, preferential dissemination of pyoverdin among adjacent cells, fine-tuning of intracellular siderophore concentrations, and fitness advantages to pyoverdin-producing versus nonproducing cells, indicate control of location and release. Here, using time-lapse fluorescence microscopy to track single cells in growing microcolonies of Pseudomonas fluorescens SBW25, we show accumulation of pyoverdin at cell poles. Accumulation is induced by arrest of cell division, is achieved by cross-feeding in pyoverdin-nonproducing mutants, is independent of cell shape, and is reversible. Furthermore, it occurs in multi-species communities. Analysis of the performance of pyoverdin-producing and nonproducing cells under conditions promoting polar localization shows an advantage to accumulation on resumption of growth after stress. While the genetic basis of polarization remains unclear, evaluation of deletion mutants of pyoverdin transporters (opmQ, fpvA) establishes non-involvement of these candidate loci. Examination of pyoverdin polar accumulation in a model community and in a range of laboratory and natural species of Pseudomonas, including P. aeruginosa PAO1 and P. putida KT2440, confirms that the phenotype is characteristic of Pseudomonas. Significance Bacteria secrete extracellular products that enable nutrients to be obtained from the environment. A secreted product of relevance for medicine, agriculture and biotechnology is the iron-chelating siderophore, pyoverdin, which is produced by members of the genus Pseudomonas. By analyzing the behavior of single cells we show that on cessation of cell division, pyoverdin localizes to cell poles, but is then released to the environment prior to resumption of cell growth. Of particular significance is the ecological relevance of this behavior: cells that accumulate the siderophore resume growth with minimal delay. Our study reveals a hitherto unrecognized dimension to the biology of Pseudomonas that may prove central to understanding the broader ecological and physiological relevance of pyoverdin.

/pdf/single-cell-imaging-of-pseudomonas-reveals-dynamic-polar-51n6ryo9qt.pdf

Single-cell imaging of Pseudomonas reveals dynamic polar accumulation of the extracellular iron-scavenger pyoverdin

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Causes and Biophysical Consequences of Cellulose Production by Pseudomonas fluorescens SBW25 at the Air-Liquid Interface.

Causes and consequences of cellulose production by Pseudomonas fluorescens SBW25 at the air-liquid interface

Single-cell imaging of Pseudomonas reveals dynamic polar accumulation of the extracellular iron-scavenger pyoverdin