Bacterial biofilm shows persistent resistance to liquid wetting and gas penetration

Isolation and characterization of Salmonella spp. from food and food contact surfaces in a chicken processing factory

The presence of Salmonella serotypes is a major safety concern of the food industry and poultry farmers. This study aimed to isolate and identify Salmonella spp. from a chicken processing facility by PCR and pulsed-field gel electrophoresis (PFGE). In addition, the biofilm-forming abilities of the isolated bacteria on stainless steel, silicone rubber, plastic, and chicken skin were also investigated. PCR was used for the confirmation of Salmonella serotypes, and then gene similarity within the same serotype was analyzed by PFGE. As a result, 26 S. Enteritidis isolates were detected at a high rate from both food contact surfaces and chicken products during processing. All of them were 100% genetically identical to the same bacteria. The results indicated that the virulence factors and effective biofilm-forming ability of S. Enteritidis isolates could affect human health and economic revenue. It was also suggested that the visual observation of food and food contact surfaces could be a great concern in the future. The continuous monitoring of S. Enteritidis molecular and biofilm characteristics is needed to increase food safety.

Collective colony growth is optimized by branching pattern formation in Pseudomonas aeruginosa

Branching pattern formation is common in many microbes. Extensive studies have focused on addressing how such patterns emerge from local cell-cell and cell-environment interactions. However, little is known about whether and to what extent these patterns play a physiological role. Here, we consider the colonization of bacteria as an optimization problem to find the colony patterns that maximize colony growth efficiency under different environmental conditions. We demonstrate that Pseudomonas aeruginosa colonies develop branching patterns with characteristics comparable to the prediction of modeling; for example, colonies form thin branches in a nutrient-poor environment. Hence, the formation of branching patterns represents an optimal strategy for the growth of Pseudomonas aeruginosa colonies. The quantitative relationship between colony patterns and growth conditions enables us to develop a coarse-grained model to predict diverse colony patterns under more complex conditions, which we validated experimentally. Our results offer new insights into branching pattern formation as a problem-solving social behavior in microbes and enable fast and accurate predictions of complex spatial patterns in branching colonies.

Swarming bacteria undergo localized dynamic phase transition to form stress-induced biofilms

Self-organized multicellular behaviors enable cells to adapt and tolerate stressors to a greater degree than isolated cells. However, whether and how cellular communities alter their collective behaviors adaptively upon exposure to stress is largely unclear. Here, we investigate this question using Bacillus subtilis, a model system for bacterial multicellularity. We discover that, upon exposure to a spatial gradient of kanamycin, swarming bacteria activate matrix genes and transit to biofilms. The initial stage of this transition is underpinned by a stress-induced multilayer formation, emerging from a biophysical mechanism reminiscent of motility-induced phase separation (MIPS). The physical nature of the process suggests that stressors which suppress the expansion of swarms would induce biofilm formation. Indeed, a simple physical barrier also induces a swarm-to-biofilm transition. Based on the gained insight, we propose a strategy of antibiotic treatment to inhibit the transition from swarms to biofilms by targeting the localized phase transition.

The Good, the Bad, and the Ugly: Mycotoxin Production During Postharvest Decay and Their Influence on Tritrophic Host-Pathogen-Microbe Interactions

Mycotoxins are a prevalent problem for stored fruits, grains, and vegetables. Alternariol, aflatoxin, and patulin, produced by Alternaria spp., Aspergillus spp., and Penicillium spp., are the major mycotoxins that negatively affect human and animal health and reduce fruit and produce quality. Control strategies for these toxins are varied, but one method that is increasing in interest is through host microbiome manipulation, mirroring a biocontrol approach. While the majority of mycotoxins and other secondary metabolites (SM) produced by fungi impact host–fungal interactions, there is also an interplay between the various organisms within the host microbiome. In addition to SMs, these interactions involve compounds such as signaling molecules, plant defense and growth hormones, and metabolites produced by both the plants and microbial community. Therefore, studies to understand the impact of the various toxins impacting the beneficial and harmful microorganisms that reside within the microbiome is warranted, and could lead to identification of safe analogs for antimicrobial activity to reduce fruit decay. Additionally, exploring the composition of the microbial carposphere of host plants is likely to shed light on developing a microbial consortium to maintain quality during storage and abate mycotoxin contamination.

Precision Design of Antimicrobial Surfaces

The overall expectation from an antimicrobial surface has been high considering the need for efficiency in preventing the attachment and growth of pathogenic microbes, durability, safety to both humans and environment as well as cost-effectiveness. To date, antimicrobial surface design has been mostly conducted liberally, without rigorous consideration of establishing robust structure-activity relationships for each design strategy or of the use intended for a specific antimicrobial material. However, the variability among the domain bacteria, which is the most diverse of all, alongside the highly dynamic nature of the bacteria-surface interface have taught us that the likelihood of finding universal antimicrobial surfaces is low. In this perspective we discuss some of the current hurdles faced by research in this promising field, emphasizing the relevance and complexity of probing the bacteria-surface interface, and explain why we feel it would greatly benefit from a more streamlined ad-hoc approach.

Comparative performance and mechanism of bacterial inactivation induced by metal-free modified g-C3N4 under visible light: Escherichia coli versus Staphylococcus aureus

The inactivation mechanism of pathogenic microorganisms in water needs to be comprehensively explored in order to better guide the development of an effective and green disinfection method for drinking water safety. Here, metal-free modified g-C₃N₄ was prepared and used to inactivate two typical bacteria (namely, Gram-positive E. coli and Gram-negative S. aureus) in water under visible light from a comparative perspective. These two bacteria could be inactivated in the presence of modified g-C₃N₄ within 6 h of visible light, but their inactivation kinetics were quite different. E. coli were inactivated slowly in the early disinfection stage and rapidly in the later disinfection stage, whereas S. aureus were inactivated steadily during the entire disinfection process. Moreover, the impacts of important water parameters (pH, salt, temperature, and water matrix) on photocatalytic inactivation of E. coli and S. aureus were also distinct. In addition, scavenger experiments indicated that superoxide radicals played the most important role in E. coli inactivation, while both superoxide and hydroxyl radicals were important for S. aureus inactivation. Quantitative changes in fatty acids, potassium ions, proteins and DNA of the bacterial suspensions suggested that the higher resistance of E. coli in the early inactivation stage could be originated from the difference in the phospholipid repair system in cell membrane structures. This study can provide new insights into research and development of a safe and effective disinfection technology for drinking water.

Pseudomonas aeruginosa detachment from surfaces via a self-made small molecule

Pseudomonas aeruginosa is a significant threat in both healthcare and industrial biofouling. Surface attachment of P. aeruginosa is particularly problematic as surface association induces virulence and is necessary for the ensuing process of biofilm formation, which hampers antibiotic treatments. Previous efforts have searched for dispersal agents of mature biofilm collectives, but there are no known factors that specifically disperse individual surface-attached P. aeruginosa. In this study, we develop a quantitative single-cell surface-dispersal assay and use it to show that P. aeruginosa itself produces factors that can stimulate its dispersal. Through bioactivity-guided fractionation, mass spectrometry, and nuclear magnetic resonance, we elucidated the structure of one such factor, 2-methyl-4-hydroxyquinoline (MHQ). MHQ is an alkyl quinolone with a previously unknown activity and is synthesized by the PqsABC enzymes. Pure MHQ is sufficient to disperse P. aeruginosa, but the dispersal activity of natural P. aeruginosa conditioned media requires additional factors. Whereas other alkyl quinolones have been shown to act as antibiotics or membrane depolarizers, MHQ lacks these activities and known antibiotics do not induce dispersal. In contrast, we show that MHQ inhibits the activity of Type IV Pili (TFP) and that TFP targeting can explain its dispersal activity. Our work thus identifies single-cell surface dispersal as a new activity of P. aeruginosa-produced small molecules, characterizes MHQ as a promising dispersal agent, and establishes TFP inhibition as a viable mechanism for P. aeruginosa dispersal.

Biofilm and swarming emergent behaviours controlled through the aid of biophysical understanding and tools

Bacteria can organise themselves into communities in the forms of biofilms and swarms. Through chemical and physical interactions between cells, these communities exhibit emergent properties that individual cells alone do not have. While bacterial communities have been mainly studied in the context of biochemistry and molecular biology, recent years have seen rapid advancements in the biophysical understanding of emergent phenomena through physical interactions in biofilms and swarms. Moreover, new technologies to control bacterial emergent behaviours by physical means are emerging in synthetic biology. Such technologies are particularly promising for developing engineered living materials (ELM) and devices and controlling contamination and biofouling. In this minireview, we overview recent studies unveiling physical and mechanical cues that trigger and affect swarming and biofilm development. In particular, we focus on cell shape, motion and density as the key parameters for mechanical cell-cell interactions within a community. We then showcase recent studies that use physical stimuli for patterning bacterial communities, altering collective behaviours and preventing biofilm formation. Finally, we discuss the future potential extension of biophysical and bioengineering research on microbial communities through computational modelling and deeper investigation of mechano-electrophysiological coupling.

Bioadhesion in the oral cavity and approaches for biofilm management by surface modifications

BACKGROUND

All soft and solid surface structures in the oral cavity are covered by the acquired pellicle followed by bacterial colonization. This applies for natural structures as well as for restorative or prosthetic materials; the adherent bacterial biofilm is associated among others with the development of caries, periodontal diseases, peri-implantitis, or denture-associated stomatitis. Accordingly, there is a considerable demand for novel materials and coatings that limit and modulate bacterial attachment and/or propagation of microorganisms.

OBJECTIVES AND FINDINGS

The present paper depicts the current knowledge on the impact of different physicochemical surface characteristics on bioadsorption in the oral cavity. Furthermore, it was carved out which strategies were developed in dental research and general surface science to inhibit bacterial colonization and to delay biofilm formation by low-fouling or "easy-to-clean" surfaces. These include the modulation of physicochemical properties such as periodic topographies, roughness, surface free energy, or hardness. In recent years, a large emphasis was laid on micro- and nanostructured surfaces and on liquid repellent superhydrophic as well as superhydrophilic interfaces. Materials incorporating mobile or bound nanoparticles promoting bacteriostatic or bacteriotoxic properties were also used. Recently, chemically textured interfaces gained increasing interest and could represent promising solutions for innovative antibioadhesion interfaces. Due to the unique conditions in the oral cavity, mainly in vivo or in situ studies were considered in the review.

CONCLUSION

Despite many promising approaches for modulation of biofilm formation in the oral cavity, the ubiquitous phenomenon of bioadsorption and adhesion pellicle formation in the challenging oral milieu masks surface properties and therewith hampers low-fouling strategies.

CLINICAL RELEVANCE

Improved dental materials and surface coatings with easy-to-clean properties have the potential to improve oral health, but extensive and systematic research is required in this field to develop biocompatible and effective substances.

Broadly protective semi-synthetic glycoconjugate vaccine against pathogens capable of producing poly-β-(1→6)-N-acetyl-d-glucosamine exopolysaccharide

Poly-β-(1→6)-N-acetylglucosamine (PNAG) was first discovered as a major component of biofilms formed by Staphylococcus aureus and some other staphylococci but later this exopolysaccharide was also found to be produced by pathogens of various nature. This common antigen is considered as a promising target for construction of a broadly protective vaccine. Extensive studies of PNAG, its de-N-acetylated derivative (dPNAG, containing around 15% of residual N-acetates) and their conjugates with Tetanus Toxoid (TT) revealed the crucial role of de-N-acetylated glucosamine units for the induction of protective immunity. Conjugates of synthetic penta- (5GlcNH₂) and nona-β-(1→6)-d-glucosamines (9GlcNH₂) were tested in vitro and in different animal models and proved to be effective in passive and active protection against different microbial pathogens. Presently conjugate 5GlcNH₂-TT is being produced under GMP conditions and undergoes safety and effectiveness evaluation in humans and economically important animals. Current review summarizes all stages of this long-termed study.

Biofilm Produced In Vitro by Piscirickettsia salmonis Generates Differential Cytotoxicity Levels and Expression Patterns of Immune Genes in the Atlantic Salmon Cell Line SHK-1

Piscirickettsia salmonis is the causative agent of Piscirickettsiosis, an infectious disease with a high economic impact on the Chilean salmonid aquaculture industry. This bacterium produces biofilm as a potential resistance and persistence strategy against stressful environmental stimuli. However, the in vitro culture conditions that modulate biofilm formation as well as the effect of sessile bacteria on virulence and immune gene expression in host cells have not been described for P. salmonis. Therefore, this study aimed to analyze the biofilm formation by P. salmonis isolates under several NaCl and iron concentrations and to evaluate the virulence of planktonic and sessile bacteria, together with the immune gene expression induced by these bacterial conditions in an Atlantic salmon macrophage cell line. Our results showed that NaCl and Fe significantly increased biofilm production in the LF-89 type strain and EM-90-like isolates. Additionally, the planktonic EM-90 isolate and sessile LF-89 generated the highest virulence levels, associated with differential expression of il-1β, il-8, nf-κb, and iκb-α genes in SHK-1 cells. These results suggest that there is no single virulence pattern or gene expression profile induced by the planktonic or sessile condition of P. salmonis, which are dependent on each strain and bacterial condition used.

Reduction of Biofilm Formation on Cooling Tower Heat Exchangers using Nano-silica Coating : Environmentally sustainable antifouling coating demonstrated on stainless steel heat exchanger tubes

Cooling towers are industrial cooling units operating to dissipate heat. As with any surface in contact with aqueous systems, biofilm formation appears on the surface of heat exchangers. Although biofilm formation on plastic tower fill in wet cooling towers has been studied widely, no studies were found regarding biofilm formation on steel heat exchangers in closed-loop systems. In this study, heat exchangers were coated with nano-silica, which is known to reduce the formation of biofilm. Natural biofilm formation was monitored for six months. Biofouling was examined monthly using epifluorescence microscopy by assessing the numbers of live and dead bacteria. It was observed that the biofilm layer formed on the nano-silica coated heat exchanger surfaces was significantly lower than on the control surfaces. 3 log microbial reduction was recorded on coated surfaces in the first month. After six months, total biomass on control surfaces reached 1.28 × 1012 cell cm−2, while the biomass on nano-silica coated surfaces was 6.3 × 104 cell cm−2.

A nanostructured anti-biofilm surface widens the efficacy against spindle-shaped and chain-forming rod-like bacteria

Current control of pathogenic bacteria at all biomaterial interfaces is poorly attuned to a broad range of disease-causing pathogens. Leading antimicrobial surface functionalization strategies with antimicrobial peptides (AMPs), defensins, have not shown their promised efficacy. One of the main problems is the lack of stability and swift clearance from the surface. Surface nanotopography bearing sharp protrusions is a non-chemical solution that is intrinsically stable and long-lasting. Previously, the geometrically ordered arrays of nanotipped spines repelled or rapidly ruptured bacteria that come into contact. The killing properties so far work on cocci and rod-like bacteria, but there is no validation of the efficacy of protrusional surfaces on pathogenic bacteria with different sizes and morphologies, thus broadening the utility of such surfaces to cover increasingly more disease entities. Here, we report a synthetic analogue of nanotipped spines with a pyramidal shape that show great effectiveness on species of bacteria with strongly contrasting shapes and sizes. To highlight this phenomenon in the field of dental applications where selective bacterial control is vital to the clinical success of biomaterial functions, we modified the poly(methyl)-methacrylate (PMMA) texture and tested it against Streptococcus mutans, Enterococcus faecalis, Porphyromonas gingivalis, and Fusobacterium nucleatum. These nanopyramids performed effectively at levels well above those of normal and roughened PMMA biomaterials for dentistry and a model material for general use in medicine and disease transmission in hospital environments.

Rhamnolipid exhibits anti-biofilm activity against the dermatophytic fungi Trichophyton rubrum and Trichophyton mentagrophytes

Dermatophytes are responsible for a majority of fungal infections in humans and other vertebrates, causing dermatophytosis. Treatment failures are often associated with biofilm formation, making dermatophytes resistant to antifungals. In this study, effects of a rhamnolipid (RL-SS14) produced by Pseudomonas aeruginosa SS14 on planktonic cells of Trichophyton rubrum and Trichophyton mentagrophytes, their biofilm formation, and disruption of mature biofilms were assessed. The composition of RL-SS14 was analysed using FTIR, HPLC-ESI-MS, and GC-MS. Minimum inhibitory concentrations against the planktonic forms of T. rubrum and T. mentagrophytes were 0.5 mg/mL and 0.125 mg/mL, respectively. Crystal-violet (biofilm biomass) and safranin (extracellular matrix) staining revealed that RL-SS14 significantly inhibited biofilm formation and also reduced preformed biofilms in a dose-dependent manner. Microscopic visualization of treated biofilms via SEM, AFM, and CLSM revealed marked morphological damage, cell death, and reduced extracellular matrix. The results indicate the potential of RL-SS14 as an anti-biofilm agent against dermatophytes.

A fungal mycelium templates the growth of aragonite needles

Fungi live within diverse environments and survive well under extreme conditions that are usually beyond the tolerance of most other organisms. In different environments fungi are known to induce precipitation of a wide range of minerals. Various species of fungi have been shown to facilitate calcium carbonate mineralization. Here, inspired by examples of needle-fiber calcite formed via fungus-induced biomineralization typically observed in soils and sediments, we utilized inactivated fungus to synthetically induce precipitation of CaCO3 needles. To our knowledge, the feasibility of growing aragonitic needles within fungal mycelium in vitro has not been previously demonstrated. The needles we obtained were curved, displayed hexagonal facets, and demonstrated high-aspect ratios close to 60. The size and shape of these synthetic needles matched those of the mycelium of the natural fungus. Utilizing high-resolution characterization techniques, we studied the morphology and the micro- and nanostructures of the aragonitic needles. Our findings showed that even inactivated fungal mycelium, if present in the crystallization environment, can serve as a template for the formation of high-aspect ratio fibers and can stabilize metastable polymorphs.

Efficacy of imidazolium and piperidinium based ionic liquids on inhibiting biofilm formation on titanium and carbon steel surfaces

In the present study, the efficacies of three different cationic and anionic ionic liquids (ILs) on biofilm formation on materials used in cooling water systems were evaluated. Two imidazolium based ILs; 1-Ethyl 3-Methylimidazolium tetrafluoroborate - (IL-E) and 1-Butyl-3-methylimidazolium chloride - (IL-I) with anionic fluoride and chloride groups and one piperidinium based IL, N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide - (IL-M) with fluoromethyl group as anion were used. The efficacy of these ILs were evaluated on planktonic and sessile cells of major biofilm formers in cooling water systems using Gram negative bacterium Pseudomonas sp. and Gram positive bacterium Bacillus sp. Further their effect on inhibiting biofilm formation on titanium and carbon steel surfaces were also evaluated. Results showed that planktonic cells of Pseudomonas sp. and Bacillus sp. were effectively inhibited by 25 ppm of IL-M and IL-E, respectively. For both bacteria, 50 ppm of IL-I was enough to inhibit and eradicate the sessile cell formation. Among the three ILs, IL-E was the best in inhibiting the adhesion of bacterial cells on Ti and CS surfaces. These results suggest that Imidazolium based ILs are effective in controlling sessile cell formation and eradicating mature biofilm as compared to piperidinium based IL. Further, Imidazolium based IL with fluoride anion (IL-E) was the best in inhibiting adhesion of these bacterial cells and thereby biofilm formation on material surfaces. This study establishes the feasibility of using ILs in cooling water system for bacterial biofilm control along with other conventional biofouling control methods.

Acid soluble extracellular matrix confers structural stability to marine Bacillus haynesii pellicle biofilms

In natural and engineered settings, bacteria predominantly thrive in biofilms, which are complex microbial communities embedded in a self-produced extracellular polymeric substances (EPSs) matrix. Pellicles are complex macroscopic biofilms floating at air-water interface. Though pellicle formation has been studied in detail in Bacillus subtilis, a soil bacterium, it is not reported in aquatic bacteria, which may use pellicle-growth as survival-strategy. This study shows that Bacillus haynesii isolated from a marine environment forms robust pellicle biofilms at air-water interface. B. haynesii pellicles showed complex architecture, involving dense cell-aggregates with interconnecting thread-like structures in an extracellular matrix. In situ staining by Alcian blue, Concanavalin A and ThioflavinT (ThT), respectively, localized acidic polymers, glycoconjugates and amyloid-like fibers in the pellicle. The pellicle was rigid and not disrupted by common EPS extraction protocols. Hence, a set of reagents and conditions were evaluated for solubilizing the EPS and pellicle. Acetic acid was able to effectively solubilize the structural EPS and pellicle structure. Acid soluble structural EPS contained chemical signatures for both proteins and carbohydrates, as revealed by elemental analysis, Fourier Transform Infrared Spectroscopy and Raman Spectroscopy. Ex situ staining of acid soluble EPS by ThT showed recovery of amyloid-forming proteins from pellicle. Results show that structural stability of the pellicle is mainly conferred by amyloid-like fibers of the EPS matrix. The robust pellicle-growth reported here may represent a survival-strategy in the aquatic bacterium. The findings reported here can support future research on biofilm structure, EPS matrix and its formation, which are critical for understanding how microbes thrive in natural and engineered settings.

The role of flow in bacterial biofilm morphology and wetting properties

Biofilms are bacterial communities embedded in an extracellular matrix, able to adhere to surfaces. Different experimental set-ups are widely used for in vitro biofilm cultivation; however, a well-defined comparison among different culture conditions, especially suited to interfacial characterization, is still lacking in the literature. The main objective of this work is to study the role of flow on biofilm formation, morphology and interfacial properties. Three different in vitro setups, corresponding to stagnant, shaking, and laminar flow conditions (custom-made flow cell), are used in this work to grow single strain biofilms of Pseudomonas fluorescens AR 11 on glass coupons. Results show that flow conditions significantly influenced biofilm formation kinetics, affecting mass transfer and cell attachment/detachment processes. Distinct morphological patterns are found under different flow regimes. Static contact angle data do not depend significantly on biofilm growth conditions in the parametric range investigated in this work.

Diffusion maps of Bacillus subtilis biofilms via magnetic resonance imaging highlight a complex network of channels

Bacillus subtilis microorganism when cultivated under chemically-defined conditions developed a biofilm with an unusual pattern of wrinkles on the surface. Some questions were raised about whether there was a special function of these wrinkles for the biofilm itself, since they resembled microchannels that could be involved in the transport of nutrients within the biofilm. Since the diffusion is the main mechanism for nutrient transport to biofilm from the medium, the role of these wrinkled structures in the whole diffusion within the biofilm was investigated using diffusion-weighted magnetic resonance imaging (DW-MRI). Data from these diffusion images was used to generate 2D diffusion maps which highlighted the striking channel features of the biofilm surface. The diffusion maps revealed a network of interconnected channels, with self-diffusion coefficients higher in the microchannels than in other regions of the biofilms. Polar plots made from 2D diffusion maps obtained from the plane of the biofilm show an anisotropy of the diffusion inside the microchannels, with the diffusion higher when along the principal direction of the microchannels. These results agree with the model, that the buckling of the biofilm surface from the B. subtilis creates microchannels that can enhance diffusion throughout the biofilm.

Bioinspired Smart Liquid Directional Transport Control

Developments in bioinspired superwetting materials have triggered technological revolutions in many disciplines. One representative area is liquid directional transport dominated by interface properties, which has experienced rapid progress recently. To improve the controllability, scientists try to use the external field, such as light, electricity, thermal, and so on, to assist or achieve controllable smart, responsive liquid directional transport. However, there are still some intractable problems and challenges behind prosperity. Here, we summarize the relevant basic theory of surface wettability and the processes of the development of bioinspired superwetting materials. We discuss the different essential mechanisms of liquid directional transport. Furthermore, smart external field-controlled fluid directional transport is the primary focus of this feature article. We briefly put forward our views on some outstanding problems, existing challenges, and trends in this field.

Metal ions weaken the hydrophobicity and antibiotic resistance of Bacillus subtilis NCIB 3610 biofilms

Surface superhydrophobicity makes bacterial biofilms very difficult to fight, and it is a combination of their matrix composition and complex surface roughness which synergistically protects these biomaterials from wetting. Although trying to eradicate biofilms with aqueous (antibiotic) solutions is common practice, this can be a futile approach if the biofilms have superhydrophobic properties. To date, there are not many options available to reduce the liquid repellency of biofilms or to prevent this material property from developing. Here, we present a solution to this challenge. We demonstrate how the addition of metal ions such as copper and zinc during or after biofilm formation can render the surface of otherwise superhydrophobic B. subtilis NCIB 3610 biofilms completely wettable. As a result of this procedure, these smoother, hydrophilic biofilms are more susceptible to aqueous antibiotics solutions. Our strategy proposes a scalable and widely applicable step in a multi-faceted approach to eradicate biofilms.

Regulatory Role of PlaR (YiaJ) for Plant Utilization in Escherichia coli K-12

Outside a warm-blooded animal host, the enterobacterium Escherichia coli K-12 is also able to grow and survive in stressful nature. The major organic substance in nature is plant, but the genetic system of E. coli how to utilize plant-derived materials as nutrients is poorly understood. Here we describe the set of regulatory targets for uncharacterized IclR-family transcription factor YiaJ on the E. coli genome, using gSELEX screening system. Among a total of 18 high-affinity binding targets of YiaJ, the major regulatory target was identified to be the yiaLMNOPQRS operon for utilization of ascorbate from fruits and galacturonate from plant pectin. The targets of YiaJ also include the genes involved in the utilization for other plant-derived materials as nutrients such as fructose, sorbitol, glycerol and fructoselysine. Detailed in vitro and in vivo analyses suggest that L-ascorbate and α-D-galacturonate are the effector ligands for regulation of YiaJ function. These findings altogether indicate that YiaJ plays a major regulatory role in expression of a set of the genes for the utilization of plant-derived materials as nutrients for survival. PlaR was also suggested to play protecting roles of E. coli under stressful environments in nature, including the formation of biofilm. We then propose renaming YiaJ to PlaR (regulator of plant utilization). The natural hosts of enterobacterium Escherichia coli are warm-blooded animals, but even outside hosts, E. coli can survive even under stressful environments. On earth, the most common organic materials to be used as nutrients by E. coli are plant-derived components, but up to the present time, the genetic system of E. coli for plant utilization is poorly understand. In the course of gSELEX screening of the regulatory targets for hitherto uncharacterized TFs, we identified in this study the involvement of the IclR-family YiaJ in the regulation of about 20 genes or operons, of which the majority are related to the catabolism of plant-derived materials such as ascorbate, galacturonate, sorbitol, fructose and fructoselysine. Therefore, we propose to rename YiaJ to PlaR (regulator of plant utilization).

OxyR-controlled surface polysaccharide production and biofilm formation in Acinetobacter oleivorans DR1

The genomes of several Acinetobacter species possess three distinct polysaccharide-producing operons [two poly-N-acetyl glucosamine (PNAG) and one K-locus]. Using a microfluidic device, an increased amount of polysaccharides and enhanced biofilm formation were observed following continuous exposure to H₂O₂ and removal of the H₂O₂-sensing key regulator, OxyR, in Acinetobacter oleivorans DR1 cells. Gene expression analysis revealed that genes located in PNAG1, but not those in PNAG2, were induced and that genes in the K-locus were expressed in the presence of H₂O₂. Interestingly, the expression of the K-locus gene was enhanced in the PNAG1 mutant and vice versa. The absence of either OxyR or PNAG1 resulted in enhanced biofilm formation, higher surface hydrophobicity, and increased motility, implying that K-locus-driven polysaccharide production in both the oxyR and PNAG1 deletion mutants may be related to these phenotypes. Both the oxyR and K-locus deletion mutants were more sensitive to H₂O₂ compared with the wildtype and PNAG1 mutant strains. Purified OxyR binds to the promoter regions of both polysaccharide operons with a higher affinity toward the K-locus promoter. Although oxidized OxyR could bind to both promoter regions, the addition of dithiothreitol further enhanced the binding efficiency of OxyR, suggesting that OxyR might function as a repressor for controlling these polysaccharide operons.

Plant and soil communities are associated with the response of soil water repellency to environmental stress

A warming climate and expected changes in average and extreme rainfall emphasise the importance of understanding how the land surface routes and stores surface water. The availability and movement of water within an ecosystem is a fundamental control on biological and geophysical activity, and influences many climatic feedbacks. A key phenomenon influencing water infiltration into the land surface is soil hydrophobicity, or water repellency. Despite repellency dictating the speed, volume and pattern of water infiltration, there is still major uncertainty over whether this critical hydrological process is biologically or physicochemically controlled. Here we show that soil water repellency is likely driven by changes in the plant and soil microbial communities in response to environmental stressors. We carried out a field survey in the summers of 2013 to 2016 in a variety of temperate habitats ranging across arable, grassland, forest and bog sites. We found that moderate to extreme repellency occurs in 68% of soils at a national scale in temperate ecosystems, with 92% showing some repellency. Taking a systems approach, we show that a wetter climate and low nutrient availability alter plant, bacterial and fungal community structure, which in turn are associated with increased soil water repellency across a large-scale gradient of soil, vegetation and land-use. The stress tolerance of the plant community and associated changes in soil microbial communities were more closely linked to changes in repellency than soil physicochemical properties. Our results indicate that there are consistent responses to diverse ecosystem stresses that will impact plant and microbial community composition, soil properties, and hydrological behaviour. We suggest that the ability of a biological community to induce such hydrological responses will influence the resilience of the whole ecosystem to environmental stress. This highlights the crucial role of above-belowground interactions in mediating climatic feedbacks and dictating ecosystem health.

Antibiotic Susceptibility of Escherichia coli Cells during Early-Stage Biofilm Formation

Bacteria form complex multicellular structures on solid surfaces known as biofilms, which allow them to survive in harsh environments. A hallmark characteristic of mature biofilms is the high-level antibiotic tolerance (up to 1,000 times) compared with that of planktonic cells. Here, we report our new findings that biofilm cells are not always more tolerant to antibiotics than planktonic cells in the same culture. Specifically, Escherichia coli RP437 exhibited a dynamic change in antibiotic susceptibility during its early-stage biofilm formation. This phenomenon was not strain specific. Upon initial attachment, surface-associated cells became more sensitive to antibiotics than planktonic cells. By controlling the cell adhesion and cluster size using patterned E. coli biofilms, cells involved in the interaction between cell clusters during microcolony formation were found to be more susceptible to ampicillin than cells within clusters, suggesting a role of cell-cell interactions in biofilm-associated antibiotic tolerance. After this stage, biofilm cells became less susceptible to ampicillin and ofloxacin than planktonic cells. However, when the cells were detached by sonication, both antibiotics were more effective in killing the detached biofilm cells than the planktonic cells. Collectively, these results indicate that biofilm formation involves active cellular activities in adaption to the attached life form and interactions between cell clusters to build the complex structure of a biofilm, which can render these cells more susceptible to antibiotics. These findings shed new light on bacterial antibiotic susceptibility during biofilm formation and can guide the design of better antifouling surfaces, e.g., those with micron-scale topographic structures to interrupt cell-cell interactions.IMPORTANCE Mature biofilms are known for their high-level tolerance to antibiotics; however, antibiotic susceptibility of sessile cells during early-stage biofilm formation is not well understood. In this study, we aim to fill this knowledge gap by following bacterial antibiotic susceptibility during early-stage biofilm formation. We found that the attached cells have a dynamic change in antibiotic susceptibility, and during certain phases, they can be more sensitive to antibiotics than planktonic counterparts in the same culture. Using surface chemistry-controlled patterned biofilm formation, cell-surface and cell-cell interactions were found to affect the antibiotic susceptibility of attached cells. Collectively, these findings provide new insights into biofilm physiology and reveal how adaptation to the attached life form may influence antibiotic susceptibility of bacterial cells.

Biofilm and methods of its eradication

Microorganisms occur in the natural environment in the form of planktonic or create biofilms, i.e. communities of cells surrounded by the extracellular matrix. This is possible due to the phenomenon of quorum sensing, i.e. the ability of microorganisms to estimate their own density and change the expression of genes in response to them. Within such a structure, microorganisms are protected against harmful environmental conditions, their metabolic profile and the level of expression of individual genes are also changed, which leads to an increase in the pathogenicity of organisms associated in the form of biofilms. They pose a huge threat to hospital patients because they are capable of residing abiotic surfaces, such as catheters and endoprostheses, and can cause infection. The current methods of combating microbes with antibiotics and fungicides lose their effectiveness, both due to the increasing drug resistance of clinically relevant strains, but also to the very properties of biofilms. This determines the need to search for new and effective methods (physical, chemical and biological) to eradicate biofilms

Bio-enzymes for inhibition and elimination of Escherichia coli O157:H7 biofilm and their synergistic effect with sodium hypochlorite

Escherichia coli O157:H7 is one of the most important pathogens worldwide. In this study, three different kinds of enzymes, DNase I, proteinase K and cellulase were evaluated for inhibitory or degrading activity against E. coli O157:H7 biofilm by targeting extracellular DNA, proteins, and cellulose, respectively. The cell number of biofilms formed under proteinase K resulted in a 2.43 log CFU/cm² reduction with an additional synergistic 3.72 log CFU/cm² reduction after NaClO post-treatment, while no significant reduction occurred with NaClO treatment alone. It suggests that protein degradation could be a good way to control the biofilm effectively. In preformed biofilms, all enzymes showed a significant reduction of 16.4–36.7% in biofilm matrix in 10-fold diluted media (p < 0.05). The sequential treatment with proteinase K, cellulase, and NaClO showed a significantly higher synergistic inactivation of 2.83 log CFU/cm² compared to 1.58 log CFU/cm² in the sequence of cellulase, proteinase K, and NaClO (p < 0.05). It suggests that the sequence of multiple enzymes can make a significant difference in the susceptibility of biofilms to NaClO. This study indicates that the combination of extracellular polymeric substance-degrading enzymes with NaClO could be useful for the efficient control of E. coli O157:H7 biofilms.

Surface topographies of biomimetic superamphiphobic materials: design criteria, fabrication and performance

Superamphiphobicity is a wetting phenomenon that not only water but also oils or organic solvents with low surface tension exhibit large contact angles above 150° along with low contact angle hysteresis on solid surface. It is well known that both chemical constituent and surface roughness have impacts on the wettability of solid surface. Herein, several fundamental wetting states and design criteria for re-entrant structures are introduced first. Then, various chemical modification materials endowing solid substrates low surface energy are summarized subsequently. Furthermore, roughening processes conferring hierarchical or re-entrant topographic structures on surfaces are classified based on different types of topographies abstracted from the natural oil-repellent creatures (mushroom-like structures) as well as bio-inspired superamphiphobic surfaces (i.e., randomly distributed nanostructures, regularly patterned microstructures and other complex hierarchical structures). Significantly, the impalement pressure and formulated rules of various re-entrant profiles are recommended in detail. At the same time, fabrication, outstanding performances such as mechanical durability, chemical stability are also mentioned according to different types of morphologies. Beyond that, current fabrication obstacles and future prospects are proposed simultaneously in the end.

Viscoelastic response of Escherichia coli biofilms to genetically altered expression of extracellular matrix components

How the viscoelastic properties of the extracellular matrix affect the various biological functions conferred by biofilms is an important question in microbiology. In this study, the viscoelastic response of Escherichia coli biofilms to the genetically altered expression of extracellular matrix components was studied. Biofilms of the wild type E. coli MG1655 and its mutant strains producing different amounts of extracellular matrix components (curli, colanic acid, and poly-β-1,6-N-acetyl-d-glucosamine) were used to examine the viscoelastic behavior of biofilms grown at the solid-atmosphere interface. The results suggest that the presence of curli proteins dominates biofilm mechanical behavior. The rheological data indicate that the cohesive energy of the biofilm was the highest in the wild type strain. The results demonstrate the importance of extracellular matrix composition for biofilm mechanical properties. We propose that by genetically altering the expression of extracellular matrix polymers, bacteria are able to modulate the mechanical properties of their local environment in accordance with bulk environmental conditions.

Pulcherrimin formation controls growth arrest of the Bacillus subtilis biofilm

Understanding the processes that underpin the mechanism of biofilm formation, dispersal, and inhibition is critical to allow exploitation and to understand how microbes thrive in the environment. Here, we reveal that the formation of an extracellular iron chelate restricts the expansion of a biofilm. The countering benefit to self-restriction of growth is protection of an environmental niche. These findings highlight the complex options and outcomes that bacteria need to balance to modulate their local environment to maximize colonization, and therefore survival.

Biofilm formation by Bacillus subtilis is a communal process that culminates in the formation of architecturally complex multicellular communities. Here we reveal that the transition of the biofilm into a nonexpanding phase constitutes a distinct step in the process of biofilm development. Using genetic analysis we show that B. subtilis strains lacking the ability to synthesize pulcherriminic acid form biofilms that sustain the expansion phase, thereby linking pulcherriminic acid to growth arrest. However, production of pulcherriminic acid is not sufficient to block expansion of the biofilm. It needs to be secreted into the extracellular environment where it chelates Fe³⁺ from the growth medium in a nonenzymatic reaction. Utilizing mathematical modeling and a series of experimental methodologies we show that when the level of freely available iron in the environment drops below a critical threshold, expansion of the biofilm stops. Bioinformatics analysis allows us to identify the genes required for pulcherriminic acid synthesis in other Firmicutes but the patchwork presence both within and across closely related species suggests loss of these genes through multiple independent recombination events. The seemingly counterintuitive self-restriction of growth led us to explore if there were any benefits associated with pulcherriminic acid production. We identified that pulcherriminic acid producers can prevent invasion by neighboring communities through the generation of an “iron-free” zone, thereby addressing the paradox of pulcherriminic acid production by B. subtilis.

Deep-Subsurface Pressure Stimulates Metabolic Plasticity in Shale-Colonizing Halanaerobium spp

Bacterial Halanaerobium strains become the dominant persisting microbial community member in produced fluids across geographically distinct hydraulically fractured shales. Halanaerobium is believed to be inadvertently introduced into this environment during the drilling and fracturing process and must therefore tolerate large changes in pressure, temperature, and salinity. Here, we used a Halanaerobium strain isolated from a natural gas well in the Utica Point Pleasant formation to investigate metabolic and physiological responses to growth under high-pressure subsurface conditions. Laboratory incubations confirmed the ability of Halanaerobium congolense strain WG8 to grow under pressures representative of deep shale formations (21 to 48 MPa). Under these conditions, broad metabolic and physiological shifts were identified, including higher abundances of proteins associated with the production of extracellular polymeric substances. Confocal laser scanning microscopy indicated that extracellular polymeric substance (EPS) production was associated with greater cell aggregation when biomass was cultured at high pressure. Changes in Halanaerobium central carbon metabolism under the same conditions were inferred from nuclear magnetic resonance (NMR) and gas chromatography measurements, revealing large per-cell increases in production of ethanol, acetate, and propanol and cessation of hydrogen production. These metabolic shifts were associated with carbon flux through 1,2-propanediol in response to slower fluxes of carbon through stage 3 of glycolysis. Together, these results reveal the potential for bioclogging and corrosion (via organic acid fermentation products) associated with persistent Halanaerobium growth in deep, hydraulically fractured shale ecosystems, and offer new insights into cellular mechanisms that enable these strains to dominate deep-shale microbiomes.IMPORTANCE The hydraulic fracturing of deep-shale formations for hydrocarbon recovery accounts for approximately 60% of U.S. natural gas production. Microbial activity associated with this process is generally considered deleterious due to issues associated with sulfide production, microbially induced corrosion, and bioclogging in the subsurface. Here we demonstrate that a representative Halanaerobium species, frequently the dominant microbial taxon in hydraulically fractured shales, responds to pressures characteristic of the deep subsurface by shifting its metabolism to generate more corrosive organic acids and produce more polymeric substances that cause "clumping" of biomass. While the potential for increased corrosion of steel infrastructure and clogging of pores and fractures in the subsurface may significantly impact hydrocarbon recovery, these data also offer new insights for microbial control in these ecosystems.

Stimulation of anaerobic biofilm development in the presence of low concentrations of toxic aromatic pollutants

The main aim of this work was to stimulate biofilm formation in the presence of wastewater containing aromatic compounds with different toxicities (EC₅₀). The results indicated that wastewater with an EC₅₀ value >85% accelerates the attachment of bacteria onto the bio-carriers because the toxic wastewater stimulates the production of extracellular polymeric substances (EPS) from the seed sludge. In order to understand the role of EPS on biofilm development, experiments were conducted using the seed sludge, from which the soluble, loosely bound, and tightly bound EPS were removed. The soluble EPS fraction was determined to be crucial for biofilm development. Firmicutes bacterium and Clostridium chromoreductans survived and were enriched in the formed biofilms in our study, which can resist toxic aromatics.

Fengycin Produced by Bacillus amyloliquefaciens FZB42 Inhibits Fusarium graminearum Growth and Mycotoxins Biosynthesis

Fusarium graminearum is a notorious pathogen that causes Fusarium head blight (FHB) in cereal crops. It produces secondary metabolites, such as deoxynivalenol, diminishing grain quality and leading to lesser crop yield. Many strategies have been developed to combat this pathogenic fungus; however, considering the lack of resistant cultivars and likelihood of environmental hazards upon using chemical pesticides, efforts have shifted toward the biocontrol of plant diseases, which is a sustainable and eco-friendly approach. Fengycin, derived from Bacillus amyloliquefaciens FZB42, was purified from the crude extract by HPLC and further analyzed by MALDI-TOF-MS. Its application resulted in structural deformations in fungal hyphae, as observed via scanning electron microscopy. In planta experiment revealed the ability of fengycin to suppress F. graminearum growth and highlighted its capacity to combat disease incidence. Fengycin significantly suppressed F. graminearum, and also reduced the deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-ADON), 15-acetyldeoxynivalenol (15-ADON), and zearalenone (ZEN) production in infected grains. To conclude, we report that fengycin produced by B. amyloliquefaciens FZB42 has potential as a biocontrol agent against F. graminearum and can also inhibit the mycotoxins produced by this fungus.

A series of MOF/Ce-based nanozymes with dual enzyme-like activity disrupting biofilms and hindering recolonization of bacteria

Notorious bacterial biofilms are becoming severe threats to public health worldwide. As the important component in biofilm extracellular polymeric substances (EPS), extracellular DNA (eDNA) has been manifested to connect different EPS components and bacteria together, leading biofilms hard to eliminate. Herein a series of MOF/Ce-based nanozymes with deoxyribonuclease (DNase) and peroxidase mimetic activities have been designed and synthesized for combating biofilms. The cerium (IV) complexes (DNase mimics) are capable of hydrolyzing eDNA and disrupting established biofilms, while the MOF with peroxidase-like activity can kill bacteria exposed in dispersed biofilms in the presence of H₂O₂. This can avoid the recolonization of bacteria and recurrence of biofilms. Given the fact that single-modal antibacterial agent is difficult to drastically eradicate biofilms, the marriage of two kinds of nanozymes is a rational strategy to acquire enhanced performance in combating biofilms. Besides, the utilization of nanozymes circumvents drawbacks of natural enzymes which are costly and vulnerable. Further studies have demonstrated that this kind of artificial enzyme with dual enzyme-mimetic activities can penetrate the biofilms, and inhibit bacterial biofilm formation intensively. Consistently, in vivo anti-biofilm application in treating subcutaneous abscess exhibits commendable wound healing and admirable bactericidal effect. To the best of our knowledge, it is the first time to devise an integrated nanozyme based on the peroxidase-like activity of MOF to eliminate biofilms and kill bacteria on site. This work may promote the application of MOF in the antibacterial field.

Topical, systemic and biologic therapies in hidradenitis suppurativa: pathogenic insights by examining therapeutic mechanisms

Hidradenitis suppurativa (HS) is a chronic inflammatory disease of the skin, manifesting in chronic, recurrent painful pustules, nodules, boils and purulent draining abscesses. Our current understanding of the pathogenesis of the disease is incomplete. This review aims to identify available treatment options in HS and discuss the pharmacological mechanisms through which such agents function. Identifying common pathways may inform our understanding of the pathogenesis of HS as well as identify future therapeutic targets. The pharmacological mechanisms implicated in topical therapies, antibiotic, hormonal, systemic immunomodulatory and biologic therapies for HS are discussed. Significant differences exist between agents and implicated pathways in therapy for mild and severe disease. This is an expression of the possible dichotomy in inflammatory pathways (and treatment responses) in HS. Studies involving monoclonal antibodies provide the greatest insight into what these specific mechanisms may be. Their variable levels of clinical efficacy compared with placebo bolsters the suggestion that differential inflammatory pathways may be involved in different presentations and severity of disease. Nuclear factor kappa B (NF-κB), tumor necrosis factor (TNF)-α and other innate immune mechanisms are strongly represented in treatments which are effective in mild to moderate disease in the absence of scarring or draining fistulae, however complex feed-forward mechanisms in severe disease respond to interleukin (IL)-1 inhibition but are less likely to respond to innate immune inhibition (through NF-κB or TNF-α) alone. It is unclear whether IL-17 inhibition will parallel TNF-α or IL-1 inhibition in effect, however it is plausible that small molecule targets (Janus kinase1 and phosphodiesterase 4) may provide effective new strategies for treatment of HS.

Evolved Biofilm: Review on the Experimental Evolution Studies of Bacillus subtilis Pellicles

For several decades, laboratory evolution has served as a powerful method to manipulate microorganisms and to explore long-term dynamics in microbial populations. Next to canonical Escherichia coli planktonic cultures, experimental evolution has expanded into alternative cultivation methods and species, opening the doors to new research questions. Bacillus subtilis, the spore-forming and root-colonizing bacterium, can easily develop in the laboratory as a liquid-air interface colonizing pellicle biofilm. Here, we summarize recent findings derived from this tractable experimental model. Clonal pellicle biofilms of B. subtilis can rapidly undergo morphological and genetic diversification creating new ecological interactions, for example, exploitation by biofilm non-producers. Moreover, long-term exposure to such matrix non-producers can modulate cooperation in biofilms, leading to different phenotypic heterogeneity pattern of matrix production with larger subpopulation of "ON" cells. Alternatively, complementary variants of biofilm non-producers, each lacking a distinct matrix component, can engage in a genetic division of labor, resulting in superior biofilm productivity compared to the "generalist" wild type. Nevertheless, inter-genetic cooperation appears to be evanescent and rapidly vanquished by individual biofilm formation strategies altering the amount or the properties of the remaining matrix component. Finally, fast-evolving mobile genetic elements can unpredictably shift intra-species interactions in B. subtilis biofilms. Understanding evolution in clonal biofilm populations will facilitate future studies in complex multispecies biofilms that are more representative of nature.

PolyGlcNAc-containing exopolymers enable surface penetration by non-motile Enterococcus faecalis

Bacterial pathogens have evolved strategies that enable them to invade tissues and spread within the host. Enterococcus faecalis is a leading cause of local and disseminated multidrug-resistant hospital infections, but the molecular mechanisms used by this non-motile bacterium to penetrate surfaces and translocate through tissues remain largely unexplored. Here we present experimental evidence indicating that E. faecalis generates exopolysaccharides containing β-1,6-linked poly-N-acetylglucosamine (polyGlcNAc) as a mechanism to successfully penetrate semisolid surfaces and translocate through human epithelial cell monolayers. Genetic screening and molecular analyses of mutant strains identified glnA, rpiA and epaX as genes critically required for optimal E. faecalis penetration and translocation. Mechanistically, GlnA and RpiA cooperated to generate uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) that was utilized by EpaX to synthesize polyGlcNAc-containing polymers. Notably, exogenous supplementation with polymeric N-acetylglucosamine (PNAG) restored surface penetration by E. faecalis mutants devoid of EpaX. Our study uncovers an unexpected mechanism whereby the RpiA-GlnA-EpaX metabolic axis enables production of polyGlcNAc-containing polysaccharides that endow E. faecalis with the ability to penetrate surfaces. Hence, targeting carbohydrate metabolism or inhibiting biosynthesis of polyGlcNAc-containing exopolymers may represent a new strategy to more effectively confront enterococcal infections in the clinic.

Enterococcus faecalis is a microbial inhabitant of the human gastrointestinal tract that can cause lethal infections. Typically classified as a non-motile bacterium, E. faecalis can readily migrate and translocate across epithelial barriers to invade distant organs. Nevertheless, the molecular pathways driving enterococcal invasive attributes remain poorly understood. In this study, we uncover that E. faecalis produces a polyGlcNAc-containing extracellular glycopolymer to efficiently migrate into semisolid surfaces and translocate through human epithelial cell monolayers. Our work provides evidence that non-motile bacterial pathogens can exploit endogenous carbohydrate metabolic pathways to penetrate surfaces. Thus, targeting glycopolymer biosynthetic programs might be useful to control infections by Gram-positive cocci in the clinic.

Biological Engineered Living Materials: Growing Functional Materials with Genetically Programmable Properties

Natural biological materials exhibit remarkable properties: self-assembly from simple raw materials, precise control of morphology, diverse physical and chemical properties, self-repair, and the ability to sense-and-respond to environmental stimuli. Despite having found numerous uses in human industry and society, the utility of natural biological materials is limited. But, could it be possible to genetically program microbes to create entirely new and useful biological materials? At the intersection between microbiology, material science, and synthetic biology, the emerging field of biological engineered living materials (ELMs) aims to answer this question. Here we review recent efforts to program cells to produce living materials with novel functional properties, focusing on microbial systems that can be engineered to grow materials and on new genetic circuits for pattern formation that could be used to produce the more complex systems of the future.

Recent advances of bioinspired functional materials with specific wettability: from nature and beyond nature

Through 3.7 billion years of evolution and natural selection, plants and animals in nature have ingeniously fulfilled a broad range of fascinating functions to achieve optimized performance in responding and adapting to changes in the process of interacting with complex natural environments. It is clear that the hierarchically organized micro/nanostructures of the surfaces of living organisms decisively manage fascinating and amazing functions, regardless of the chemical components of their building blocks. This conclusion now allows us to elucidate the underlying mechanisms whereby these hierarchical structures have a great impact on the properties of the bulk material. In this review, we mainly focus on advances over the last three years in bioinspired multiscale functional materials with specific wettability. Starting from selected naturally occurring surfaces, manmade bioinspired surfaces with specific wettability are introduced, with an emphasis on the cooperation between structural characteristics and macroscopic properties, including lotus leaf-inspired superhydrophobic surfaces, fish scale-inspired superhydrophilic/underwater superoleophobic surfaces, springtail-inspired superoleophobic surfaces, and Nepenthes (pitcher plant)-inspired slippery liquid-infused porous surfaces (SLIPSs), as well as other multifunctional surfaces that combine specific wettability with mechanical properties, optical properties and the unidirectional transport of liquid droplets. Afterwards, various top-down and bottom-up fabrication techniques are presented, as well as emerging cutting-edge applications. Finally, our personal perspectives and conclusions with regard to the transfer of micro- and nanostructures to engineered materials are provided.

Biomimetic polymeric superamphiphobic surfaces: their fabrication and applications

In this review, we summarize recent developments in polymeric superamphiphobic surfaces, including their design, fabrication, and potential applications.

Importance of the biofilm matrix for the erosion stability of Bacillus subtilis NCIB 3610 biofilms

Erosion of bacterial biofilms is dependent on the composition of the biofilm matrix and the surrounding chemical environment.

Topographical alterations render bacterial biofilms susceptible to chemical and mechanical stress

Treatment with concentrated ethanol, saline or glucose solutions smoothens biofilm surface topography and initially superhydrophobic/omniphobic biofilms are rendered hydrophilic.

Monitoring of bacterial film formation and its breakdown with an angular-based surface plasmon resonance biosensor

Bacterial biofilms are a leading cause of infection in health-care settings. Surface plasmon resonance (SPR) biosensors stand as valuable tools not only for the detection of biological entities and the characterisation of biomaterials but also as a suitable means to monitor bacterial film formation. This article reports on a proof-of-concept study for the use of an angular-based SPR biosensor for the monitoring of bacterial cell growth and biofilm formation and removal under the effect of different cleaning agents. The benefit of this custom-made SPR instrument is that it records simultaneously both the critical and resonant angles. This provides unique information on the growth of bacterial cells which is otherwise not obtainable with commonly used intensity-based SPR systems. The results clearly showed that a multilayer biofilm can be formed in 48 hours and the steps involved can be monitored in real-time with the SPR instrument through the measurement of the refractive index change and following the evolution in the shape of the SPR curve. The number, the depth and the sharpness of the reflection ripples varied as the film became thicker. Simulation results confirmed that the number of layers of bacteria affected the number of ripples at the critical angle. Real-time monitoring of the film breakdown with three cleaning agents indicated that bleach solution at 4.5% was the most effective in disrupting the biofilm from the gold sensor. Our overall findings suggest that the SPR biosensor with angular modulation presented in this article can perform real-time monitoring of biofilm formation and has the potential to be used as a platform to test the efficiency of disinfectants.

Social behaviours by Bacillus subtilis: quorum sensing, kin discrimination and beyond

Here, we review the multiple mechanisms that the Gram‐positive bacterium Bacillus subtilis uses to allow it to communicate between cells and establish community structures. The modes of action that are used are highly varied and include routes that sense pheromone levels during quorum sensing and control gene regulation, the intimate coupling of cells via nanotubes to share cytoplasmic contents, and long‐range electrical signalling to couple metabolic processes both within and between biofilms. We explore the ability of B. subtilis to detect ‘kin’ (and ‘cheater cells’) by looking at the mechanisms used to potentially ensure beneficial sharing (or limit exploitation) of extracellular ‘public goods’. Finally, reflecting on the array of methods that a single bacterium has at its disposal to ensure maximal benefit for its progeny, we highlight that a large future challenge will be integrating how these systems interact in mixed‐species communities.