Microbial biofilms in nature: unlocking their potential for agricultural applications

Enterococcus mundtii A2 biofilm and its anti-adherence potential against pathogenic microorganisms on stainless steel 316L

Pathogenic bacterial biofilms present significant challenges, particularly in food safety and material deterioration. Therefore, using Enterococcus mundtii A2, known for its antagonistic activity against pathogen adhesion, could serve as a novel strategy to reduce pathogenic colonization within the food sector. This study aimed to investigate the biofilm-forming ability of E. mundtii A2, isolated from camel milk, on two widely used stainless steels within the agri-food domain and to assess its anti-adhesive properties against various pathogens, especially on stainless steel 316L. Additionally, investigations into auto-aggregation and co-aggregation were also conducted. Plate count methodologies revealed increased biofilm formation by E. mundtii A2 on 316L, followed by 304L. Scanning electron microscopy (SEM) analysis revealed a dense yet thin biofilm layer, playing a critical role in reducing the adhesion of L. monocytogenes CECT 4032 and Staphylococcus aureus CECT 976, with a significant reduction of ≈ 2 Log CFU/cm2. However, Gram-negative strains, P. aeruginosa ATCC 27853 and E. coli ATCC 25922, exhibit modest adhesion reduction (~ 0.7 Log CFU/cm2). The findings demonstrate the potential of applying E. mundtii A2 biofilms as an effective strategy to reduce the adhesion and propagation of potentially pathogenic bacterial species on stainless steel 316L.

Development of a Pseudomonas-based biocontrol consortium with effective root colonization and extended beneficial side effects for plants under high-temperature stress

The root microbiota plays a crucial role in plant performance. The use of microbial consortia is considered a very useful tool for studying microbial interactions in the rhizosphere of different agricultural crop plants. Thus, a consortium of 3 compatible beneficial rhizospheric Pseudomonas strains previously isolated from the avocado rhizosphere, was constructed. The consortium is composed of two compatible biocontrol P. chlororaphis strains (PCL1601 and PCL1606), and the biocontrol rhizobacterium Pseudomonas alcaligenes AVO110, which are all efficient root colonizers of avocado and tomato plants. These three strains were compatible with each other and reached stable levels both in liquid media and on plant roots. Bacterial strains were fluorescent tagged, and colonization-related traits were analyzed in vitro, revealing formation of mixed biofilm networks without exclusion of any of the strains. Additionally, bacterial colonization patterns compatible with the different strains were observed, with high survival traits on avocado and tomato roots. The bacteria composing the consortium shared the same root habitat and exhibited biocontrol activity against soil-borne fungal pathogens at similar levels to those displayed by the individual strains. As expected, because these strains were isolated from avocado roots, this Pseudomonas-based consortium had more stable bacterial counts on avocado roots than on tomato roots; however, inoculation of tomato roots with this consortium was shown to protect tomato plants under high-temperature stress. The results revealed that this consortium has side beneficial effect for tomato plants under high-temperature stress, thus improving the potential performance of the individual strains. We concluded that this rhizobacterial consortium do not improve the plant protection against soil-borne phytopathogenic fungi displayed by the single strains; however, its inoculation can show an specific improvement of plant performance on a horticultural non-host plant (such as tomato) when the plant was challenged by high temperature stress, thus extending the beneficial role of this bacterial consortium.

Plant-microbe interactions through a lens: tales from the mycorrhizosphere

BACKGROUND

The soil microbiome plays a pivotal role in maintaining ecological balance, supporting food production, preserving water quality and safeguarding human health. Understanding the intricate dynamics within the soil microbiome necessitates unravelling complex bacterial-fungal interactions (BFIs). BFIs occur in diverse habitats, such as the phyllosphere, rhizosphere and bulk soil, where they exert substantial influence on plant-microbe associations, nutrient cycling and overall ecosystem functions. In various symbiotic associations, fungi form mycorrhizal connections with plant roots, enhancing nutrient uptake through the root and mycorrhizal pathways. Concurrently, specific soil bacteria, including mycorrhiza helper bacteria, play a pivotal role in nutrient acquisition and promoting plant growth. Chemical communication and biofilm formation further shape plant-microbial interactions, affecting plant growth, disease resistance and nutrient acquisition processes.

SCOPE

Promoting synergistic interactions between mycorrhizal fungi and soil microbes holds immense potential for advancing ecological knowledge and conservation. However, despite the significant progress, gaps remain in our understanding of the evolutionary significance, perception, functional traits and ecological relevance of BFIs. Here we review recent findings obtained with respect to complex microbial communities - particularly in the mycorrhizosphere - and include the latest advances in the field, outlining their profound impacts on our understanding of ecosystem dynamics and plant physiology and function.

CONCLUSIONS

Deepening our understanding of plant BFIs can help assess their capabilities with regard to ecological and agricultural safe-guarding, in particular buffering soil stresses, and ensuring sustainable land management practices. Preserving and enhancing soil biodiversity emerge as critical imperatives in sustaining life on Earth amidst pressures of anthropogenic climate change. A holistic approach integrates scientific knowledge on bacteria and fungi, which includes their potential to foster resilient soil ecosystems for present and future generations.

Characterization of the Fusarium circinatum biofilm environmental response role

The capacity to form biofilms is a common trait among many microorganisms present on Earth. In this study, we demonstrate for the first time that the fatal pine pitch canker agent, Fusarium circinatum, can lead a biofilm-like lifestyle with aggregated hyphal bundles wrapped in extracellular matrix (ECM). Our research shows F. circinatum's ability to adapt to environmental changes by assuming a biofilm-like lifestyle. This was demonstrated by varying metabolic activities exhibited by the biofilms in response to factors like temperature and pH. Further analysis revealed that while planktonic cells produced small amounts of ECM per unit of the biomass, heat- and azole-exposed biofilms produced significantly more ECM than nonexposed biofilms, further demonstrating the adaptability of F. circinatum to changing environments. The increased synthesis of ECM triggered by these abiotic factors highlights the link between ECM production in biofilm and resistance to abiotic stress. This suggests that ECM-mediated response may be one of the key survival strategies of F. circinatum biofilms in response to changing environments. Interestingly, azole exposure also led to biofilms that were resistant to DNase, which typically uncouples biofilms by penetrating the biofilm and degrading its extracellular DNA; we propose that DNases were likely hindered from reaching target cells by the ECM barricade. The interplay between antifungal treatment and DNase enzyme suggests a complex relationship between eDNA, ECM, and antifungal agents in F. circinatum biofilms. Therefore, our results show how a phytopathogen's sessile (biofilm) lifestyle could influence its response to the surrounding environment.

Understanding the intricacies of microbial biofilm formation and its endurance in chronic infections: a key to advancing biofilm-targeted therapeutic strategies

Bacterial biofilms can adhere to various surfaces in the environment with human beings being no exception. Enclosed in a self-secreted matrix which contains extracellular polymeric substances, biofilms are intricate communities of bacteria that play a significant role across various sectors and raise concerns for public health, medicine and industries. These complex structures allow free-floating planktonic cells to adopt multicellular mode of growth which leads to persistent infections. This is of great concern as biofilms can withstand external attacks which include antibiotics and immune responses. A more comprehensive and innovative approach to therapy is needed in view of the increasing issue of bacterial resistance brought on by the overuse of conventional antimicrobial medications. Thus, to oppose the challenges posed by biofilm-related infections, innovative therapeutic strategies are being explored which include targeting extracellular polymeric substances, quorum sensing, and persister cells. Biofilm-responsive nanoparticles show promising results by improving drug delivery and reducing the side effects. This review comprehensively examines the factors influencing biofilm formation, host immune defence mechanisms, infections caused by biofilms, diagnostic approaches, and biofilm-targeted therapies.

Efficacy of High-Altitude Biofilm-Forming Novel Bacillus subtilis Species as Plant Growth-Promoting Rhizobacteria on Zea mays L

With the global population explosion, the need for increasing crop productivity is reaching its peak. The significance of organic means of cultivation including biofertilizers and biopesticides is undeniable in this context. Over the last few decades, the use of rhizobacteria to induce crop productivity has gained particular interest of researchers. Of these, several Bacillus spp. have been known for their potential plant growth-promoting and phyto-pathogenic actions. Keeping this background in mind, this study was formulated with an aim to unravel the PGPR and phyto-pathogenic potency of Bacillus sp. isolated from extreme environmental conditions, viz. high-altitude waters of Ganges at Gangotri (Basin Extent Longitude Latitude-73° 2' to 89° 5' E 21° 6' to 31° 21' N). Based on recent studies showing the impact of biofilm on bacterial PGPR potency, three novel strains of Bacillus subtilis were isolated on basis of their extremely high biofilm-producing abilities (BRAM_G1: Accession Number MW006633; BRAM_G2: Accession Numbers MT998278-MT998280; BRAM_G3: Accession Number MT998617), and were tested for their PGPR properties like nutrient sequestration, growth hormone production (IAA, GA3), stress-responsive enzyme production (ACC deaminase) and lignocellulolytic and agriculturally important enzyme productions. The strains were further tested for the plethora of metabolites (liquid and VOCs) exuded by them. Finally, the strains both in individually and in an association, i.e. consortium was tested on a test crop, viz. Zea mays L., and the data were collected at regular intervals and the results were statistically analysed. In the present study, the role of high-altitude novel Bacillus subtilis strains as potent PGPR has been analysed statistically.

Characterization of the IAA-Producing and -Degrading Pseudomonas Strains Regulating Growth of the Common Duckweed (Lemna minor L.)

The rhizosphere represents a center of complex and dynamic interactions between plants and microbes, resulting in various positive effects on plant growth and development. However, less is known about the effects of indole-3-acetic acid (IAA) on aquatic plants. In this study, we report the characterization of four Pseudomonas strains isolated from the rhizosphere of the common duckweed (Lemna minor) with IAA-degradation and -utilization ability. Our results confirm previous reports on the negative effect of IAA on aquatic plants, contrary to the effect on terrestrial plants. P. putida A3-104/5 demonstrated particularly beneficial traits, as it exhibited not only IAA-degrading and -producing activity but also a positive effect on the doubling time of duckweeds in the presence of IAA, positive chemotaxis in the presence of IAA, increased tolerance to oxidative stress in the presence of IAA and increased biofilm formation related to IAA. Similarly, P. gessardii C31-106/3 significantly shortened the doubling time of duckweeds in the presence of IAA, while having a neutral effect in the absence of IAA. These traits are important in the context of plant-bacteria interactions and highlight the role of IAA as a common metabolite in these interactions, especially in aquatic environments where plants are facing unique challenges compared to their terrestrial counterparts. We conclude that IAA-degrading and -producing strains presented in this study might regulate IAA effects on aquatic plants and confer evolutionary benefits under adverse conditions (e.g., under oxidative stress, excess of IAA or nutrient scarcity).

Biofilm formation in xenobiotic-degrading microorganisms

The increased presence of xenobiotics affects living organisms and the environment at large on a global scale. Microbial degradation is effective for the removal of xenobiotics from the ecosystem. In natural habitats, biofilms are formed by single or multiple populations attached to biotic/abiotic surfaces and interfaces. The attachment of microbial cells to these surfaces is possible via the matrix of extracellular polymeric substances (EPSs). However, the molecular machinery underlying the development of biofilms differs depending on the microbial species. Biofilms act as biocatalysts and degrade xenobiotic compounds, thereby removing them from the environment. Quorum sensing (QS) helps with biofilm formation and is linked to the development of biofilms in natural contaminated sites. To date, scant information is available about the biofilm-mediated degradation of toxic chemicals from the environment. Therefore, we review novel insights into the impact of microbial biofilms in xenobiotic contamination remediation, the regulation of biofilms in contaminated sites, and the implications for large-scale xenobiotic compound treatment.

Pressure-dependent growth controls 3D architecture of Pseudomonas putida microcolonies

Colony formation is key to many ecological and biotechnological processes. In its early stages, colony formation involves the concourse of a number of physical and biological parameters for generation of a distinct 3D structure-the specific influence of which remains unclear. We focused on a thus far neglected aspect of the process, specifically the consequences of the differential pressure experienced by cells in the middle of a colony versus that endured by bacteria located in the growing periphery. This feature was characterized experimentally in the soil bacterium Pseudomonas putida. Using an agent-based model we recreated the growth of microcolonies in a scenario in which pressure was the only parameter affecting proliferation of cells. Simulations exposed that, due to constant collisions with other growing bacteria, cells have virtually no free space to move sideways, thereby delaying growth and boosting chances of overlapping on top of each other. This scenario was tested experimentally on agar surfaces. Comparison between experiments and simulations suggested that the inside/outside differential pressure determines growth, both timewise and in terms of spatial directions, eventually moulding colony shape. We thus argue that-at least in the case studied-mere physical pressure of growing cells suffices to explain key dynamics of colony formation.

Microbial Primer: An introduction to biofilms - what they are, why they form and their impact on built and natural environments

Biofilms are complex communities of microbes that are bound by an extracellular macromolecular matrix produced by the residents. Biofilms are the predominant form of microbial life in the natural environment and although they are the leading cause of chronic infections, they are equally deeply connected to our ability to bioremediate waste and toxic materials. Here we highlight the emergent properties of biofilm communities and explore notable biofilms before concluding by providing examples of their major impact on our health and both natural and built environments.

Electrochemical Impedance Spectroscopy-Based Sensing of Biofilms: A Comprehensive Review

Biofilms are complex communities of microorganisms that can form on various surfaces, including medical devices, industrial equipment, and natural environments. The presence of biofilms can lead to a range of problems, including infections, reduced efficiency and failure of equipment, biofouling or spoilage, and environmental damage. As a result, there is a growing need for tools to measure and monitor levels of biofilms in various biomedical, pharmaceutical, and food processing settings. In recent years, electrochemical impedance sensing has emerged as a promising approach for real-time, non-destructive, and rapid monitoring of biofilms. This article sheds light on electrochemical sensing for measuring biofilms, including its high sensitivity, non-destructive nature, versatility, low cost, and real-time monitoring capabilities. We also discussed some electrochemical sensing applications for studying biofilms in medical, environmental, and industrial settings. This article also presents future perspectives for research that would lead to the creation of reliable, quick, easy-to-use biosensors mounted on unmanned aerial vehicles (UAVs), and unmanned ground vehicles (UGVs), utilizing artificial intelligence-based terminologies to detect biofilms.

Microbial Biofilms: Applications, Clinical Consequences, and Alternative Therapies

Biofilms are complex communities of microorganisms that grow on surfaces and are embedded in a matrix of extracellular polymeric substances. These are prevalent in various natural and man-made environments, ranging from industrial settings to medical devices, where they can have both positive and negative impacts. This review explores the diverse applications of microbial biofilms, their clinical consequences, and alternative therapies targeting these resilient structures. We have discussed beneficial applications of microbial biofilms, including their role in wastewater treatment, bioremediation, food industries, agriculture, and biotechnology. Additionally, we have highlighted the mechanisms of biofilm formation and clinical consequences of biofilms in the context of human health. We have also focused on the association of biofilms with antibiotic resistance, chronic infections, and medical device-related infections. To overcome these challenges, alternative therapeutic strategies are explored. The review examines the potential of various antimicrobial agents, such as antimicrobial peptides, quorum-sensing inhibitors, phytoextracts, and nanoparticles, in targeting biofilms. Furthermore, we highlight the future directions for research in this area and the potential of phytotherapy for the prevention and treatment of biofilm-related infections in clinical settings.

Fourier Transform Infrared (FTIR) Spectroscopic Study of Biofilms Formed by the Rhizobacterium Azospirillum baldaniorum Sp245: Aspects of Methodology and Matrix Composition

Biofilms represent the main mode of existence of bacteria and play very significant roles in many industrial, medical and agricultural fields. Analysis of biofilms is a challenging task owing to their sophisticated composition, heterogeneity and variability. In this study, biofilms formed by the rhizobacterium Azospirillum baldaniorum (strain Sp245), isolated biofilm matrix and its macrocomponents have for the first time been studied in detail, using Fourier transform infrared (FTIR) spectroscopy, with a special emphasis on the methodology. The accompanying novel data of comparative chemical analyses of the biofilm matrix, its fractions and lipopolysaccharide isolated from the outer membrane of the cells of this strain, as well as their electrophoretic analyses (SDS-PAGE) have been found to be in good agreement with the FTIR spectroscopic results.

Horizontal Gene Transfer of Antibiotic Resistance Genes in Biofilms

Most bacteria attach to biotic or abiotic surfaces and are embedded in a complex matrix which is known as biofilm. Biofilm formation is especially worrisome in clinical settings as it hinders the treatment of infections with antibiotics due to the facilitated acquisition of antibiotic resistance genes (ARGs). Environmental settings are now considered as pivotal for driving biofilm formation, biofilm-mediated antibiotic resistance development and dissemination. Several studies have demonstrated that environmental biofilms can be hotspots for the dissemination of ARGs. These genes can be encoded on mobile genetic elements (MGEs) such as conjugative and mobilizable plasmids or integrative and conjugative elements (ICEs). ARGs can be rapidly transferred through horizontal gene transfer (HGT) which has been shown to occur more frequently in biofilms than in planktonic cultures. Biofilm models are promising tools to mimic natural biofilms to study the dissemination of ARGs via HGT. This review summarizes the state-of-the-art of biofilm studies and the techniques that visualize the three main HGT mechanisms in biofilms: transformation, transduction, and conjugation.

Polyamine metabolizing rhizobacteria Pseudomonas sp. GBPI_506 modulates hormone signaling to enhance lateral roots and nicotine biosynthesis in Nicotiana benthamiana

Beneficial rhizobacteria in the soil are important drivers of plant health and growth. In this study, we provide the draft genome of a root colonizing and auxin-producing Pseudomonas sp. strain GBPI_506. The bacterium was investigated for its contribution in the growth of Nicotiana benthamiana (Nb) and biosynthesis of nicotine. The bacterium showed chemotaxis towards root exudates potentially mediated by putrescine, a polyamine compound, to colonize the roots of Nb. Application of the bacterium with the roots of Nb, increased plant biomass and total soluble sugars in the leaves, and promoted lateral root (LR) development as compared to the un-inoculated plants. Confocal analysis using transgenic (DR5:GFP) Arabidopsis showed increased auxin trafficking in the LR of inoculated plants. Upregulation of nicotine biosynthesis genes and genes involved in salicylic acid (SA) and jasmonic acid (JA) signaling in the roots of inoculated plants suggested increased nicotine biosynthesis as a result of bacterial application. An increased JA content in roots and nicotine accumulation in leaves provided evidence on JA-mediated upregulation of nicotine biosynthesis in the bacterized plants. The findings suggested that the bacterial root colonization triggered networking between auxin, SA, and JA to facilitate LR development leading to enhanced plant growth and nicotine biosynthesis in Nb.

Plant Growth-Promoting Bacteria (PGPB) with Biofilm-Forming Ability: A Multifaceted Agent for Sustainable Agriculture

Plant growth-promoting bacteria (PGPB) enhance plant growth, as well as protect plants from several biotic and abiotic stresses through a variety of mechanisms. Therefore, the exploitation of PGPB in agriculture is feasible as it offers sustainable and eco-friendly approaches to maintaining soil health while increasing crop productivity. The vital key of PGPB application in agriculture is its effectiveness in colonizing plant roots and the phyllosphere, and in developing a protective umbrella through the formation of microcolonies and biofilms. Biofilms offer several benefits to PGPB, such as enhancing resistance to adverse environmental conditions, protecting against pathogens, improving the acquisition of nutrients released in the plant environment, and facilitating beneficial bacteria–plant interactions. Therefore, bacterial biofilms can successfully compete with other microorganisms found on plant surfaces. In addition, plant-associated PGPB biofilms are capable of protecting colonization sites, cycling nutrients, enhancing pathogen defenses, and increasing tolerance to abiotic stresses, thereby increasing agricultural productivity and crop yields. This review highlights the role of biofilms in bacterial colonization of plant surfaces and the strategies used by biofilm-forming PGPB. Moreover, the factors influencing PGPB biofilm formation at plant root and shoot interfaces are critically discussed. This will pave the role of PGPB biofilms in developing bacterial formulations and addressing the challenges related to their efficacy and competence in agriculture for sustainability.

Signaling and Detoxification Strategies in Plant-Microbes Symbiosis under Heavy Metal Stress: A Mechanistic Understanding

Plants typically interact with a variety of microorganisms, including bacteria, mycorrhizal fungi, and other organisms, in their above- and below-ground parts. In the biosphere, the interactions of plants with diverse microbes enable them to acquire a wide range of symbiotic advantages, resulting in enhanced plant growth and development and stress tolerance to toxic metals (TMs). Recent studies have shown that certain microorganisms can reduce the accumulation of TMs in plants through various mechanisms and can reduce the bioavailability of TMs in soil. However, relevant progress is lacking in summarization. This review mechanistically summarizes the common mediating pathways, detoxification strategies, and homeostatic mechanisms based on the research progress of the joint prevention and control of TMs by arbuscular mycorrhizal fungi (AMF)-plant and Rhizobium-plant interactions. Given the importance of tripartite mutualism in the plant-microbe system, it is necessary to further explore key signaling molecules to understand the role of plant-microbe mutualism in improving plant tolerance under heavy metal stress in the contaminated soil environments. It is hoped that our findings will be useful in studying plant stress tolerance under a broad range of environmental conditions and will help in developing new technologies for ensuring crop health and performance in future.

Micro-fractionation shows microbial community changes in soil particles below 20 μm

Introduction

Micro-scale analysis of microbes in soil is essential to the overall understanding of microbial organization, interactions, and ecosystem functioning. Soil fractionation according to its aggregated structure has been used to access microbial habitats. While bacterial communities have been extensively described, little is known about the fungal communities at scales relevant to microbial interactions.

Methods

We applied a gentle soil fractionation method to preserve stable aggregated structures within the range of micro-aggregates and studied fungal and bacterial communities as well as nitrogen cycling potentials in the pristine Rothamsted Park Grass soil (bulk soil) as well as in its particle size fractions (PSFs; >250 μm, 250–63 μm, 63–20 μm, 20–2 μm, <2 μm, and supernatant).

Results

Overall bacterial and fungal community structures changed in PSFs below 20 μm. The relative abundance of Basidiomycota decreased with decreasing particle size over the entire measure range, while Ascomycota showed an increase and Mucoromycota became more prominent in particles below 20 μm. Bacterial diversity was found highest in the < 2 μm fraction, but only a few taxa were washed-off during the procedure and found in supernatant samples. These taxa have been associated with exopolysaccharide production and biofilm formation (e.g., Pseudomonas, Massilia, Mucilaginibacter, Edaphobaculum, Duganella, Janthinobacterium, and Variovorax). The potential for nitrogen reduction was found elevated in bigger aggregates.

Discussion

The observed changes below 20 μm particle are in line with scales where microbes operate and interact, highlighting the potential to focus on little researched sub-fractions of micro-aggregates. The applied method shows potential for use in studies focusing on the role of microbial biofilms in soil and might also be adapted to research various other soil microbial functions. Technical advances in combination with micro-sampling methods in soil promise valuable output in soil studies when particles below 20 μm are included.

Physiological Benefits of Oxygen-Terminating Extracellular Electron Transfer

Extracellular electron transfer (EET) is a process via which certain microorganisms, such as bacteria, exchange electrons with extracellular materials by creating an electrical link across their membranes. EET has been studied for the reactions on solid materials such as minerals and electrodes with implication in geobiology and biotechnology. EET-capable bacteria exhibit broad phylogenetic diversity, and some are found in environments with various types of electron acceptors/donors not limited to electrodes or minerals. Oxygen has also been shown to serve as the terminal electron acceptor for EET of Pseudomonas aeruginosa and Faecalibacterium prausnitzii. However, the physiological significance of such oxygen-terminating EETs, as well as the mechanisms underlying them, remain unclear. In order to understand the physiological advantage of oxygen-terminating EET and its link with energy metabolism, in this review, we compared oxygen-terminating EET with aerobic respiration, fermentation, and electrode-terminating EET. We also summarized benefits and limitations of oxygen-terminating EET in a biofilm setting, which indicate that EET capability enables bacteria to create a niche in the anoxic zone of aerobic biofilms, thereby remodeling bacterial metabolic activities in biofilms.

Geographically Disperse, Culturable Seed-Associated Microbiota in Forage Plants of Alfalfa (Medicago sativa L.) and Pitch Clover (Bituminaria bituminosa L.): Characterization of Beneficial Inherited Strains as Plant Stress-Tolerance Enhancers

Agricultural production is being affected by increasingly harsh conditions caused by climate change. The vast majority of crops suffer growth and yield declines due to a lack of water or intense heat. Hence, commercial legume crops suffer intense losses of production (20-80%). This situation is even more noticeable in plants used as fodder for animals, such as alfalfa and pitch trefoil, since their productivity is linked not only to the number of seeds produced, but also to the vegetative growth of the plant itself. Thus, we decided to study the microbiota associated with their seeds in different locations on the Iberian Peninsula, with the aim of identifying culturable bacteria strains that have adapted to harsh environments and that can be used as biotreatments to improve plant growth and resistance to stress. As potentially inherited microbiota, they may also represent a treatment with medium- and long-term adaptative effects. Hence, isolated strains showed no clear relationship with their geographical sampling location, but had about 50% internal similarity with their model plants. Moreover, out of the 51 strains isolated, about 80% were capable of producing biofilms; around 50% produced mid/high concentrations of auxins and grew notably in ACC medium; only 15% were characterized as xerotolerant, while more than 75% were able to sporulate; and finally, 65% produced siderophores and more than 40% produced compounds to solubilize phosphates. Thus, Paenibacillus amylolyticus BB B2-A, Paenibacillus xylanexedens MS M1-C, Paenibacillus pabuli BB Oeiras A, Stenotrophomonas maltophilia MS M1-B and Enterobacter hormaechei BB B2-C strains were tested as plant bioinoculants in lentil plants (Lens culinaris Medik.), showing promising results as future treatments to improve plant growth under stressful conditions.

Interplay between rhizospheric Pseudomonas chlororaphis strains lays the basis for beneficial bacterial consortia

Pseudomonas chlororaphis (Pc) representatives are found as part of the rhizosphere-associated microbiome, and different rhizospheric Pc strains frequently perform beneficial activities for the plant. In this study we described the interactions between the rhizospheric Pc strains PCL1601, PCL1606 and PCL1607 with a focus on their effects on root performance. Differences among the three rhizospheric Pc strains selected were first observed in phylogenetic studies and confirmed by genome analysis, which showed variation in the presence of genes related to antifungal compounds or siderophore production, among others. Observation of the interactions among these strains under lab conditions revealed that PCL1606 has a better adaptation to environments rich in nutrients, and forms biofilms. Interaction experiments on plant roots confirmed the role of the different phenotypes in their lifestyle. The PCL1606 strain was the best adapted to the habitat of avocado roots, and PCL1607 was the least, and disappeared from the plant root scenario after a few days of interaction. These results confirm that 2 out 3 rhizospheric Pc strains were fully compatible (PCL1601 and PCL1606), efficiently colonizing avocado roots and showing biocontrol activity against the fungal pathogen Rosellinia necatrix. The third strain (PCL1607) has colonizing abilities when it is alone on the root but displayed difficulties under the competition scenario, and did not cause deleterious effects on the other Pc competitors when they were present. These results suggest that strains PCL1601 and PCL1606 are very well adapted to the avocado root environment and could constitute a basis for constructing a more complex beneficial microbial synthetic community associated with avocado plant roots.

A review on biofilms and the currently available antibiofilm approaches: Matrix-destabilizing hydrolases and anti-bacterial peptides as promising candidates for the food industries

Biofilms are communities of microorganisms that can be harmful and/or beneficial, depending on location and cell content. Since in most cases (such as the formation of biofilms in laboratory/medicinal equipment, water pipes, high humidity-placed structures, and the food packaging machinery) these bacterial and fungal communities are troublesome, researchers in various fields are trying to find a promising strategy to destroy or slow down their formation. In general, anti-biofilm strategies are divided into the plant-based and non-plant categories, with the latter including nanoparticles, bacteriophages, enzymes, surfactants, active peptides and free fatty acids. In most cases, using a single strategy will not be sufficient to eliminate biofilm, and consequently, two or more strategies will inevitably be used to deal with this unwanted phenomenon. According to the analysis of potential biofilm inhibition strategies, the best option for the food industry would be the use of hydrolase enzymes and peptides extracted from natural sources. This article represents a systematic review of the previous efforts made in these directions.

Pseudomonas putida mediates bacterial killing, biofilm invasion and biocontrol with a type IVB secretion system

Many bacteria utilize contact-dependent killing machineries to eliminate rivals in their environmental niches. Here we show that the plant root colonizer Pseudomonas putida strain IsoF is able to kill a wide range of soil and plant-associated Gram-negative bacteria with the aid of a type IVB secretion system (T4BSS) that delivers a toxic effector into bacterial competitors in a contact-dependent manner. This extends the range of targets of T4BSSs—so far thought to transfer effectors only into eukaryotic cells—to prokaryotes. Bioinformatic and genetic analyses showed that this killing machine is entirely encoded by the kib gene cluster located within a rare genomic island, which was recently acquired by horizontal gene transfer. P. putida IsoF utilizes this secretion system not only as a defensive weapon to kill bacterial competitors but also as an offensive weapon to invade existing biofilms, allowing the strain to persist in its natural environment. Furthermore, we show that strain IsoF can protect tomato plants against the phytopathogen Ralstonia solanacearum in a T4BSS-dependent manner, suggesting that IsoF can be exploited for pest control and sustainable agriculture.

Pseudomonas putida uses a type IVB secretion system to kill a broad range of Gram-negative bacteria, invade biofilms and prevent phytopathogen Ralstonia solanacearum infection in tomato plants.

Harnessing microbial multitrophic interactions for rhizosphere microbiome engineering

The rhizosphere is a narrow and dynamic region of plant root-soil interfaces, and it's considered one of the most intricate and functionally active ecosystems on the Earth, which boosts plant health and alleviates the impact of biotic and abiotic stresses. Improving the key functions of the microbiome via engineering the rhizosphere microbiome is an emerging tool for improving plant growth, resilience, and soil-borne diseases. Recently, the advent of omics tools, gene-editing techniques, and sequencing technology has allowed us to unravel the entangled webs of plant-microbes interactions, enhancing plant fitness and tolerance to biotic and abiotic challenges. Plants secrete signaling compounds with low molecular weight into the rhizosphere, that engage various species to generate a massive deep complex array. The underlying principle governing the multitrophic interactions of the rhizosphere microbiome is yet unknown, however, some efforts have been made for disease management and agricultural sustainability. This review discussed the intra- and inter- microbe-microbe and microbe-animal interactions and their multifunctional roles in rhizosphere microbiome engineering for plant health and soil-borne disease management. Simultaneously, it investigates the significant impact of immunity utilizing PGPR and cover crop strategy in increasing rhizosphere microbiome functions for plant development and protection using omics techniques. The ecological engineering of rhizosphere plant interactions could be used as a potential alternative technology for plant growth improvement, sustainable disease control management, and increased production of economically significant crops.

Manipulating Bacterial Biofilms Using Materiobiology and Synthetic Biology Approaches

Bacteria form biofilms on material surfaces within hours. Biofilms are often considered problematic substances in the fields such as biomedical devices and the food industry; however, they are beneficial in other fields such as fermentation, water remediation, and civil engineering. Biofilm properties depend on their genome and the extracellular environment, including pH, shear stress, and matrices topography, stiffness, wettability, and charges during biofilm formation. These surface properties have feedback effects on biofilm formation at different stages. Due to emerging technology such as synthetic biology and genome editing, many studies have focused on functionalizing biofilm for specific applications. Nevertheless, few studies combine these two approaches to produce or modify biofilms. This review summarizes up-to-date materials science and synthetic biology approaches to controlling biofilms. The review proposed a potential research direction in the future that can gain better control of bacteria and biofilms.

Inhibition of Agrobacterium tumefaciens Growth and Biofilm Formation by Tannic Acid

Agrobacterium tumefaciens underlies the pathogenesis of crown gall disease and is characterized by tumor-like gall formation on the stems and roots of a wide variety of economically important plant species. The bacterium initiates infection by colonizing and forming biofilms on plant surfaces, and thus, novel compounds are required to prevent its growth and biofilm formation. In this study, we investigated the ability of tannic acid, which is ubiquitously present in woody plants, to specifically inhibit the growth and biofilm formation of A. tumefaciens. Tannic acid showed antibacterial activity and significantly reduced the biofilm formation on polystyrene and on the roots of Raphanus sativus as determined by 3D bright-field and scanning electron microscopy (SEM) images. Furthermore, tannic acid dose-dependently reduced the virulence features of A. tumefaciens, which are swimming motility, exopolysaccharide production, protease production, and cell surface hydrophobicity. Transcriptional analysis of cells (Abs600 nm = 1.0) incubated with tannic acid for 24 h at 30 °C showed tannic acid most significantly downregulated the exoR gene, which is required for adhesion to surfaces. Tannic acid at 100 or 200 µg/mL limited the iron supply to A. tumefaciens and similarly reduced the biofilm formation to that performed by 0.1 mM EDTA. Notably, tannic acid did not significantly affect R. sativus germination even at 400 µg/mL. The findings of this study suggest that tannic acid has the potential to prevent growth and biofilm formation by A. tumefaciens and thus infections resulting from A. tumefaciens colonization.

Mycorrhizae Helper Bacteria: Unlocking Their Potential as Bioenhancers of Plant-Arbuscular Mycorrhizal Fungal Associations

The dynamic interactions of plants and arbuscular mycorrhizal fungi (AMF) that facilitate the efficient uptake of minerals from soil and provide protection from various environmental stresses (biotic and abiotic) are now also attributed to a third component of the symbiosis. These are the less investigated mycorrhizae helper bacteria (MHB), which constitute a dense, active bacterial community, tightly associated with AMF, and involved in the development and functioning of AMF. Although AMF spores are known to host several bacteria in their spore walls and cytoplasm, their role in promoting the ecological fitness and establishment of AMF symbiosis by influencing spore germination, mycelial growth, root colonization, metabolic diversity, and biocontrol of soil borne diseases is now being deciphered. MHB also promote the functioning of arbuscular mycorrhizal symbiosis by triggering various plant growth factors, leading to better availability of nutrients in the soil and uptake by plants. In order to develop strategies to promote mycorrhization by AMF, and particularly to stimulate the ability to utilize phosphorus from the soil, there is a need to decipher crucial metabolic signalling pathways of MHB and elucidate their functional significance as mycorrhiza helper bacteria. MHB, also referred to as AMF bioenhancers, also improve agronomic efficiency and formulations using AMF along with enriched population of MHB are a promising option. This review covers the aspects related to the specificity and mechanisms of action of MHB, which positively impact the formation and functioning of AMF in mycorrhizal symbiosis, and the need to advocate MHB as AMF bioenhancers towards their inclusion in integrated nutrient management practices in sustainable agriculture.

Towards understanding mechanisms and functional consequences of bacterial interactions with members of various kingdoms in complex biofilms that abound in nature

The microbial world represents a phenomenal diversity of microorganisms from different kingdoms of life which occupy an impressive set of ecological niches. Most, if not all, microorganisms once colonise a surface develop architecturally complex surface-adhered communities which we refer to as biofilms. They are embedded in polymeric structural scaffolds serve as a dynamic milieu for intercellular communication through physical and chemical signalling. Deciphering microbial ecology of biofilms in various natural or engineered settings has revealed co-existence of microorganisms from all domains of life, including Bacteria, Archaea and Eukarya. The coexistence of these dynamic microbes is not arbitrary, as a highly coordinated architectural setup and physiological complexity show ecological interdependence and myriads of underlying interactions. In this review, we describe how species from different kingdoms interact in biofilms and discuss the functional consequences of such interactions. We highlight metabolic advances of collaboration among species from different kingdoms, and advocate that these interactions are of great importance and need to be addressed in future research. Since trans-kingdom biofilms impact diverse contexts, ranging from complicated infections to efficient growth of plants, future knowledge within this field will be beneficial for medical microbiology, biotechnology, and our general understanding of microbial life in nature.

Economic significance of biofilms: a multidisciplinary and cross-sectoral challenge

The increasing awareness of the significance of microbial biofilms across different sectors is continuously revealing new areas of opportunity in the development of innovative technologies in translational research, which can address their detrimental effects, as well as exploit their benefits. Due to the extent of sectors affected by microbial biofilms, capturing their real financial impact has been difficult. This perspective highlights this impact globally, based on figures identified in a recent in-depth market analysis commissioned by the UK’s National Biofilms Innovation Centre (NBIC). The outputs from this analysis and the workshops organised by NBIC on its research strategic themes have revealed the breath of opportunities for translational research in microbial biofilms. However, there are still many outstanding scientific and technological challenges which must be addressed in order to catalyse these opportunities. This perspective discusses some of these challenges.

Decisive Role of Polymer-Bovine Serum Albumin Interactions in Biofilm Substrates on "Philicity" and Extracellular Polymeric Substances Composition

Formation of extracellular polymeric substances (EPS) is a crucial step for bacterial biofilm growth. The dependence of EPS composition on growth substrate and conditioning of the latter is thus of primary importance. We present results of studies on the growth of biofilms of two different strains each, of the Gram-negative bacteria Escherichia coli and Klebsiella pneumoniae, on four polymers used commonly in indwelling medical devices ─polyethene, polypropylene, polycarbonate, and polytetrafluoroethylene─immersed in bovine serum albumin (BSA) for 24 h. The polymer substrates are studied before and after immersing in BSA for 9 and 24 h, using contact angle measurement (CAM) and field emission scanning electron microscopy (FE-SEM) to extract, respectively, the "philicity" φ (defined as -cos θ, where θ is the contact angle of the liquid on the solid at a particular temperature and ambient pressure) and spatial Hirsch parameter H (defined from the relation F(r) ∼ r^2H, where F(r) is the mean squared density fluctuation at the sample surface). H = 0.5, <0.5, or >0.5 signifies no correlation, anticorrelation, and correlation, respectively. The substrates are seen to transform from large hydrophobicity to near amphiphilicity with the formation of a BSA conditioning surface layer, and the H-values distinguish the length scales of 100, 500, and 2000 nm, with the anticorrelation increasing with length scale. Biofilms of E. coli did not grow on bare PTFE and HDPE substrates. Biofilms grown on BSA-covered surfaces are studied with CAM, FE-SEM, Fourier transform infrared (FTIR), and surface-enhanced Raman spectroscopy (SERS). Both spectra and φ-values were independent of bacterial species but dependent on the polymer, while H-values show some bacterial variation. Thus, EPS composition and wetting properties of the corresponding bacterial biofilms seem to be decided by the interaction of the conditioning BSA layer with the specific polymer substrate.

Niches and Seasonal Changes, Rather Than Transgenic Events, Affect the Microbial Community of Populus × euramericana ‘Neva’

Exploring the complex spatiotemporal changes and colonization mechanism of microbial communities will enable microbial communities to be better used to serve agricultural and ecological operations. In addition, evaluating the impact of transgenic plants on endogenous microbial communities is necessary for their commercial application. In this study, microbial communities of Populus × euramericana ‘Neva’ carrying Cry1Ac-Cry3A-BADH genes (ECAA1 line), Populus × euramericana ‘Neva’ carrying Cry1Ac-Cry3A-NTHK1 genes (ECAB1 line), and non-transgenic Populus × euramericana ‘Neva’ from rhizosphere soil, roots, and phloem collected in different seasons were compared and analyzed. Our analyses indicate that the richness and diversity of bacterial communities were higher in the three Populus × euramericana ‘Neva’ habitats than in those of fungi. Bacterial and fungal genetic-distance-clustering results were similar; rhizosphere soil clustered in one category, with roots and phloem in another. The diversity and evenness values of the microbial community were: rhizosphere soil > phloem > root system. The bacterial communities in the three habitats were dominated by the Proteobacteria, and fungal communities were dominated by the Ascomycota. The community composition and abundance of each part were quite different; those of Populus × euramericana ‘Neva’ were similar among seasons, but community abundance fluctuated. Seasonal fluctuation in the bacterial community was greatest in rhizosphere soil, while that of the fungal community was greatest in phloem. The transgenic lines ECAA1 and ECAB1 had a bacterial and fungal community composition similar to that of the control samples, with no significant differences in community structure or diversity among the lines. The abundances of operational taxonomic units (OTUs) were low, and differed significantly among the lines. These differences did not affect the functioning of the whole specific community. Sampling time and location were the main driving factors of changes in the Populus × euramericana ‘Neva’ microbial community. Transgenic events did not affect the Populus × euramericana ‘Neva’ rhizosphere or endophytic microbial communities. This study provides a reference for the safety evaluation of transgenic plants and the internal colonization mechanism of microorganisms in plants.

Isolation and Characterization of a Novel Autographiviridae Phage and Its Combined Effect with Tigecycline in Controlling Multidrug-Resistant Acinetobacter baumannii-Associated Skin and Soft Tissue Infections

Multidrug-resistant Acinetobacter baumannii (MDR A. baumannii) is one of the ESKAPE pathogens that restricts available treatment options. MDR A. baumannii is responsible for a dramatic increase in case numbers of a wide variety of infections, including skin and soft tissue infections (SSTIs), resulting in pyoderma, surgical debridement, and necrotizing fasciitis. To investigate an alternative medical treatment for SSTIs, a broad range lytic Acinetobacter phage, vB _AbP_ABWU2101 (phage vABWU2101), for lysing MDR A. baumannii in associated SSTIs was isolated and the biological aspects of this phage were investigated. Morphological characterization and genomic analysis revealed that phage vABWU2101 was a new species in the Friunavirus, Beijerinckvirinae, family Autographiviridae, and order Caudovirales. Antibiofilm activity of phage vABWU2101 demonstrated good activity against both preformed biofilms and biofilm formation. The combination of phage vABWU2101 and tigecycline showed synergistic antimicrobial activities against planktonic and biofilm cells. Scanning electron microscopy confirmed that the antibacterial efficacy of the combination of phage vABWU2101 and tigecycline was more effective than the phage or antibiotic alone. Hence, our findings could potentially be used to develop a therapeutic option for the treatment of SSTIs caused by MDR A. baumannii.

Biogels in Soils: Plant Mucilage as a Biofilm Matrix That Shapes the Rhizosphere Microbial Habitat

Mucilage is a gelatinous high-molecular-weight substance produced by almost all plants, serving numerous functions for plant and soil. To date, research has mainly focused on hydraulic and physical functions of mucilage in the rhizosphere. Studies on the relevance of mucilage as a microbial habitat are scarce. Extracellular polymeric substances (EPS) are similarly gelatinous high-molecular-weight substances produced by microorganisms. EPS support the establishment of microbial assemblages in soils, mainly through providing a moist environment, a protective barrier, and serving as carbon and nutrient sources. We propose that mucilage shares physical and chemical properties with EPS, functioning similarly as a biofilm matrix covering a large extent of the rhizosphere. Our analyses found no evidence of consistent differences in viscosity and surface tension between EPS and mucilage, these being important physical properties. With regard to chemical composition, polysaccharide, protein, neutral monosaccharide, and uronic acid composition also showed no consistent differences between these biogels. Our analyses and literature review suggest that all major functions known for EPS and required for biofilm formation are also provided by mucilage, offering a protected habitat optimized for nutrient mobilization. Mucilage enables high rhizo-microbial abundance and activity by functioning as carbon and nutrient source. We suggest that the role of mucilage as a biofilm matrix has been underestimated, and should be considered in conceptual models of the rhizosphere.

Diversity and Functionalities of Unknown Mycorrhizal Fungal Microbiota

Beneficial ecosystem services provided by arbuscular mycorrhizal fungi (AMF) are the outcome of their synergistic actions with diverse bacterial communities (AMF-associated bacteria; AAB) living in strict association with AMF hyphae and spores. Herein, bacterial diversity associated with 6 AMF species from 33 different co-cultures belonging to order Glomerales and Diversisporales were identified, using a combination of culture-dependent functional analyses and amplicon sequencing. Overall, 231 bacterial strains were isolated from the AMF spores and hyphae which covered 30 bacterial genera and 52 species. Hierarchical clustering based on plant growth promoting traits identified 9 clades comprising diverse bacterial genera with clades 7, 8 and 9 representing the most functionally rich AAB. High-throughput amplicon sequencing across a small subset of 8 AMF co-cultures spread across 3 AMF genera identified Operational Taxonomic Units belonging to 118 bacterial genera. The study revealed a greater diversity of AAB from spores of in vitro transformed AMF root co-cultures rather than in situ, pot AMF cultures. Functionally active, culturable AABs with multiple plant growth promoting traits such as phosphate solubilisation, nitrogen fixation, biofilm formation, enzyme and plant growth regulator production along with biocontrol activity were identified. These properties could be utilized individually and/or as consortia with AMF, as biological growth enhancers.

A call to arms for cell-cell interactions between bacteria in the plant microbiome

Next-generation sequencing and computational biology has unravelled the different bacterial groups populating plant microbiomes. In addition, microbiologists have discovered many different mechanisms of cell-cell interactions that take place between bacteria. Bacteria use four prevalent mechanisms for intercellular interactions; however, their pertinent role in the formation and maintenance of plant microbiomes is currently unknown. We argue that it is overdue to speed up research on the biotic cell-cell interactions that take place between bacteria in plant microbiomes. This research will have a major impact on both fundamental sciences and translational agriculture via the development of bacterial prebiotic compounds as well probiotics competence, resulting in a more sustainable agriculture of economically important crops.

Genome-Based Characterization of Plant-Associated Rhodococcus qingshengii RL1 Reveals Stress Tolerance and Plant-Microbe Interaction Traits

Stress tolerant, plant-associated bacteria can play an important role in maintaining a functional plant microbiome and protecting plants against various (a)biotic stresses. Members of the stress tolerant genus Rhodococcus are frequently found in the plant microbiome. Rhodococcus qingshengii RL1 was isolated from Eruca sativa and the complete genome was sequenced, annotated and analyzed using different bioinformatic tools. A special focus was laid on functional analyses of stress tolerance and interactions with plants. The genome annotation of RL1 indicated that it contains a repertoire of genes which could enable it to survive under different abiotic stress conditions for e.g., elevated mercury concentrations, to interact with plants via root colonization, to produce phytohormones and siderophores, to fix nitrogen and to interact with bacterial signaling via a LuxR-solo and quorum quenching. Based on the identified genes, functional analyses were performed in vitro with RL1 under different growth conditions. The R. qingshengii type strain djl6 and a closely related Rhodococcus erythropolis BG43 were included in the experiments to find common and distinct traits between the strains. Genome based phylogenetic analysis of 15 available and complete R. erythropolis and R. qingshengii genome sequences revealed a separation of the R. erythropolis clade in two subgroups. First one harbors only R. erythropolis strains including the R. erythropolis type strain. The second group consisted of the R. qingshengii type strain and a mix of R. qingshengii and R. erythropolis strains indicating that some strains of the second group should be considered for taxonomic re-assignment. However, BG43 was clearly identified as R. erythropolis and RL1 clearly as R. qingshengii and the strains had most tested traits in common, indicating a close functional overlap of traits between the two species.

Revealing of Non-Cultivable Bacteria Associated with the Mycelium of Fungi in the Kerosene-Degrading Community Isolated from the Contaminated Jet Fuel

Fuel (especially kerosene) biodamage is a challenge for global industry. In aviation, where kerosene is a widely used type of fuel, its biodeterioration leads to significant damage. Six isolates of micromycetes from the TS-1 aviation kerosene samples were obtained. Their ability to grow on the fuel was studied, and the difference between biodegradation ability was shown. Micromycetes belonged to the Talaromyces, Penicillium, and Aspergillus genera. It was impossible to obtain bacterial isolates associated with their mycelium. However, 16S rRNA metabarcoding and microscopic observations revealed the presence of bacteria in the micromycete isolates. It seems to be that kerosene-degrading fungi were associated with uncultured bacteria. Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes were abundant in the fungal cultures isolated from the TS-1 jet fuel samples. Most genera among these phyla are known as hydrocarbon degraders. Only bacteria-containing micromycete isolates were able to grow on the kerosene. Most likely, kerosene degradation mechanisms are based on synergism of bacteria and fungi.

Towards sustainable performance of urban horticulture: ten challenging fields of action for modern integrated pest management in cities

We identified ten current key challenges for plant protection in cities each of them belonging to a specific field of action of IPM in urban horticulture according to Directive 2009/128/EC. The challenges are: appropriate plant selection, microbiome engineering, nutrient recycling, smart, digital solutions, diversification of vegetation, avoidance of pesticide side effects on beneficials, biorational efficacy assessment, effective pest diagnosis, efficient outbreak control and holistic approaches. They are discussed on the background of the defined urban horticultural core sectors (a) public green infrastructure, including professional plant care, (b) professional field and greenhouse production systems and (c) non-professional private homegardens and allotments.

Extracellular DNA Promotes Efficient Extracellular Electron Transfer by Pyocyanin in Pseudomonas aeruginosa Biofilms

Redox cycling of extracellular electron shuttles can enable the metabolic activity of subpopulations within multicellular bacterial biofilms that lack direct access to electron acceptors or donors. How these shuttles catalyze extracellular electron transfer (EET) within biofilms without being lost to the environment has been a long-standing question. Here, we show that phenazines mediate efficient EET through interactions with extracellular DNA (eDNA) in Pseudomonas aeruginosa biofilms. Retention of pyocyanin (PYO) and phenazine carboxamide in the biofilm matrix is facilitated by eDNA binding. In vitro, different phenazines can exchange electrons in the presence or absence of DNA and can participate directly in redox reactions through DNA. In vivo, biofilm eDNA can also support rapid electron transfer between redox active intercalators. Together, these results establish that PYO:eDNA interactions support an efficient redox cycle with rapid EET that is faster than the rate of PYO loss from the biofilm.