Coating individual bacterial cells with conjugated polymers to endow them with more functionalities is highly desirable. Here, we developed an in situ polymerization method to coat polypyrrole on the surface of individual Shewanella oneidensis MR-1, Escherichia coli, Ochrobacterium anthropic or Streptococcus thermophilus. All of these as-coated cells from different bacterial species displayed enhanced conductivities without affecting viability, suggesting the generality of our coating method. Because of their excellent conductivity, we employed polypyrrole-coated Shewanella oneidensis MR-1 as an anode in microbial fuel cells (MFCs) and found that not only direct contact-based extracellular electron transfer is dramatically enhanced, but also the viability of bacterial cells in MFCs is improved. Our results indicate that coating individual bacteria with conjugated polymers could be a promising strategy to enhance their performance or enrich them with more functionalities.
We report a facile method for the antimicrobial modification of a thin-film composite polyamide reverse osmosis (RO) membrane. The membrane surface was first coated with polydopamine (PDA), whose reducing catechol groups subsequently immobilized silver ions in situ to form uniformly dispersed silver nanoparticles (AgNPs) inside the coating layer. Agglomeration of AgNPs was not observed despite a high silver loading of 13.3 ± 0.3 μg/cm(2) (corresponding to a surface coverage of 18.5% by the nanoparticles). Both diffusion inhibition zone tests and colony formation unit tests showed clear antimicrobial effects of the silver loaded membranes on model bacteria Bacillus subtilis and Escherichia coli. Furthermore, the silver immobilized membrane had significantly enhanced salt rejection compared to the control PDA coated membrane, which is attributed to the preferential formation of AgNPs at defect sides within the PDA layer. This self-healing mechanism can be used to prepare antimicrobial RO membranes with improved salt rejection without scarifying the membrane permeability, which provides a new dimension for membrane surface modification.
The bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) is a ubiquitous second messenger that determines bacterial lifestyle between the planktonic and biofilm modes of life. Although the role of c-di-GMP signaling in biofilm development and dispersal has been extensively studied, how c-di-GMP signaling influences environmental bioprocess activities such as biodegradation remains unexplored. To elucidate the impacts of elevating c-di-GMP level on environmental bioprocesses, we constructed a Comamonas testosteroni strain constitutively expressing a c-di-GMP synthase YedQ from Escherichia coli and examined its capability in biofilm formation and biodegradation of 3-chloroaniline (3-CA). The high c-di-GMP strain exhibited an increased binding to Congo red dye, a decreased motility, and an enhanced biofilm formation capability. In planktonic cultures, the strain with an elevated c-di-GMP concentration and the wild type could degrade 3-CA comparably well. However, under batch growth conditions with a high surface to volume ratio, an elevated c-di-GMP concentration in C. testosteroni significantly increased the contribution of biofilms in 3-CA biodegradation. In continuous submerged biofilm reactors, C. testosteroni with an elevated c-di-GMP level exhibited an enhanced 3-CA biodegradation and a decreased cell detachment rate. Taken together, this study provides a novel strategy to enhance biofilm-based biodegradation of toxic xenobiotic compounds through manipulating bacterial c-di-GMP signaling.
Comamonas is one of the most abundant microorganisms in biofilm communities driving wastewater treatment. Little has been known about the role of this group of organisms and their biofilm mode of life. In this study, using Comamonas testosteroni as a model organism, we demonstrated the involvement of Comamonas biofilms in denitrification under bulk aerobic conditions and elucidated the influence of nitrate respiration on its biofilm lifestyle. Our results showed that C. testosteroni could use nitrate as the sole electron acceptor for anaerobic growth. Under bulk aerobic condition, biofilms of C. testosteroni were capable of reducing nitrate, and intriguingly, nitrate reduction significantly enhanced viability of the biofilm-cells and reduced cell detachment from the biofilms. Nitrate respiration was further shown to play an essential role in maintaining high cell viability in the biofilms. RNA-seq analysis, quantitative polymerase chain reaction, and liquid chromatography-mass spectrometry revealed a higher level of bis(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) in cells respiring on nitrate than those grown aerobically (1.3 × 10(-4) fmol/cell vs 7.9 × 10(-6) fmol/cell; P < 0.01). C-di-GMP is one universal signaling molecule that regulates the biofilm mode of life, and a higher c-di-GMP concentration reduces cell detachment from biofilms. Taking these factors together, this study reveals that nitrate reduction occurs in mature biofilms of C. testosteroni under bulk aerobic conditions, and the respiratory reduction of nitrate is beneficial to the biofilm lifestyle by providing more metabolic energy to maintain high viability and a higher level of c-di-GMP to reduce cell detachment.
Soil is inhabited by a myriad of microorganisms, many of which can form supracellular structures, called biofilms, comprised of surface-associated microbial cells embedded in hydrated extracellular polymeric substance that facilitates adhesion and survival. Biofilms enable intensive inter-and intra-species interactions that can increase the degradation efficiency of soil organic matter and materials commonly regarded as toxins. Here, we first discuss organization, dynamics and properties of soil biofilms in the context of traditional approaches to probe the soil microbiome. Social interactions among bacteria, such as cooperation and competition, are discussed. We also summarize different biofilm cultivation devices in combination with optics and fluorescence microscopes as well as sequencing techniques for the study of soil biofilms. Microfluidic platforms, which can be applied to mimic the complex soil environment and study microbial behaviors at the microscale with highthroughput screening and novel measurements, are also highlighted. This review aims to highlight soil biofilm research in order to expand the current limited knowledge about soil microbiomes which until now has mostly ignored biofilms as a dominant growth form.
Microbial fuel cell (MFC) is a promising technology for energy harvesting from biomass, however, reported MFCs with wild-type or biologically modified exoelectrogenic bacteria such as Shewanella oneidensis often exhibited poor performance in generating electricity from sugars. Herein, a synthetic fermenter-exoelectrogen (Escherichia coli-S. oneidensis) microbial consortium was developed to expand the spectrum of carbon sources for MFC through establishing a highly electroactive anodic biofilm by rationally tuning its microbial community profile to favor efficient electron transfer. Specifically, a synthetic riboflavin pathway from Bacillus subtilis was incorporated into E. coli to overproduce flavins to facilitate flavin-mediated electron transfer, and a highly hydrophobic S. oneidensis strain CP2-1-S1 was adopted as the exoelectrogen to increase its adhesion to the carbon electrode. The highly hydrophobic interactions between S. oneidensis and the anode along with the overproduced flavins (increased from 3.3 µM to 115.2 µM) by the recombinant E. coli provided a definite advantage for S. oneidensis over E. coli in the attachment to the anode surface. Compared with the structure of the wild-type community immobilized on the anode, the cell number of S. oneidensis increased by ~3 times, while the cell number of E. coli decreased by 93.3% in the engineered electrode-attached community. Such rationally engineered anodic biofilm with the tuned microbial community profile (the percentage of S.oneidensis cells in the anodic biofilm increased from 48.2% to 98.2%) showed a much higher catalytic current (from 0.19 to 1.84 A/m 2 at 0 V vs. SHE). The xylose-fed MFC inoculated with our engineered microbial consortium generated a maximum power density of 728.6 mW/m 2 , which was 6.8 times higher than that inoculated with wild-type co-culture (92.8 mW/m 2 ).
Background: Bacterial biofilms are surface-adherent microbial communities in which individual cells are surrounded by a self-produced extracellular matrix of polysaccharides, extracellular DNA (eDNA) and proteins. Interactions among matrix components within biofilms are responsible for creating an adaptable structure during biofilm development. However, it is unclear how the interactions among matrix components contribute to the construction of the three-dimensional (3D) biofilm architecture. Results: DNase I treatment significantly inhibited Bacillus subtilis biofilm formation in the early phases of biofilm development. Confocal laser scanning microscopy (CLSM) and image analysis revealed that eDNA was cooperative with exopolysaccharide (EPS) in the early stages of B. subtilis biofilm development, while EPS played a major structural role in the later stages. In addition, deletion of the EPS production gene epsG in B. subtilis SBE1 resulted in loss of the interaction between EPS and eDNA and reduced the biofilm biomass in pellicles at the air-liquid interface. The physical interaction between these two essential biofilm matrix components was confirmed by isothermal titration calorimetry (ITC). Conclusions: Biofilm 3D structures become interconnected through surrounding eDNA and EPS. eDNA interacts with EPS in the early phases of biofilm development, while EPS mainly participates in the maturation of biofilms. The findings of this study provide a better understanding of the role of the interaction between eDNA and EPS in shaping the biofilm 3D matrix structure and biofilm formation.
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