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The genus Shewanella comprises about 70 species of Gram-negative, facultative anaerobic bacteria inhabiting various environments, which have shown great potential in various biotechnological applications ranging from environmental bioremediation, metal(loid) recovery and material synthesis to bioenergy generation. Most environmental and energy applications of Shewanella involve the biofilm mode of growth on surfaces of solid minerals or electrodes. In this article, we first provide an overview of Shewanella biofilm biology with the focus on biofilm dynamics, biofilm matrix, and key signalling systems involved in Shewanella biofilm development. Then we review strategies recently exploited to engineer Shewanella biofilms to improve biofilm-mediated bioprocesses., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In green chemical synthesis, biofilms as biocatalysts have shown great promise. Efficient biofilm-mediated biocatalysis requires the modulation of biofilm formation. Optogenetic tools are ideal to control biofilms because light is noninvasive, easily controllable, and cost-efficient. In this study, a gene circuit responsive to near-infrared (NIR) light was used to modulate the cellular level of bis-(3'-5') cyclic dimeric guanosine monophosphate (c-di-GMP), a central regulator of the prokaryote biofilm lifestyle, which allowed the regulation of biofilm formation by using NIR light. The engineered biofilm was applied to catalyze the biotransformation of indole into tryptophan in submerged biofilm reactors and NIR-light-enhanced biofilm formation resulted in an approximately 30 % increase in tryptophan yield, which demonstrates the feasibility of the application of light to modulate the formation and performance of catalytic biofilms for chemical production. The c-di-GMP-targeted optogenetic approach to modulate catalytic biofilms showcases applications for biofilm-mediated biocatalysis., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Understanding the dynamics of biofilm development in response to chemical cues and signals is required toward the development of controllable biofilm-mediated bioprocesses. In this study, we report a new biofilm growth system that integrates a microfluidic gradient mixer with a biofilm growth chamber. The biofilm growth system allows biofilms to grow under defined solute gradients and enables nondestructive monitoring of the biofilm development dynamics in response to the defined gradients. The solute gradients generated in the system were simulated and then validated experimentally. We then demonstrated the applicability of the biofilm growth system in studying biofilm development under defined solute gradients. Specifically, we examined biofilm development of Shewanella oneidensis and Comamonas testosteroni under a defined calcium and nitrate gradient, respectively. Using two C. testosteroni strains (WDL7 and I2), we further demonstrated the applicability of our biofilm growth system to study the development of coculture biofilms under a defined solute gradient. Our results show that the biofilm growth system we have developed here can be a promising tool to reveal the dynamics of biofilm development in response to chemical cues and signals as well as the interorganism interactions in coculture biofilms., (© 2018 Wiley Periodicals, Inc.)

Quorum quenching (QQ) has been reported to be a promising approach for membrane biofouling control. Entrapment of QQ bacteria in porous matrices is required to retain them in continuously operated membrane processes and to prevent uncontrollable biofilm formation by the QQ bacteria on membrane surfaces. It would be more desirable if the formation and dispersal of biofilms by QQ bacteria could be controlled so that the QQ bacterial cells are self-immobilized, but the QQ biofilm itself still does not compromise membrane performance. In this study, we engineered a QQ bacterial biofilm whose growth and dispersal can be modulated by light through a dichromatic, optogenetic c-di-GMP gene circuit in which the bacterial cells sense near-infrared (NIR) light and blue light to adjust its biofilm formation by regulating the c-di-GMP level. We also demonstrated the potential application of the engineered light-responsive QQ biofilm in mitigating biofouling of water purification forward osmosis membranes. The c-di-GMP-targeted optogenetic approach for controllable biofilm development we have demonstrated here should prove widely applicable for designing other controllable biofilm-enabled applications such as biofilm-based biocatalysis.

Molecular mapping of live biofilms at submicrometer resolution presents a grand challenge. Here, we present the first chemical mapping results of biofilm extracellular polymeric substance (EPS) in biofilms using correlative imaging between super resolution fluorescence microscopy and liquid time-of-flight secondary ion mass spectrometry (TOF-SIMS). Shewanella oneidensis is used as a model organism. Heavy metal chromate (Cr 2 O 7 ) anions consisting of chromium Cr(VI) was used as a model environmental stressor to treat the biofilms. Of particular interest, biologically relevant water clusters have been first observed in the biofilms. Characteristic fragments of biofilm matrix components such as proteins, polysaccharides, and lipids can be spatially imaged. Furthermore, characteristic fatty acids (e.g., palmitic acid), quinolone signal, and riboflavin fragments were found to respond after the biofilm is treated with Cr(VI), leading to biofilm dispersal. Significant changes in water clusters and quorum sensing signals indicative of intercellular communication in the aqueous environment were observed, suggesting that they might result in fatty acid synthesis and inhibition of riboflavin production. The Cr(VI) reduction seems to follow the Mtr pathway leading to Cr(III) formation. Our approach potentially opens a new avenue for mechanistic insight of microbial community processes and communications using in situ imaging mass spectrometry and super resolution optical microscopy.2- ) anions consisting of chromium Cr(VI) was used as a model environmental stressor to treat the biofilms. Of particular interest, biologically relevant water clusters have been first observed in the biofilms. Characteristic fragments of biofilm matrix components such as proteins, polysaccharides, and lipids can be spatially imaged. Furthermore, characteristic fatty acids (e.g., palmitic acid), quinolone signal, and riboflavin fragments were found to respond after the biofilm is treated with Cr(VI), leading to biofilm dispersal. Significant changes in water clusters and quorum sensing signals indicative of intercellular communication in the aqueous environment were observed, suggesting that they might result in fatty acid synthesis and inhibition of riboflavin production. The Cr(VI) reduction seems to follow the Mtr pathway leading to Cr(III) formation. Our approach potentially opens a new avenue for mechanistic insight of microbial community processes and communications using in situ imaging mass spectrometry and super resolution optical microscopy.

In natural and engineered environments, microorganisms often co-exist and interact with various minerals or mineral-containing solids. Microorganism-mineral interactions contribute significantly to environmental processes, including biogeochemical cycles in natural ecosystems and biodeterioration of materials in engineered environments. In this mini-review, we provide a summary of several key mechanisms involved in microorganism-mineral interactions, including the following: (i) solid minerals serve as substrata for biofilm development; (ii) solid minerals serve as an electron source or sink for microbial respiration; (iii) solid minerals provide microorganisms with macro or micronutrients for cell growth; and (iv) (semi)conductive solid minerals serve as extracellular electron conduits facilitating cell-to-cell interactions. We also highlight recent developments in harnessing microbe-mineral interactions for biotechnological applications.

Unlabelled: Bioaugmentation has been frequently proposed in wastewater and soil treatment to remove toxic aromatic compounds. The performance of bioaugmentation is affected by a number of biological and environmental factors, including the interaction between the target pollutant and the augmented bacterial cells. In this study, using Comamonas testosteroni and 3-chloroaniline (3-CA) as the model organism and target pollutant, we explored the influence of toxic aromatic pollutants on the biofilm lifestyle of bacteria capable of degrading aromatic compounds toward a better understanding of cell-pollutant interaction in bioaugmentation. Our results showed that the exposure to 3-CA greatly reduced the retention of C. testosteroni cells in packed-bed bioreactors (from 22% to 15% after three pore volumes), which could be attributed to the altered bacterial motility and cell surface hydrophobicity. To further understand the molecular mechanisms, we employed an integrated genomic and transcriptomic analysis to examine the influence of 3-CA on the expression of genes important to the biofilm lifestyle of C. testosteroni We found that exposure to 3-CA reduced the intracellular c-di-GMP level by downregulating the expression of genes encoding c-di-GMP synthases and induced massive cell dispersal from the biofilms. Our findings provide novel environmental implications on bioaugmentation, particularly in biofilm reactors, for the treatment of wastewater containing recalcitrant industrial pollutants., Importance: Bioaugmentation is a bioremediation approach that often has been described in the literature but has almost never been successfully applied in practice. Many biological and environmental factors influence the overall performance of bioaugmentation. Among these, the interaction between the target pollutant and the augmented bacterial cells is one of the most important factors. In this study, we revealed the influence of toxic aromatic pollutants on the biofilm lifestyle of bacteria capable of degrading aromatic compounds toward a better understanding of cell-pollutant interaction in bioaugmentation. Our findings provide novel environmental implications on bioaugmentation for the treatment of wastewater containing recalcitrant industrial pollutants; in particular, the exposure to toxic pollutants may reduce the retention of augmented organisms in biofilm reactors by reducing the c-di-GMP level, and approaches to elevating or maintaining a high c-di-GMP level may be promising to establish and maintain sustainable bioaugmentation activity., (Copyright © 2016, American Society for Microbiology. All Rights Reserved.)

Electroactive biofilms play essential roles in determining the power output of microbial fuel cells (MFCs). To engineer the electroactive biofilm formation of Shewanella oneidensis MR-1, a model exoelectrogen, we herein heterologously overexpressed a c-di-GMP biosynthesis gene ydeH in S. oneidensis MR-1, constructing a mutant strain in which the expression of ydeH is under the control of IPTG-inducible promoter, and a strain in which ydeH is under the control of a constitutive promoter. Such engineered Shewanella strains had significantly enhanced biofilm formation and bioelectricity generation. The MFCs inoculated with these engineered strains accomplished a maximum power density of 167.6 ± 3.6 mW/m(2) , which was ∼ 2.8 times of that achieved by the wild-type MR-1 (61.0 ± 1.9 mW/m(2) ). In addition, the engineered strains in the bioelectrochemical system at poised potential of 0.2 V vs. saturated calomel electrode (SCE) generated a stable current density of 1100 mA/m(2) , ∼ 3.4 times of that by wild-type MR-1 (320 mA/m(2) )., (© 2015 Wiley Periodicals, Inc.)

Stress response plays an important role on microbial adaptation under hostile environmental conditions. It is generally unclear how the signaling transduction pathway mediates a stress response in planktonic and biofilm modes of microbial communities simultaneously. Here, we showed that metalloid tellurite (TeO3(2-)) exposure induced the intracellular content of the secondary messenger cyclic di-GMP (c-di-GMP) of Pseudomonas aeruginosa. Two diguanylate cyclases (DGCs), SadC and SiaD, were responsible for the increased intracellular content of c-di-GMP. Enhanced c-di-GMP levels by TeO3(2-) further increased P. aeruginosa biofilm formation and resistance to TeO3(2-). P. aeruginosa ΔsadCΔsiaD and PAO1/p(lac)-yhjH mutants with low intracellular c-di-GMP content were more sensitive to TeO3(2-) exposure and had low relative fitness compared to the wild-type PAO1 planktonic and biofilm cultures exposed to TeO3(2-). Our study provided evidence that c-di-GMP level can play an important role in mediating stress response in microbial communities during both planktonic and biofilm modes of growth.

Comamonas testosteroni is an important environmental bacterium capable of degrading a variety of toxic aromatic pollutants and has been demonstrated to be a promising biocatalyst for environmental decontamination. This organism is often found to be among the primary surface colonizers in various natural and engineered ecosystems, suggesting an extraordinary capability of this organism in environmental adaptation and biofilm formation. The goal of this study was to gain genetic insights into the adaption of C. testosteroni to versatile environments and the importance of a biofilm lifestyle. Specifically, a draft genome of C. testosteroni I2 was obtained. The draft genome is 5,778,710 bp in length and comprises 110 contigs. The average G+C content was 61.88 %. A total of 5365 genes with 5263 protein-coding genes were predicted, whereas 4324 (80.60 % of total genes) protein-encoding genes were associated with predicted functions. The catabolic genes responsible for biodegradation of steroid and other aromatic compounds on draft genome were identified. Plasmid pI2 was found to encode a complete pathway for aniline degradation and a partial catabolic pathway for chloroaniline. This organism was found to be equipped with a sophisticated signaling system which helps it find ideal niches and switch between planktonic and biofilm lifestyles. A large number of putative multi-drug-resistant genes coding for abundant outer membrane transporters, chaperones, and heat shock proteins for the protection of cellular function were identified in the genome of strain I2. In addition, the genome of strain I2 was predicted to encode several proteins involved in producing, secreting, and uptaking siderophores under iron-limiting conditions. The genome of strain I2 contains a number of genes responsible for the synthesis and secretion of exopolysaccharides, an extracellular component essential for biofilm formation. Overall, our results reveal the genomic features underlying the adaption of C. testosteroni to versatile environments and highlighting the importance of its biofilm lifestyle.

Biofilms are the most ubiquitous and resilient form of microbial life on earth. One most important feature of a biofilm is the presence of a self-produced matrix, which creates highly heterogeneous and dynamic microenvironments within biofilms. Redox status in biofilm microenvironments plays a critical role in biofilm development and function. However, there is a lack of non-intrusive tools to quantify extracellular redox status of microenvironments within a biofilm matrix. In this study, using Shewanella oneidensis as a model organism, we demonstrated a novel approach to monitor extracellular redox status in biofilm microenvironments. Specifically, we displayed a redox sensitive fluorescence protein roGFP onto the cell surface of S. oneidensis by fusing it to the C-terminus of BpfA, a large surface protein, and used the surface displayed roGFP as a sensor to quantify the extracellular redox status in the matrix of S. oneidensis biofilms. The fusion of roGFP into BpfA has no negative impacts on cell growth and biofilm formation. Upon exposure to oxidizing agents such as H2 O2 , Ag(+) , and SeO3 (2-) , S. oneidensis BpfA-roGFP cells exhibited a characteristic fluorescence of roGFP. Proteinase treatment assay and super-resolution structured illumination microscopy confirmed the surface localization of BpfA-roGFP. We further used the surface displayed roGFP monitored the extracellular redox status in the matrix at different depths of a biofilm exposed to H2 O2 . This study provides a novel approach to non-invasively monitor extracellular redox status in microenvironments within biofilms, which can be used to understand redox responses of biofilms to environmental perturbations., (© 2014 Wiley Periodicals, Inc.)

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.

The performance of biofilm-based bioprocesses is difficult to predict and control because of the intrinsic heterogeneous and dynamic properties of microbial biofilms. Biofilm mimics, such as microbial cells entrapped in polymeric scaffolds that are permeable for nutrients, have been proposed to replace real biofilms to achieve long-term robust performance in engineering applications. However, the physiological differences between cells that are physically entrapped in a synthetic polymeric matrix and biofilm cells that are encased in a self-produced polymeric matrix remain unknown. In this study, using Shewanella oneidensis as a model organism and alginate hydrogel as a model synthetic matrix, we compared the cell growth and protein expression in entrapped cultures and biofilms. The hydrogel-entrapped cultures were found to exhibit a growth rate comparable with biofilms. There was no substantial difference in cell viability, surface charge, as well as hydrophobicity between the cells grown in alginate hydrogel and those grown in biofilms. However, the gel-entrapped cultures were found to be physiologically different from biofilms. The gel-entrapped cultures had a higher demand for metabolic energy. The siderophore-mediated iron uptake was repressed in the gel-entrapped cells. The presence of the hydrogel matrix decreased the expression of proteins involved in biofilm formation, while inducing the production of extracellular DNA (eDNA) in the gel-entrapped cultures. These results advance the fundamental understanding of the physiology of hydrogel-entrapped cells, which can lead to more efficient biofilm mimic-based applications.

Microbial species coexist in natural or engineered settings, where they encounter extensive competition and cooperation. Interactions occurring through metabolite exchange or direct contact might be important in establishment of functional biodegradation consortium. Understanding these interactions can facilitate manipulation of selected communities and exploitation of their capacity for specific industrial applications. Here, a simple dual-species consortium (Pseudomonas putida and Shewanella oneidensis) was established for examining simultaneous Congo red bioremediation in planktonic culture and power generation in anode biofilms. Compared to mono-species cultures, co-cultures generated higher current densities and could concurrently degrade Congo red over 72h. Disabling the large secreted adhesion protein, LapA, of P. putida greatly enhanced S. oneidensis biofilm formation on the anode, which increased power generation in co-cultures. This demonstrates simultaneous control of specific planktonic and biofilm communities could be effective in manipulating microbial communities for targeted applications., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Although biofilm-based bioprocesses have been increasingly used in various applications, the long-term robust and efficient biofilm performance remains one of the main bottlenecks. In this study, we demonstrated that biofilm cohesiveness and performance of Shewanella oneidensis can be enhanced through disrupting putrescine biosynthesis. Through random transposon mutagenesis library screening, one hyperadherent mutant strain, CP2-1-S1, exhibiting an enhanced capability in biofilm formation, was obtained. Comparative analysis of the performance of biofilms formed by S. oneidensis MR-1 wild type (WT) and CP2-1-S1 in removing dichromate (Cr2O7(2-)), i.e., Cr(VI), from the aqueous phase showed that, compared with the WT biofilms, CP2-1-S1 biofilms displayed a substantially lower rate of cell detachment upon exposure to Cr(VI), suggesting a higher cohesiveness of the mutant biofilms. In addition, the amount of Cr(III) immobilized by CP2-1-S1 biofilms was much larger, indicating an enhanced performance in Cr(VI) bioremediation. We further showed that speF, a putrescine biosynthesis gene, was disrupted in CP2-1-S1 and that the biofilm phenotypes could be restored by both genetic and chemical complementations. Our results also demonstrated an important role of putrescine in mediating matrix disassembly in S. oneidensis biofilms.

Biofilms are core to a range of biological processes, including the bioremediation of environmental contaminants. Within a biofilm population, cells with diverse genotypes and phenotypes coexist, suggesting that distinct metabolic pathways may be expressed based on the local environmental conditions in a biofilm. However, metabolic responses to local environmental conditions in a metabolically active biofilm interacting with environmental contaminants have never been quantitatively elucidated. In this study, we monitored the spatiotemporal metabolic responses of metabolically active Shewanella oneidensis MR-1 biofilms to U(VI) (uranyl, UO(2)(2+)) and Cr(VI) (chromate, CrO(4) (2-)) using non-invasive nuclear magnetic resonance imaging (MRI) and spectroscopy (MRS) approaches to obtain insights into adaptation in biofilms during biofilm-contaminant interactions. While overall biomass distribution was not significantly altered upon exposure to U(VI) or Cr(VI), MRI and spatial mapping of the diffusion revealed localized changes in the water diffusion coefficients in the biofilms, suggesting significant contaminant-induced changes in structural or hydrodynamic properties during bioremediation. Finally, we quantitatively demonstrated that the metabolic responses of biofilms to contaminant exposure are spatially stratified, implying that adaptation in biofilms is custom-developed based on local microenvironments., (© 2012 Society for Applied Microbiology and Blackwell Publishing Ltd.)

The presence and importance of microenvironments in the subsurface at contaminated sites were suggested by previous geochemical studies. However, no direct quantitative characterization of the geochemical microenvironments had been reported. We quantitatively characterized microscale geochemical gradients (dissolved oxygen (DO), H(2), pH, and redox potential) in Hanford 300A subsurface sediment biofilms. Our results revealed significant differences in geochemical parameters across the sediment biofilm/water interface in the presence and absence of U(VI) under oxic and anoxic conditions. While the pH was relatively constant within the sediment biofilm, the redox potential and the DO and H(2) concentrations were heterogeneous at the microscale (<500-1000 μm). We found microenvironments with high DO levels (DO hotspots) when the sediment biofilm was exposed to U(VI). On the other hand, we found hotspots (high concentrations) of H(2) under anoxic conditions both in the presence and in the absence of U(VI). The presence of anoxic microenvironments inside the sediment biofilms suggests that U(VI) reduction proceeds under bulk oxic conditions. To test this, we operated our biofilm reactor under air-saturated conditions in the presence of U(VI) and characterized U speciation in the sediment biofilm. U L(III)-edge X-ray absorption spectroscopy (XANES and EXAFS) showed that 80-85% of the U was in the U(IV) valence state., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The goal of this study was to quantify the contribution of extracellular polymeric substances (EPS) to U(VI) immobilization by Shewanella sp. HRCR-1. Through comparison of U(VI) immobilization using cells with bound EPS (bEPS) and cells with minimal EPS, we show that (i) bEPS from Shewanella sp. HRCR-1 biofilms contribute significantly to U(VI) immobilization, especially at low initial U(VI) concentrations, through both sorption and reduction; (ii) bEPS can be considered a functional extension of the cells for U(VI) immobilization and they likely play more important roles at lower initial U(VI) concentrations; and (iii) the U(VI) reduction efficiency is dependent upon the initial U(VI) concentration and decreases at lower concentrations. To quantify the relative contributions of sorption and reduction to U(VI) immobilization by EPS fractions, we isolated loosely associated EPS (laEPS) and bEPS from Shewanella sp. HRCR-1 biofilms grown in a hollow fiber membrane biofilm reactor and tested their reactivity with U(VI). We found that, when reduced, the isolated cell-free EPS fractions could reduce U(VI). Polysaccharides in the EPS likely contributed to U(VI) sorption and dominated the reactivity of laEPS, while redox active components (e.g., outer membrane c-type cytochromes), especially in bEPS, possibly facilitated U(VI) reduction.

The composition of extracellular polymeric substances (EPS) from Shewanella sp. HRCR-1 biofilms was investigated using infrared spectroscopy and proteomics to provide insight into potential ecophysiological functions and redox activity of the EPS. Both bound and loosely associated EPS were extracted from Shewanella sp. HRCR-1 biofilms prepared using a hollow-fibre membrane biofilm reactor. Fourier transform infrared spectra revealed the presence of proteins, polysaccharides, nucleic acids, membrane lipids and fatty acids in the EPS fractions. Using a global proteomic approach, a total of 58 extracellular and outer membrane proteins were identified in the EPS. These included homologues of multiple Shewanella oneidensis MR-1 proteins that potentially contribute to key physiological biofilm processes, such as biofilm-promoting protein BpfA, surface-associated serine protease, nucleotidases (CpdB and UshA), an extracellular lipase, and oligopeptidases (PtrB and a M13 family oligopeptidase lipoprotein). In addition, 20 redox proteins were found in extracted EPS. Among the detected redox proteins were the homologues of two S. oneidensis MR-1 c-type cytochromes, MtrC and OmcA, which have been implicated in extracellular electron transfer. Given their detection in the EPS of Shewanella sp. HRCR-1 biofilms, c-type cytochromes may contribute to the possible redox activity of the biofilm matrix and play important roles in extracellular electron transfer reactions., (© 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.)

Soil, a potential reservoir of antibiotic resistance genes (ARGs), is inhabited by numerous microorganisms. Many microorganisms in soil are embedded within a self-produced matrix of extracellular polymeric substances to form supracellular structures, i.e., biofilms. Representing the predominant microbial lifestyle in soil, soil biofilms are considered hot spots of horizontal gene transfer. Herein, we discuss the distribution, transfer, and fate of ARGs in the soil environment at macro- and micro-scales. Applications of microfluidic platforms, with an advantage of mimicking complex soil environments and permitting the study of microbial behaviors at a micro-scale, coupled with high-throughput sequencing and other innovative platforms, to study soil biofilms and transfer of ARGs are also discussed. This review aims to highlight the neglected role of soil biofilms in the spread of ARGs to expand the current limited knowledge about ARGs in the soil microenvironment. [ABSTRACT FROM AUTHOR]

The nucleotide signalling molecule bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di- GMP) plays an essential role in regulating microbial virulence and biofilm formation. C-di- GMP is synthesized by diguanylate cyclase ( DGC) enzymes and degraded by phosphodiesterase ( PDE) enzymes. One intrinsic feature of c-di- GMP signalling is the abundance of DGCs and PDEs encoded by many bacterial species. It is unclear whether the different DGCs or PDEs coordinately establish the c-di- GMP regulation or function independently of each other. Here, we provide evidence that multiple DGCs are involved in regulation of c-di- GMP on synthesis of the major iron siderophore pyoverdine in P seudomonas aeruginosa. Constitutive expression of the Wsp G or Yed Q DGC in P . aeruginosa is able to induce its pyoverdine synthesis. Induction of pyoverdine synthesis by high intracellular c-di- GMP depends on the synthesis of exopolysaccharides and another two DGCs, Sia D and Sad C. Sia D was found to boost the c-di- GMP synthesis together with constitutively expressing Yed Q. The exopolysaccharides and the Sia D DGC were found to modulate the expression of the Rsm Y/ Rsm Z nc RNAs. Induction of the Rsm Y/ Rsm Z nc RNAs might enhance the pyoverdine synthesis through Sad C. Our study sheds light on a novel multiple DGC-coordinated c-di- GMP regulatory mechanism of bacteria. [ABSTRACT FROM AUTHOR]

Efficiently transporting extracellular electrons from microbial biofilms to the electrodes is challenging and critical in achieving high-performance microbial fuel cells (MFCs). In this work, we develop a simple and effective method to fabricate hybrid electroactive biofilms by inserting bacteria into graphene-carbon-nanotube (G-CNT) networks (namely, G-CNT-biofilm) as an anode for MFCs. This novel architecture greatly enhances direct extracellular electron transfer between Shewanella oneidensis and the electrode, due to strong adhesion of the hybrid conducting biofilm onto the anode surface, as well as the large surface area of graphene and the high conductivity of CNTs. A current density of 120 μA cm−2 and a maximum power density of 97.9 μW cm−2 are obtained in the MFC with the hybrid biofilm anode, which is significantly higher than those of a naturally growing biofilm anode (20 μA cm−2 and 6.5 μW cm−2). [ABSTRACT FROM AUTHOR]

A facultative iron-reducing [Fe(III)-reducing] Paenibacillus sp. strain was isolated from Hanford 300A subsurface sediment biofilms that was capable of reducing soluble Fe(III) complexes [Fe(III)-nitrilotriacetic acid and Fe(III)-citrate] but unable to reduce poorly crystalline ferrihydrite (Fh). However, Paenibacillus sp. 300A was capable of reducing Fh in the presence of low concentrations (2 (xM) of either of the electron transfer mediators (ETMs) flavin mononucleotide (FMN) or anthraquinone-2,6-disulfonate (AQDS). Maximum initial Fh reduction rates were observed at catalytic concentrations (< 10 μM) of either FMN or AQDS. Higher FMN concentrations inhibited Fh reduction, while increased AQDS concentrations did not. We also found that Paenibacillus sp. 300 A could reduce Fh in the presence of natural ETMs from Hanford 300 A subsurface sediments. In the absence of ETMs, Paenibacillus sp. 300A was capable of immobilizing U(VI) through both reduction and adsorption. The relative contributions of adsorption and microbial reduction to U(VT) removal from the aqueous phase were …7:3 in PIPES [piperazine-N,N'-bis(2-ethanesulfonic acid)] and …1:4 in bicarbonate buffer. Our study demonstrated that Paenibacillus sp. 300A catalyzes Fe(III) reduction and U(VI) immobilization and that these reactions benefit from externally added or naturally existing ETMs in 300A subsurface sediments [ABSTRACT FROM AUTHOR]

Bidirectional extracellular electron transfer of strain Comamonas testosteroni I2 was for the first time investigated with electrochemical active biofilms developed under different conditions. The electrochemical active biofilm developed under microbial fuel cell conditions was capable of anodic electron transfer via attached redox species with standard potential of 0.04 V (vs. SCE). Meanwhile the above redox species lost its catalytic capability when the biofilm was developed under a constant potential (− 0.4 V vs. SCE). Instead, the microbe adjusted its electron transfer strategy to a soluble shuttle (standard potential − 0.20 V vs. SCE) and enabled a cathodic current. Air exposure experiment verified that the soluble shuttle at negative potential had a positive response to the oxygen; meanwhile the anodic electron transfer via the attached species was rarely influenced. [ABSTRACT FROM AUTHOR]

Gut microbial communities of plastic-munching worms provide novel insights for the development of plastic-processing biotechnologies. Considering the complexity of worm maintenance and the gut microbial communities, it is challenging to apply the worms directly in plastic processing. Harnessing the power of microbial communities derived from the worm gut microbiomes in vitro may enable a promising bioprocess for plastic degradation. Here, we established stable and reproducible plastic-associated biofilm communities derived from the gut microbiome of a superworm, Zophobas atratus , through a two-stage enrichment process: feeding with plastics (HDPE, PP, and PS) and in vitro incubation of gut microbiomes obtained from the plastic-fed worms. Plastic feeding exhibited marginal influence on bacterial diversity but substantially changed the relative abundance of different bacterial groups, and intriguingly, enriched potential plastic degraders. More prominent shifts of microbial communities were observed during the in vitro incubation of the gut microbiomes. Taxa containing plastic-degrading strains were further enriched, while other taxa represented by lactic acid bacteria were depleted. Additionally, the plastic characterization confirmed the degradation of the incubated plastics by the plastic-associated microbial communities. Community functional inference for both gene abundance and community phenotype suggested that the in vitro incubation enhanced plastic-degrading potential. Deterministic ecological effects, in particular, selection processes, were identified as the main driving force of the observed community shifts. Our findings provide novel insights into plastic-munching-worm-inspired bioprocessing of plastic wastes. [ABSTRACT FROM AUTHOR]

In situ liquid secondary ion mass spectrometry (SIMS) enabled by system for analysis at the liquid vacuum interface (SALVI) has proven to be a promising new tool to provide molecular information at solid-liquid and liquid-vacuum interfaces. However, the initial data showed that useful signals in positive ion spectra are too weak to be meaningful in most cases. In addition, it is difficult to obtain strong negative molecular ion signals when m/z>200. These two drawbacks have been the biggest obstacle towards practical use of this new analytical approach. In this study, we report that strong and reliable positive and negative molecular signals are achievable after optimizing the SIMS experimental conditions. Four model systems, including a 1,8-diazabicycloundec-7-ene (DBU)-base switchable ionic liquid, a live Shewanella oneidensis biofilm, a hydrated mammalian epithelia cell, and an electrolyte popularly used in Li ion batteries were studied. A signal enhancement of about two orders of magnitude was obtained in comparison with non-optimized conditions. Therefore, molecular ion signal intensity has become very acceptable for use of in situ liquid SIMS to study solid-liquid and liquid-vacuum interfaces. [ABSTRACT FROM AUTHOR]

Abstract: Slow extracellular electron transfer (EET) rates at the biofilm/electrode interface hinder the application of microbial bioelectronic technology in bioremediation as well as energy recovery from wastewater. Conjugated oligoelectrolytes (COEs) have been shown to increase EET in viable microorganisms. However, confirmation of these results on model electrochemically active microorganisms (EAMs), such as Shewanella oneidensis MR-1, is still lacking. Here, chemical modification of S. oneidensis is achieved through spontaneous intercalation of the amphiphilic water-soluble conjugated oligoelectrolyte, 4,4′-bis(4′-(N,N-bis(6″-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+). Various electrochemical techniques are used to compare the EET enhancement afforded to S. oneidensis by microbially produced flavins and addition of DSSN+. The effect of DSSN+ on the EET rate increases as the working electrode potential increases. However, DSSN+ addition did not fully restore the wild-type EET rate in MtrC–OmcA knockout mutants. These results drive the design of more effective COEs that will serve as an exact molecular surrogate for outer membrane cytochromes. [Copyright &y& Elsevier]