Facet-engineered hematite boosts microbial electrogenesis by synergy of promoting electroactive biofilm formation and extracellular electron transfer

AbstractEnterococcus faecalisis an opportunistic human pathogen and the cause of biofilm-associated infections of the heart, catheterized urinary tract, wounds, and the dysbiotic gut where it can expand to high numbers upon microbiome perturbations. TheE. faecalissortase-assembled endocarditis and biofilm associated pilus (Ebp) is involved in adhesion and biofilm formationin vitroandin vivo. Extracellular electron transfer (EET) also promotesE. faecalisbiofilm formation in iron-rich environments, however neither the mechanism underlying EET nor its role in virulence was previously known. Here we show that iron associated with Ebp serve as a terminal electron acceptor for EET, leading to extracellular iron reduction and intracellular iron accumulation. We found that a MIDAS motif within the EbpA tip adhesin is required for interaction with iron, EET, and FeoB-mediated iron uptake. We demonstrate that MenB and Ndh3, essential components of the aerobic respiratory chain and a specialized flavin-mediated electron transport chain, respectively, are required for iron-mediated EET. In addition, using a mouse gastrointestinal (GI) colonization model, we show that EET is essential for colonization of the GI tract, and Ebp is essential for augmentedE. faecalisGI colonization when dietary iron is in excess. Taken together, our findings show that pilus mediated capture of iron within biofilms enables EET-mediated iron acquisition inE. faecalis, and that these processes plays an important role inE. faecalisexpansion in the GI tract.SignificanceUnderstanding enterococcal biofilm development is the first step towards improved therapeutics for the often antimicrobial resistant infections caused by these bacteria. Here we report a role forEnterococcus faecalisendocarditis and biofilm associated pili (Ebp) in mediating iron-dependent biofilm growth and contributing to extracellular electron transfer (EET) which in turn promotes iron acquisition. Furthermore, we characterize the mechanisms underlying electron transfer in theE. faecalisbiofilm. Our findings support a model in whichE. faecalisuse EET to drive the reduction of pilus-associated ferric iron, leading to iron acquisition inE. faecalisbiofilm, and contributing to enterococcal virulence in the GI tract.

Download Full-text

Interfacing anoxic Shewanella oneidensis biofilms with electrically conducting nanostructures

10.5194/biofilms9-139 ◽

2020 ◽

Author(s):

Edina Klein ◽

René Wurst ◽

David Rehnlund ◽

Johannes Gescher

Keyword(s):

Electron Transfer ◽

Biofilm Formation ◽

Electronic Communication ◽

Shewanella Oneidensis ◽

Model Organism ◽

Laser Scanning Microscopy ◽

Extracellular Electron Transfer ◽

Metal Nanostructures ◽

Special Importance ◽

Anoxic Conditions

Shewanella oneidensis MR1 is the best understood model organism with regards to dissimilatory metal reduction and extracellular electron transfer onto carbon electrodes in bioelectrochemical systems (BES)1. However, under anoxic conditions S. oneidensis is known to form very thin biofilms resulting in low current density output. In contrast, another exoelectrogenic model organism Geobacter surfurreduscens can form electroactive biofilms up to 100 &#181;m in thickness. This organism is known for its ability to transport electrons over a long range (> 10 &#181;m) along a network of protein filaments, called microbial nanowires. Although still controversial, it was recently reported that OmcS has a special importance for the conductivity of these nanowires2. One of the key differences between G. surfurreduscens and S. oneidensis lies in how cell-to-cell electronic communication occurs, which dictate the range of electronic communication between distant cells. S. oneidensis relies on direct cell-to-cell communication via electron transfer between outer membrane cytochromes or via soluble redox active flavins that are secreted by the cells3. Our research is based on the question, what if the S. oneidensis biofilm formation could be improved by introducing an artificial electronic network, similar to the native microbial nanowires for G. sulfurreducens? We hypothesize that synthetic biofilms containing conductive nanostructure additives would allow S. oneidensis to build multilayer thick biofilms under anoxic conditions on solid electron acceptors. To answer this question of how conductive materials affect the formation of anoxic S. oneidensis biofilms, we integrated both biological and synthetic conductive nanostructures into these biofilms. As biological additive, the c-type cytochrome OmcS purified from G. sulfurreducens was utilized. As synthetic additives, both commercially available biotinylated gold nanorods and in-house electrochemically synthesized metal nanostructures were added to anoxic S.&#160;oneidensis biofilms. Cultivation and characterization of the biofilms was performed using our newly developed microfluidic bioelectrochemical platform. Microbial cultivation with the aid of microfluidic flow chambers has a great potential to form biofilms on an easy to handle laboratory scale with simultaneously ongoing multianalytical analysis4. In our bioelectrochemical microfluidic, system S. oneidensis biofilms can be grown under anoxic conditions using an anode as sole electron acceptor. The growth behavior and bioelectrochemical performance was evaluated by a combination of electrochemical techniques (chronoamperometry, electrochemical impedance spectroscopy, cyclic voltammetry) and optical analyses (confocal laser scanning microscopy and optical coherence tomography). The strategy of conductive nanostructured additives for improved electroactive biofilm formation could be an important tool for other exoelectrogenic microorganisms in order to exploit their physiological abilities for biotechnology. References: <ol> <li>Beblawy, S. et al. (2018) Molecular Microbiology 109: 571-583.</li> <li>Wang, F. et al. (2019) Cell 177: 361&#8208;369.</li> <li>Shi, L. et al. (2016) Nature Reviews Microbiology 14: 651-662.</li> <li>Hansen, S.H. et al. (2019) Scientific Reports 9: 8933.</li> </ol> &#160;

Download Full-text