Effects of Surface Charge and Hydrophobicity on Anodic Biofilm Formation, Community Composition, and Current Generation in Bioelectrochemical Systems

ABSTRACT An electrochemical flow cell equipped with a graphite working electrode (WE) at the bottom was inoculated with Shewanella oneidensis MR-1 expressing an anaerobic fluorescent protein, and biofilm formation on the WE was observed over time during current generation at WE potentials of +0.4 and 0 V (versus standard hydrogen electrodes), under electrolyte-flow conditions. Electrochemical analyses suggested the presence of unique electron-transfer mechanisms in the +0.4-V biofilm. Microscopic analyses revealed that, in contrast to aerobic biofilms, current-generating biofilm (at +0.4 V) was thin and flat (∼10 μm in thickness), and cells were evenly and densely distributed in the biofilm. In contrast, cells were unevenly distributed in biofilm formed at 0 V. In situ fluorescence staining and biofilm recovery experiments showed that the amounts of extracellular polysaccharides (EPSs) in the +0.4-V biofilm were much smaller than those in the aerobic and 0-V biofilms, suggesting that Shewanella cells suppress the production of EPSs at +0.4 V under flow conditions. We suggest that Shewanella cells perceive electrode potentials and modulate the structure and composition of biofilms to efficiently transfer electrons to electrodes. IMPORTANCE A promising application of microbial fuel cells (MFCs) is to save energy in wastewater treatment. Since current is generated in these MFCs by biofilm microbes under horizontal flows of wastewater, it is important to understand the mechanisms for biofilm formation and current generation under water-flow conditions. Although massive work has been done to analyze the molecular mechanisms for current generation by model exoelectrogenic bacteria, such as Shewanella oneidensis, limited information is available regarding the formation of current-generating biofilms over time under water-flow conditions. The present study developed electrochemical flow cells and used them to examine the electrochemical and structural features of current-generating biofilms under water-flow conditions. We show unique features of mature biofilms actively generating current, creating opportunities to search for as-yet-undiscovered current-generating mechanisms in Shewanella biofilms. Furthermore, information provided in the present study is useful for researchers attempting to develop anode architectures suitable for wastewater treatment MFCs.

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Increased biofilm in Shewanella oneidensis MR-1 leads to higher current generation in METs

10.5194/biofilms9-18 ◽

2020 ◽

Author(s):

Ana V. Silva ◽

Miriam Edel ◽

Johannes Gescher ◽

Catarina M. Paquete

Keyword(s):

Biofilm Formation ◽

Large Scale ◽

Shewanella Oneidensis ◽

Extracellular Electron Transfer ◽

Central Process ◽

Current Generation ◽

Promising Alternative ◽

Over Expression ◽

Current Production ◽

Low Levels

Biofilm formation is a central process in the function of Microbial Electrochemical Technologies (METs). These technologies have emerged in recent years as a promising alternative green source of energy, in which microbes consume organic matter to produce energy or valuable by-products. It is the ability of performing extracellular electron transfer that allows these microbes, called electroactive organisms, to exchange electrons with an electrode in these systems. The low levels of current achieved have been the set-back for the large-scale application of METs. Shewanella oneidensis MR-1 is one of the most studied electroactive organisms, and it has been demonstrated that its increased biofilm formation can lead to higher current generation. The bolA gene has been identified as a central player in biofilm formation in different organisms, with its overexpression leading to increased biofilm production. In this work, we explored the effect of this gene in biofilm formation and current production by S. oneidensis MR-1. Our results demonstrate that this gene is involved in the biofilm formation by this organism, with its over expression leading to an increased biofilm formation. We could also show that this increase in biofilm formation lead to a consequent higher current generation. This information is a relevant step for the optimization of electroactive organisms towards their practical application in METs.

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Effect of Surface Charge and Hydrophobicity Modulation on the Antibacterial and Antibiofilm Potential of Magnetic Iron Nanoparticles

Journal of Nanomaterials ◽

10.1155/2017/3528295 ◽

2017 ◽

Vol 2017 ◽

pp. 1-15 ◽

Cited By ~ 10

Author(s):

Rania Ibrahim Shebl ◽

Faten Farouk ◽

Hassan Mohamed El-Said Azzazy

Keyword(s):

Surface Charge ◽

Biofilm Formation ◽

E Coli ◽

Inhibitory Potential ◽

Average Size ◽

Positively Charged ◽

Significant Concentration ◽

Effect Of Surface ◽

Antibacterial Potential ◽

Trimethoxy Silane

Unmodified magnetic nanoparticles (MNPs) lack antibacterial potential. We investigated MNPs surface modifications that can impart antibacterial activity. Six MNPs species were prepared and characterized. Their antibacterial and antibiofilm potentials, surface affinity, and cytotoxicity were evaluated. Prepared MNPs were functionalized with citric acid, amine group, amino-propyl trimethoxy silane (APTMS), arginine, or oleic acid (OA) to give hydrophilic and hydrophobic MNPs with surface charge ranging from −30 to +30 mV. Prepared MNPs were spherical in shape with an average size of 6–15 nm. Hydrophobic (OA-MNPs) and positively charged MNPs (APTMS-MNPs) had significant concentration dependent antibacterial effect. OA-MNPs showed higher inhibitory potential againstS. aureusandE. coli(80%) than APTMS-MNPs (70%). Both particles exhibited surface affinity toS. aureusandE. coli.Different concentrations of OA-MNPs decreasedS. aureusandE. colibiofilm formation by 50–90%, while APTMS-MNPs reduced it by 30–90%, respectively. Up to 90% of preformed biofilms ofS. aureusandE. coliwere destroyed by OA-MNPs and APTMS-MNPs. In conclusion, surface positivity and hydrophobicity enhance antibacterial and antibiofilm properties of MNPs.

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