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Plant extracts have been regarded as “green” alternatives as inhibitors for metal corrosion prevention and mitigation. Therefore, understanding the electrochemical properties and the reaction mechanisms of the electro-active compounds from the plant extracts is necessary to further explore the mechanism and application of the plant extract-based additives for corrosion prevention and mitigation. Among different plant derived chemicals, aromatic compounds are among the most effective for corrosion inhibition and mitigation. Thus, the electrochemical properties of seven aromatic active compounds from the plant extracts – caffeic acid, thymol (2‑isopropyl‑5‑methylphenol, IPMP), gallic acid (3,4,5‑trihydroxybenzoic acid), tannic acid, lawsone (2‑hydroxy‑1,4‑naphthoquinone), wedelolactone, and ellagic acid are studied using multiwalled carbon nanotube modified glassy‑carbon electrode, and reported to enhance the fundamental understanding of their redox behavior at different environmental pH conditions.

Titanium and titanium alloys are used in biomedical implants such as dental screws due to their excellent mechanical strength and high resistance to corrosion. The corrosion resistance of these alloys is largely due to the formation of a passive oxide layer on the titanium surface when in contact with oxygen. For the application of use in dental implants, titanium’s ability to withstand corrosion in the presence of oral bacteria is of utmost importance, specifically in the presence of Streptococcus mutans, the most common plaque causing oral bacteria. Previous literature has explored the effects of the formation of a S. mutans biofilm on the corrosion resistance of commercially pure titanium [1]. A decrease in corrosion resistance is observed following the formation of the biofilm, however this decrease in corrosion resistance does not invalidate the viability of titanium for use in orthodontic systems. Due to the electrochemical and material similarities between titanium and zirconium, including the formation of a passive oxide layer on the zirconium surface and high material strength, there is evidence to suggest zirconium and zirconium alloys may be a viable alternative to titanium for these applications [2]. Previous literature has explored the use of titanium-zirconium alloys in such applications and found no decrease in their ability to withstand colonization and microbiologically induced corrosion in the presence of Streptococci species relative to commercially available titanium [3]. The aim of this current research is to begin the exploration of the feasibility of zirconium based materials in orthodontic applications by investigating the microbiologically induced corrosion of commercially pure zirconium and a zirconium-niobium alloy in the presence of S. mutans and compare them against commercially pure titanium. References: [1] Souza, Júlio C.M., et al. “Corrosion Behaviour of Titanium in the Presence of Streptococcus Mutans.” Journal of Dentistry, vol. 41, no. 6, 2013, pp. 528–534., https://doi.org/10.1016/j.jdent.2013.03.008. [2] Renganathan, Gunarajulu, et al. “Orthopedical and Biomedical Applications of Titanium and Zirconium Metals.” Fundamental Biomaterials: Metals, 2018, pp. 211–241., https://doi.org/10.1016/b978-0-08-102205-4.00010-6. [3] Siddiqui, Danyal A., et al. “Evaluation of Oral Microbial Corrosion on the Surface Degradation of Dental Implant Materials.” Journal of Periodontology, vol. 90, no. 1, 2018, pp. 72–81., https://doi.org/10.1002/jper.18-0110.

Listeria monocytogenes (L. monocytogenes) is a common foodborne pathogen that has been responsible for many foodborne illness outbreaks in recent years. Currently, Listeria contamination in food products is identified only through molecular tests conducted in diagnostic laboratories. No established phage based diagnostic methods for L. monocytogenes during food production or processing are used. Here we report a potentially disruptive rapid diagnostic method based on electrochemical biosensing principles that use bacteriophages as bioreceptors for selective identification and quantification of L. monocytogenes. Electrochemical biosensors are good alternatives to molecular detection methods due to their ease of use, high specificity, sensitivity, and low cost. Bacteriophages can serve as excellent biorecognition elements in biosensors due to their robust stability in a range of environmental conditions and their ability to distinguish between live and dead bacterial cells. The impedimetric biosensing platform for L. monocytogenes detection was developed by immobilizing P100 bacteriophage onto quarternized polyethylenimine modified carbon nanotubes using an in-house developed molecular tethering method. The resulting sensor showed high selectivity and sensitivity toward L. monocytogenes with a limit of detection of 8.4 CFU/ml. Initial results demonstrate that the biosensing platform is highly reliable in its selectivity towards its target analyte, L. monocytogenes.

The clinical application of magnesium (Mg)-based alloys as temporary orthopedic implants is highly limited by their rapid corrosion rate in the physiological environment. Herein, an anti-corrosive polymeric coating based on polycaprolactone (PCL) and lawsone was prepared on AZ31 Mg alloy to improve its corrosion resistance. Lawsone was incorporated into the coating as a corrosion inhibitor to enhance the passive corrosion protection of the PCL coating through its strong chelation ability of dissolving Mg2+. Anti-corrosion properties of the coatings were assessed by electrochemical techniques and in vitro immersion tests, and the results demonstrated a remarkable improvement in corrosion resistance of the bare Mg alloy. In addition to the corrosion inhibition effect, incorporation of lawsone provided the coating with a strong antibacterial activity against Escherichia coli and Staphylococcus aureus bacterial strains. Moreover, the fabricated coating was cytocompatible (viability of > 85 %) toward human fetal osteoblast cells. The findings of this work highlighted the great potential of lawsone as a natural corrosion inhibitor for fabrication of corrosion protective, antibacterial, and biocompatible coatings on Mg-based biodegradable implants.

A hyperthermophilic archaeon called Pyrococcus furiosus (Pf), is being explored as potential microbial catalyst for use microbial fuel cells (MFCs) [Sekar et al. (2017)]. The two main enzymes membrane bound hydrogenase (MBH) and cytoplasmic soluble hydrogenases (SH) are involved in its oxidative fermentative pathways. In P. furiosus the membrane bound hydrogenase (MBH) uses reducing equivalents from the oxidative fermentative pathway to produce hydrogen, which is believed to be used by soluble hydrogenases (SHI and SHII) for nicotinamide cofactor generation. However, in anaerobic respiratory systems, the oxidative fermentative pathways and the activity of MBH and SH enzyme complexes are not fully understood. In this study, we hypothesize that genetically manipulating the expressions of SH and MBH could influence extracellular electron transfer, which could be characterized by an enhancement in organism’s ability to reduce a metal ion (e.g. soluble ferric citrate or and insoluble ferric oxide). Herein, genetic traceable Pf strain was genetically engineered to produce strains with over-expressed SHI (OESHI), over-expressed MbhJ-N (OEMbhJ-N), knocked-out SHI/SHII (ΔSHI/II) or knocked-out MbhL (ΔMbhL). Soluble ferric citrate and insoluble ferric oxide were used to study the ability of engineered Pf strains to reduce the extracellular oxidants. Experiments revealed that the ΔMbhL strain, produced the highest exo-electrogenic ability among these Pf strains. To the best of our knowledge this is the first report that compares the exoelectrogenic ability of different strains of genetically engineered Pf.

In cyanobacteria, the excess electrons produced through photosynthetic electron transport chain at light intensities, are re-oxidized by respiratory terminal oxidases (RTOs) present in the respiratory electron transport chain providing an overflow pathway for excess electrons to minimize photo damage [1]. We have previously demonstrated enhanced photo-bioelectrochemical activity by Synechococcus elongatus if the organism was genetically modified to express an outer membrane cytochrome namely OmcS [2]. We hypothesize that by knocking out the genes corresponding to the RTOs in the genetically engineered Synechococcus elongatus PCC7942 with outer membrane cytochrome (OmcS), the organism’s extracellular electron transfer ability towards the electrode could be further enhanced through the blockage of the overflow pathways. In this study, the genes responsible for the various RTOs in PCC7942 include bd-type quinol oxidase encoded by cydBA (cyd), aa3-type cytochrome oxidase encoded by coxBAC (cox) and cbb3-type cytochrome oxidase encoded by ccoNQ (cco) were knocked out and the resulting mutants were evaluated for their extracellular electron transfer ability through both chemical and electrochemical tests. PCR was carried out to confirm the successful construction of single mutants. Further, double and triple mutants of Synechococcus elongatus PCC7942 in different combinations of the RTO knockouts were also performed and the resulting electrochemical performance was measured using conventional electrochemical techniques. References: J. Lea Smith, N. Ross, M. Zori, D.S. Bendall, J.S. Dennis, S.A. Scott, A.G. Smith and C.J. Howe (2013). Thylakoid Terminal oxidases are essential for the Cyanobacterium Synechocystis sp. PCC 6803 to survive rapidly changing light intensities. Plant Physiology. 162. 484- 495. N. Sekar, R. Jain, Y. Yan, and R.P. Ramasamy (2016). Enhanced Photo-Bio electrochemical energy conversion by genetically engineered Cyanobacteria. Biotechnology and Bioengineering. 113 (3). 675-679 Figure 1