Optimizing electrogenic activity from photosynthetic bacteria in bioelectrochemical systems

The aims of this project were to investigate a range of limitations affecting the electrical performance of bioelectrochemical systems (BES) and their use as analytical tools. The model cyanobacterium Synechocystis sp. PCC6803 was used to characterize light-driven BESs, or biophotovoltaic (BPV) devices. The phycobilisome (PBS) antenna size was altered to modify light absorption. At low to medium light intensities the optimum PBS antenna size was found to consist of one phycocyanin (PC) disc. Incorporating pulsed amplitude fluorescence (PAM) measurements into the BPV characterization allowed simultaneous comparison of photosynthetic efficiency to EET in Synechocystis. Non-photochemical quenching (NPQ) was investigated as a limiting factor in biophotovoltaic efficiency and was found to be reduced in the PBS antenna-truncated mutants. Fluorescence and electrochemical data were combined to develop a framework for quantifying the efficiency of light to bioelectricity conversion. This approach is a first step towards a more comprehensive and detailed set of analytical tools to monitor EET in direct relation to the underlying photosynthetic biology. A set of metabolic electron sinks were deleted to remove a selection of pathways that might compete with extracellular electron transfer (EET). The combined deletion of a bi-directional hydrogenase – HoxH, nitric oxide reductase – NorB, cytochrome-c oxidase – COX, bd-quinol oxidase – cyd, and the respiratory terminal oxidase – ARTO, roughly doubled light driven electron flux to EET. Deletion of nitrate reductase – NarB, and nitrite reductase – NirA, increased EET to a similar degree, but combination with the other knockouts compromised cell viability and did not increase output further. In addition to Synechocystis, the purple non-sulphur α-proteobacterium Rhodopseudomonas palustris CGA009 was used to test the effect of storage molecule synthesis knockout in a more industrially relevant organic carbon source driven BES, or microbial fuel cell (MFC). However, the removal of glycogen and poly-ß-hydroxybutyrate (PHB) did not have a significant effect on electrical output. Finally, the importance of electrode material and design for cell to anode connections in an MFC was investigated. EET from R. palustris was greatly enhanced using custom designed graphene and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) aerogels. Pristine graphene is also shown for the first time to be a viable, low cost alternative to platinum as a cathodic catalyst. Together, these results present a holistic view of major limitations on electrical output from BESs that may contribute to enhancing EET for power generation from MFCs in the long term, and optimization of BPV devices as reliable analytical tools in the short term

Planetary Defense team project: READI (Roadmap for EArth Defense Initiatives)

Planetary Defense is a complex problem, not well understood by policy makers and the general public. The recent Chelyabinsk incident in Russia created temporary international attention but has failed to effectively stimulate public action. The lack of long-term attention to cosmic hazards has resulted in limited funding to defend our planet. Hence, it is hard to realistically address this challenge and achieve the high test and operational readiness needed for an effective Planetary Defense strategy. To address this problem, we have created a set of recommendations for the development of a Planetary Defense Program, for the purpose of contributing to the protection of Earth from asteroids and comets. The SSP15 READI Project focused on threats for which there is only a short-term warning, specifically a warning of two years or less from detection of the object to impact. We have provided recommendations in five areas of Planetary Defense including detection and tracking, deflection techniques, global collaboration, outreach and education, and evacuation and recovery. We have applied this set of recommendations in a narrative scenario to make our report more impactful and engaging. We contrast optimistic and pessimistic outcomes for a comet threat, differing from each other in terms of the level of readiness achieved during the years leading up to the discovery of the threat. In our optimistic scenario, the deflection system has achieved high test and operational readiness. The world’s governments have realized the importance of being prepared against cosmic hazards and put in place all of the necessary measures for a successful defense, leading to a positive deflection of the comet. In contrast, in the pessimistic scenario no preparation is done before the detection, and the comet strikes a heavily populated area releasing energy equivalent to 80 times the most powerful nuclear bomb ever detonated. The recommendations that we have identified in this report constitute a roadmap to avoid this horrible outcome, and we believe they should be taken seriously and swiftly implemented

Additional file 1: of Modulating the import of medium-chain alkanes in E. coli through tuned expression of FadL

Supplementary Information [35, 36]. (DOCX 25764 kb

Platinum-free, graphene based anodes and air cathodes for single chamber microbial fuel cells.

Microbial fuel cells (MFCs) exploit the ability of microorganisms to generate electrical power during metabolism of substrates. However, the low efficiency of extracellular electron transfer from cells to the anode and the use of expensive rare metals as catalysts, such as platinum, limit their application and scalability. In this study we investigate the use of pristine graphene based electrodes at both the anode and the cathode of a MFC for efficient electrical energy production from the metabolically versatile bacterium Rhodopseudomonas palustris CGA009. We achieve a volumetric peak power output (PV) of up to 3.51 ± 0.50 W m-3 using graphene based aerogel anodes with a surface area of 8.2 m2 g-1. We demonstrate that enhanced MFC output arises from the interplay of the improved surface area, enhanced conductivity, and catalytic surface groups of the graphene based electrode. In addition, we show a 500-fold increase in PV to 1.3 ± 0.23 W m-3 when using a graphene coated stainless steel (SS) air cathode, compared to an uncoated SS cathode, demonstrating the feasibility of a platinum-free, graphene catalysed MFCs. Finally, we show a direct application for microwatt-consuming electronics by connecting several of these coin sized devices in series to power a digital clock

Risk of COVID-19 after natural infection or vaccinationResearch in context

Summary: Background: While vaccines have established utility against COVID-19, phase 3 efficacy studies have generally not comprehensively evaluated protection provided by previous infection or hybrid immunity (previous infection plus vaccination). Individual patient data from US government-supported harmonized vaccine trials provide an unprecedented sample population to address this issue. We characterized the protective efficacy of previous SARS-CoV-2 infection and hybrid immunity against COVID-19 early in the pandemic over three-to six-month follow-up and compared with vaccine-associated protection. Methods: In this post-hoc cross-protocol analysis of the Moderna, AstraZeneca, Janssen, and Novavax COVID-19 vaccine clinical trials, we allocated participants into four groups based on previous-infection status at enrolment and treatment: no previous infection/placebo; previous infection/placebo; no previous infection/vaccine; and previous infection/vaccine. The main outcome was RT-PCR-confirmed COVID-19 >7–15 days (per original protocols) after final study injection. We calculated crude and adjusted efficacy measures. Findings: Previous infection/placebo participants had a 92% decreased risk of future COVID-19 compared to no previous infection/placebo participants (overall hazard ratio [HR] ratio: 0.08; 95% CI: 0.05–0.13). Among single-dose Janssen participants, hybrid immunity conferred greater protection than vaccine alone (HR: 0.03; 95% CI: 0.01–0.10). Too few infections were observed to draw statistical inferences comparing hybrid immunity to vaccine alone for other trials. Vaccination, previous infection, and hybrid immunity all provided near-complete protection against severe disease. Interpretation: Previous infection, any hybrid immunity, and two-dose vaccination all provided substantial protection against symptomatic and severe COVID-19 through the early Delta period. Thus, as a surrogate for natural infection, vaccination remains the safest approach to protection. Funding: National Institutes of Health