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ABSTRACT Quinones play a central role in maintaining redox balance and conserving energy but can trigger oxidative stress at high levels. However, the mechanisms by which microbes regulate quinone levels remain poorly understood, hindering effective metabolic engineering to modulate microbes for quinone production. Here, we show that the biosynthesis of the menaquinone precursor 1,4-dihydroxy-2-naphthoic acid (DHNA) in the lactic acid bacteriumLactococcus lactisis regulated by a combined genetic, enzymatic, and metabolic mechanism. Using synthetic biology approaches, we found that enzymes MenF and MenD both contribute to DHNA regulation, with MenD playing a more prominent role in controlling DHNA concentrations. A mathematical model elucidates a two-phase regulatory pattern resulting from the interplay of reversible flux and allosteric feedback inhibition, where either MenF or MenD can serve as the regulatory enzyme, depending on their relative expression ratio. In addition, the overproduction of DHNA is constrained by substrate availability, ensuring a sufficient but not excessive DHNA level to benefit cell growth while mitigating cytotoxicity. Collectively, these mechanisms maintain a fine-tuned physiological quinone level and suggest that modulating substrate supplement and MenF-to-MenD ratio could be keys for engineering DHNA production. IMPORTANCEQuinones are crucial molecules in cellular respiration, helping cells produce energy and maintain balance in their redox state. However, excessive quinone levels can be toxic, making it vital for microbes to tightly regulate their production. Our study uncovers howLactococcus lactis, a key food fermenting bacterium, uses a multi-layer mechanism to maintain optimal levels of the menaquinone precursor 1,4-dihydroxy-2-naphthoic acid (DHNA). By combining biosensors, genetic perturbations, and modeling, we show how cells balance the benefits and toxicity of quinones. These findings not only reveal fundamental microbial physiology but also provide strategies to engineer microbes for improved quinone production. 

Organic electrochemical transistors (OECTs) are thin-film devices operated in aqueous and biological environments for sensing chemicals and biomolecules. However, most sensor configurations involve introducing the target biomolecule directly in the OECT device. This has drawbacks because it may not be possible to have an electrolyte compatible with the target biomolecule or an environment optimal for the OECT. Here, we demonstrate a general and modular approach to building electrochemical sensors by coupling OECTs electronically with either an enzymatic fuel cell (EFC) or microbial fuel cell (MFC). We demonstrate that this modular approach can amplify currents by three orders of magnitude and enhance the signal-to-noise ratio. We also show that the power generated by the fuel cell can help tune the sensor’s response for different applications. This work demonstrates a simple and versatile approach for amplifying currents from MFCs and EFCs useful for the development of bioelectronic sensors. 

In a world confronting pollution across diverse environments, fast, sensitive and cost-efficient methods are required to monitor complex chemicals. In particular, microbial bioelectronic sensors can report on the presence of chemicals through electrical signals enabled by biological processes. For example, microbial bioelectronic sensors have been developed for the rapid detection of riverine toxins within minutes of contact, for selective sensing of redox-active pharmaceuticals, and for monitoring of pesticide degradation. However, transferring these laboratory-tested technologies into field-deployable products poses several challenges: sensor sensitivity, specificity, longevity and robustness need to be improved. In this Review, we discuss the design of field-deployable microbial bioelectronic sensors, including chassis selection, approaches for rewiring electron transfer, strategies to establish the cell–electrode interface and fabrication methods. Importantly, we outline key challenges and possible solutions for the application of such sensors in the real world.