Over-expression of an electron transport protein OmcS provides sufficient NADH for D-lactate production in cyanobacterium

Revisiting Solar Energy Flow in Nanomaterial-Microorganism Hybrid Systems

Nanomaterial-microorganism hybrid systems (NMHSs), integrating semiconductor nanomaterials with microorganisms, present a promising platform for broadband solar energy harvesting, high-efficiency carbon reduction, and sustainable chemical production. While studies underscore its potential in diverse solar-to-chemical energy conversions, prevailing NMHSs grapple with suboptimal energy conversion efficiency. Such limitations stem predominantly from an insufficient systematic exploration of the mechanisms dictating solar energy flow. This review provides a systematic overview of the notable advancements in this nascent field, with a particular focus on the discussion of three pivotal steps of energy flow: solar energy capture, cross-membrane energy transport, and energy conversion into chemicals. While key challenges faced in each stage are independently identified and discussed, viable solutions are correspondingly postulated. In view of the interplay of the three steps in affecting the overall efficiency of solar-to-chemical energy conversion, subsequent discussions thus take an integrative and systematic viewpoint to comprehend, analyze and improve the solar energy flow in the current NMHSs of different configurations, and highlighting the contemporary techniques that can be employed to investigate various aspects of energy flow within NMHSs. Finally, a concluding section summarizes opportunities for future research, providing a roadmap for the continued development and optimization of NMHSs.

Insight into the potential mechanism of bicarbonate assimilation promoted by mixotrophic in CO2 absorption and microalgae conversion system

CO2 absorption-microalgae conversion (CAMC) system is a promising carbon capture and utilization technology. However, the use of HCO3- as a carbon source often led to a slower growth rate of microalgae, which also limited the application of CAMC system. In this study, the assimilation efficiency of HCO3- in CAMC system was improved through mixotrophic, and the potential mechanism was investigated. The HCO3- assimilation efficiency and biomass under mixotrophic were 34.79% and 31.76% higher than that of control. Mixotrophic increased chlorophyll and phycocyanin content, which were beneficial to capture more light energy. The content of ATP and NADPH reached 566.86 μmol/gprot and 672.86 nmol/mgprot, which increased by 31.83% and 27.67% compared to autotrophic. The activity of carbonic anhydrase and Rubisco increased by 18.52% and 22.08%, respectively. Transcriptome showed that genes related to photosynthetic and respiratory electron transport were up-regulated. The synergy of photophosphorylation and oxidative phosphorylation greatly improved energy metabolism efficiency, thus accelerating the assimilation of HCO3-. These results revealed a potential mechanism of promoting the HCO3- assimilation under mixotrophic, it also provided a guidance for using CAMC system to serve carbon neutrality.

Biophotovoltaics: Recent advances and perspectives

Biophotovoltaics (BPV) is a clean power generation technology that uses self-renewing photosynthetic microorganisms to capture solar energy and generate electrical current. Although the internal quantum efficiency of charge separation in photosynthetic microorganisms is very high, the inefficient electron transfer from photosystems to the extracellular electrodes hampered the electrical outputs of BPV systems. This review summarizes the approaches that have been taken to increase the electrical outputs of BPV systems in recent years. These mainly include redirecting intracellular electron transfer, broadening available photosynthetic microorganisms, reinforcing interfacial electron transfer and design high-performance devices with different configurations. Furthermore, three strategies developed to extract photosynthetic electrons were discussed. Among them, the strategy of using synthetic microbial consortia could circumvent the weak exoelectrogenic activity of photosynthetic microorganisms and the cytotoxicity of exogenous electron mediators, thus show great potential in enhancing the power output and prolonging the lifetime of BPV systems. Lastly, we prospected how to facilitate electron extraction and further improve the performance of BPV systems.

Living electronics: A catalogue of engineered living electronic components

Biology leverages a range of electrical phenomena to extract and store energy, control molecular reactions and enable multicellular communication. Microbes, in particular, have evolved genetically encoded machinery enabling them to utilize the abundant redox-active molecules and minerals available on Earth, which in turn drive global-scale biogeochemical cycles. Recently, the microbial machinery enabling these redox reactions have been leveraged for interfacing cells and biomolecules with electrical circuits for biotechnological applications. Synthetic biology is allowing for the use of these machinery as components of engineered living materials with tuneable electrical properties. Herein, we review the state of such living electronic components including wires, capacitors, transistors, diodes, optoelectronic components, spin filters, sensors, logic processors, bioactuators, information storage media and methods for assembling these components into living electronic circuits.

Changes in intracellular energetic and metabolite states due to increased galactolipid levels in Synechococcus elongatus PCC 7942

The lipid composition of thylakoid membranes is conserved from cyanobacteria to green plants. However, the biosynthetic pathways of galactolipids, the major components of thylakoid membranes, are known to differ substantially between cyanobacteria and green plants. We previously reported on a transformant of the unicellular rod-shaped cyanobacterium Synechococcus elongatus PCC 7942, namely SeGPT, in which the synthesis pathways of the galactolipids monogalactosyldiacylglycerol and digalactosyldiacylglycerol are completely replaced by those of green plants. SeGPT exhibited increased galactolipid content and could grow photoautotrophically, but its growth rate was slower than that of wild-type S. elongatus PCC 7942. In the present study, we investigated pleiotropic effects that occur in SeGPT and determined how its increased lipid content affects cell proliferation. Microscopic observations revealed that cell division and thylakoid membrane development are impaired in SeGPT. Furthermore, physiological analyses indicated that the bioenergetic state of SeGPT is altered toward energy storage, as indicated by increased levels of intracellular ATP and glycogen. We hereby report that we have identified a new promising candidate as a platform for material production by modifying the lipid synthesis system in this way.

Microbial biofilms as living photoconductors due to ultrafast electron transfer in cytochrome OmcS nanowires

Light-induced microbial electron transfer has potential for efficient production of value-added chemicals, biofuels and biodegradable materials owing to diversified metabolic pathways. However, most microbes lack photoactive proteins and require synthetic photosensitizers that suffer from photocorrosion, photodegradation, cytotoxicity, and generation of photoexcited radicals that are harmful to cells, thus severely limiting the catalytic performance. Therefore, there is a pressing need for biocompatible photoconductive materials for efficient electronic interface between microbes and electrodes. Here we show that living biofilms of Geobacter sulfurreducens use nanowires of cytochrome OmcS as intrinsic photoconductors. Photoconductive atomic force microscopy shows up to 100-fold increase in photocurrent in purified individual nanowires. Photocurrents respond rapidly (<100 ms) to the excitation and persist reversibly for hours. Femtosecond transient absorption spectroscopy and quantum dynamics simulations reveal ultrafast (~200 fs) electron transfer between nanowire hemes upon photoexcitation, enhancing carrier density and mobility. Our work reveals a new class of natural photoconductors for whole-cell catalysis.

Despite enormous potential of solar-driven biocatalysis, most living systems lack photoactive proteins and require toxic and expensive synthetic materials limiting the performance. Here, a class of natural photoconductors is demonstrated through sub-picosecond heme-to-heme electron transfer in bacteria-produced protein nanowires.

Biosynthetic approaches to efficient assimilation of CO2via photorespiration modification in plant chassis

Plant chassis has emerged as the platform with great potential for bioproduction of high value-added products such as recombinant protein, vaccine and natural product. However, as the primary metabolic pathway, photorespiration results in the loss of photosynthetically fixed carbon compounds and limits the exploration of plant chassis. People are endeavored to reduce the photorespiration energy or carbon loss based on variation screening or genetic engineering. Insomuch as protein engineering of Rubisco has not resulted in the significant improvement of Rubisco specificity which is linked to the direct CO2 fixation, the biosynthetic approaches of photorespiration bypass are gaining much more attention and manifested great potentiality in conferring efficient assimilation of CO2 in plant chassis. In this review, we summarize the recent studies on the metabolic pathway design and implementation of photorespiration alternative pathway aiming to provide clues to efficiently enhance carbon fixation via the modification of photorespiration in plant chassis for bioproduction. These will benefit the development of plant synthetic metabolism for biorefineries via improvement of artificial carbon sequestration cycle, particularly for the mitigation of serious challenges such as extreme climate change, food and energy shortages in the future.

A 300-fold conductivity increase in microbial cytochrome nanowires due to temperature-induced restructuring of hydrogen bonding networks

Although proteins are considered as nonconductors that transfer electrons only up to 1 to 2 nanometers via tunneling, Geobacter sulfurreducens transports respiratory electrons over micrometers, to insoluble acceptors or syntrophic partner cells, via nanowires composed of polymerized cytochrome OmcS. However, the mechanism enabling this long-range conduction is unclear. Here, we demonstrate that individual nanowires exhibit theoretically predicted hopping conductance, at rate (>10¹⁰ s^-1) comparable to synthetic molecular wires, with negligible carrier loss over micrometers. Unexpectedly, nanowires show a 300-fold increase in their intrinsic conductance upon cooling, which vanishes upon deuteration. Computations show that cooling causes a massive rearrangement of hydrogen bonding networks in nanowires. Cooling makes hemes more planar, as revealed by Raman spectroscopy and simulations, and lowers their reduction potential. We find that the protein surrounding the hemes acts as a temperature-sensitive switch that controls charge transport by sensing environmental perturbations. Rational engineering of heme environments could enable systematic tuning of extracellular respiration.

Synthetic Biology Approaches for Improving Chemical Production in Cyanobacteria

Biological chemical production has gained traction in recent years as a promising renewable alternative to traditional petrochemical based synthesis. Of particular interest in the field of metabolic engineering are photosynthetic microorganisms capable of sequestering atmospheric carbon dioxide. CO₂ levels have continued to rise at alarming rates leading to an increasingly uncertain climate. CO₂ can be sequestered by engineered photosynthetic microorganisms and used for chemical production, representing a renewable production method for valuable chemical commodities such as biofuels, plastics, and food additives. The main challenges in using photosynthetic microorganisms for chemical production stem from the seemingly inherent limitations of carbon fixation and photosynthesis resulting in slower growth and lower average product titers compared to heterotrophic organisms. Recently, there has been an increase in research around improving photosynthetic microorganisms as renewable chemical production hosts. This review will discuss the various efforts to overcome the intrinsic inefficiencies of carbon fixation and photosynthesis, including rewiring carbon fixation and photosynthesis, investigating alternative carbon fixation pathways, installing sugar catabolism to supplement carbon fixation, investigating newly discovered fast growing photosynthetic species, and using new synthetic biology tools such as CRISPR to radically alter metabolism.