Rhodopseudomonas Palustris Research Articles

Nitrate-dependent antimony oxidase in an uncultured Symbiobacteriaceae member.

Autotrophic antimony (Sb) oxidation coupled to nitrate reduction plays an important role in the transformation and detoxification of Sb. However, the specific oxidase involved in this process has yet to be identified. Herein, we enriched the microbiota capable of nitrate-dependent Sb(III) oxidation and identified a new Sb(III) oxidase in an uncultured member of Symbiobacteriaceae. Incubation experiments demonstrated that nitrate-dependent Sb(III) oxidation occurred in the microcosm supplemented with Sb(III) and nitrate. Both the 16S rRNA gene and metagenomic analyses indicated that a species within Symbiobacteriaceae played a crucial role in this process. Furthermore, carbon-13 isotope labelling with carbon dioxide-fixing Rhodopseudomonas palustris in combination with nanoscale secondary ion mass spectrometry revealed that a newly characterized oxidase from the dimethylsulfoxide reductase family, designated as NaoABC, was responsible for autotrophic Sb(III) oxidation coupled with nitrate reduction. The NaoABC complex functions in conjunction with the nitrate reductase NarGHI, forming a redox loop that transfers electrons from Sb(III) to nitrate, thereby generating the energy necessary for autotrophic growth. This research offers new insights into the understanding of how microbes link Sb and nitrogen biogeochemical cycles in the environment.

Complete genome sequence of polylactic acid degrading Rhodopseudomonas palustris strain R1 isolated from rice field soil.

Rhodopseudomonas palustris R1 is a phototrophic, purple, non-sulfur Gram-negative bacterium first isolated from the soils of rice fields, known for its polylactic acid degradability. Here, we present the complete circular genome sequence of this bacterium, spanning 5.32 Mbp and 4,949 protein-coding sequences.

The ammonium transporter AmtB is dispensable for the uptake of ammonium in the phototrophic diazotroph Rhodopseudomonas palustris

Ammonium (NH4+) transport across cell membranes plays an important role in assimilation or removal of the environmental nitrogen. The membrane protein AmtB has been considered to be the NH4+ transporter that is responsible for the NH4+ uptake. The phototrophic diazotroph Rhodopseudomonas palustris harboring two amtB genes has been widely used in wastewater treatment and bioremediation. However, the role of AmtB in NH4+ uptake remains unclear in R. palustris. Here, we employed an innovative approach combining stable isotope probing (SIP) with Raman spectroscopy to determine the physiological functions of AmtB1 and AmtB2 in R. palustris. This powerful technique allowed us to investigate NH4+ uptake at the single-cell level. The generated R. palustris ΔamtB1 ΔamtB2 mutant lacking AmtB1 and AmtB2 proteins was still capable of utilizing 15NH4+ even the 15NH4+ concentration was as low as 5 μM. These data demonstrate that both of the AmtB proteins are not essential for R. palustris to take up NH4+ regardless of environmental NH4+ levels. However, both AmtB1 and AmtB2 can contribute to NH4+ uptake under nitrogen-limiting conditions. Given that R. palustris primarily expresses AmtB2 in these conditions, AmtB2 plays a more important role in NH4+ uptake compared to AmtB1. In addition, transcriptomic analysis showed that the deletion of the amtB1 and amtB2 genes resulted in the upregulation of many transporter genes, providing potential targets for future investigation of alternative NH4+ uptake systems.

Photocatalytic scaffolds enhance anticancer performances of bacterial consortium AUN

Microbial metabolism and function are regulated by ambient microenvironment, yet no functional microporous materials are known to regulate anticancer activity of complex bacterial systems. Here we show that a simple scaffold-mediated bacterial culture is useful for enhancing the anticancer therapeutic abilities of a microbial consortium designated as AUN and composed of intratumoural bacteria Proteus mirabilis (A-gyo) and purple photosynthetic bacteria Rhodopseudomonas palustris (UN-gyo). Our discovery of the mechanism by which porous scaffolds influence the bacterial activities of AUN will facilitate further designs of artificial scaffold material for effective treatment against drug-resistant, triple-negative breast cancer models. A polydimethylsiloxane composite artificial scaffold encapsulating light-activatable TiO2 particularly enhanced the therapeutic outcomes of AUN in syngeneic and orthotopic models. These strong anticancer efficacies were synergistically expressed in tumours because of the potent oncolytic ability of AUN with the help of various immune cells. AUN administration to canines showed well tolerability in an exploratory study.

Rhodopseudomonas palustris Atp2 Protein Exerts Antifungal Effects by Targeting the Ribosomal Protein MoRpl12 in Magnaporthe oryzae.

Rice blast is one of the most hazardous diseases affecting rice production. Previously, we discovered that the Atp2 protein of Rhodopseudomonas palustris could significantly inhibit the appressorium formation and pathogenicity of Magnaporthe oryzae. However, the molecular mechanism of this fungus has remained unknown. This study revealed that Atp2 can enter the cell and interact with the ribosomal protein MoRpl12 of M. oryzae, directly affecting the expression of the MoRpl12 protein. Silencing the MoRPL12 gene can affect cell wall integrity, growth, conidiogenesis, and fungal pathogenicity. The quantitative reverse transcription PCR results showed significant changes in the expression of conidiation-related genes in the MoRPL12 gene-silenced mutants or in the Atp2 protein-treated plants. We further found that Atp2 treatment can influence the expression of ribosomal-related genes, such as RPL, in M. oryzae. Our study revealed a novel antifungal mechanism by which the Atp2 protein binds to the ribosomal protein MoRpl12 and inhibits the pathogenicity of rice blast fungus, providing a new potential target for rice blast prevention and control.

Feasibility and mechanism of adsorption and bioreduction of hexavalent chromium using Rhodopseudomonas palustris immobilized on multiple materials

Rhodopseudomonas palustris immobilized on multiple materials was used to invistigate Cr(VI) adsorption and bioreduction. The highest Cr(VI) removal (97.5%) was achieved at 276h under the opitimed conditions of 2.5% SA, 8% PVA, and 50% filling degree. The highest adsorption capacity was obtained at 11.75 mg g−1 under 300 mg L−1 Cr(VI). Results from adsorption kinetics and isotherms indicated that Cr(VI) adsorption of immobilized photosynthetic bacteria (IPSB) was consistent with the Freundich model and the pseudo-second-order kinetic model (qe = 14.00 mg g−1). SEM and FTIR analyses verified that the porous multilayer network structure of IPSB provided more adsorption sites and functional groups for the removal of Cr(VI). Furthermore, the maximum Cr(VI) reduction efficiency of IPSB was achieved at 10.80 mg g−1, which correlated with the up-regulation of chrR gene expressions at 100 mg L−1 Cr(VI). This study demonstrated the dual mechanisms of Cr(VI) removal in IPSB-treated Cr wastewater, involving both chemisorption and bioreduction working synergistically.

Methyl red dye decolourization by the photosynthetic bacteria, Rhodopseudomonas palustris and Afifellamarina

Anoxygenic photosynthetic bacteria are common inhabitants of wastewater: we found that Rhodopseudomonas palustris and Afifella marina in eutrophic conditions only partially degraded the azo dye (50 mmol m−3), Methyl Red, but completely degraded it under specially defined conditions. The azo dye is potentially a source of both carbon and fixed nitrogen. Rhodopseudomonas palustris and Afifella marina can live heterotrophically, photoheterotrophically or photoautotrophically under anoxic conditions where they can fix N2 if no organic nitrogen or NH3 is available. If organic carbon sources are available or if NH3 is present, the cells again only partially catabolised Methyl Red. In the absence of no alternative organic carbon sources and no NH3, the cells almost completely spectroscopically decolourised Methyl Red in 4 days. In sewage ponds the ready availability of alternative organic carbon and NH3 would result in only partial removal of Methyl Red. Rhodopseudomonas cells responded to the availability of Methyl Red in N-free media, by increasing both Optimum irradiance and maximum ETR (Eopt 276.3 μmol quanta m−2 s−1; ETRmax 391.4 μmol e− g−1 BChl a s−1) compared to control cells incubated in PM media with no organic carbon source and no fixed N-source (Eopt 115.2 μmol quanta m−2 s−1; ETRmax = 153.0 μmol e− g−1 BChl a s−1. If no alternative C or N sources are available, Rhodopseudomonas embedded in alginate biobeads will completely and repeatedly break down Methyl Red. The marine Afifella readily broke down Methyl Red but again breakdown was only complete if alternative carbon and no fixed nitrogen sources were available. The toxicity of the breakdown products produced by photosynthetic bacteria from azo-dyes needs to be followed up. Photosynthetic bacterial-alginate biobeads have long lifetimes (Rhodopseudomonas ≈ 2 months, Afifella > 6 months) making them of great biotechnological potential.

Tunneling Mechanisms of Quinones in Photosynthetic Reaction Center–Light Harvesting 1 Supercomplexes

In photosynthesis, light energy is absorbed and transferred to the reaction center, ultimately leading to the reduction of quinone molecules through the electron transfer chain. The oxidation and reduction of quinones generate an electrochemical potential difference used for adenosine triphosphate synthesis. The trafficking of quinone/quinol molecules between electron transport components has been a long‐standing question. Here, an atomic‐level investigation into the molecular mechanism of quinol dissociation in the photosynthetic reaction center–light‐harvesting complex 1 (RC–LH1) supercomplexes from Rhodopseudomonas palustris, using classical molecular dynamics (MD) simulations combined with self‐random acceleration MD‐MD simulations and umbrella sampling methods, is conducted. Results reveal a significant increase in the mobility of quinone molecules upon reduction within RC–LH1, which is accompanied by conformational modifications in the local protein environment. Quinol molecules have a tendency to escape from RC–LH1 in a tail‐first mode, exhibiting channel selectivity, with distinct preferred dissociation pathways in the closed and open LH1 rings. Furthermore, comparative analysis of free energy profiles indicates that alternations in the protein environment accelerate the dissociation of quinol molecules through the open LH1 ring. In particular, aromatic amino acids form π‐stacking interactions with the quinol headgroup, resembling the key components in a conveyor belt system. This study provides insights into the molecular mechanisms that govern quinone/quinol exchange in bacterial photosynthesis and lays the framework for tuning electron flow and energy conversion to improve metabolic performance.

Engineering of a Malonyl-CoA Ligase for Production of Fluorinated Polyketide Extender Units.

Enzymatic platforms for producing malonyl-CoA-based extender units required for polyketide biosynthesis are often based on malonyl-CoA ligases such as MatB from Rhizobium trifolii and Rhodopseudomonas palustris. However, despite broad interest in the fluorination of polyketides and prior success with engineering MatB homologs, the suitability of MatB for accessing the tertiary substituted fluoromethylmalonyl-CoA needed to produce flurithromycin and solithromycin has not yet been reported. Herein, we report the structure-guided engineering of a MatB homolog to optimize the production of fluoromethylmalonyl-CoA, resulting in a variant with increased conversion and providing a platform to produce a suitable building block mixture for fluorinated macrolide production. Additionally, the mutant demonstrated broad utility for various substituted malonyl-CoAs. The MatB mutant sets the stage to access fluorinated macrolides by coupling it with altered PKS machinery to install fluorinated malonyl-CoA into macrolide scaffolds.

Trace metal interaction with thermophilic phototrophic anaerobic bacterium Chloroflexus aurantiacus

Towards improving the knowledge of possible paleo-microorganisms interaction with trace metals (micro-nutrients and toxicants), we studied adsorption of Mn, Zn, Sr, Cd, and Pb onto modern Chloroflexus aurantiacus, thermophilic anoxygenic phototrophic bacterium which could be highly abundant in the Precambiran aquatic environments. Acid-base surface titrations allowed quantifying the number of proton-active surface groups, whereas non-electrostatic linear programming method (LPM) was used to assess the surface site concentrations and adsorption reaction constants between divalent cations (Zn, Mb, Sr, Cd, Pb) and bacterial surface, based on results of pH-dependent adsorption edge and constant-pH ‘langmuirian’ adsorption experiments. The total proton/hydroxyl binding site number of Chl. aurantiacus surfaces was sizably lower than that of other phototrophic anaerobic bacteria studied previously using similar experimental and modeling approach. Divalent metals exhibited a decreasing order of adsorption affinity (Pb > Cd ≥ Zn ≥ Mn > Sr), which reflected the order of cation hydrolysis and was similar to adsorption order on other phototrophic bacteria. At the same time, adsorption of Zn increased with increasing of temperature, from 4 °C to 60 °C and was stronger under light compared to the darkness. This suggested some active metabolic control involved in this metal interaction with bacterial surfaces. Overall, Chl. aurantiacus exhibited trace metal adsorption parameters (site number and binding constants) which were lower compared to other anoxygenic phototrophic bacteria (Rhodopseudomonas palustris; Rhodobacter blasticus) and cyanobacteria. This may reflect different bioavailability of trace metals in the paleo-ocean, given that thermophilic Chl. aurantiacus are among the oldest phototrophs on the planet.

A novel antifungal peptide, SP1.2, from Rhodopseudomonas palustris against the rice blast pathogen.

Rice blast has a significant detrimental impact on rice yields, so developing efficient biological control technologies is an effective means for rice blast prevention and control. The GroEL protein has proven to be effective at preventing and managing the pathogenicity of rice blast. Here, we analyzed the amino acid sequence of the GroEL protein and synthesized the '60 kDa chaperonin signature' (350-373 amino acids) peptide SP1.2, which has potent antifungal activity. Notably, the SP1.2 peptide exhibited potent fungicidal activity against Magnaporthe oryzae, effectively inhibiting appressorium germination. Electron microscopy revealed that SP1.2 disrupted the fungal plasma membrane and bound to multiple bioactive phosphoinositides in vitro, triggering the production of reactive oxygen species. Furthermore, it also caused an increase in the acetylation of M. oryzae and induced autophagy in cells. The spray application of SP1.2 significantly reduced the number of disease spots caused by the fungal pathogen M. oryzae in rice, enhancing the defense response of rice plants. Field trials showed that the control effect was 64.59% after spraying SP1.2. Our study illustrates the antifungal activity of the structurally unique SP1.2 peptide against plant fungal pathogens and paves the way for the future development of this class of peptides as antifungal agents. © 2024 Society of Chemical Industry.

Overexpression of RuBisCO form I and II genes in Rhodopseudomonas palustris TIE-1 augments polyhydroxyalkanoate production heterotrophically and autotrophically.

With the rising demand for sustainable renewable resources, microorganisms capable of producing bioproducts such as bioplastics are attractive. While many bioproduction systems are well-studied in model organisms, investigating non-model organisms is essential to expand the field and utilize metabolically versatile strains. This investigation centers on Rhodopseudomonas palustris TIE-1, a purple non-sulfur bacterium capable of producing bioplastics. To increase bioplastic production, genes encoding the putative regulatory protein PhaR and the depolymerase PhaZ of the polyhydroxyalkanoate (PHA) biosynthesis pathway were deleted. Genes associated with pathways that might compete with PHA production, specifically those linked to glycogen production and nitrogen fixation, were deleted. Additionally, RuBisCO form I and II genes were integrated into TIE-1's genome by a phage integration system, developed in this study. Our results show that deletion of phaR increases PHA production when TIE-1 is grown photoheterotrophically with butyrate and ammonium chloride (NH4Cl). Mutants unable to produce glycogen or fix nitrogen show increased PHA production under photoautotrophic growth with hydrogen and NH4Cl. The most significant increase in PHA production was observed when RuBisCO form I and form I & II genes were overexpressed, five times under photoheterotrophy with butyrate, two times with hydrogen and NH4Cl, and two times under photoelectrotrophic growth with N2 . In summary, inserting copies of RuBisCO genes into the TIE-1 genome is a more effective strategy than deleting competing pathways to increase PHA production in TIE-1. The successful use of the phage integration system opens numerous opportunities for synthetic biology in TIE-1.IMPORTANCEOur planet has been burdened by pollution resulting from the extensive use of petroleum-derived plastics for the last few decades. Since the discovery of biodegradable plastic alternatives, concerted efforts have been made to enhance their bioproduction. The versatile microorganism Rhodopseudomonas palustris TIE-1 (TIE-1) stands out as a promising candidate for bioplastic synthesis, owing to its ability to use multiple electron sources, fix the greenhouse gas CO2, and use light as an energy source. Two categories of strains were meticulously designed from the TIE-1 wild-type to augment the production of polyhydroxyalkanoate (PHA), one such bioplastic produced. The first group includes mutants carrying a deletion of the phaR or phaZ genes in the PHA pathway, and those lacking potential competitive carbon and energy sinks to the PHA pathway (namely, glycogen biosynthesis and nitrogen fixation). The second group comprises TIE-1 strains that overexpress RuBisCO form I or form I & II genes inserted via a phage integration system. By studying numerous metabolic mutants and overexpression strains, we conclude that genetic modifications in the environmental microbe TIE-1 can improve PHA production. When combined with other approaches (such as reactor design, use of microbial consortia, and different feedstocks), genetic and metabolic manipulations of purple nonsulfur bacteria like TIE-1 are essential for replacing petroleum-derived plastics with biodegradable plastics like PHA.

Catalyzing the metabolism through CoFe2O4 magnetic photocatalyst for photo fermentative biohydrogen production: Selectivity and recyclability across diverse strains

The interaction between the photo-induced charges from photo nanocatalysts (PNCs) and biohydrogen production strains plays a key role in controlling the metabolism mechanism in fermentative biohydrogen production from lignocellulosic biomass wastes. Thus, in the present study, two strains of Rhodopseudomonas palustris (PNSB) and a mixed consortium of HAU-M1 were evaluated for their biohydrogen production potential from corn stover (CS), whereas metabolism was catalyzed through photo-induced electrons from magnetic PNCs of cobalt ferrite (CoFe2O4). The threshold concentration of CoFe2O4 (400 mg/L) produced 428.62 mL and 373.30 mL biohydrogen in PNSB and HAU-M1, which is 129.0 % and 81.12 % higher as compared to respective control groups (CGs), respectively. The presence of PNCs provides the photo-induced electrons, which catalyze the metabolic processes as butyric acid increases by 96.29 % and 94.87 % in PNSB and HAU-M1, respectively, hence increasing hydrogen production. The results were supported by microbial community investigation, which showed that the incorporation of the appropriate concentration of PNCs effectively changes the bacterial community dynamics and diversifies the phyla (Firmicutes, Proteobacteria, and Bacteroidetes) and hydrogen-producing genus Clostridium. The recovered yield of CoFe2O4 PNCs from PNSB and HAU-M1 fermentative mediums in three consecutive cycles was (90.87 %, 88.94 %), (80.25 %, 72.25 %), and (69.75 %, 60.80 %) respectively showing potential for recycling catalysts during the fermentation process. Thus, selecting the right photocatalysts and strain can affect metabolism and biohydrogen production, while recyclability reduces environmental leaching.

The phototrophic purple non-sulfur bacteria Rhodomicrobium spp. are novel chassis for bioplastic production.

Petroleum-based plastics levy significant environmental and economic costs that can be alleviated with sustainably sourced, biodegradable, and bio-based polymers such as polyhydroxyalkanoates (PHAs). However, industrial-scale production of PHAs faces barriers stemming from insufficient product yields and high costs. To address these challenges, we must look beyond the current suite of microbes for PHA production and investigate non-model organisms with versatile metabolisms. In that vein, we assessed PHA production by the photosynthetic purple non-sulfur bacteria (PNSB) Rhodomicrobium vannielii and Rhodomicrobium udaipurense. We show that both species accumulate PHA across photo-heterotrophic, photo-hydrogenotrophic, photo-ferrotrophic, and photo-electrotrophic growth conditions, with either ammonium chloride (NH4Cl) or dinitrogen gas (N2) as nitrogen sources. Our data indicate that nitrogen source plays a significant role in dictating PHA synthesis, with N2 fixation promoting PHA production during photoheterotrophy and photoelectrotrophy but inhibiting production during photohydrogenotrophy and photoferrotrophy. We observed the highest PHA titres (up to 44.08 mg/L, or 43.61% cell dry weight) when cells were grown photoheterotrophically on sodium butyrate with N2, while production was at its lowest during photoelectrotrophy (as low as 0.04 mg/L, or 0.16% cell dry weight). We also find that photohydrogenotrophically grown cells supplemented with NH4Cl exhibit the highest electron yields - up to 58.89% - while photoheterotrophy demonstrated the lowest (0.27%-1.39%). Finally, we highlight superior electron conversion and PHA production compared to a related PNSB, Rhodopseudomonas palustris TIE-1. This study illustrates the value of studying non-model organisms like Rhodomicrobium for sustainable PHA production and indicates future directions for exploring PNSB metabolisms.

Mechanical energy drives the growth and carbon fixation of electroactive microorganisms

Phototrophy and chemotrophy are two dominant types of microbial metabolism. However, to date, the potential of the ubiquitous and versatile mechanical energy as a renewable energy source to drive the growth of microorganisms has remained unknown and not utilized. Here, we present evidence in favor of a previously unidentified metabolic pathway, in which the electronic energy produced from mechanical energy by the piezoelectric materials is used to support the growth of microorganisms. When electroactive microorganism Rhodopseudomonas palustris (R. palustris; with barium titanate nanoparticles) was mechanically stirred, a powerful biohybrid piezoelectric effect (BPE) enabled sustainable carbon fixation coupled with nitrate reduction. Transcriptomic analyses demonstrated that mechanical stirring of the bacteria–barium titanate biohybrid led to upregulation of genes encoding functions involved in electron and energy transfer in R. palustris. Studies with other electroactive microorganisms suggested that the ability of microbes to utilize BPE may be a common phenomenon in the microbial world. Taken together, these findings imply a long-neglected and potentially important microbial metabolic pathway, with potential importance to microbial survival in the energy-limited environments.

Light-driven extracellular electron transfer accelerates microbiologically influenced corrosion by Rhodopseudomonas palustris TIE-1

This study investigates the microbiologically influenced corrosion (MIC) of X80 steel accelerated by the phototrophic bacterium Rhodopseudomonas palustris TIE-1. The photorespiration plays a key role in promoting extracellular electron transfer (EET)-induced MIC. In the early corrosion stage, unstable localized corrosion dominated in the dark, while intense diffusion-controlled corrosion occurs in light. Compared to the sterile anaerobic medium, R. palustris TIE-1 accelerated corrosion of X80 steel, with a significantly higher corrosion rate under light conditions, approximately three times that of dark conditions. Inhibition of photosynthetic electron transfer or cessation of photostimulation resulted in pronounced reduction in the corrosion rate.

Selecting Phosphorus-Solubilizing Strains of Purple Nonsulfur Bacteria Isolated From Pineapple Cultivated Acid Sulfate Soils

The presence of acid sulfate soils is such an obstacle for pineapple cultivation in Vietnam due to their low pH, high toxicity and poor nutrient availability, especially phosphorus (P), which is immobilized by cations in the soils. Therefore, the study occurred to select purple nonsulfur bacteria (PNSB) strains that can solubilize P under toxic and acidic conditions. There were 33 strains that can tolerate the acidic condition, and they were selected and tested for viability and P solubilization under conditions containing Al3+, Fe2+, and Mn2+ toxins. Four strains, including W15, W39, W42 and W48 suffered from growth inhibition by Al3+, Fe2+ and Mn2+ less than the other strains under both microaerobic light and aerobic dark conditions (ML and AD conditions). In addition, there were four strains (W15, W25, W42 and W48) solubilizing Al-P well (21.4-25.2 mg L-1), two strains (W23 and W42) solubilizing Fe-P well (15.9-17.3 mg L-1), and two strains (W17 and W42) solubilizing Ca-P well (23.0-36.4 mg L-1) under both ML and AD conditions. Ultimately, there were five strains selected (W17, W23, W25, W42 and W48) and identified as Rhodopseudomonas palustris strain W17 and W23, Cereibacter sphaeroides strain W23, W42 and W48 based on the 16S rRNA technique. The selected strains also produced ALA, EPS and siderophores at 1.31-2.19 mg L-1, 0.78-1.89 mg L-1, and 16.2-55.6%, respectively. Therefore, these strains were promising in providing nutrients for pineapples in the form of biofertilizer.

Unnatural Direct Interspecies Electron Transfer Enabled by Living Cell-Cell Click Chemistry.

Direct interspecies electron transfer (DIET) is essential for maintaining the function and stability of anaerobic microbial consortia. However, only limited natural DIET modes have been identified and DIET engineering remains highly challenging. In this study, an unnatural DIET between Shewanella oneidensis MR-1 (SO, electron donating partner) and Rhodopseudomonas palustris (RP, electron accepting partner) was artificially established by a facile living cell-cell click chemistry strategy. By introducing alkyne- or azide-modified monosaccharides onto the cell outer surface of the target species, precise covalent connections between different species in high proximity were realized through a fast click chemistry reaction. Remarkably, upon covalent connection, outer cell surface C-type cytochromes mediated DIET between SO and RP was achieved and identified, although this was never realized naturally. Moreover, this connection directly shifted the natural H2 mediated interspecies electron transfer (MIET) to DIET between SO and RP, which delivered superior interspecies electron exchange efficiency. Therefore, this work demonstrated a naturally unachievable DIET and an unprecedented MIET shift to DIET accomplished by cell-cell distance engineering, offering an efficient and versatile solution for DIET engineering, which extends our understanding of DIET and opens up new avenues for DIET exploration and applications.

Unnatural Direct Interspecies Electron Transfer Enabled by Living Cell‐Cell Click Chemistry

AbstractDirect interspecies electron transfer (DIET) is essential for maintaining the function and stability of anaerobic microbial consortia. However, only limited natural DIET modes have been identified and DIET engineering remains highly challenging. In this study, an unnatural DIET between Shewanella oneidensis MR‐1 (SO, electron donating partner) and Rhodopseudomonas palustris (RP, electron accepting partner) was artificially established by a facile living cell‐cell click chemistry strategy. By introducing alkyne‐ or azide‐modified monosaccharides onto the cell outer surface of the target species, precise covalent connections between different species in high proximity were realized through a fast click chemistry reaction. Remarkably, upon covalent connection, outer cell surface C‐type cytochromes mediated DIET between SO and RP was achieved and identified, although this was never realized naturally. Moreover, this connection directly shifted the natural H2 mediated interspecies electron transfer (MIET) to DIET between SO and RP, which delivered superior interspecies electron exchange efficiency. Therefore, this work demonstrated a naturally unachievable DIET and an unprecedented MIET shift to DIET accomplished by cell‐cell distance engineering, offering an efficient and versatile solution for DIET engineering, which extends our understanding of DIET and opens up new avenues for DIET exploration and applications.

Growth of electroautotrophic microorganisms using hydrovoltaic energy through natural water evaporation

It has been previously shown that devices based on microbial biofilms can generate hydrovoltaic energy from water evaporation. However, the potential of hydrovoltaic energy as an energy source for microbial growth has remained unexplored. Here, we show that the electroautotrophic bacterium Rhodopseudomonas palustris can directly utilize evaporation-induced hydrovoltaic electrons for growth within biofilms through extracellular electron uptake, with a strong reliance on carbon fixation coupled with nitrate reduction. We obtained similar results with two other electroautotrophic bacterial species. Although the energy conversion efficiency for microbial growth based on hydrovoltaic energy is low compared to other processes such as photosynthesis, we hypothesize that hydrovoltaic energy may potentially contribute to microbial survival and growth in energy-limited environments, given the ubiquity of microbial biofilms and water evaporation conditions.