mLife

Multidrug-resistant hypervirulent Klebsiella pneumoniae (MDR-hvKP) poses a severe global health threat. Phage therapy is a promising alternative, but requires precise matching of phage to the bacterial strain. Here, we present a proof-of-concept method that integrates single-cell Raman spectroscopy with deep learning to enable rapid and precise selection of lytic phages against MDR-hvKP. By profiling Raman signatures of strains across multiple KL-types (capsule locus types), we trained three deep learning architectures for phage-host matching. Among them, the CNN_MLP-Transformer achieved the best performance (99.7%), slightly outperforming CNN_MLP (99.2%) and CNN_MLP-Attention (99.5%). Validation using 10 hvKP clinical isolates yielded an average phage selection accuracy of 78.3%. These findings demonstrate the feasibility and clinical potential of AI- augmented Raman spectroscopy as a rapid, label-free, precise strategy for guiding phage therapy against MDR-hvKP infections. TeaserAI-guided single-cell Raman profiling enables rapid precision phage selection against multidrug-resistant K. pneumoniae.

Tree phenology, periodic biological events in trees, is highly sensitive to climate change. It has been reported that forest greening can influence the local climate by altering the seasonal surface energy budget. However, tree phenological responses to forest greening remains poorly understood at large spatial scales. Combining remote-sensing derived phenological and leaf area indices since 2001, herein we show that forest greening led to earlier spring (-1.05 {+/-} 0.17 d) and autumn phenology (-1.95 {+/-} 0.14 d) in temperate and boreal forests. Our results show that forest greening in winter and spring decreased surface albedo and thus resulted in biophysical warming that caused earlier spring leaf phenology. In contrast, forest greening in summer and autumn triggered biophysical cooling by enhancing evapotranspiration, which led to earlier autumn leaf phenology. These findings suggest that forest greening could significantly alter tree phenology through seasonal biophysical impacts. Therefore, it is essential to incorporate these complicated biophysical impacts of greening into tree phenology models to accurately predict future shifts in tree phenology under future climate change.

Copper is an essential enzyme cofactor in bacteria, but excess copper is highly toxic. Bacteria can cope with copper stress by increasing copper resistance and initiating chemorepellent response. However, it remains unclear how bacteria coordinate chemotaxis and resistance to copper. By screening proteins that interacted with the chemotaxis kinase CheA, we identified a copper-binding repressor CsoR that interacted with CheA in Pseudomonas putida. CsoR interacted with the HPT (P1), Dimer (P3), and HATPase_c (P4) domains of CheA and inhibited CheA autophosphorylation, resulting in decreased chemotaxis. The copper-binding of CsoR weakened its interaction with CheA, which relieved the inhibition of chemotaxis by CsoR. In addition, CsoR bound to the promoter of copper-resistance genes to inhibit gene expression, and copper-binding released CsoR from the promoter, leading to increased gene expression and copper resistance. P. putida cells exhibited a chemorepellent response to copper in a CheA-dependent manner, and CsoR inhibited the chemorepellent response to copper. Besides, the CheA-CsoR interaction also existed in proteins from several other bacterial species. Our results revealed a mechanism by which bacteria coordinately regulated chemotaxis and resistance to copper by CsoR.

The pheromone MAPK is essential for the vital activities of fungi and is widely identified in filamentous fungi of agricultural, medical, and industrial relevance. The targets have rarely been reported and it is difficult to understand the mechanism of pheromone MAPK signaling pathway. Aflatoxins (AFs), highly carcinogenic natural products, are produced by the secondary metabolism of fungi, such as Aspergillus flavus. Our previous studies demonstrated that Fus3 regulates AFs by modulating substrate levels in Aspergillus flavus, but no mechanism explain that in fungi. Here we show Gal83, a new target of Fus3, and identified the pheromone Fus3-MAPK signaling pathway regulates the Snf1/AMPK energy-sensing pathway to modulate aflatoxins synthesis substrates. In the screening for target proteins of Fus3, the Snf1/AMPK complexes {beta} subunit was identified by using tandem affinity purification and multi-omics, which physically interacted with Fus3 in vivo and vitro and received phosphorylation from Fus3. While neither aflatoxin transcript levels were down-regulated in gal83-mutant and fus3-mutant strains, significant decreases in aflatoxin B1, aflatoxin synthetic substrates levels and gene expression levels of primary metabolic enzymes were shown that both the Fus3-MAPK and Snf1/AMPK pathways could response energy signal. In conclusion, all the evidence unlocks a novel pathway of Fus3-MAPK to regulate AFs synthesis substrates by cross-talking to the Snf1/AMPK complexes. ImportanceAflatoxin poses a great threat to human and animal health and the economy, thus the mechanisms regulating aflatoxin synthesis have been of great interest. We have previously demonstrated that MAPK regulates aflatoxin biosynthesis significantly, but the regulatory mechanism of Fus3-MAPK is not clear. Here we found that Pheromone Fus3-MAPK responds to energy and transmits to Snf1/AMPK through phosphorylation, which regulates the level of secondary metabolic substrates in Aspergillus flavus, as a novel pathway of Fus3-MAPK. Fus3 interacts stably with Gal83 and colocalizes in the cytoplasm and nucleus, directly regulating the levels of aflatoxin synthetic substrates. These data advance our understanding of the regulation of aflatoxin by pheromone MAPK, and the mechanism of pheromone MAPK and Snf1/AMPK crosstalk regulation is confirmed. Overall, this has a positive effect on both fungal regulatory mechanisms and aflatoxin prevention and control.

Plant bacterial wilt caused by the Ralstonia solanacearum species complex results in huge food and economic losses. Accordingly, the development of an effective control method for this disease is urgently required. Traditional lytic phage biocontrol methods have inherent limitations. However, filamentous phages, which do not lyse host bacteria and exert minimal burden, offer a potential solution. A filamentous phage RSCq that infects R. solanacearum was isolated in this study through genome mining. We constructed engineered filamentous phages based on RSCq by employing our proposed approach with a wide applicability to non-model phages, enabling the infection of R. solanacearum in medium and soil and delivering exogenous genes into bacterial cells. Similar to the Greek soldiers hidden within the Trojan horse, CRISPR-AsCas12f1 gene editing system that targets the key virulence regulator gene hrpB was implanted into the engineered phage, generating the engineered phage RSCqCRISPR-Cas. Our findings demonstrated that RSCqCRISPR-Cas could disarm the key "weapon", hrpB, of R. solanacearum, in medium and in plants. Remarkably, pretreatment with RSCqCRISPR-Cas significantly controlled tobacco bacterial wilt, highlighting the potential of engineered filamentous phages as promising biocontrol agents against plant bacterial wilt and other bacterial diseases.

Mycobacterium tuberculosis (M.tb) causes the current leading infectious disease. Examination of the functional genomics of M.tb and development of drugs and vaccines are hampered by the complicated and time-consuming genetic manipulation techniques for M.tb. Here, we reprogrammed M.tb endogenous type III-A CRISPR-Cas10 system for simple and efficient gene editing, RNA interference and screening via simple delivery of a plasmid harboring a mini-CRISPR array, thereby avoiding the introduction of exogenous proteins and minimizing proteotoxicity. We demonstrated that M.tb genes were efficiently and specifically knocked-in/out by this system, which was confirmed by whole-genome sequencing. This system was further employed for single and simultaneous multiple-gene RNA interference. Moreover, we successfully applied this system for genome-wide CRISPR interference screening to identify the in-vitro and intracellular growth-regulating genes. This system can be extensively used to explore the functional genomics of M.tb and facilitate the development of new anti-Mycobacterial drugs and vaccines. SummaryTuberculosis caused by Mycobacterium tuberculosis (M.tb) is the current leading infectious disease affecting more than ten million people annually. To dissect the functional genomics and understand its virulence, persistence, and antibiotics resistance, a powerful genome editing tool and high-throughput screening methods are desperately wanted. Our study developed an efficient and a robust tool for genome editing and RNA interference in M.tb using its endogenous CRISPR cas10 system. Moreover, the system has been successfully applied for genome-wide CRISPR interference screening. This tool could be employed to explore the functional genomics of M.tb and facilitate the development of anti-M.tb drugs and vaccines.

Biotrophic and hemibiotrophic fungi have evolved the ability to colonize living plant cells, but how they establish biotrophic growth by remodeling gene expression is poorly understood. By using in planta invasive hyphae (IH) of Magnaporthe oryzae to perform an integrated Chromatin immunoprecipitation sequencing (ChIPseq) and RNA-seq analysis, combining with biological and cellular analyses, we found Polycomb repressive complex 2 (PRC2)-mediated epigenetic repression plays a key role in regulating biotrophic growth. ChIPseq for biotrophic IH samples identified 1701 PRC2 target genes. RNA-seq analysis showed that expression of 462 PRC2 target genes were up-regulated in the {Delta}suz12 mutant, while 82 were down-regulated, indicating a major role of PRC2 in gene repression of IH. During biotrophic growth, PRC2 repressed fungal cell wall synthesis genes and extracellular enzyme genes required for penetration, and secondary metabolites biosynthesis genes required for necrotrophic growth. A great number of effector-encoding genes were repressed by PRC2, which were highly expressed during penetration stage, suggesting PRC2 coordinates biotrophic growth by regulating effector suppression for immune evasion. This regulation was finely coordinated by Pmk1, through regulating phosphorylation, nuclear localization and protein abundance of Suz12. Our results indicate that the Pmk1-PRC2 regulatory module is required for gene remodeling to facilitate biotrophic growth in M. oryzae. IMPORTANCEBiotrophic and hemibiotrophic fungi establish a biotrophic stage for infection in host cells. For example, M. oryzae forms appressoria to penetrate host cell and establish a biotrophic growth stage for infection. How gene expression patterns are elaborately controlled for fungal biotrophic growth is largely unknown. In this study, we found that, the PRC2-mediated H3K27me3 repressed fungal penetration-required cell wall synthesis genes and extracellular enzyme genes, and necrotrophic growth-required secondary metabolites biosynthesis genes for biotrophic growth. Interestingly, a great number of effector-encoding genes were also repressed by PRC2 at biotrophic stage, which were highly expressed at penetration stage, suggesting PRC2 coordinates biotrophic growth by regulating effector suppression for immune evasion. The PRC2-mediated epigenetic repression is therefore required for the gene expression remodeling during fungal infection. This regulation was finely coordinated by Pmk1, through regulating nuclear localization and protein abundance of the PRC2 component Suz12.

Bacteria have developed numerous defense systems to counter phage infections. However, the extent to which phages possess countermeasures against these defense systems remains unclear. In this study, we combined a phage gene knockout library with a defense system library to analyze the mechanisms by which phages counteract bacterial defense systems. After attempting gene deletions of 105 open reading frames (ORFs) in the DruSM1 phage ({Phi}DruSM1), we successfully generated 73 different ORF knockout phages. By infecting this library with bacteria harboring defense system expression plasmids, we identified inactivators of Druantia type I (Druad1), Brex type I, AVAST type III, Sir2+HerA, DUF4297+HerA, and hhe, as well as an activator of Retron Ec86, in a single phage genome. Synthetic phages incorporating Druad1 effectively eradicated Escherichia coli harboring the robust Druantia type I defense system by altering DNA methylation at m6A sites of the phage. This study highlighted the prevalence of various antidefense mechanisms employed by phages to overcome bacterial defense systems.

IncX4 plasmids are one of the most epidemiologically successful vehicles for mcr-1 spread. Here we found that the IncX4 plasmids carried two different replication proteins encoded by genes pir-1 and pir-2, respectively, but mcr-1 was only carried by IncX4 plasmid encoding pir-1. The copy number of pir-2 encoding plasmids (3.15{+/-}0.9 copies) are higher than that of pir-1 encoding plasmids (0.85{+/-}0.5 copies). When mcr-1 was cloned into IncX4 plasmid encoding pir-2, the higher copy number of these plasmids resulted in increased expression of mcr-1 and a greater fitness burden on their host cells. However, these plasmids exhibited a lower rate of invasion into the bacterial population compared to mcr-1 positive plasmids encoding the pir-1 gene. These findings collectively explain the absence of mcr-1 in all IncX4 plasmids encoding pir-2. Our results further confirmed that low-copy numbers are important for the spread of mcr-1 plasmid from the perspective of natural evolution.

Studying the swimming behaviour of bacteria in 3 dimensions (3D) allows us to understand critical biological processes, such as biofilm formation. It is still unclear how near wall swimming behaviour may regulate the initial attachment and biofilm formation. It is challenging to address this as visualizing the movement of bacteria with reasonable spatial and temporal resolution in a high-throughput manner is technically difficult. Here, we compared the near wall (vertical) swimming behaviour of P. aeruginosa (PAO1) and its mutants {Delta}dipA (reduced in swarming motility and increased in biofilm formation) and {Delta}fimX (deficient in twitching motility and reduced in biofilm formation) using our new imaging technique based on light sheet microscopy. We found that P. aeruginosa (PAO1) increases its speed and changes its swimming angle drastically when it gets closer to a wall. In contrast, {Delta}dipA mutant moves toward the wall with steady speed without changing of swimming angle. The near wall behavior of {Delta}dipA allows it to be more effective to interact with the wall or wall-attached cells, thus leading to more capture events and a larger biofilm volume during initial attachment when compared with PAO1. Furthermore, we found that {Delta}fimX has a similar near wall swimming behavior as PAO1, however, it has a higher dispersal frequency and smaller biofilm formation when compared with PAO1 which can be explained by its poor twitching motility. Together, we propose that near wall swimming behavior of P. aeruginosa plays an important role in the regulation of initial attachment and biofilm formation. ImportanceBacterial biofilm is a community of bacteria on surfaces which leads to serious problems in medical devices, food industry, and aquaculture. The initial attachment and subsequent microcolony formation play critical roles in bacterial biofilm formation. However, it is unclear how the initial attachment is regulated, in particular, on a vertical surface. To study this, we have developed a novel imaging technique based on light sheet microscopy, which overcame the limitations of other imaging techniques, to understand how 3D bacterial motility near a wall may regulate initial attachment during biofilm formation. Using our technique, we discovered that near wall swimming behavior of the bacteria, P. aeruginosa, plays an important role in the regulation of biofilm formation during initial attachment.

Single-stranded DNA binding proteins (SSBs) have been regarded as indispensable factors in all three domains of life since they play vital roles in DNA replication. Herein, we report that genes coding for the canonical SSB (SisSSB) and the non-canonical SSB (SisDBP) in the hyperthermophilic archaeon Saccharolobus islandicus REY15A can both be deleted. The growth is not affected, and the cell cycle progression and genome stability of the deletion strains is not impaired, suggesting that SisSSB and SisDBP are not essential for cell viability. Interestingly, at a lower temperature (55{degrees}C), the protein level of SisSSB increases [~]1.8 fold in the wild type and the growth of {Delta}Sisssb and {Delta}Sisssb{Delta}Sisdbp is retarded. SisSSB exhibits melting activity on dsRNA and DNA/RNA hybrid in vitro and unwinding RNA hairpin in Escherichia coli. Furthermore, the core SisSSB domain is able to complement the absence of the cold shock proteins CspABGE in E. coli, suggesting that SisSSB functions as RNA chaperon. We show that a two-fold overexpression of SisSSB is beneficial to the cell growth at lower temperature, but it has detrimental effect on the cell growth and cell cycle progression at normal growth temperature, which differs from bacterial Csp proteins. Importantly, these in vitro and in vivo activities are conserved in SSB subtype SSB-1 in Crenarchaeota species that lack bacterial Csp homologs. Overall, we have clarified the function of the archaeal canonical SSB which does not function as a DNA processing factor, but plays a role in processes requiring dsRNA or DNA/RNA hybrid unwinding.

Purple non-sulfur photosynthetic bacteria (PNSB) such as R. capsulatus serve as a versatile platform for fundamental studies and various biotechnological applications. In this study, we sought to develop the class II RNA-guided CRISPR/Cas12a system from Francisella novicida for both genome editing and gene down-regulation in R. capsulatus. About 90% editing efficiency was achieved by using CRISPR/Cas12a driven by a strong promoter Ppuc when targeting ccoO or nifH gene. When both genes were simultaneously targeted, the multiplex gene editing efficiency reached >63%. In addition, CRISPR interference using deactivated Cas12a was also evaluated using reporter genes gfp and lacZ, and the repression efficiency reached >80%. In summary, our work represents the first report to develop CRISPR/Cas12a mediated genome editing/transcriptional repression in R. capsulatus, which would greatly accelerate PNSB-related researches. IMPORTANCEPurple non-sulfur photosynthetic bacteria (PNSB) such as R. capsulatus serve as a versatile platform for fundamental studies and various biotechnological applications. However, lack of efficient gene editing tools remains a main obstacle for progressing in PNSB-related researches. Here, we developed CRISPR/Cas12a for genome editing via the non-homologous end joining (NHEJ) repair machinery in R. capsulatus. In addition, DNase-deactivated Cas12a was found to simultaneously suppress multiple targeted genes. Taken together, our work offers a new set of tools for efficient genome engineering in PNSB such as R. capsulatus.

Rifampin is the most effective drug in the treatment of tuberculosis, whose major pathogen is Mycobacterium tuberculosis (MTB), whereas there are still certain MTB strains resistant to the therapy of rifampin. The rpoB mutations play a central role in MTB resistance to the rifampin therapy, so it is crucial to identify these mutations in order to discover novel therapeutic approaches to these drug-resistant MTB strains. Here we show that a CRISPR-Cas12a-based detection platform with recombinase polymerase amplification and fluorescence reporter can be utilized to detect and visualize an MTB drug-resistant point mutation (rpoBL378R) from its rpoB wild type. Notably, this detection system is highly specific because it did not cross-react with contrived reference samples containing the genomes of MTB H37Rv, Mycobacterium smegmatis (M. smegmatis), Mycobacterium aureus (M. aureus), and Escherichia coli (E. coli). Collectively, this strategy based on CRISPR-Cas12a that we show in this report is simple, sensitive as well as specific for detection of the rifampin-resistant MTB H37Rv with the rpoBL378R mutation, indicating that this CRISPR-Cas12a-based detection platform has high potential to be exploited for clinic application to identify MTB mutations.

DNA nucleases TnpB and IscB were regarded as new antibacterial strategy to combat the drug-resistant bacteria represented by Escherichia coli due to its specificity in targeting DNA and smallest size, but the genome-editing of TnpB/IscB in E. coli remains unclear. This study characterized the genome-editing of TnpB/IscB in E. coli strains. First, the toxicity and cleavage results showed TnpB only worked in E. coli MG1655, while IscB and enIscB could perform in ATCC9637 and BL21(DE3). Next, TnpB-based genome-editing tool was established in MG1655, while IscB/enIscB achieved in ATCC9637/BL21(DE3). The copy number of TnpB/IscB/enIscB were changed to explore the impact of editing efficiency. Moreover, the editing plasmids were successfully cured. Finally, the escaping mechanism of E. coli under editing of TnpB/IscB was revealed. Overall, this study successfully applied TnpB/IscB/enIscB to genome-editing in E. coli, which will broaden genetic manipulation toolbox in E. coli and facilitate the development of new antimicrobial drugs.

Microalgae are highly efficient photosynthetic organisms that hold enormous potential as sources of renewable energy. In particular, Chlorella pyrenoidosa displays a rapid growth rate, high tolerance to light, and high lipid content, making it especially valuable for applications such as flue gas CO2 fixation, biofuel production, and nutritional extracts. In order to unveil its full potential, it is necessary to characterize its subcellular architecture. Here, we achieved three-dimensional (3D) visualization of the architectures of C. pyrenoidosa cells, by combining focused ion beam scanning electron microscopy (FIB/SEM), cryo-FIB milling, and cryo-electron tomography (cryo-ET). These high-resolution images bring to light intricate features of intact organelles, including thylakoid membranes, pyrenoid, starch granules, mitochondria, nucleus, lipid droplets and vacuoles, as well as the fine architectures within the chloroplast, including the concave-convex pyrenoid, plastoglobules, thylakoid tips, and convergence zones. Significantly, comparative analysis of wild-type and nuclear-irradiated mutagenic strains determined that cell volume and surface area of mutant cells have increased substantially to 2.2-fold and 1.7-fold, respectively, consistent with up-regulation of the enzyme Rubisco and enhanced photosynthetic metabolic processes. Moreover, quantitative analysis established that the thylakoid membrane width in mutant cells increased to 1.3-fold, while the membrane gap decreased to 0.8-fold, possibly contributing to the higher biomass growth rate of mutant cells. Our work reveals the first 3D subcellular architectures of C. pyrenoidosa cell and provides a structural framework for unlocking the higher growth rate in microalgae relevant to a wide range of industrial applications.

Antimicrobial resistance poses an escalating global threat, renewing interest in bacteriophage therapy as a precision alternative to antibiotics. However, clinical translation remains hindered by the lack of rapid and quantitative phage susceptibility testing (PST) platforms capable of evaluating host range, infection potency, and effective multiplicity of infection (MOI). Here we present RPST, a ramanome-based phenotypic platform that captures infection-induced remodeling of bacterial macromolecular composition to unify these diagnostic requirements within a single workflow. RPST integrates four Raman biomarkers into a Composite Infection Index (CII), enabling rapid and lysis-independent discrimination between susceptible and resistant bacterial populations within [~]1 hour, with 96.0% categorical concordance (24/25) to plaque assays. As a continuous population-level metric, CII quantifies the proportion of infected cells, allowing quantitative ranking of phage potency against shared hosts. By resolving CII trajectories across the MOI and time, RPST further determines the minimal effective MOI, which is the lowest phage-to-bacterium ratio sustaining self-propagating infection, thereby defining the lower boundary for therapeutic feasibility. Together, these capabilities transform PST from static compatibility assays into a dynamic and quantitative framework that bridges in vitro infectivity assessment and infection dynamics relevant to phage therapy. Impact StatementBased on the rapid emergence of antimicrobial resistance, this study introduces RPST, a novel ramanome-based phage susceptibility testing platform. RPST detects phage-induced biochemical remodeling in bacteria within [~]1 hour, achieving 96.0% concordance with gold-standard plaque assays. By integrating four Raman biomarkers into a Composite Infection Index, it not only distinguishes susceptible from resistant strains but also quantifies phage potency and determines the minimal effective multiplicity of infection required for self-sustaining infection. This transformative approach moves beyond binary diagnostics to offer a dynamic, quantitative framework for precision phage therapy, significantly accelerating therapeutic decision-making and enhancing our ability to combat resistant infections.

Bacterial two-component systems (TCSs) sense and respond to environmental changes and modulate downstream gene expression. However, the mechanism of cross-talk between multiple TCSs is unclear. In this study, we report a previously uncharacterized mechanism by which the TCS protein RpfG interacts with hybrid two-component system (HyTCS) proteins HtsH1, HtsH2 and HtsH3 to regulate antibiotic biosynthesis in Lysobacter. RpfG, a phosphodiesterase (PDE), can degrade c-di-GMP to 5-pGpG and can regulate antibiotic heat-stable antifungal factor (HSAF) biosynthesis in a PDE- independent manner. Thus, we wondered whether RpfG regulate HSAF biosynthesis through interactions with other factors. Subsequently, we demonstrated that RpfG interacts with three HyTCS proteins (HtsH1, HtsH2 and HtsH3), that can inhibit the PDE enzymatic activity of RpfG. Importantly, deletion of htsH1, htsH2 and htsH3 resulted in significantly decreased HSAF production, and we showed that HtsH1, HtsH2 and HtsH3 depend on their phosphorylation activity to directly regulate HSAF biosynthesis gene expression. Our results reveal that RpfG does not depend on PDE activity to regulate HSAF biosynthesis, rather it interacts with HtsH1, HtsH2 and HtsH3 to do so, a regulatory mechanism that may be a conserved paradigm in Lysobacter and Xanthomonas.

BackgroundThe functions and stability of a community depend on its species, which form complex interaction networks. The keystone taxa identified by network analysis are generally considered to play a vital role in the structure and function of microbial communities, but there is no uniformly accepted operational definition of such taxa. Further, what species and how they affect the communitys stability and function are still poorly understood. MethodsTo solve this problem, we performed a large-scale network analysis of the microbial communities residing in 1186 activated sludge (AS) samples. ResultsWe found that the AS co-occurrence network is a typical scale-free network. While most taxa in the AS co-occurrence network have little association, there are still a small number of taxa that are strongly interconnected. We defined a group of keystone taxa that have an important impact on network stability. Further analysis results indicate that the communities harboring the keystone taxa maintain higher stability, but these communities possess lower pollutant removal rates. In addition, we found that keystone taxa were more likely to appear in samples with lower sludge load. ConclusionsOur work identified the keystone taxa that maintain the stability of microbial communities in the AS systems but at the cost of reducing their function. This finding shed light on the relationship between composition, stability, and function within microbial communities. It also provides novel insights into manipulating the function of microbial communities by modifying their composition.

Phage recombinase function units (PRFUs) such as lambda-Red or Rac RecET have been proven to be powerful genetic tools in the recombineering of Escherichia coli. Studies have focused on developing such systems in other bacteria as it is believed that these PRFUs have limited efficiency in distant species. However, how the species evolution distance relates to the efficiency of recombineering remains unclear. Here, we present a thorough study of PRFUs to find features that might be related to the efficiency of PRFUs for recombineering. We first identified 59 unique sets of PRFUs in the genus Corynebacterium and classified them based on their sequence as well as secondary structure similarities. Then both PRFUs from this genus and other bacteria were chosen for experiment based on sequential and secondary structure similarity as well as species distance. These PRFUs were compared for their ability in mediating recombineering with oligo or double-stranded DNA substrates in Corynebacterium glutamicum. We demonstrate that the source of the PRFU is more critical than species distance for the efficiency of recombineering. Our work will provide new ideas for efficient recombineering using PRFUs.\n\nImportanceRecombineering using phage recombinase function units (PRFUs) such as lambda-Red or Rac RecET has gained success in Escherichia coli, while efforts applying these systems in other bacteria were limited by the efficiency. It is believed that the species distance may be a major reason for the low efficiency. In this study, however, we showed that it is the source of PRFU rather than the species distance that matters for the recombineering in Corynebacterium glutamicum. Besides, we also showed that the lower transformation efficiency in other bacteria compared to that of E. coli could be a major reason for the low performance of heterogeneously expressed RecET. These findings will be helpful for the recombineering using PRFUs.

Trichodesmium, the predominant marine diazotrophic cyanobacterium, concurrently performs nitrogen (N2) fixation and photosynthesis, the latter of which produces oxygen (O2) that inhibits N2 fixation. Hopanoid lipids in Trichodesmium may play a role in dynamically regulating membrane permeability to O2, potentially alleviating O2 stress on N2 fixation. However, the physiological impacts of this dynamic permeability are not well understood. We developed a model showing that dynamically modulating membrane O2 permeability can enhance N2 fixation and growth of Trichodesmium by over 50%. High O2 permeability (1.5x10-4 of O2 diffusivity in seawater) during strong photosynthesis accelerates O2 exhaust, reducing energy-consuming photorespiration by [~]40%, while low O2 permeability (1.0x10-5 diffusivity) during active N2 fixation minimizes O2 stress on N2 fixation. Together, these mechanisms increase the carbon and iron use efficiencies by [~]70%. Our study provides a mechanistic and quantitative framework for how dynamic O2 permeability benefits Trichodesmium, offering insights potentially applicable to other diazotrophs. IMPORTANCETrichodesmium is a key player in marine N2 fixation, essential for oceanic productivity and global biogeochemical cycles. However, a significant challenge arises from the concurrent photosynthetic production of O2 during N2 fixation, which can inhibit N2 fixation and cause energy-wasting photorespiration. We develop a physiological model showing that Trichodesmium may dynamically regulate membrane O2 permeability to enhance N2 fixation and growth. The model suggests two mechanisms: elevated O2 permeability during the early daytime of strong photosynthesis accelerates O2 exhaust to environment, reducing photorespiration, while reduced O2 permeability later limits O2 influx from environment, lowering wasteful respiration and maintaining a low intracellular O2 level for active N2 fixation. These adaptations improve the efficiency of carbon and iron utilization, thereby facilitating N2 fixation and growth in Trichodesmium. This study sheds light on how Trichodesmium and other N2-fixing microorganisms can optimize their physiological processes in response to environmental challenges. HIGHLIGHTSO_LIWe developed a metabolic flux model of Trichodesmium, which resolves Dynamic cellular Permeability to O2 (DPO2). C_LIO_LIDPO2 increases N2 fixation and growth rates. C_LIO_LIDPO2 increases growth efficiency by reducing carbon wasting processes such as photorespiration and respiratory protection. C_LIO_LIDPO2, as a result, also increases iron utilization efficiency. C_LI