Analyzing AbrB-Knockout Effects through Genome and Transcriptome Sequencing of Bacillus licheniformis DW2

Response of a new rumen-derived Bacillus licheniformis to different carbon sources

Introduction

Bacillus licheniformis (B. licheniformis) is a microorganism with a wide range of probiotic properties and applications. Isolation and identification of novel strains is a major aspect of microbial research. Besides, different carbon sources have varying effects on B. licheniformis in regulating the microenvironment, and these mechanisms need to be investigated further.

Methods

In this study, we isolated and identified a new strain of B. licheniformis from bovine rumen fluid and named it B. licheniformis NXU98. The strain was treated with two distinct carbon sources-microcrystalline cellulose (MC) and cellobiose (CB). A combination of transcriptome and proteome analyses was used to investigate different carbon source effects.

Results

The results showed that B. licheniformis NXU98 ABC transporter proteins, antibiotic synthesis, flagellar assembly, cellulase-related pathways, and proteins were significantly upregulated in the MC treatment compared to the CB treatment, and lactate metabolism was inhibited. In addition, we used MC as a distinct carbon source to enhance the antibacterial ability of B. licheniformis NXU98, to improve its disease resistance, and to regulate the rumen microenvironment.

Discussion

Our research provides a potential new probiotic for feed research and a theoretical basis for investigating the mechanisms by which bacteria respond to different carbon sources.

Microbial synthesis of bacitracin: Recent progress, challenges, and prospects

Microorganisms are important sources of various natural products that have been commercialized for human medicine and animal healthcare. Bacitracin is an important antibacterial natural product predominantly produced by Bacillus licheniformis and Bacillus subtilis, and it is characterized by a broad antimicrobial spectrum, strong activity and low resistance, thus bacitracin is extensively applied in animal feed and veterinary medicine industries. In recent years, various strategies have been proposed to improve bacitracin production. Herein, we systematically describe the regulation of bacitracin biosynthesis in genus Bacillus and its associated mechanism, to provide a theoretical basis for bacitracin overproduction. The metabolic engineering strategies applied for bacitracin production are explored, including improving substrate utilization, using an enlarged precursor amino acid pool, increasing ATP supply and NADPH generation, and engineering transcription regulators. We also present several approaches of fermentation process optimization to facilitate the industrial large-scale production of bacitracin. Finally, the challenges and prospects associated with microbial bacitracin synthesis are discussed to facilitate the establishment of high-yield and low-cost biological factories.

Genome Sequencing and Genetic Engineering Reveal the Contribution of Bacitracin Produced by Bacillus paralicheniformis CPL618 to Anti-Staphylococcus aureus Activity

Staphylococcus aureus is one of the important pathogens causing human diseases, especially its treatment has great challenges due to its resistance to methicillin and vancomycin. The Bacillus strains are known to be major sources of second metabolites that can function as drugs. Therefore, it is of great value to excavate metabolites with good inhibitory activity against S. aureus from Bacillus strains. In this study, a strain Bacillus paralicheniformis CPL618 with good antagonistic activity against S. aureus was isolated and genome analysis showed that the size was 4,447,938 bp and contained four gene clusters fen, bac, dhb, and lch which are potentially responsible for four cyclic peptides fengycin, bacitracin, bacillibactin, and lichenysin biosynthesis, respectively. These gene clusters were knockout by homologous recombination. The bacteriostatic experiment results showed that the antibacterial activity of ∆bac decreased 72.3% while Δfen, Δdhb, and ΔlchA did not significantly changed as that of wild type. Interestingly, the maximum bacitracin yield was up to 92 U/mL in the LB medium, which was extremely unusual in wild type strains. To further improve the production of bacitracin, transcription regulators abrB and lrp were knocked out, the bacitracin produced by ΔabrB, Δlrp, and ΔabrB + lrp was 124 U/mL, 112 U/mL, and 160 U/ml, respectively. Although no new anti-S. aureus compounds was found by using genome mining in this study, the molecular mechanisms of high yield of bacitracin and anti-S. aureus in B. paralicheniformis CPL618 were clarified. Moreover, B. paralicheniformis CPL618 was further genetically engineered for industrial production of bacitracin.

Complete genome sequence of Bacillus Licheniformis NWMCC0046, a candidate for the laundry industry

In this study, selected properties of protease and the complete genome sequence of Bacillus licheniformis NWMCC0046 were investigated, to discover laundry applications and other potential probiotic properties of this strain. Partial characterization of B. licheniformis NWMCC0046 showed that its protease has good activity both in alkaline environments and at low temperatures. Also, the protease is compatible with commercial detergents and can be used as a detergent additive for effective stain removal at low temperatures. The complete genome sequence of B. licheniformis NWMCC0046 is comprised of a 4,321,565 bp linear chromosome with a G + C content of 46.78% and no plasmids. It had 4504 protein-encoding genes, 81 transfer RNA (tRNA) genes, and 24 ribosomal RNA (rRNA) genes. Genomic analysis revealed genes involved in exocellular enzyme production and probiotic properties. In addition, genomic sequence analysis revealed specific genes encoding carbohydrate metabolism pathways, resistance, and cold adaptation capacity. Overall, protease properties show its potential as a detergent additive enzyme. The complete genome sequence information of B. licheniformis NWMCC0046 was obtained, and functional prediction revealed its numerous probiotic properties.

The Physiological Functions of AbrB on Sporulation, Biofilm Formation and Carbon Source Utilization in Clostridium tyrobutyricum

As a pleiotropic regulator, Antibiotic resistant protein B (AbrB) was reported to play important roles in various cellular processes in Bacilli and some Clostridia strains. In Clostridium tyrobutyricum, abrB (CTK_C 00640) was identified to encode AbrB by amino acid sequence alignment and functional domain prediction. The results of abrB deletion or overexpression in C. tyrobutyricum showed that AbrB not only exhibited the reported characteristics such as the negative regulation on sporulation, positive effects on biofilm formation and stress resistance but also exhibited new functions, especially the negative regulation of carbon metabolism. AbrB knockout strain (Ct/ΔabrB) could alleviate glucose-mediated carbon catabolite repression (CCR) and enhance the utilization of xylose compared with the parental strain, resulting in a higher butyrate titer (14.79 g/L vs. 7.91 g/L) and xylose utilization rate (0.19 g/L·h vs. 0.02 g/L·h) from the glucose and xylose mixture. This study confirmed the pleiotropic regulatory function of AbrB in C. tyrobutyricum, suggesting that Ct/ΔabrB was the potential candidate for butyrate production from abundant, renewable lignocellulosic biomass mainly composed of glucose and xylose.

Designer bacterial cell factories for improved production of commercially valuable non-ribosomal peptides

Non-ribosomal peptides have gained significant attention as secondary metabolites of high commercial importance. This group houses a diverse range of bioactive compounds, ranging from biosurfactants to antimicrobial and cytotoxic agents. However, low yield of synthesis by bacteria and excessive losses during purification hinders the industrial-scale production of non-ribosomal peptides, and subsequently limits their widespread applicability. While isolation of efficient producer strains and optimization of bioprocesses have been extensively used to enhance yield, further improvement can be made by optimization of the microbial strain using the tools and techniques of metabolic engineering, synthetic biology, systems biology, and adaptive laboratory evolution. These techniques, which directly target the genome of producer strains, aim to redirect carbon and nitrogen fluxes of the metabolic network towards the desired product, bypass the feedback inhibition and repression mechanisms that limit the maximum productivity of the strain, and even extend the substrate range of the cell for synthesis of the target product. The present review takes a comprehensive look into the biosynthesis of bacterial NRPs, how the same is regulated by the cell, and dives deep into the strategies that have been undertaken for enhancing the yield of NRPs, while also providing a perspective on other potential strategies that can allow for further yield improvement. Furthermore, this review provides the reader with a holistic perspective on the design of cellular factories of NRP production, starting from general techniques performed in the laboratory to the computational techniques that help a biochemical engineer model and subsequently strategize the architectural plan.

Molecular Mechanisms Underlying Vibrio Tolerance in Ruditapes philippinarum Revealed by Comparative Transcriptome Profiling

The clam Ruditapes philippinarum is an important species in the marine aquaculture industry in China. However, in recent years, the aquaculture of R. philippinarum has been negatively impacted by various bacterial pathogens. In this study, the transcriptome libraries of R. philippinarum showing different levels of resistance to challenge with Vibrio anguillarum were constructed and RNA-seq was performed using the Illumina sequencing platform. Host immune factors were identified that responded to V. anguillarum infection, including C-type lectin domain, glutathione S-transferase 9, lysozyme, methyltransferase FkbM domain, heat shock 70 kDa protein, Ras-like GTP-binding protein RHO, C1q, F-box and BTB/POZ domain protein zf-C2H2. Ten genes were selected and verified by RT-qPCR, and nine of the gene expression results were consistent with those of RNA-seq. The lectin gene in the phagosome pathway was expressed at a significantly higher level after V. anguillarum infection, which might indicate the role of lectin in the immune response to V. anguillarum. Comparing the results from R. philippinarum resistant and nonresistant to V. anguillarum increases our understanding of the resistant genes and key pathways related to Vibrio challenge in this species. The results obtained here provide a reference for future immunological research focusing on the response of R. philippinarum to V. anguillarum infection.

Multilevel metabolic engineering of Bacillus licheniformis for de novo biosynthesis of 2-phenylethanol

Due to its pleasant rose-like scent, 2-phenylethanol (2-PE) has been widely used in the fields of cosmetics and food. Microbial production of 2-PE offers a natural and sustainable production process. However, the current bioprocesses for de novo production of 2-PE suffer from low titer, yield, and productivity. In this work, a multilevel metabolic engineering strategy was employed for the high-level production of 2-PE. Firstly, the native alcohol dehydrogenase YugJ was identified and characterized for 2-PE production via genome mining and gene function analysis. Subsequently, the redirection of carbon flux into 2-PE biosynthesis by combining optimization of Ehrlich pathway, central metabolic pathway, and phenylpyruvate pathway enabled the production of 2-PE to a titer of 1.81 g/L. Specifically, AroK and AroD were identified as the rate-limiting enzymes of 2-PE production through transcription and metabolite analyses, and overexpression of aroK and aroD efficiently boosted 2-PE synthesis. The precursor competing pathways were blocked by eliminating byproduct formation pathways and modulating the glucose transport system. Under the optimal condition, the engineered strain PE23 produced 6.24 g/L of 2-PE with a yield and productivity of 0.14 g/g glucose and 0.13 g/L/h, respectively, using a complex medium in shake flasks. This work achieves the highest titer, yield, and productivity of 2-PE from glucose via the phenylpyruvate pathway. This study provides a promising platform that might be widely useful for improving the production of aromatic-derived chemicals.

Metabolic Engineering of Aspartic Acid Supply Modules for Enhanced Production of Bacitracin in Bacillus licheniformis

Bacitracin, a type of cyclic dodecapeptide antibiotic mainly produced by Bacillus, is widely used in fields of veterinary drug and feed additive. Modularization of metabolic pathways based on the concept of synthetic biology has been widely used in the efficient synthesis of target products. Here, we want to improve bacitracin production through strengthening aspartic acid (Asp) supply in B. licheniformis DW2. First, exogenous Asp addition assays implied that strengthening Asp supply benefited bacitracin production. Second, Asp synthetic pathways were strengthened via overexpressing aspartate dehydrogenase AspD and asparaginase AnsB, attaining recombinant strain DW2-ASP2, and bacitracin yield produced by DW2-ASP2 was 862.81 U/mL, increased by 14.05% compared with that of DW2 (756.49 U/mL). Then, to improve precursor oxaloacetate (OAA) accumulation for Asp synthesis, pyruvate carboxylase PycA and carbonic anhydrase EcaA were co-overexpressed in DW2-ASP2, and malic enzyme gene malS was deleted to weak overflow metabolism of tricarboxylic acid, and the attained strain DW2-ASP7 showed further increased bacitracin production from 862.81 to 989.23 U/mL. Subsequently, transporter YveA was identified as an Asp exporter, and bacitracin yield was increased to 1025.26 U/mL via deleting yveA, attaining strain DW2-ASP9. Finally, Asp ammonia-lyase gene aspA was disrupted to weaken Asp degradation, and bacitracin yield of attained strain DW2-ASP10 reached 1059.86 U/mL, increased by 40.10% compared to DW2. Taken together, this research demonstrated that metabolic engineering of Asp metabolic modules is an efficient strategy for enhancing bacitracin production, and these strategies could also be applied in the production of other peptide-related metabolites.

Construction and Characterization of a Gradient Strength Promoter Library for Fine-Tuned Gene Expression in Bacillus licheniformis

Bacillus licheniformis DW2 is an important industrial strain for bacitracin production, and it is also used for biochemical production, however, the lack of effective toolkit for precise regulation of gene expression hindered its application seriously. Here, a gradient strength promoter library was constructed based on bacitracin synthetase gene cluster promoter PbacA. First, different PbacA promoter variants were constructed via coupling PbacA with various 5'-UTRs, and expression ranges of 32.6-741.8% were attained among these promoters. Then, three promoters, PUbay (strong), PbacA (middle), and PUndh (weakest), were applied for red fluorescent protein (RFP) and keratinase expression assays, and these promoters were proven to have good universality for different proteins. Second, the promoter of bacitracin synthetase gene cluster was replaced by these three promoters, and bacitraicn titer was enhanced by 14.62% when PUbay was applied, which was decreased by 98.05% under the mediation of PUndh compared with that of the original strain DW2. Third, promoters PUbay, PUyvgO, and PUndh were selected to regulate the expression levels of critical genes that are responsible for pucheriminic acid synthesis, and pucheriminic acid yield was increased by 194.1% via manipulating synthetic and competitive pathways. Finally, promoters PUbay, PbacA, and PUndh were applied for green fluorescent protein (GFP) and RFP expression in Escherichia coli, and consistent effects were attained based on our results. Taken together, a gradient strength promoter library was constructed in this research, which provided an effective toolkit for fine-tuning gene expression and reprogramming metabolite metabolic flux in B. licheniformis.

Transcriptome based functional identification and application of regulator AbrB on alkaline protease synthesis in Bacillus licheniformis 2709

Bacillus licheniformis 2709 is the major alkaline protease producer, which has great potential value of industrial application, but how the high-producer can be regulated rationally is still not completely understood. It's meaningful to understand the metabolic processes during alkaline protease production in industrial fermentation medium. Here, we collected the transcription database at various enzyme-producing stages (preliminary stage, stable phase and decline phase) to specifically research the synthesized and regulatory mechanism of alkaline protease in B. licheniformis. The RNA-sequencing analysis showed differential expression of numerous genes related to several processes, among which genes correlated with regulators were concerned, especially the major differential gene abrB on enzyme (AprE) synthesis was investigated. It was further verified that AbrB is a repressor of AprE by plasmid-mediated over-expression due to the severely descending enzyme activity (11,300 U/mL to 2695 U/mL), but interestingly it is indispensable for alkaline protease production because the enzyme activity of the null abrB mutant was just about 2279 U/mL. Thus, we investigated the aprE transcription by eliminating the theoretical binding site (TGGAA) of AbrB protein predicated by computational strategy, which significantly improved the enzyme activity by 1.21-fold and gene transcription level by 1.77-fold in the mid-log phase at a cultivation time of 18 h. Taken together, it is of great significance to improve the production strategy, control the metabolic process and oriented engineering by rational molecular modification of regulatory network based on the high throughput sequencing and computational prediction.

New insights into the Manila clam and PAMPs interaction based on RNA-seq analysis of clam through in vitro challenges with LPS, PGN, and poly(I:C)

Background

Manila clam (Ruditapes philippinarum) is a worldwide commercially important marine bivalve species. In recent years, however, microbial diseases caused high economic losses and have received increasing attention. To understand the molecular basis of the immune response to pathogen-associated molecular patterns (PAMPs) in R. philippinarum, transcriptome libraries of clam hepatopancreas were constructed at 24 h post-injection with Lipopolysaccharide (LPS), peptidoglycan (PGN), and polyinosinic-polycytidylic acid (poly(I:C)) and phosphate-buffered saline (PBS) control by using RNA sequencing technology (RNA-seq).

Results

A total of 832, 839, and 188 differentially expressed genes (DEGs) were found in LPS, PGN, and poly(I:C) challenge group compared with PBS control, respectively. Several immune-related genes and pathways were activated in response to the different PAMPs, suggesting these genes and pathways might specifically participate in the immune response to pathogens. Besides, the analyses provided useful complementary data to compare different PAMPs challenges in vivo. Functional enrichment analysis of DEGs demonstrated that PAMPs responsive signal pathways were related to apoptosis, signal transduction, immune system, and signaling molecules and interaction. Several shared or specific DEGs response to different PAMPs were revealed in R. philippinarum, including pattern recognition receptors (PRRs), antimicrobial peptides (AMPs), interferon-induced proteins (IFI), and some other immune-related genes were found in the present work.

Conclusions

This is the first study employing high throughput transcriptomic sequencing to provide valuable genomic resources and investigate Manila clam response to different PAMPs through in vivo challenges with LPS, PGN, and poly(I:C). The results obtained here provide new insights to understanding the immune characteristics of R. philippinarum response to different PAMPs. This information is critical to elucidate the molecular basis of R. philippinarum response to different pathogens invasion, which potentially can be used to develop effective control strategies for different pathogens.

Engineering Expression Cassette of pgdS for Efficient Production of Poly-γ-Glutamic Acids With Specific Molecular Weights in Bacillus licheniformis

Poly-γ-glutamic acid (γ-PGA) is an emerging biopolymer with various applications and γ-PGAs with different molecular weights exhibit distinctive properties. However, studies on the controllable molecular weights of biopolymers are limited. The purpose of this study is to achieve production of γ-PGAs with a wide range of molecular weights through manipulating the expression of γ-PGA depolymerase (PgdS) in Bacillus licheniformis WX-02. Firstly, the expression and secretion of PgdS were regulated through engineering its expression elements (four promoters and eight signal peptides), which generated γ-PGAs with molecular weights ranging from 6.82 × 10⁴ to 1.78 × 10⁶ Da. Subsequently, through combination of promoters with signal peptides, the production of γ-PGAs with a specific molecular weight could be efficiently obtained. Interestingly, the γ-PGA yield increased with the reduced molecular weight in flask cultures (Pearson correlation coefficient of −0.968, P < 0.01). Finally, in batch fermentation, the highest yield of γ-PGA with a weight-average molecular weight of 7.80 × 10⁴ Da reached 39.13 g/L under glutamate-free medium. Collectively, we developed an efficient strategy for one-step production of γ-PGAs with specific molecular weights, which have potential application for industrial production of desirable γ-PGAs.

Enhanced Bacitracin Production by Systematically Engineering S-Adenosylmethionine Supply Modules in Bacillus licheniformis

Bacitracin is a broad-spectrum veterinary antibiotic that widely used in the fields of veterinary drug and feed additive. S-Adenosylmethionine (SAM) is a critical factor involved in many biochemical reactions, especially antibiotic production. However, whether SAM affects bacitracin synthesis is still unknown. Here, we want to analyze the relationship between SAM supply and bacitracin synthesis, and then metabolic engineering of SAM synthetic pathway for bacitracin production in Bacillus licheniformis. Firstly, our results implied that SAM exogenous addition benefited bacitracin production, which yield was increased by 12.13% under the condition of 40 mg/L SAM addition. Then, SAM synthetases and Methionine (Met) synthetases from B. licheniformis, Corynebacterium glutamicum, and Saccharomyces cerevisiae were screened and overexpressed to improve SAM accumulation, and the combination of SAM synthetase from S. cerevisiae and Met synthetase from B. licheniformis showed the best performance, and 70.12% increase of intracellular SAM concentration (31.54 mg/L) and 13.08% increase of bacitraicn yield (839.54 U/mL) were achieved in resultant strain DW2-KE. Furthermore, Met transporters MetN and MetP were, respectively, identified as Met exporter and importer, and bacitracin yield was further increased by 5.94% to 889.42 U/mL via deleting metN and overexpressing metP in DW2-KE, attaining strain DW2-KENP. Finally, SAM nucleosidase gene mtnN and SAM decarboxylase gene speD were deleted to block SAM degradation pathways, and bacitracin yield of resultant strain DW2-KENPND reached 957.53 U/mL, increased by 28.97% compared to DW2. Collectively, this study demonstrated that SAM supply served as the critical role in bacitracin synthesis, and a promising strain B. licheniformis DW2-KENPND was attained for industrial production of bacitracin.

Effects of Bacillus velezensis FKM10 for Promoting the Growth of Malus hupehensis Rehd. and Inhibiting Fusarium verticillioides

Bacillus velezensis is a novel species of Bacillus that has been widely investigated and used because of its direct or indirect growth improvement effect for many plants. B. velezensis FKM10 was previously isolated from rhizosphere soil of apple trees and shows potential as a plant growth-promoting and biocontrol bacterium. In this study, strain FKM10 was verified to inhibit some fungal pathogens of soil-borne plant diseases, produce siderophores to absorb ferric iron for plants, and degrade proteins. Pot experiments showed that the application of strain FKM10 could directly promote the growth of Malus hupehensis Rehd. by increasing biomass, promoting the absorption of nutrients, improving soil fertility, changing the soil microbial community structure, and reducing fungal diversity. The results of this study provided a basis for using strain FKM10 to improve crop yield and overcome diseases of plants. The mechanism of strain FKM10 to control the phytopathogenic fungus Fusarium verticillioides was studied by interoperation with RNA sequencing. Strain FKM10 can destroy the cell wall and cell membrane of F. verticillioides. The secretion of glucosidases, such as β-glucanase, might be one of the causes of the destruction of the fungal cell wall. The regulation of amino acid metabolism might also play an important role in the antibacterial process of strain FKM10. During the antibacterial process, strain FKM10 attacks F. verticillioides and strain FKM10 itself is also affected: the expression of spores is increased, the number of viable cells is decreased, and the ribonucleoprotein complex and flagellar assembly-related genes are downregulated. The results of this study indicate that both strain FKM10 and F. verticillioides have mutually inhibitory activities in a liquid environment. Comparative genome analysis of B. velezensis FKM10 reveals that the general features of their genomes are similar overall and contain the core genome for this species. The results of this study further reveal that B. velezensis can also serve as a basis for developing new biocontrol agents or microbial fertilizers.

Improving the utilization rate of soybean meal for efficient production of bacitracin and heterologous proteins in the aprA-deficient strain of Bacillus licheniformis

Soybean meal is commonly applied as the raw material in the bio-fermentation industry, and bacitracin is a widely used feed additive in the feed industry. In this study, we investigated the influence of subtilisin enhancement on soybean meal utilization and bacitracin production in Bacillus licheniformis DW2, an industrial strain for bacitracin production. Firstly, blocking sRNA aprA expression benefited bacitracin synthesis, and the bacitracin yield produced by aprA-deficient strain DW2△PaprA reached 931.43 U/mL, 18.92% higher than that of DW2 (783.25 U/mL). The bacitracin yield was reduced by 14.27% in the aprA overexpression strain. Furthermore, our results showed that deficiency of aprA led to a 6.54-fold increase of the aprE transcriptional level and a 1.84-fold increase of subtilisin activity, respectively, which led to the increases of soybean meal utilization rate (28.86%) and precursor amino acid supplies for bacitracin synthesis. Additionally, strengthening the utilization rate of soybean meal also benefited heterologous protein production, and the α-amylase and nattokinase activities were respectively enhanced by 59.81% and 50.53% in aprA-deficient strains. Collectively, this research demonstrated that strengthening subtilisin production could improve the utilization rate of soybean meal and thereby enhance bacitracin and target protein production; also, this strategy would be useful for the improvement of protein/peptide production using soybean meal as the main nitrogen source in the fermentation process.

Metabolic Engineering of Main Transcription Factors in Carbon, Nitrogen, and Phosphorus Metabolisms for Enhanced Production of Bacitracin in Bacillus licheniformis

Primary metabolism plays a key role in the synthesis of secondary metabolite. In this study, the main transcription factors in carbon, nitrogen, and phosphorus metabolisms (CcpA, CcpC, CcpN, CodY, TnrA, GlnR, and PhoP) were engineered to improve bacitracin yield in Bacillus licheniformis DW2, an industrial strain for bacitracin production. First, our results demonstrated that deletions of ccpC and ccpN improved ATP and NADPH supplies, and the bacitracin yields were respectively increased by 14.02% and 16.06% compared with that of DW2, while it was decreased significantly in ccpA deficient strain DW2ΔccpA. Second, excessive branched chain amino acids (BCAAs) were accumulated in codY, tnrA, and glnR deletion strains DW2ΔcodY, DW2ΔtnrA, and DW2ΔglnR, which resulted in the nitrogen catabolite repressions and reductions of bacitracin yields. Moreover, overexpression of these regulators improved intracellular BCAA supplies, and further enhanced bacitracin yields by 14.17%, 12.98%, and 16.20%, respectively. Furthermore, our results confirmed that phosphate addition reduced bacitracin synthesis capability, and bacitracin yield was improved by 15.71% in gene phop deletion strain. On the contrary, overexpression of PhoP led to a 19.40% decrease of bacitracin yield. Finally, a combinatorial engineering of these above metabolic manipulations was applied, and bacitracin yield produced by the final strain DW2-CNCTGP (Simultaneously deleting ccpC, ccpN, phop and overexpressing glnR, codY, and tnrA in DW2) reached 1014.38 U/mL, increased by 35.72% compared to DW2, and this yield was the highest bacitracin yield currently reported. Taken together, this study implied that metabolic engineering of carbon, nitrogen, and phosphorus metabolism regulators is an efficient strategy to enhance bacitracin production, and provided a promising B. licheniformis strain for industrial production of bacitracin.

Environmental interactions are regulated by temperature in Burkholderia seminalis TC3.4.2R3

Burkholderia seminalis strain TC3.4.2R3 is an endophytic bacterium isolated from sugarcane roots that produces antimicrobial compounds, facilitating its ability to act as a biocontrol agent against phytopathogenic bacteria. In this study, we investigated the thermoregulation of B. seminalis TC3.4.2R3 at 28 °C (environmental stimulus) and 37 °C (host-associated stimulus) at the transcriptional and phenotypic levels. The production of biofilms and exopolysaccharides such as capsular polysaccharides and the biocontrol of phytopathogenic fungi were enhanced at 28 °C. At 37 °C, several metabolic pathways were activated, particularly those implicated in energy production, stress responses and the biosynthesis of transporters. Motility, growth and virulence in the Galleria mellonella larvae infection model were more significant at 37 °C. Our data suggest that the regulation of capsule expression could be important in virulence against G. mellonella larvae at 37 °C. In contrast, B. seminalis TC3.4.2R3 failed to cause death in infected BALB/c mice, even at an infective dose of 10⁷ CFU.mL^-1. We conclude that temperature drives the regulation of gene expression in B. seminalis during its interactions with the environment.