Functional analysis and application of the cryptic plasmid pBSG3 harboring the RapQ–PhrQ system in Bacillus amyloliquefaciens B3

Research advances in the identification of regulatory mechanisms of surfactin production by Bacillus: a review

Surfactin is a cyclic hexalipopeptide compound, nonribosomal synthesized by representatives of the Bacillus subtilis species complex which includes B. subtilis group and its closely related species, such as B. subtilis subsp subtilis, B. subtilis subsp spizizenii, B. subtilis subsp inaquosorum, B. atrophaeus, B. amyloliquefaciens, B. velezensis (Steinke mSystems 6: e00057, 2021) It functions as a biosurfactant and signaling molecule and has antibacterial, antiviral, antitumor, and plant disease resistance properties. The Bacillus lipopeptides play an important role in agriculture, oil recovery, cosmetics, food processing and pharmaceuticals, but the natural yield of surfactin synthesized by Bacillus is low. This paper reviews the regulatory pathways and mechanisms that affect surfactin synthesis and release, highlighting the regulatory genes involved in the transcription of the srfAA-AD operon. The several ways to enhance surfactin production, such as governing expression of the genes involved in synthesis and regulation of surfactin synthesis and transport, removal of competitive pathways, optimization of media, and fermentation conditions were commented. This review will provide a theoretical platform for the systematic genetic modification of high-yielding strains of surfactin.

Recent advances and prospects of Bacillus amyloliquefaciens as microbial cell factories: from rational design to industrial applications

Bacillus amyloliquefaciens is one of the most characterized Gram-positive bacteria. This species has unique characteristics that are beneficial for industrial applications, including its utilization of: cheap carbon as a substrate, a transparent genetic background, and large-scale robustness in fermentation. Indeed, the productivity characteristics of B. amyloliquefaciens have been thoroughly analyzed and further optimized through systems biology and synthetic biology techniques. Following the analysis of multiple engineering design strategies, B. amyloliquefaciens is now considered an efficient cell factory capable of producing large quantities of multiple products from various raw materials. In this review, we discuss the significant potential advantages offered by B. amyloliquefaciens as a platform for metabolic engineering and industrial applications. In addition, we systematically summarize the recent laboratory research and industrial application of B. amyloliquefaciens, including: relevant advances in systems and synthetic biology, various strategies adopted to improve the cellular performances of synthetic chemicals, as well as the latest progress in the synthesis of certain important products by B. amyloliquefaciens. Finally, we propose the current challenges and essential strategies to usher in an era of broader B. amyloliquefaciens use as microbial cell factories.

Synergistic effects of crop residue and microbial inoculant on soil properties and soil disease resistance in a Chinese Mollisol

The soil-borne disease caused by Fusarium graminearum seriously affects the corn quality. Straw can greatly improve soil quality, but the effect is limited by its nature and environmental factors. This study explored the impact of straw-JF-1(biocontrol bacteria) combination on soil environment and soil disease resistance. The results showed that the combined treatment increased the proportion of soil large and small macro-aggregates by 22.50 and 3.84%, with soil organic carbon (SOC) content by 16.18 and 16.95%, respectively. Compared to treatment with returning straw to the field alone, the straw-JF-1 combination increased the soil content of humic acid, fulvic acid, and humin by 14.06, 5.50, and 4.37%, respectively. Moreover, A metagenomics showed that returning straw to the field alone increased the abundance of disease-causing fungi (Fusarium and Plectosphaerella), however, the straw-JF-1 combination significantly suppressed this phenomenon as well as improved the abundance of probiotic microorganisms such as Sphingomonas, Mortierella, Bacillus, and Pseudomonas. Functional analysis indicated that the combination of straw and JF-1 improved some bacterial functions, including inorganic ion transport and metabolism, post-translational modification/protein turnover/chaperones and function unknown, fungal functions associated with plant and animal pathogens were effectively inhibited. Pot experiments showed that the straw-JF-1 combination effectively inhibited the Fusarium graminearum induced damage to maize seedlings. Therefore, the combination of straw and JF-1 could be a practical method for soil management.

Genetic transformation system for Bacillus velezensis NSZ-YBGJ001 and curing of the endogenous plasmid pBV01

OBJECTIVES

To construct a genetic transformation system for Bacillus velezensis NSZ-YBGJ001 and identify the origin element in an endogenous plasmidpBV01 for curing pBV01 by plasmid incompatibility.

RESULTS

A plasmid pUBC01 was constructed, and then an electrotransformation system for B. velezensis NSZ-YBGJ001 was developed, which reached ~ 1000 transformants per microgram of pUBC01 DNA. Additionally, a 7276-bp circular plasmid pBV01 with a G + C content of 37.5% was isolated from B. velezensis NSZ-YBGJ001 and analyzed via sequence analysis. To cure pBV01, an incompatible plasmid pBV02 harboring the replication element of pBV01 was developed and functionally replicated in both Bacillus subtilis WB600 and B. velezensis NSZ-YBGJ001. pBV01 was cured through introduction of pBV02 into B. velezensis NSZ-YBGJ001 after serial subculturing for approximately 40 generations. Finally, another plasmid, pBV03, was constructed based on pBV-ori, and exogenous genes in pBV03 could be efficiently expressed in B. subtilis.

CONCLUSIONS

The results of this study, including the genetic transformation system, plasmid-curing strategy, and exogenous gene expression, will support genetic manipulation of B. velezensis to promote its application in biocontrol and industry.

Engineering a ComA Quorum-Sensing circuit to dynamically control the production of Menaquinone-4 in Bacillus subtilis

Menaquinone-4 (MK-4) plays a significant role in bone health and cardiovascular therapy. Although many strategies have been adopted to increase the yield of MK-4 in Bacillus subtilis 168, the effectiveness of MK-4 is still low due to the inherent limitations of metabolic pathways. However, dynamic regulation based on quorum sensing (QS) has been extensively applied as a fundamental tool for fine-tuning gene expression in reaction to changes in cell density without adding expensive inducers. Nevertheless, in most reports, QS systems depend on down-regulated expression rather than up-regulated expression, which greatly limit their potential as molecular switches to control metabolic flux. To address this challenge, a modular PhrQ-RapQ-ComA QS system is developed based on promoter P_A11, which is up-regulated by phosphorylated ComA (ComA-P). In this paper, firstly we analyzed the ComA-based gene expression regulation system in Bacillus subtilis 168. We constructed a promoter library of diff ;erent abilities, selected best promoters from a library, and performed mutation screening on the selected promoters. Furthermore, we constructed a PhrQ-RapQ-ComA QS system to dynamically control the synthesis of MK-4 in B. subtilis 168. Cell growth and efficient synthesis of the target product can be dynamically balanced by the QS system. Our dynamic adjustment approach increased the yield of MK-4 in shake flask from 120.1 ± 0.6 to 178.9 ± 2.8 mg/L, and reached 217 ± 4.1 mg/L in a 3-L bioreactor, which verified the effectiveness of this strategy. In summary, PhrQ-RapQ-ComA QS system can realize dynamic pathway regulation in B. subtilis 168, which can be stretched to a great deal of microorganisms to fine-tune gene expression and enhance the production of metabolites.

Comparative Genomic and Functional Evaluations of Bacillus subtilis Newly Isolated from Korean Traditional Fermented Foods

Many fermented foods are known to have beneficial effects on human and animal health, offering anti-aging and immunomodulatory benefits to host. Microorganisms contained in the fermented foods are known to provide metabolic products possibly improving host health. However, despite of a number of studies on the functional effects of the fermented foods, isolation and identification of the effective bacterial strains in the products are still in progress. The objective of this study was to isolate candidate functional strains in various Korean traditional fermented foods, including ganjang, gochujang, doenjang, and jeotgal, and evaluate their beneficial effects on the host, using Caenorhabditis elegans as a surrogate animal model. Among the 30 strains isolated, five Bacillus spp. were selected that increased the expression level of pmk-1, an innate immune gene of C. elegans. These strains extended the nematode lifespan and showed intestinal adhesion to the host. Based on the bioinformatic analyses of whole genome sequences and pangenomes, the five strains of Bacillus subtilis were genetically different from the strains found in East Asian countries and previously reported strains isolated from Korean fermented foods. Our findings suggest that the newly isolated B. subtilis strains can be a good candidate for probiotic with further in-depth investigation on health benefits and safety.

Rap-Phr Systems from Plasmids pAW63 and pHT8-1 Act Together To Regulate Sporulation in the Bacillus thuringiensis Serovar kurstaki HD73 Strain

Bacillus thuringiensis is a Gram-positive spore-forming bacterium pathogenic to various insect species. This property is due to the Cry toxins encoded by plasmid genes and mostly produced during sporulation. B. thuringiensis contains a remarkable number of extrachromosomal DNA molecules and a great number of plasmid rap-phr genes. Rap-Phr quorum-sensing systems regulate different bacterial processes, notably the commitment to sporulation in Bacillus species. Rap proteins are quorum sensors acting as phosphatases on Spo0F, an intermediate of the sporulation phosphorelay, and are inhibited by Phr peptides that function as signaling molecules. In this study, we characterize the Rap63-Phr63 system encoded by the pAW63 plasmid from the B. thuringiensis serovar kurstaki HD73 strain. Rap63 has moderate activity on sporulation and is inhibited by the Phr63 peptide. The rap63-phr63 genes are cotranscribed, and the phr63 gene is also transcribed from a σ^H-specific promoter. We show that Rap63-Phr63 regulates sporulation together with the Rap8-Phr8 system harbored by plasmid pHT8_1 of the HD73 strain. Interestingly, the deletion of both phr63 and phr8 genes in the same strain has a greater negative effect on sporulation than the sum of the loss of each phr gene. Despite the similarities in the Phr8 and Phr63 sequences, there is no cross talk between the two systems. Our results suggest a synergism of these two Rap-Phr systems in the regulation of the sporulation of B. thuringiensis at the end of the infectious cycle in insects, thus pointing out the roles of the plasmids in the fitness of the bacterium.IMPORTANCE The life cycle of Bacillus thuringiensis in insect larvae is regulated by quorum-sensing systems of the RNPP family. After the toxemia caused by Cry insecticidal toxins, the sequential activation of these systems allows the bacterium to trigger first a state of virulence (regulated by PlcR-PapR) and then a necrotrophic lifestyle (regulated by NprR-NprX); ultimately, sporulation is controlled by the Rap-Phr systems. Our study describes a new rap-phr operon carried by a B. thuringiensis plasmid and shows that the Rap protein has a moderate effect on sporulation. However, this system, in combination with another plasmidic rap-phr operon, provides effective control of sporulation when the bacteria develop in the cadavers of infected insect larvae. Overall, this study highlights the important adaptive role of the plasmid Rap-Phr systems in the developmental fate of B. thuringiensis and its survival within its ecological niche.

Complete genome sequence data of a broad-spectrum antipathogen, Bacillus amyloliquefaciens KCTC 18343P, isolated from Makgeolli, Korean traditional rice wine

Bacillus amyloliquefaciens KCTC18343P(=MBE1283) isolated from Makgeolli, Korean traditional rice wine, strongly inhibits the growth of food and plant pathogens. A complete genome sequence of B. amyloliquefaciens KCTC18343P is presented in this report. The genome is 3,979,925 bp in size and harbors 3856 genes. The BioProject has been deposited at DDBJ/EMBL/GenBank. The GenBank accession numbers are PRJNA301202 for the BioProject, NZ_CP013727 for the chromosome, and NZ_CP013728 for the plasmid.

Characterization of a Regulator pgsR on Endogenous Plasmid p2Sip and Its Complementation for Poly(γ-glutamic acid) Accumulation in Bacillus amyloliquefaciens

Bacillus amyloliquefaciens NX-2S154 is a promising poly(γ-glutamic acid) (γ-PGA) producing strain discovered in previous studies. However, the wild-type strain contains an unknown endogenous plasmid, p2Sip, which causes low transformation efficiency and instability of exogenous plasmids. In our study, p2Sip is 5622 bp with 41% G+C content and contains four putative open reading frames (ORFs), including genes repB, hsp, and mobB and γ-PGA-synthesis regulator, pgsR. Elimination of p2Sip from strain NX-2S154 delayed γ-PGA secretion and decreased production of γ-PGA by 18.1%. Integration of a pgsR expression element into the genomic BamHI locus using marker-free manipulation based on pheS* increased the γ-PGA titer by 8%. pgsR overexpression upregulated the expression of γ-PGA synthase pgsB, regulator degQ, and glutamic acid synthase gltA, thus increasing the γ-PGA production in B. amyloliquefaciens NB. Our results indicated that pgsR from p2Sip plays an important regulatory role in γ-PGA synthesis in B. amyloliquefaciens.

A plasmid-born Rap-Phr system regulates surfactin production, sporulation and genetic competence in the heterologous host, Bacillus subtilis OKB105

According to the change of environment, soil-dwelling Bacillus species differentiate into distinct subpopulations, such as spores and competent cells. Rap-Phr systems have been found to be involved in this differentiation circuit by interacting with major regulatory proteins, such as Spo0A, ComA, and DegU. In this study, we report that the plasmid-born RapQ-PhrQ system found in Bacillus amyloliquefaciens B3 affects three regulatory pathways in the heterologous host Bacillus subtilis. Expression of rapQ in B. subtilis OKB105 strongly suppressed its sporulation efficiency, transformation efficiency, and surfactin production. Co-expression of phrQ or addition of synthesized PhrQ pentapeptide in vitro could compensate for the suppressive effects caused by rapQ. We also found that expression of rapQ decreased the transcriptional level of the sporulation-related gene spoIIE and surfactin synthesis-related gene srfA; meanwhile, the transcriptional levels of these genes could be rescued by co-expression of phrQ and in vitro addition of PhrQ pentapeptide. Electrophoretic mobility shift (EMSA) result also showed that RapQ could bind to ComA without interacting with ComA binding to DNA, and PhrQ pentapeptide antagonized RapQ activity in vitro. These results indicate that this new plasmid-born RapQ-PhrQ system controls sporulation, competent cell formation, and surfactin production in B. subtilis OKB105.

The Rhizobacterium Bacillus amyloliquefaciens subsp. plantarum NAU-B3 Contains a Large Inversion within the Central Portion of the Genome

The genome of rhizobacterium Bacillus amyloliquefaciens subsp. plantarum strain NAU-B3 is 4,196,170 bp in size and harbors 4,001 genes. Nine giant gene clusters are dedicated to the nonribosomal synthesis of antimicrobial lipopeptides and polyketides. Remarkably, NAU_B3 contains a large inversion within the central portion of the genome.

Identification of Bacillus strains for biological control of catfish pathogens

Bacillus strains isolated from soil or channel catfish intestine were screened for their antagonism against Edwardsiella ictaluri and Aeromonas hydrophila, the causative agents of enteric septicemia of catfish (ESC) and motile aeromonad septicaemia (MAS), respectively. Twenty one strains were selected and their antagonistic activity against other aquatic pathogens was also tested. Each of the top 21 strains expressed antagonistic activity against multiple aquatic bacterial pathogens including Edwardsiella tarda, Streptococcus iniae, Yersinia ruckeri, Flavobacterium columnare, and/or the oomycete Saprolegnia ferax. Survival of the 21 Bacillus strains in the intestine of catfish was determined as Bacillus CFU/g of intestinal tissue of catfish after feeding Bacillus spore-supplemented feed for seven days followed by normal feed for three days. Five Bacillus strains that showed good antimicrobial activity and intestinal survival were incorporated into feed in spore form at a dose of 8×10(7) CFU/g and fed to channel catfish for 14 days before they were challenged by E. ictaluri in replicate. Two Bacillus subtilis strains conferred significant benefit in reducing catfish mortality (P<0.05). A similar challenge experiment conducted in Vietnam with four of the five Bacillus strains also showed protective effects against E. ictaluri in striped catfish. Safety of the four strains exhibiting the strongest biological control in vivo was also investigated in terms of whether the strains contain plasmids or express resistance to clinically important antibiotics. The Bacillus strains identified from this study have good potential to mediate disease control as probiotic feed additives for catfish aquaculture.