Identification and analysis of Rap-Phr system in Bacillus cereus 0-9

Engineering a PhrC-RapC-SinR quorum sensing molecular switch for dynamic fine-tuning of menaquinone-7 synthesis in Bacillus subtilis

BACKGROUND

Menaquinone-7 (MK-7) is a valuable vitamin K2 produced by Bacillus subtilis. Although many strategies have been adopted to increase the yield of MK-7 in B. subtilis, the effectiveness of these common approaches is not high because long metabolic synthesis pathways and numerous bypass pathways competing for precursors with MK-7 synthesis. Regarding the modification of bypass pathways, studies of common static metabolic engineering method such as knocking out genes involved in side pathway have been reported previously. Since byproductsphenylalanine(Phe), tyrosine (Tyr), tryptophan (Trp), folic acid, dihydroxybenzoate, hydroxybutanone in the MK-7 synthesis pathway are indispensable for cell growth, the complete knockout of the bypass pathway restricts cell growth, resulting in limited increase in MK-7 synthesis. Dynamic regulation via quorum sensing (QS) provides a cost-effective strategy to harmonize cell growth and product synthesis, eliminating the need for pricey inducers. SinR, a transcriptional repressor, is crucial in suppressing biofilm formation, a process closely intertwined with MK-7 biosynthesis. Given this link, we targeted SinR to construct a dynamic regulatory system, aiming to modulate MK-7 production by leveraging SinR's regulatory influence.

RESULTS

A modular PhrC-RapC-SinR QS system is developed to dynamic regulate side pathway of MK-7. In this study, first, we analyzed the SinR-based gene expression regulation system in B. subtilis 168 (BS168). We constructed a promoter library of different abilities, selected suitable promoters from the library, and performed mutation screening on the selected promoters. Furthermore, we constructed a PhrC-RapC-SinR QS system to dynamically control the synthesis of Phe, Tyr, Trp, folic acid, dihydroxybenzoate, hydroxybutanone in MK-7 synthesis in BS168. Cell growth and efficient synthesis of the MK-7 production can be dynamically balanced by this QS system. Using this system to balance cell growth and product fermentation, the MK-7 yield was ultimately increased by 6.27-fold, from 13.95 mg/L to 87.52 mg/L.

CONCLUSION

In summary, the PhrC-RapC-SinR QS system has been successfully integrated with biocatalytic functions to achieve dynamic metabolic pathway control in BS168, which has potential applicability to a large number of microorganisms to fine-tune gene expression and enhance the production of metabolites.

A LysR-like Transcriptional Regulator DsfB Is Required for the Daughter Cell Separation in Bacillus cereus 0-9

Bacillus cereus 0-9 is a biocontrol strain isolated from a healthy wheat root, and studying cell separation after division in this strain will improve our understanding of its growth, environmental adaptation, and spread. In this work, we identified the deletion of dsfB resulted in a chaining phenotype. Four genes, lysM1, lysM2, lysM3, and lysM4, were associated with daughter cell separation in strain 0-9. Furthermore, DsfB bound to the promoter regions of lysM1 and lysM2 and induced their transcription. The peptidoglycan hydrolase activity of the lysM1 and lysM2 gene products was confirmed in vitro by site-directed mutagenesis and biochemical analyses. The addition of purified LysM1 or LysM2 proteins in vitro or the overexpression of their coding genes inhibited the chaining phenotype of ΔdsfB. Taken together, our data indicate that DsfB is involved in daughter cell separation via the positive regulation of lysM1 and lysM2 expression in B. cereus 0-9.

Cooperation of quorum sensing and central carbon metabolism in the pathogenesis of Gram-positive bacteria

Quorum sensing (QS), an integral component of bacterial communication, is essential in coordinating the collective response of diverse bacterial pathogens. Central carbon metabolism (CCM), serving as the primary metabolic hub for substances such as sugars, lipids, and amino acids, plays a crucial role in the life cycle of bacteria. Pathogenic bacteria often utilize CCM to regulate population metabolism and enhance the synthesis of specific cellular structures, thereby facilitating in adaptation to the host microecological environment and expediting infection. Research has demonstrated that QS can both directly or indirectly affect the CCM of numerous pathogenic bacteria, thus altering their virulence and pathogenicity. This article reviews the interplay between QS and CCM in Gram-positive pathogenic bacteria, details the molecular mechanisms by which QS modulates CCM, and lays the groundwork for investigating bacterial pathogenicity and developing innovative infection treatment drugs.