is one of the most widely studied plant growth-promoting rhizobacteria. It is able to promote plant growth as well as control plant pathogens through diverse mechanisms, including the improvement of ...nutrient availability and alteration of phytohormone homeostasis as well as the production of antimicrobials and triggering induced systemic resistance, respectively. Even though its benefits for crop production have been recognized and studied extensively under laboratory conditions, the success of its application in fields varies immensely. It is widely accepted that agricultural application of
often fails because the bacteria are not able to persist in the rhizosphere. Bacterial colonization of plant roots is a crucial step in the interaction between microbe and plant and seems, therefore, to be of great importance for its growth promotion and biocontrol effects. A successful root colonization depends thereby on both bacterial traits, motility and biofilm formation, as well as on a signal interplay with the plant. This review addresses current knowledge about plant-microbial interactions of the
species, including the various mechanisms for supporting plant growth as well as the necessity for the establishment of the relationship.Formula: see text The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Endospore formation in
Bacillus subtilis
provides an ideal model system for studying development in bacteria. Sporulation studies have contributed a wealth of information about the mechanisms of ...cell-specific gene expression, chromosome dynamics, protein localization, and membrane remodeling, while helping to dispel the early view that bacteria lack internal organization and interesting cell biological phenomena. In this review, we focus on the architectural transformations that lead to a profound reorganization of the cellular landscape during sporulation, from two cells that lie side by side to the endospore, the unique cell within a cell structure that is a hallmark of sporulation in
B. subtilis
and other spore-forming
Firmicutes
. We discuss new insights into the mechanisms that drive morphogenesis, with special emphasis on polar septation, chromosome translocation, and the phagocytosis-like process of engulfment, and also the key experimental advances that have proven valuable in revealing the inner workings of bacterial cells.
Bacillus subtilis CU1 is a recently described probiotic strain with beneficial effects on immune health in elderly subjects. The following work describes a series of studies supporting the safety of ...the strain for use as an ingredient in food and supplement preparations. Using a combination of 16S rDNA and gyrB nucleotide analyses, the species was identified as a member of the Bacillus subtilis complex (B. subtilis subsp. spizizenii). Further characterization of the organism at the strain level was achieved using random amplified polymorphic DNA polymerase chain reaction (RAPD PCR) and pulsed field gel electrophoresis (PFGE) analyses. B. subtilis CU1 did not demonstrate antibiotic resistance greater than existing regulatory cutoffs against clinically important antibiotics, did not induce hemolysis or produce surfactant factors, and was absent of toxigenic activity in vitro. Use of B. subtilis CU1 as a probiotic has recently been evaluated in a 16-week randomized, double-blind, placebo-controlled, parallel-arm study, in which 2 × 109 spores per day of B. subtilis CU1 were administered for a total 40 days to healthy elderly subjects (4 consumption periods of 10 days separated by 18-day washouts). This work describes safety related endpoints not previously reported. B. subtilis CU1 was safe and well-tolerated in the clinical subjects without undesirable physiological effects on markers of liver and kidney function, complete blood counts, hemodynamic parameters, and vital signs.
•A safety assessment of the probiotic Bacillus subtilis CU1 was conducted.•Genomic analyses identified the species as a member of the B. subtilis complex.•Antibiotic resistance was not observed at levels exceeding regulatory cut-offs.•B. subtilis CU1 was absent of toxigenic activity in vitro.•B. subtilis CU1 was safely consumed (2 × 109 spores/day) by all clinical subjects.
Bacillus subtilis SR1 is a metal resistant, polyaromatic hydrocarbon-degrading bacterium isolated from petroleum contaminated sites. This study reports the characteristics of the genome of the ...isolate containing one circular chromosome (4,093,698 bp) annotated into 4155 genes and 4095 proteins. The genome analysis confirmed the presence of multiple catabolic genes: aromatic ring-hydroxylating dioxygenase (COG2146), aromatic ring hydroxylase (COG2368), catechol 2, 3 dioxygenase (COG2514), 4-hydroxybenzoate decarboxylase (COG0043), carboxymuconolactone decarboxylase (COG0599) responsible for the catabolism of aromatic hydrocarbons along with the genes for biosurfactant production and functional genes (czcD and cadA) for resistance to cadmium, zinc, and cobalt. Gas Chromatography-Mass spectroscopy analysis revealed up to 35% in-vitro degradation of benzo(a)pyrene after 21 days of growth along with the production of different intermediate metabolites. The pot trial analysis in the greenhouse condition validated the rhizodegradation of BaP, which was significantly higher in the presence of plant-microbe association (85%) than degradation in bulk soil (68%).
•Bacillus subtilis SR1 was a multifarious hydrocarbon degrading bacteria.•The genome analysis of B. subtilis SR1 revealed the genetic basis of its ability to hydrocarbon degradation.•The isolate could produce surfactin biosurfactant validated by the presence of operon for it.•The application of the bacteria in the rhizosphere of M. azedarach enhanced rhizodegradation of BaP.
Widespread utilization of polyethylene terephthalate (PET) has caused critical environmental pollution. The enzymatic degradation of PET is a promising solution to this problem. In this study, ...PETase, which exhibits much higher PET-hydrolytic activity than other enzymes, was successfully secreted into extracellular milieu from Bacillus subtilis 168 under the direction of its native signal peptide (named SPPETase). SPPETase is predicted to be a twin-arginine signal peptide. Intriguingly, inactivation of twin-arginine translocation (Tat) complexes improved the secretion amount by 3.8-fold, indicating that PETase was exported via Tat-independent pathway. To the best of our knowledge, this is the first report on the improvement of Tat-independent secretion by inactivating Tat components of B. subtilis 168 in LB medium. Furthermore, PET film degradation assay showed that the secreted PETase was fully active. This study paves the first step to construct an efficient engineered strain for PET degradation.
Rod-shaped bacteria elongate by the action of cell wall synthesis complexes linked to underlying dynamic MreB filaments. To understand how the movements of these filaments relate to cell wall ...synthesis, we characterized the dynamics of MreB and the cell wall elongation machinery using high-precision particle tracking in Bacillus subtilis. We found that MreB and the elongation machinery moved circumferentially around the cell, perpendicular to its length, with nearby synthesis complexes and MreB filaments moving independently in both directions. Inhibition of cell wall synthesis by various methods blocked the movement of MreB. Thus, bacteria elongate by the uncoordinated, circumferential movements of synthetic complexes that insert radial hoops of new peptidoglycan during their transit, possibly driving the motion of the underlying MreB filaments.
Bacteria of the genera Pseudomonas and Bacillus can promote plant growth and protect plants from pathogens. However, the interactions between these plant-beneficial bacteria are understudied. Here, ...we explore the interaction between Bacillus subtilis 3610 and Pseudomonas chlororaphis PCL1606. We show that the extracellular matrix protects B. subtilis colonies from infiltration by P. chlororaphis. The absence of extracellular matrix results in increased fluidity and loss of structure of the B. subtilis colony. The P. chlororaphis type VI secretion system (T6SS) is activated upon contact with B. subtilis cells, and stimulates B. subtilis sporulation. Furthermore, we find that B. subtilis sporulation observed prior to direct contact with P. chlororaphis is mediated by histidine kinases KinA and KinB. Finally, we demonstrate the importance of the extracellular matrix and the T6SS in modulating the coexistence of the two species on melon plant leaves and seeds.
The signaling nucleotide cyclic di-AMP (c-di-AMP) is the only known essential second messenger in bacteria. Recently, c-di-AMP has been identified as being essential for controlling potassium uptake ...in the model organism Bacillus subtilis and several other bacteria. A B. subtilis strain lacking c-di-AMP is not viable at high potassium concentrations, unless the bacteria acquire suppressor mutations. In this study, we isolated such suppressor mutants and found mutations that reduced the activities of the potassium transporters KtrCD and KimA. Although c-di-AMP–mediated control of KtrCD has previously been demonstrated, it is unknown how c-di-AMP affects KimA activity. Using the DRaCALA screening assay, we tested for any interactions of KimA and other potential target proteins in B. subtilis with c-di-AMP. This assay identified KimA, as well as the K+/H+ antiporter KhtT, the potassium exporter CpaA (YjbQ), the osmoprotectant transporter subunit OpuCA, the primary Mg2+ importer MgtE, and DarB (YkuL), a protein of unknown function, as bona fide c-di-AMP–binding proteins. Further, binding of c-di-AMP to KimA inhibited potassium uptake. Our results indicate that c-di-AMP controls KimA-mediated potassium transport at both kimA gene expression and KimA activity levels. Moreover, the discovery that potassium exporters are c-di-AMP targets indicates that this second messenger controls potassium homeostasis in B. subtilis at a global level by binding to riboswitches and to different classes of transport proteins involved in potassium uptake and export.
Biofilm formation is a complex process involving various signaling pathways and changes in gene expression. Many of the sensory mechanisms and regulatory cascades involved have been defined for ...biofilms formed by diverse organisms attached to solid surfaces. By comparison, our knowledge on the basic mechanisms underlying the formation of biofilms at air–liquid interfaces, that is, pellicles, is much less complete. In particular, the roles of flagella have been studied in multiple solid-surface biofilm models but remain largely undefined for pellicles. In this work, we characterize the contributions of flagellum-based motility, chemotaxis and oxygen sensing to pellicle formation in the Gram-positive Bacillus subtilis. We confirm that flagellum-based motility is involved in, but is not absolutely essential for, B. subtilis pellicle formation. Further, we show that flagellum-based motility, chemotaxis and oxygen sensing are important for successful competition during B. subtilis pellicle formation. We report that flagellum-based motility similarly contributes to pellicle formation and fitness in competition assays in the Gram-negative Pseudomonas aeruginosa. Time-lapse imaging of static liquid cultures demonstrates that, in both B. subtilis and P. aeruginosa, a turbulent flow forms in the tube and a zone of clearing appears below the air–liquid interface just before the formation of the pellicle but only in strains that have flagella.
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•Motility facilitates pellicle formation in B. subtilis and P. aeruginosa.•Non-motile mutants show a competitive disadvantage in pellicles.•Production of flagella is a costly process in B. subtilis.•Oxygen sensing contributes to pellicle formation in B. subtilis.
Bacteria can produce membranous nanotubes that mediate contact-dependent exchange of molecules among bacterial cells. However, it is unclear how nanotubes cross the cell wall to emerge from the donor ...or to penetrate into the recipient cell. Here, we report that Bacillus subtilis utilizes cell wall remodeling enzymes, the LytC amidase and its enhancer LytB, for efficient nanotube extrusion and penetration. Nanotube production is reduced in a lytBC mutant, and the few nanotubes formed appear deficient in penetrating into target cells. Donor-derived LytB molecules localize along nanotubes and on the surface of nanotube-connected neighbouring cells, primarily at sites of nanotube penetration. Furthermore, LytB from donor B. subtilis can activate LytC of recipient bacteria from diverse species, facilitating cell wall hydrolysis to establish nanotube connection. Our data provide a mechanistic view of how intercellular connecting devices can be formed among neighbouring bacteria.
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