- Email: [email protected]
Bacillus subtilis — The Representative of Gram-Positive Bacteria
CHAPTER
4
Bacillus subtilis — The Representative of Gram-Positive Bacteria
Phylum
Firmicutes
Class
Bacilli
Order
Bacillales
Family
Bacillaceae
Genus
Bacillus
Species
B. subtilis
Bacillus subtilis is one of the best-characterized bacterium among Gram-positives and is regarded as a model system for cell differentiation and development; B. subtilis cells produce spores under adverse conditions. In vegetative form, B. subtilis flagella are growing at apparently peritrichous positions, but in a more ordered way (see next page).
One of the distinctive differences in the flagellar structure of Gram-positive and Gramnegative species is the absence of the PL ring complex in the former.1 There appear to be no ring structures corresponding to the PL ring in intact flagella on the cell wall (left) of an osmotically-shocked cell (see Appendix) or in the isolated HBB (middle) in B. subtilis.2 Compare the structures of the hook-basal body between B. subtilis (arrow) and Salmonella in the same preparation (right). The fact that B. subtilis flagella rotate as smoothly as Salmonella flagella casts a doubt on the assumption that the PL ring works as the bushing for sustaining torque from the motor. It is more likely that the PL ring is necessary just for the hook to penetrate the outer membrane of Gram-negatives (see Introduction).
Bacillus subtilis — The Representative of Gram-Positive Bacteria
23
The genome of Bacillus subtilis subsp. subtilis str. 168 strain consists of a single 4.2-Mbp chromosome. The flagellar genes essential for assembling the basal structure form a compact cluster at 1,690 bp on the chromosome, while the late genes for HAPs and the filament are found at 3,632 bp.3 There are tentative gene names specific to B. subtilis: ylx, ylz, etc., which will be replaced by functional gene names in the future. The functional unit of the genes (flgAHIJ) required to form the PL ring complex is missing in accordance with EM observations (see Introduction: Functional units). Hag is the original name for flagellin or FliC and is used only for Firmicutes, Actinobacteria, and Cyanobacter species. The flagellar gene regulation of B. subtilis is a little different from that of S. typhimurium.4 The sigD gene encodes the flagellum specific sigma factor (corresponding to fliA). A pair of flhFG genes that place a flagellum at a pole in some species is used to place the basal bodies in a grid-like pattern symmetrically around the cell body,5 distinguishing them from the peritrichous position (see Topic: Flagellar position and shape). There are four mot genes: motA, motB, motS, and motP.6 MotA–MotB complex is the stator of the proton-driven motor, while MotP (a MotA homolog), together with MotS (a MotB homolog) forms the stator of the sodium-driven motor (see Topic: Mot proteins). Both stators may be used under different ion conditions, though this assumption awaits direct proof. The C rings (left), the rotors of the motor, are evident in this crude preparation. Strains were provided by George Ordal of the University of Illinois at Urbana– Champaign, USA.
4
Bacillus subtilis — The Representative of Gram-Positive Bacteria
Phylum
Firmicutes
Class
Bacilli
Order
Bacillales
Family
Bacillaceae
Genus
Bacillus
Species
B. subtilis
Bacillus subtilis is one of the best-characterized bacterium among Gram-positives and is regarded as a model system for cell differentiation and development; B. subtilis cells produce spores under adverse conditions. In vegetative form, B. subtilis flagella are growing at apparently peritrichous positions, but in a more ordered way (see next page).
One of the distinctive differences in the flagellar structure of Gram-positive and Gramnegative species is the absence of the PL ring complex in the former.1 There appear to be no ring structures corresponding to the PL ring in intact flagella on the cell wall (left) of an osmotically-shocked cell (see Appendix) or in the isolated HBB (middle) in B. subtilis.2 Compare the structures of the hook-basal body between B. subtilis (arrow) and Salmonella in the same preparation (right). The fact that B. subtilis flagella rotate as smoothly as Salmonella flagella casts a doubt on the assumption that the PL ring works as the bushing for sustaining torque from the motor. It is more likely that the PL ring is necessary just for the hook to penetrate the outer membrane of Gram-negatives (see Introduction).
Bacillus subtilis — The Representative of Gram-Positive Bacteria
23
The genome of Bacillus subtilis subsp. subtilis str. 168 strain consists of a single 4.2-Mbp chromosome. The flagellar genes essential for assembling the basal structure form a compact cluster at 1,690 bp on the chromosome, while the late genes for HAPs and the filament are found at 3,632 bp.3 There are tentative gene names specific to B. subtilis: ylx, ylz, etc., which will be replaced by functional gene names in the future. The functional unit of the genes (flgAHIJ) required to form the PL ring complex is missing in accordance with EM observations (see Introduction: Functional units). Hag is the original name for flagellin or FliC and is used only for Firmicutes, Actinobacteria, and Cyanobacter species. The flagellar gene regulation of B. subtilis is a little different from that of S. typhimurium.4 The sigD gene encodes the flagellum specific sigma factor (corresponding to fliA). A pair of flhFG genes that place a flagellum at a pole in some species is used to place the basal bodies in a grid-like pattern symmetrically around the cell body,5 distinguishing them from the peritrichous position (see Topic: Flagellar position and shape). There are four mot genes: motA, motB, motS, and motP.6 MotA–MotB complex is the stator of the proton-driven motor, while MotP (a MotA homolog), together with MotS (a MotB homolog) forms the stator of the sodium-driven motor (see Topic: Mot proteins). Both stators may be used under different ion conditions, though this assumption awaits direct proof. The C rings (left), the rotors of the motor, are evident in this crude preparation. Strains were provided by George Ordal of the University of Illinois at Urbana– Champaign, USA.