The nucleotide sequence of a spore germination gene (gerA) of Bacillus subtilis 168

Role of the gerA operon in L-alanine germination of Bacillus licheniformis spores

BACKGROUND

The genome of Bacillus licheniformis DSM 13 harbours three neighbouring open reading frames showing protein sequence similarities to the proteins encoded from the Bacillus subtilis subsp. subtilis 168 gerA operon, GerAA, GerAB and GerAC. In B. subtilis, these proteins are assumed to form a germinant receptor involved in spore germination induced by the amino acid L-alanine.

RESULTS

In this study we show that disruption of the gerAA gene in B. licheniformis MW3 hamper L-alanine and casein hydrolysate-triggered spore germination, measured by absorbance at 600 nm and confirmed by phase contrast microscopy. This ability was restored by complementation with a plasmid-borne copy of the gerA locus. Addition of D-alanine in the casein hydrolysate germination assay abolished germination of both B. licheniformis MW3 and the complementation mutant. Germination of both B. licheniformis MW3 and the gerA disruption mutant was induced by the non-nutrient germinant Ca2+-Dipicolinic acid.

CONCLUSIONS

These results demonstrate that the B. licheniformis MW3 gerA locus is involved in germination induced by L-alanine and potentially other components present in casein hydrolysate.

Complete sequence and organization of pBtoxis, the toxin-coding plasmid of Bacillus thuringiensis subsp. israelensis

The entire 127,923-bp sequence of the toxin-encoding plasmid pBtoxis from Bacillus thuringiensis subsp. israelensis is presented and analyzed. In addition to the four known Cry and two known Cyt toxins, a third Cyt-type sequence was found with an additional C-terminal domain previously unseen in such proteins. Many plasmid-encoded genes could be involved in several functions other than toxin production. The most striking of these are several genes potentially affecting host sporulation and germination and a set of genes for the production and export of a peptide antibiotic.

Identification and characterization of a germination operon on the virulence plasmid pXO1 of Bacillus anthracis

The spores of Bacillus anthracis, the agent of anthrax disease, germinate within professional phagocytes, such as murine macrophage-like RAW264.7 cells and alveolar macrophages. We identified a cluster of germination genes extending for 3608 nucleotides between the pag and atxA genes on the B. anthracis virulence plasmid pXO1. The three predicted proteins (40, 55 and 37 kDa in size) have significant sequence similarities to B. subtilis, B. cereus and B. megaterium germination proteins. Northern blot analysis of total RNA from sporulating cells indicated that the gerX locus was organized as a tricistronic operon (gerXB, gerXA and gerXC). Primer extension analysis identified a major potential transcriptional start site 31 bp upstream from the translation initiation codon of gerXB. Expression of the gerX operon was studied using a gerXB-lacZ transcriptional fusion. Expression began 2.5-3 h after the initiation of sporulation and was detected exclusively in the forespore compartment. A gerX null mutant was constructed. It was less virulent than the parental strain and did not germinate efficiently in vivo or in vitro within phagocytic cells. These data strongly suggest that gerX-encoded proteins are involved in the virulence of B. anthracis.

Germination of Bacillus anthracis spores within alveolar macrophages

The fatal character of the infection caused by inhalation of Bacillus anthracis spores results from a complex pathogenic cycle involving the synthesis of toxins by the bacterium. We have shown using immunofluorescent staining, confocal scanning laser microscopy and image cytometry analysis that the alveolar macrophage was the primary site of B. anthracis germination in a murine inhalation infection model. Bacillus anthracis germinated inside murine macrophage-like RAW264.7 cells and murine alveolar macrophages. Germination occurred in vesicles derived from the phagosomal compartment. We have also demonstrated that the toxin genes and their trans-activator, AtxA, were expressed within the macrophages after germination.

Immunological detection of the GerA spore germination proteins in the spore integuments of Bacillus subtilis using scanning electron microscopy

To clarify the molecular mechanisms that trigger spore germination of Bacillus subtilis, the location of GerA proteins (GerAA, GerAB and GerAC), which were reported to be putative gene products of a receptor for one of the germinants, L-alanine, was investigated by immunological techniques using anti-GerA peptide antibodies. Four antibodies were raised against the corresponding epitopes, two in GerAA, one in GerAB and the other in GerAC molecules. The binding of all four antibodies to the inner surface of the cortex-less spore coat fragments could be seen by scanning immunoelectron microscopy with colloidal gold particles. The result agreed with the fact, previously reported, that the colloidal gold particles were visualized just inside the spore coat layer by transmission immunoelectron microscopy using another anti-GerAB peptide antibody.

Cloning and sequencing of the spore germination gene of Bacillus megaterium ATCC 12872: similarities to the NaH-antiporter gene of Enterococcus hirae

The germination mutant TM-31 of Bacillus megaterium ATCC 12872, was isolated by transposon Tn917 insertional mutagenesis. Glucose, L-proline, L-leucine and KNO3 germinated TM-31 poorly. The DNA in the region of the Tn917 insertion was cloned, and its nucleotide sequence determined. One major open reading frame was present on the cloned DNA. The hydrophobic protein encoded is presumably membrane-associated. A homology search revealed that the gene encoded in the region of the Tn917 insertion is homologous to napA of Enterococcus hirae. napA codes for the NaH-antiporter. It is hypothesized that transport of cations must play an important role in spore germination in B. megaterium ATCC 12872.

The sigma factors of Bacillus subtilis

The specificity of DNA-dependent RNA polymerase for target promotes is largely due to the replaceable sigma subunit that it carries. Multiple sigma proteins, each conferring a unique promoter preference on RNA polymerase, are likely to be present in all bacteria; however, their abundance and diversity have been best characterized in Bacillus subtilis, the bacterium in which multiple sigma factors were first discovered. The 10 sigma factors thus far identified in B. subtilis directly contribute to the bacterium's ability to control gene expression. These proteins are not merely necessary for the expression of those operons whose promoters they recognize; in many instances, their appearance within the cell is sufficient to activate these operons. This review describes the discovery of each of the known B. subtilis sigma factors, their characteristics, the regulons they direct, and the complex restrictions placed on their synthesis and activities. These controls include the anticipated transcriptional regulation that modulates the expression of the sigma factor structural genes but, in the case of several of the B. subtilis sigma factors, go beyond this, adding novel posttranslational restraints on sigma factor activity. Two of the sigma factors (sigma E and sigma K) are, for example, synthesized as inactive precursor proteins. Their activities are kept in check by "pro-protein" sequences which are cleaved from the precursor molecules in response to intercellular cues. Other sigma factors (sigma B, sigma F, and sigma G) are inhibited by "anti-sigma factor" proteins that sequester them into complexes which block their ability to form RNA polymerase holoenzymes. The anti-sigma factors are, in turn, opposed by additional proteins which participate in the sigma factors' release. The devices used to control sigma factor activity in B, subtilis may prove to be as widespread as multiple sigma factors themselves, providing ways of coupling sigma factor activation to environmental or physiological signals that cannot be readily joined to other regulatory mechanisms.

Identification of germination gene of Bacillus megaterium

Glucose, KNO3, proline and leucine initiate the spore germination of B. megaterium ATCC 12872, but not of B. megaterium ATCC 19213. In order to isolate the gene concerning germination of B. megaterium ATCC 12872, we constructed its gene library in plasmid vector, and introduced into B. megaterium ATCC 19213. We obtained a transformant whose spores differed from those of the wild type strain with respect to germinability. Spores of this transformant could be germinated by glucose, proline or leucine. The recombinant plasmid prepared from this transformant was found to carry 2 kilobase pairs fragment of B. megaterium ATCC 12872 DNA. This fragment may contain the gene encoding the protein which plays an important role in germination.

The regulation of transcription of the gerA spore germination operon of Bacillus subtilis

The gerA operon of Bacillus subtilis 168 comprises three genes concerned with the triggering of spore germination by L-alanine and its analogues. The expression of this operon has been characterized using chromosomal lacZ fusions to the gerA promoter. The gerA promoter is switched on 2.5-3 hours after the initiation of sporulation, in parallel with glucose dehydrogenase. A high proportion of the gerA-driven beta-galactosidase detected in sporulating cells is found in the mature spore; the gerA promoter is therefore active in the forespore compartment of the sporulating cell. The gerA promoter is not expressed in spoO, spoII or spoIIIA, B, E and G mutant backgrounds, but is expressed in spoIIIC and D and in spoIV and V mutants. The in vivo transcriptional startpoint of the operon has been mapped by primer extension experiments; sequences upstream from this startpoint show significant homology with recognition sequences for RNA polymerase containing sigma G (E sigma G). The gerA operon was transcribed in vitro by E sigma G with a startpoint identical to that used in vivo, and expression of the gerA operon was rapidly induced in vegetative cells by induction of sigma G synthesis. These data indicate that the gerA operon is an additional member of the sigma G regulon, which includes a number of genes expressed in parallel only in the forespore compartment of sporulating B. subtilis cells.

Cloning and expression of a Bacillus subtilis division initiation gene for which a homolog has not been identified in another organism

The Bacillus subtilis 168 division initiation genes defined by the temperature-sensitive mutations ts-1 and ts-12 were cloned into a 10.5-kilobase EcoRI fragment of DNA in the lambda EMBL4 vector. The two genes were separated by approximately 3 kilobases. The gene in which the ts-1 mutation resides was shown to be the same as the B. subtilis homolog of the Escherichia coli ftsZ gene. The other gene was named divIB. It showed no homology to any previously identified gene and coded for a protein of 30.1 kilodaltons which was probably membrane bound.

Promoter specificity of sigma G-containing RNA polymerase from sporulating cells of Bacillus subtilis: identification of a group of forespore-specific promoters

During sporulation in Bacillus subtilis, expression of the genes sspA, sspB, sspC, sspD, and sspE, which encode a family of small, acid-soluble spore proteins, as well as of the spoVA and gdh operons is transcriptionally activated at stage III of sporulation only in the forespore compartment. Transcription of these genes is mediated by RNA polymerase containing sigma G (E sigma G), the product of the sigG gene, which is itself expressed at stage III in the developing forespore. We have determined the 5' ends of transcripts generated both in vivo and in vitro by the action of E sigma G on various genes of B. subtilis and other bacilli. The 5' ends of the in vivo and in vitro mRNAs were found to coincide and were therefore considered to define the transcription initiation sites for the genes examined. We identified highly homologous DNA sequences centered at 35 and 10 base pairs preceding the transcriptional start sites of the genes examined. Consequently, we propose that these sequences define a class of promoters recognized only by E sigma G which allow transcription of genes expressed uniquely at stage III in the developing forespore.

The regulation of the fumarase (citG) gene of Bacillus subtilis 168

The level of fumarase activity in Bacillus subtilis depends on the nutritional environment; in rich medium low vegetative levels increase towards the end of the exponential phase, whereas in minimal glucose medium levels are relatively high throughout growth. Analysis of the enzyme levels in spoO mutants has revealed that a functional spoOH gene is required for the efficient expression of fumarase in both media. This highlights a regulatory role for the spoOH gene product not only in control of postexponentially expressed genes, but also during vegetative growth in defined medium. S1 transcript mapping reveals three transcriptional startpoints for the fumarase structural gene (citG) in B. subtilis. The upstream promoter region P1, which appears to contain two transcriptional startpoints, is functional in both Escherichia coli and B. subtilis. Promoter P2, which is located closer to the structural gene, is only functional in B. subtilis. Transcription from this promoter is strictly dependent on a functional spoOH gene; this gene has recently been shown to encode a minor sigma factor.

The nucleotide sequence and gene organization of the gerA spore germination operon of Bacillus subtilis 168

The nucleotide sequence of the second and third genes in the Bacillus subtilis spore germination locus, gerA, has been determined and the amino acid (aa) sequence was derived. Two open reading frames (ORFs), corresponding to genes II and III, encode 364-aa residue and 373-aa residue polypeptides, respectively. The gene II product, Mr 41,257, would contain long stretches of hydrophobic aa residues and may be a membrane protein; the gene III product, Mr 42,363, is relatively hydrophilic but possesses an apparent signal peptide for transfer across, and perhaps localisation on, a membrane. The ORFs for genes I and II overlap by eleven codons and the termination codon of gene II overlaps the initiation codon of gene III. Insertional inactivation experiments using integrational plasmids have indicated that the gerA locus is a single transcriptional unit. The expression of the gerA genes has been studied using a lacZ transcriptional fusion; they constitute a developmentally regulated operon.