pXO1 and pXO2 are large plasmids – large pieces of DNA that are not the chromosome that can replicate independently of the chromosome. What can a Bacillus anthracis cell with a pXO2 plasmid do that a cell without pXO2 can’t?

I need help answering this quwhstion as short as possible based of what is said in the paper
Transcribed Image Text:The Capsule and S-Layer: Two Independent and Yet Compatible Macromolecular Structures in Bacillus anthracis STÉPHANE MESNAGE,¹ EVELYNE TOSI-COUTURE,² PIERRE GOUNON,2 MICHÈLE MOCK,¹ AND AGNÈS FOUET¹* Toxines et Pathogénie Bactériennes (CNRS URA 1858)¹ and Station Centrale de Microscopie Electronique,2 Institut Pasteur, Paris, France Received 5 September 1997/Accepted 22 October 1997 Bacillus anthracis, the etiological agent of anthrax, is a gram-positive spore-forming bacterium. Fully virulent bacilli are toxinogenic and capsulated. Two abundant surface proteins, including the major antigen, are components of the B. anthracis surface layer (S-layer). The B. anthracis paracrystalline S-layer has previously only been found in noncapsulated vegetative cells. Here we report that the S-layer proteins are also synthesized under conditions where the poly-y-D-glutamic acid capsule is present. Structural and immunological analyses show that the capsule is exterior to and completely covers the S-layer proteins. Nevertheless, analysis of single and double S-layer protein mutants shows that the presence of these proteins is not required for normal capsulation of the bacilli. Similarly, the S-layer proteins assemble as a two-dimensional crystal, even in the presence of the capsule. Thus, both structures are compatible, and yet neither is required for the correct formation of the other. Bacillus anthracis, a gram-positive spore-forming bacterium, is the causative agent of anthrax. This disease, to which many animals, including humans, are susceptible, involves toxemia and septicemia. In the mammalian host, B. anthracis bacilli synthesize two toxins (lethal and edema toxins) (31) and a capsule (18) encoded by two large plasmids, pX01 and pXO2, respectively (12, 21). The capsule is composed of poly-y-D- glutamic acid and has antiphagocytic properties (13, 31, 37). Although unusual, a similar capsule is also found on Bacillus licheniformis bacilli (9). In the absence of pXO2 or the inducer bicarbonate, the cell does not produce a capsule and the cell wall appears layered. These layers are composed of fragments displaying a highly patterned ultrastructure (10, 16). This type of cell surface is now referred to as the surface layer (S-layer). S-layers are present on the surfaces of many archaea and bacteria (for reviews, see references 29 and 30). Most are formed by noncovalent, entropy-driven assembly of a single (glyco)protein protomer on the bacterial surface, giving rise to proteinaceous paracrystalline layers. Generally, a single S- layer is present, constituting 5 to 10% of total cell protein. Its synthesis is thus presumably energy consuming for the bacte- rium. Numerous bacteria have S-layers, suggesting that they play important roles in the interaction between the cell and its environment. Various functions have been proposed for S- layers, including shape maintenance and molecular sieving, and they can serve in phage fixation. The S-layer may be a virulence factor, protecting pathogenic bacteria against com- plement killing, facilitating binding of bacteria to host mole- cules, or enhancing their ability to associate with macrophages (for reviews, see references 27 and 29). Some bacteria, such as cyanobacteria or Azotobacter spp., possess both a capsule and an S-layer; however, to our knowl- edge, their structural relationships have not been analyzed through simultaneous genetic and cytologic studies. Both of these features have been independently described for the sur- * Corresponding author. Mailing address: Toxines et Pathogénie Bactériennes, Institut Pasteur, 28, rue du Dr Roux, 75724 Paris Cedex 15, France. Phone: 33 1 45 68 86 54. Fax: 33 1 45 68 89 54. E-mail: afouet@pasteur.fr. 52 face of the pathogenic bacterium B. anthracis. The components of the B. anthracis S-layer are two abundant surface proteins, EA1 and Sap (6, 20). Previous analyses of the B. anthracis S-layer used plasmid-cured strains; consequently, the interac- tion, if any, between the capsule and the S-layer could not be studied. Temporal or environmental regulation could be such that only one or the other structure is ever present at the cell surface. However, we show that S-layer proteins are synthe- sized under conditions where the bacilli are capsulated. We determined the localizations of capsule and S-layer compo- nents and analyzed whether the S-layer is necessary for proper capsulation. Finally, the assembly of the S-layer proteins in a two-dimensional crystal was examined in the presence of the capsule. MATERIALS AND METHODS Plasmids, bacterial strains, mating experiments, and culture conditions. The plasmids used to disrupt sap (encoding Sap), eag (encoding EA1), and both genes, i.e., PEAI207, pSAL322, and pSAL303, respectively, were described pre- viously (6, 20) and are listed in Table 1. The construction of B. anthracis CAF10, a pXO2 transductant of plasmidless strain 9131, and its regulation of capsule synthesis have already been reported (8). Escherichia coli JM83 harboring pRK24 was used for mating experiments (34, 35). Allelic exchange was carried out as previously described (26) with the spectinomycin resistance cassette as a selectable marker (24). sap, eag, and both genes were disrupted in CAF10 by heterogramic conjugation, giving CBA91, CSM91, and CSM11, respectively (Ta- ble 1). E. coli cells were grown in Luria broth or on L agar plates (22). Capsule synthesis was induced by growing B. anthracis cells in brain heart infusion me- dium (Difco Laboratories) in the presence of 0.6% sodium bicarbonate or on CAP plates (28) in a 5% CO₂ atmosphere for electron microscopy. Antibiotics were used at the following concentrations: kanamycin, 40 µg/ml for E. coli; erythromycin, 5 µg/ml for B. anthracis; and spectinomycin, 60 µg/ml for both E. coli and B. anthracis. Protein analysis. To test the in vivo expression of EA1 and Sap, the synthesis of antibodies was assayed. The rationale of this experiment is that antibodies are produced only if the antigen is synthesized in vivo. Seven Swiss mice were injected with 10° spores of strain CAF10 and sacrificed after 30 days. Their sera were pooled. The gel loading samples were obtained as follows. B. anthracis cells were harvested at an optical density at 600 nm of =2. Pellets were washed in 25 mM Tris-HCl (pH 8.0), sonicated until complete clarification, and resuspended in Laemmli buffer (19). Samples (3 µg of pellet protein and 20 µl of trichloro- acetic acid-precipitated supernatant protein) were loaded on sodium dodecyl sulfate-10% polyacrylamide gels. Separated proteins were transferred to nitro- cellulose sheets by use of the Bio-Rad Trans-Blot system. The sera were used at a 1/200 dilution. Western blots were developed with the ECL Western blotting analysis system (Amersham), with a 1/10,000 dilution of the second antibody.

Question

pXO1 and pXO2 are large plasmids – large pieces of DNA that are not the chromosome that can replicate independently of the chromosome. What can a Bacillus anthracis cell with a pXO2 plasmid do that a cell without pXO2 can’t?

I need help answering this quwhstion as short as possible based of what is said in the paper

The Capsule and S-Layer: Two Independent and Yet
Compatible Macromolecular Structures in Bacillus anthracis
STÉPHANE MESNAGE,¹ EVELYNE TOSI-COUTURE,² PIERRE GOUNON,2 MICHÈLE MOCK,¹
AND AGNÈS FOUET¹*
Toxines et Pathogénie Bactériennes (CNRS URA 1858)¹ and Station Centrale de Microscopie Electronique,2
Institut Pasteur, Paris, France
Received 5 September 1997/Accepted 22 October 1997
Bacillus anthracis, the etiological agent of anthrax, is a gram-positive spore-forming bacterium. Fully virulent
bacilli are toxinogenic and capsulated. Two abundant surface proteins, including the major antigen, are
components of the B. anthracis surface layer (S-layer). The B. anthracis paracrystalline S-layer has previously
only been found in noncapsulated vegetative cells. Here we report that the S-layer proteins are also synthesized
under conditions where the poly-y-D-glutamic acid capsule is present. Structural and immunological analyses
show that the capsule is exterior to and completely covers the S-layer proteins. Nevertheless, analysis of single
and double S-layer protein mutants shows that the presence of these proteins is not required for normal
capsulation of the bacilli. Similarly, the S-layer proteins assemble as a two-dimensional crystal, even in the
presence of the capsule. Thus, both structures are compatible, and yet neither is required for the correct
formation of the other.
Bacillus anthracis, a gram-positive spore-forming bacterium,
is the causative agent of anthrax. This disease, to which many
animals, including humans, are susceptible, involves toxemia
and septicemia. In the mammalian host, B. anthracis bacilli
synthesize two toxins (lethal and edema toxins) (31) and a
capsule (18) encoded by two large plasmids, pX01 and pXO2,
respectively (12, 21). The capsule is composed of poly-y-D-
glutamic acid and has antiphagocytic properties (13, 31, 37).
Although unusual, a similar capsule is also found on Bacillus
licheniformis bacilli (9). In the absence of pXO2 or the inducer
bicarbonate, the cell does not produce a capsule and the cell
wall appears layered. These layers are composed of fragments
displaying a highly patterned ultrastructure (10, 16). This type
of cell surface is now referred to as the surface layer (S-layer).
S-layers are present on the surfaces of many archaea and
bacteria (for reviews, see references 29 and 30). Most are
formed by noncovalent, entropy-driven assembly of a single
(glyco)protein protomer on the bacterial surface, giving rise to
proteinaceous paracrystalline layers. Generally, a single S-
layer is present, constituting 5 to 10% of total cell protein. Its
synthesis is thus presumably energy consuming for the bacte-
rium. Numerous bacteria have S-layers, suggesting that they
play important roles in the interaction between the cell and its
environment. Various functions have been proposed for S-
layers, including shape maintenance and molecular sieving,
and they can serve in phage fixation. The S-layer may be a
virulence factor, protecting pathogenic bacteria against com-
plement killing, facilitating binding of bacteria to host mole-
cules, or enhancing their ability to associate with macrophages
(for reviews, see references 27 and 29).
Some bacteria, such as cyanobacteria or Azotobacter spp.,
possess both a capsule and an S-layer; however, to our knowl-
edge, their structural relationships have not been analyzed
through simultaneous genetic and cytologic studies. Both of
these features have been independently described for the sur-
* Corresponding author. Mailing address: Toxines et Pathogénie
Bactériennes, Institut Pasteur, 28, rue du Dr Roux, 75724 Paris Cedex
15, France. Phone: 33 1 45 68 86 54. Fax: 33 1 45 68 89 54. E-mail:
afouet@pasteur.fr.
52
face of the pathogenic bacterium B. anthracis. The components
of the B. anthracis S-layer are two abundant surface proteins,
EA1 and Sap (6, 20). Previous analyses of the B. anthracis
S-layer used plasmid-cured strains; consequently, the interac-
tion, if any, between the capsule and the S-layer could not be
studied. Temporal or environmental regulation could be such
that only one or the other structure is ever present at the cell
surface. However, we show that S-layer proteins are synthe-
sized under conditions where the bacilli are capsulated. We
determined the localizations of capsule and S-layer compo-
nents and analyzed whether the S-layer is necessary for proper
capsulation. Finally, the assembly of the S-layer proteins in a
two-dimensional crystal was examined in the presence of the
capsule.
MATERIALS AND METHODS
Plasmids, bacterial strains, mating experiments, and culture conditions. The
plasmids used to disrupt sap (encoding Sap), eag (encoding EA1), and both
genes, i.e., PEAI207, pSAL322, and pSAL303, respectively, were described pre-
viously (6, 20) and are listed in Table 1. The construction of B. anthracis CAF10,
a pXO2 transductant of plasmidless strain 9131, and its regulation of capsule
synthesis have already been reported (8). Escherichia coli JM83 harboring
pRK24 was used for mating experiments (34, 35). Allelic exchange was carried
out as previously described (26) with the spectinomycin resistance cassette as a
selectable marker (24). sap, eag, and both genes were disrupted in CAF10 by
heterogramic conjugation, giving CBA91, CSM91, and CSM11, respectively (Ta-
ble 1). E. coli cells were grown in Luria broth or on L agar plates (22). Capsule
synthesis was induced by growing B. anthracis cells in brain heart infusion me-
dium (Difco Laboratories) in the presence of 0.6% sodium bicarbonate or on
CAP plates (28) in a 5% CO₂ atmosphere for electron microscopy. Antibiotics
were used at the following concentrations: kanamycin, 40 µg/ml for E. coli;
erythromycin, 5 µg/ml for B. anthracis; and spectinomycin, 60 µg/ml for both E.
coli and B. anthracis.
Protein analysis. To test the in vivo expression of EA1 and Sap, the synthesis
of antibodies was assayed. The rationale of this experiment is that antibodies are
produced only if the antigen is synthesized in vivo. Seven Swiss mice were
injected with 10° spores of strain CAF10 and sacrificed after 30 days. Their sera
were pooled. The gel loading samples were obtained as follows. B. anthracis cells
were harvested at an optical density at 600 nm of =2. Pellets were washed in 25
mM Tris-HCl (pH 8.0), sonicated until complete clarification, and resuspended
in Laemmli buffer (19). Samples (3 µg of pellet protein and 20 µl of trichloro-
acetic acid-precipitated supernatant protein) were loaded on sodium dodecyl
sulfate-10% polyacrylamide gels. Separated proteins were transferred to nitro-
cellulose sheets by use of the Bio-Rad Trans-Blot system. The sera were used at
a 1/200 dilution. Western blots were developed with the ECL Western blotting
analysis system (Amersham), with a 1/10,000 dilution of the second antibody.

Accepted Answer

Plasmids are the extra chromosomal material which are present independently of  the main…