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Comparative transcriptional profiling of Bacillus cereus sensu lato strains during growth in CO2-bicarbonate and aerobic atmospheres.

Passalacqua KD, Varadarajan A, Byrd B, Bergman NH - PLoS ONE (2009)

Bottom Line: Although much of this phenotypic range can be attributed to the presence or absence of a few key virulence factors, there are other virulence-associated loci that are conserved throughout the B. cereus group, and we hypothesized that these genes may be regulated differently in pathogenic and non-pathogenic strains.We have shown that homologous and even identical genes within the genomes of three closely related members of the B. cereus sensu lato group are in some instances regulated very differently, and that these differences can have important implications for virulence.This study provides insights into the evolution of the B. cereus group, and highlights the importance of looking beyond differences in gene content in comparative genomics studies.

View Article: PubMed Central - PubMed

Affiliation: School of Biology, Georgia Institute of Technology, Atlanta, Georgia, United States of America.

ABSTRACT

Background: Bacillus species are spore-forming bacteria that are ubiquitous in the environment and display a range of virulent and avirulent phenotypes. This range is particularly evident in the Bacillus cereus sensu lato group; where closely related strains cause anthrax, food-borne illnesses, and pneumonia, but can also be non-pathogenic. Although much of this phenotypic range can be attributed to the presence or absence of a few key virulence factors, there are other virulence-associated loci that are conserved throughout the B. cereus group, and we hypothesized that these genes may be regulated differently in pathogenic and non-pathogenic strains.

Methodology/principal findings: Here we report transcriptional profiles of three closely related but phenotypically unique members of the Bacillus cereus group--a pneumonia-causing B. cereus strain (G9241), an attenuated strain of B. anthracis (Sterne 34F(2)), and an avirulent B. cereus strain (10987)--during exponential growth in two distinct atmospheric environments: 14% CO(2)/bicarbonate and ambient air. We show that the disease-causing Bacillus strains undergo more distinctive transcriptional changes between the two environments, and that the expression of plasmid-encoded virulence genes was increased exclusively in the CO(2) environment. We observed a core of conserved metabolic genes that were differentially expressed in all three strains in both conditions. Additionally, the expression profiles of putative virulence genes in G9241 suggest that this strain, unlike Bacillus anthracis, may regulate gene expression with both PlcR and AtxA transcriptional regulators, each acting in a different environment.

Conclusions/significance: We have shown that homologous and even identical genes within the genomes of three closely related members of the B. cereus sensu lato group are in some instances regulated very differently, and that these differences can have important implications for virulence. This study provides insights into the evolution of the B. cereus group, and highlights the importance of looking beyond differences in gene content in comparative genomics studies.

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Spearman correlations comparing microarray and SYBR-Green qRT-PCR gene expression results for select genes in two conditions - CO2 and O2.(A) B. cereus G9241; expression for 12 genes in 2 conditions (5 chromosomal, 4 from pBC218, and 3 from pBCXO1); Spearman r = −0.7797; p<0.0001; and (B) B. anthracis Sterne 34F2; 8 genes in two conditions (5 chromosomal, 3 from pXO1); Spearman r = −0.7735; p = 0.0004. Genes and primer sequences listed in Tables S11 and S12.
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pone-0004904-g004: Spearman correlations comparing microarray and SYBR-Green qRT-PCR gene expression results for select genes in two conditions - CO2 and O2.(A) B. cereus G9241; expression for 12 genes in 2 conditions (5 chromosomal, 4 from pBC218, and 3 from pBCXO1); Spearman r = −0.7797; p<0.0001; and (B) B. anthracis Sterne 34F2; 8 genes in two conditions (5 chromosomal, 3 from pXO1); Spearman r = −0.7735; p = 0.0004. Genes and primer sequences listed in Tables S11 and S12.

Mentions: Because our array data showed that the two pathogens, B. anthracis and G9241, exhibited such pronounced differential expression patterns between the two conditions (often >9–200 fold difference), we performed qRT-PCR on a select set of genes for these two strains to verify that the trends we had observed were reproducible by a complementary approach. The genes assayed were from both chromosomal and plasmid loci, and represent both up- and down-regulated genes between the two growth conditions (see Tables S11 and S12 for gene names and primer sequences). These results are shown in Figure 4, and clearly display good correlation between the two assays (Pearson r = −0.7735 for B. anthracis and −0.7757 for G9241, p<0.0004 for both).


Comparative transcriptional profiling of Bacillus cereus sensu lato strains during growth in CO2-bicarbonate and aerobic atmospheres.

Passalacqua KD, Varadarajan A, Byrd B, Bergman NH - PLoS ONE (2009)

Spearman correlations comparing microarray and SYBR-Green qRT-PCR gene expression results for select genes in two conditions - CO2 and O2.(A) B. cereus G9241; expression for 12 genes in 2 conditions (5 chromosomal, 4 from pBC218, and 3 from pBCXO1); Spearman r = −0.7797; p<0.0001; and (B) B. anthracis Sterne 34F2; 8 genes in two conditions (5 chromosomal, 3 from pXO1); Spearman r = −0.7735; p = 0.0004. Genes and primer sequences listed in Tables S11 and S12.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2654142&req=5

pone-0004904-g004: Spearman correlations comparing microarray and SYBR-Green qRT-PCR gene expression results for select genes in two conditions - CO2 and O2.(A) B. cereus G9241; expression for 12 genes in 2 conditions (5 chromosomal, 4 from pBC218, and 3 from pBCXO1); Spearman r = −0.7797; p<0.0001; and (B) B. anthracis Sterne 34F2; 8 genes in two conditions (5 chromosomal, 3 from pXO1); Spearman r = −0.7735; p = 0.0004. Genes and primer sequences listed in Tables S11 and S12.
Mentions: Because our array data showed that the two pathogens, B. anthracis and G9241, exhibited such pronounced differential expression patterns between the two conditions (often >9–200 fold difference), we performed qRT-PCR on a select set of genes for these two strains to verify that the trends we had observed were reproducible by a complementary approach. The genes assayed were from both chromosomal and plasmid loci, and represent both up- and down-regulated genes between the two growth conditions (see Tables S11 and S12 for gene names and primer sequences). These results are shown in Figure 4, and clearly display good correlation between the two assays (Pearson r = −0.7735 for B. anthracis and −0.7757 for G9241, p<0.0004 for both).

Bottom Line: Although much of this phenotypic range can be attributed to the presence or absence of a few key virulence factors, there are other virulence-associated loci that are conserved throughout the B. cereus group, and we hypothesized that these genes may be regulated differently in pathogenic and non-pathogenic strains.We have shown that homologous and even identical genes within the genomes of three closely related members of the B. cereus sensu lato group are in some instances regulated very differently, and that these differences can have important implications for virulence.This study provides insights into the evolution of the B. cereus group, and highlights the importance of looking beyond differences in gene content in comparative genomics studies.

View Article: PubMed Central - PubMed

Affiliation: School of Biology, Georgia Institute of Technology, Atlanta, Georgia, United States of America.

ABSTRACT

Background: Bacillus species are spore-forming bacteria that are ubiquitous in the environment and display a range of virulent and avirulent phenotypes. This range is particularly evident in the Bacillus cereus sensu lato group; where closely related strains cause anthrax, food-borne illnesses, and pneumonia, but can also be non-pathogenic. Although much of this phenotypic range can be attributed to the presence or absence of a few key virulence factors, there are other virulence-associated loci that are conserved throughout the B. cereus group, and we hypothesized that these genes may be regulated differently in pathogenic and non-pathogenic strains.

Methodology/principal findings: Here we report transcriptional profiles of three closely related but phenotypically unique members of the Bacillus cereus group--a pneumonia-causing B. cereus strain (G9241), an attenuated strain of B. anthracis (Sterne 34F(2)), and an avirulent B. cereus strain (10987)--during exponential growth in two distinct atmospheric environments: 14% CO(2)/bicarbonate and ambient air. We show that the disease-causing Bacillus strains undergo more distinctive transcriptional changes between the two environments, and that the expression of plasmid-encoded virulence genes was increased exclusively in the CO(2) environment. We observed a core of conserved metabolic genes that were differentially expressed in all three strains in both conditions. Additionally, the expression profiles of putative virulence genes in G9241 suggest that this strain, unlike Bacillus anthracis, may regulate gene expression with both PlcR and AtxA transcriptional regulators, each acting in a different environment.

Conclusions/significance: We have shown that homologous and even identical genes within the genomes of three closely related members of the B. cereus sensu lato group are in some instances regulated very differently, and that these differences can have important implications for virulence. This study provides insights into the evolution of the B. cereus group, and highlights the importance of looking beyond differences in gene content in comparative genomics studies.

Show MeSH
Related in: MedlinePlus