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Hyperosmotic response of streptococcus mutans: from microscopic physiology to transcriptomic profile.

Liu C, Niu Y, Zhou X, Zhang K, Cheng L, Li M, Li Y, Wang R, Yang Y, Xu X - BMC Microbiol. (2013)

Bottom Line: We found that the hyperosmotic condition was able to initiate S. mutans biofilm dispersal by reducing both microbial content and extracellular polysaccharides matrix.Further analysis of microarray data showed significant up-regulation of genes and pathways involved in carbohydrate metabolism.Hyperosmotic condition induces significant stress response on S. mutans at both phenotypic and transcriptomic levels.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, PR China. nixux1982@hotmail.com.

ABSTRACT

Background: Oral streptococci metabolize carbohydrate to produce organic acids, which not only decrease the environmental pH, but also increase osmolality of dental plaque fluid due to tooth demineralization and consequent calcium and phosphate accumulation. Despite these unfavorable environmental changes, the bacteria continue to thrive. The aim of this study was to obtain a global view on strategies taken by Streptococcus mutans to deal with physiologically relevant elevated osmolality, and perseveres within a cariogenic dental plaque.

Results: We investigated phenotypic change of S. mutans biofilm upon hyperosmotic challenge. We found that the hyperosmotic condition was able to initiate S. mutans biofilm dispersal by reducing both microbial content and extracellular polysaccharides matrix. We then used whole-genome microarray with quantitative RT-PCR validation to systemically investigate the underlying molecular machineries of this bacterium in response to the hyperosmotic stimuli. Among those identified 40 deferentially regulated genes, down-regulation of gtfB and comC were believed to be responsible for the observed biofilm dispersal. Further analysis of microarray data showed significant up-regulation of genes and pathways involved in carbohydrate metabolism. Specific genes involved in heat shock response and acid tolerance were also upregulated, indicating potential cross-talk between hyperosmotic and other environmental stress.

Conclusions: Hyperosmotic condition induces significant stress response on S. mutans at both phenotypic and transcriptomic levels. In the meantime, it may take full advantage of these environmental stimuli to better fit the fluctuating environments within oral cavity, and thus emerges as numeric-predominant bacterium under cariogenic conditions.

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KEGG pathway analyses for differentially expressed genes. (A) Significant up- and down-regulated pathways upon hyperosmotic challenge. P-value < 0.05 and FDR < 0.25 were used as a threshold. Log2P is the logarithm of P-value. (B) Gene set enrichment analysis (GSEA) of representative up-regulated KEGG pathways under short-term hyperosmotic stress. The four scoring plots represent galactose metabolism (upper left), fructose and mannose metabolism (upper right), phosphotransferase system (lower left) and pyruvate metabolism (lower right) with FDR of 0.010, 0.054, 0.110, and 0.184 respectively. The upper left section of each plot shows the progression of the running enrichment score and the maximum peak therein. The middle left section shows the genes in the pathways as “hits” against the ranked list of genes. The bottom left section shows the histogram for the ranked list of all genes in the expression data set. The right section of each plot shows the expression intensity of genes mapped into each pathway: red (high expression value), blue (low expression value).
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Figure 4: KEGG pathway analyses for differentially expressed genes. (A) Significant up- and down-regulated pathways upon hyperosmotic challenge. P-value < 0.05 and FDR < 0.25 were used as a threshold. Log2P is the logarithm of P-value. (B) Gene set enrichment analysis (GSEA) of representative up-regulated KEGG pathways under short-term hyperosmotic stress. The four scoring plots represent galactose metabolism (upper left), fructose and mannose metabolism (upper right), phosphotransferase system (lower left) and pyruvate metabolism (lower right) with FDR of 0.010, 0.054, 0.110, and 0.184 respectively. The upper left section of each plot shows the progression of the running enrichment score and the maximum peak therein. The middle left section shows the genes in the pathways as “hits” against the ranked list of genes. The bottom left section shows the histogram for the ranked list of all genes in the expression data set. The right section of each plot shows the expression intensity of genes mapped into each pathway: red (high expression value), blue (low expression value).

Mentions: Most bacteria do not possess active water transport mechanisms to maintain cell turgor, which is essential for survival [20]. Instead, bacteria usually pool “compatible solutes” to deal with hyperosmotic conditions. Although some compatible solutes, such as glycine betaine and carnitine, can be synthesized and accumulated intracellularly during osmotic stress, bacteria also adopt efficient transport systems to internalize necessary compounds to counter hyperosmotic stress [6]. Burne’s previous study has suggested that S. mutans may take up compatible solutes from the environment by up-regulating the ABC transporter homologous genes (opcA and opuAA) upon short-term exposure to hyperosmotic challenge [10]. Although no significant up-regulation of compatible solutes internalization related genes was detected by our high throughput transcriptomic profiling at a differentiation power of ≥ 2 fold changes, genes involved in the phosphotransferase system (PTS) and carbohydrate metabolism were significantly up-regulated upon short-term hyperosmotic challenge (Table 1). We further categorized the majority of those differentially expressed genes into 12 KEGG pathways. We found that pathways involved in carbohydrates consumption, including PTS, galactose metabolism, fructose/mannose metabolism, and pyruvate metabolism were significantly up-regulated (Figure 4). Based on these findings, we propose that in order to counter the detrimental effects of short-term hyperosmotic challenge, S. mutans needs to actively internalize compatible solutes to recover from hyperosmotic stress. In the meantime, the bacterial cells have to up-regulate genes involved in carbohydrates transportation and metabolism, so as to couple the increased demand for ATP consumption. Interestingly, most of these aforementioned carbohydrates metabolism related genes and pathways are also up-regulated during oxygen challenge [13], further suggesting that S. mutans has developed sophisticated energy mobilization strategy to counter environmental adversity.


Hyperosmotic response of streptococcus mutans: from microscopic physiology to transcriptomic profile.

Liu C, Niu Y, Zhou X, Zhang K, Cheng L, Li M, Li Y, Wang R, Yang Y, Xu X - BMC Microbiol. (2013)

KEGG pathway analyses for differentially expressed genes. (A) Significant up- and down-regulated pathways upon hyperosmotic challenge. P-value < 0.05 and FDR < 0.25 were used as a threshold. Log2P is the logarithm of P-value. (B) Gene set enrichment analysis (GSEA) of representative up-regulated KEGG pathways under short-term hyperosmotic stress. The four scoring plots represent galactose metabolism (upper left), fructose and mannose metabolism (upper right), phosphotransferase system (lower left) and pyruvate metabolism (lower right) with FDR of 0.010, 0.054, 0.110, and 0.184 respectively. The upper left section of each plot shows the progression of the running enrichment score and the maximum peak therein. The middle left section shows the genes in the pathways as “hits” against the ranked list of genes. The bottom left section shows the histogram for the ranked list of all genes in the expression data set. The right section of each plot shows the expression intensity of genes mapped into each pathway: red (high expression value), blue (low expression value).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4219374&req=5

Figure 4: KEGG pathway analyses for differentially expressed genes. (A) Significant up- and down-regulated pathways upon hyperosmotic challenge. P-value < 0.05 and FDR < 0.25 were used as a threshold. Log2P is the logarithm of P-value. (B) Gene set enrichment analysis (GSEA) of representative up-regulated KEGG pathways under short-term hyperosmotic stress. The four scoring plots represent galactose metabolism (upper left), fructose and mannose metabolism (upper right), phosphotransferase system (lower left) and pyruvate metabolism (lower right) with FDR of 0.010, 0.054, 0.110, and 0.184 respectively. The upper left section of each plot shows the progression of the running enrichment score and the maximum peak therein. The middle left section shows the genes in the pathways as “hits” against the ranked list of genes. The bottom left section shows the histogram for the ranked list of all genes in the expression data set. The right section of each plot shows the expression intensity of genes mapped into each pathway: red (high expression value), blue (low expression value).
Mentions: Most bacteria do not possess active water transport mechanisms to maintain cell turgor, which is essential for survival [20]. Instead, bacteria usually pool “compatible solutes” to deal with hyperosmotic conditions. Although some compatible solutes, such as glycine betaine and carnitine, can be synthesized and accumulated intracellularly during osmotic stress, bacteria also adopt efficient transport systems to internalize necessary compounds to counter hyperosmotic stress [6]. Burne’s previous study has suggested that S. mutans may take up compatible solutes from the environment by up-regulating the ABC transporter homologous genes (opcA and opuAA) upon short-term exposure to hyperosmotic challenge [10]. Although no significant up-regulation of compatible solutes internalization related genes was detected by our high throughput transcriptomic profiling at a differentiation power of ≥ 2 fold changes, genes involved in the phosphotransferase system (PTS) and carbohydrate metabolism were significantly up-regulated upon short-term hyperosmotic challenge (Table 1). We further categorized the majority of those differentially expressed genes into 12 KEGG pathways. We found that pathways involved in carbohydrates consumption, including PTS, galactose metabolism, fructose/mannose metabolism, and pyruvate metabolism were significantly up-regulated (Figure 4). Based on these findings, we propose that in order to counter the detrimental effects of short-term hyperosmotic challenge, S. mutans needs to actively internalize compatible solutes to recover from hyperosmotic stress. In the meantime, the bacterial cells have to up-regulate genes involved in carbohydrates transportation and metabolism, so as to couple the increased demand for ATP consumption. Interestingly, most of these aforementioned carbohydrates metabolism related genes and pathways are also up-regulated during oxygen challenge [13], further suggesting that S. mutans has developed sophisticated energy mobilization strategy to counter environmental adversity.

Bottom Line: We found that the hyperosmotic condition was able to initiate S. mutans biofilm dispersal by reducing both microbial content and extracellular polysaccharides matrix.Further analysis of microarray data showed significant up-regulation of genes and pathways involved in carbohydrate metabolism.Hyperosmotic condition induces significant stress response on S. mutans at both phenotypic and transcriptomic levels.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, PR China. nixux1982@hotmail.com.

ABSTRACT

Background: Oral streptococci metabolize carbohydrate to produce organic acids, which not only decrease the environmental pH, but also increase osmolality of dental plaque fluid due to tooth demineralization and consequent calcium and phosphate accumulation. Despite these unfavorable environmental changes, the bacteria continue to thrive. The aim of this study was to obtain a global view on strategies taken by Streptococcus mutans to deal with physiologically relevant elevated osmolality, and perseveres within a cariogenic dental plaque.

Results: We investigated phenotypic change of S. mutans biofilm upon hyperosmotic challenge. We found that the hyperosmotic condition was able to initiate S. mutans biofilm dispersal by reducing both microbial content and extracellular polysaccharides matrix. We then used whole-genome microarray with quantitative RT-PCR validation to systemically investigate the underlying molecular machineries of this bacterium in response to the hyperosmotic stimuli. Among those identified 40 deferentially regulated genes, down-regulation of gtfB and comC were believed to be responsible for the observed biofilm dispersal. Further analysis of microarray data showed significant up-regulation of genes and pathways involved in carbohydrate metabolism. Specific genes involved in heat shock response and acid tolerance were also upregulated, indicating potential cross-talk between hyperosmotic and other environmental stress.

Conclusions: Hyperosmotic condition induces significant stress response on S. mutans at both phenotypic and transcriptomic levels. In the meantime, it may take full advantage of these environmental stimuli to better fit the fluctuating environments within oral cavity, and thus emerges as numeric-predominant bacterium under cariogenic conditions.

Show MeSH
Related in: MedlinePlus