Abstract
BackgroundTo act as a commensal bacterium and a pathogen in humans and animals, Streptococcus agalactiae (group B streptococcus, GBS) must be able to monitor and adapt to different environmental conditions. Temperature variation is a one of the most commonly encountered variables.Methodology/Principal FindingsTo understand the extent to which GBS modify gene expression in response to temperatures encountered in the various hosts, we conducted a whole genome transcriptome analysis of organisms grown at 30°C and 40°C. We identified extensive transcriptome remodeling at various stages of growth, especially in the stationary phase (significant transcript changes occurred for 25% of the genes). A large proportion of genes involved in metabolism was up-regulated at 30°C in stationary phase. Conversely, genes up-regulated at 40°C relative to 30°C include those encoding virulence factors such as hemolysins and extracellular secreted proteins with LPXTG motifs. Over-expression of hemolysins was linked to larger zones of hemolysis and enhanced hemolytic activity at 40°C. A key theme identified by our study was that genes involved in purine metabolism and iron acquisition were significantly up-regulated at 40°C.Conclusion/SignificanceGrowth of GBS in vitro at different temperatures resulted in extensive remodeling of the transcriptome, including genes encoding proven and putative virulence genes. The data provide extensive new leads for molecular pathogenesis research.
Highlights
Streptococcus agalactiae, known as group B streptococcus (GBS), is a common inhabitant of the human gut and asymptomatically colonizes the vagina of one-third of women [1]
GBS has no known environmental reservoir, given its widespread host, anatomic, and disease range, it is clear that the bacterium must adapt to many environmental conditions to survive and thrive
We showed that contains genes encoding the hemolysin molecule (cylE) but all of the cyl operon is up-regulated at 40uC, which is consistent with the fact that most if not all of the genes of the operon are necessary for a complete hemolytic phenotype [23,27]
Summary
Streptococcus agalactiae, known as group B streptococcus (GBS), is a common inhabitant of the human gut and asymptomatically colonizes the vagina of one-third of women [1]. Temperature variation is one of the most commonly encountered environmental changes, and it has been reported that bacteria can modify expression of at least 10% of their genes in response to an increase or decrease in growth temperature [8,9,10]. Dynamic changes in expression of genes implicated in metabolism, general adaptive responses, membrane structure, and virulence have been reported [8,9,10]. To act as a commensal bacterium and a pathogen in humans and animals, Streptococcus agalactiae (group B streptococcus, GBS) must be able to monitor and adapt to different environmental conditions. Temperature variation is a one of the most commonly encountered variables
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