Abstract
Exopolysaccharides have a diverse set of functions in most bacteria including a mechanistic role in protecting bacteria against environmental stresses. Among the many functions attributed to the exopolysaccharides, biofilm formation, antibiotic resistance, immune evasion and colonization have been studied most extensively. The exopolysaccharide produced by many Gram positive as well as Gram negative bacteria including the oral pathogen Aggregatibacter actinomycetemcomitans is the homopolymer of β(1,6)-linked N-acetylglucosamine. Recently, we reported that the PGA-deficient mutant of A. actinomycetemcomitans failed to colonize or induce bone resorption in a rat model of periodontal disease, and the colonization genes, apiA and aae, were significantly down regulated in the mutant strain. To understand the role of exopolysaccharide and the pga locus in the global expression of A. actinomycetemcomitans, we have used comparative transcriptome profiling to identify differentially expressed genes in the wild-type strain in relation to the PGA-deficient strain. Transcriptome analysis revealed that about 50% of the genes are differently expressed (P < 0.05 and fold change >1.5). Our study demonstrated that the absence of the pga locus affects the genes involved in peptidoglycan recycling, glycogen storage, and virulence. Further, using confocal microscopy and plating assays, we show that the viability of pga mutant strain is significantly reduced during biofilm growth. Thus, this study highlights the importance of pga genes and the exopolysaccharide in the virulence of A. actinomycetemcomitans.
Highlights
Bacteria find themselves in diverse environmental conditions and as a necessity to cope with those of stress, resort to a surface-associated biofilm state
To investigate the role played by PGA in A. actinomycetemcomitans, transcriptome analysis was conducted with both IDH781 and EA1002 samples taken at 16 h under in vitro biofilm condition
The A. actinomycetemcomitans genome sequence available for the strain D7S-1 was used for mapping and to identify differentially expressed genes by comparing IDH781 and EA1002 transcriptomes
Summary
The aim of the present study was to assess the role of PGA in the pathophysiology of the periodontal pathogen A. actinomycetemcomitans
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