Dynamics of the Streptococcus gordonii Transcriptome in Response to Medium, Salivary α-Amylase, and Starch

Abstract

Streptococcus gordonii, a primary colonizer of the tooth surface, interacts with salivary ␣-amylase via amylase-binding protein A (AbpA). This enzyme hydrolyzes starch to glucose, maltose, and maltodextrins that can be utilized by various oral bacteria for nutrition. Microarray studies demonstrated that AbpA modulates gene expression in response to amylase, suggesting that the amylase-streptococcal interaction may function in ways other than nutrition. The goal of this study was to explore the role of AbpA in gene regulation through comparative transcriptional profiling of wild-type KS1 and AbpA ؊ mutant KS1⍀abpA under various environmental conditions. A portion of the total RNA isolated from mid-log-phase cells grown in 5% CO 2 in (i) complex medium with or without amylase, (ii) defined medium (DM) containing 0.8% glucose with/without amylase, and (iii) DM containing 0.2% glucose and amylase with or without starch was reverse transcribed to cDNA and the rest used for RNA sequencing. Changes in the expression of selected genes were validated by quantitative reverse transcription-PCR. Maltodextrin-associated genes, fatty acid synthesis genes and competence genes were differentially expressed in a medium-dependent manner. Genes in another cluster containing a putative histidine kinase/response regulator, peptide methionine sulfoxide reductase, thioredoxin protein, lipoprotein, and cytochrome c-type protein were downregulated in KS1⍀abpA under all of the environmental conditions tested. Thus, AbpA appears to modulate genes associated with maltodextrin utilization/transport and fatty acid synthesis. Importantly, in all growth conditions AbpA was associated with increased expression of a potential two-component signaling system associated with genes involved in reducing oxidative stress, suggesting a role in signal transduction and stress tolerance. It is well known that dental plaque is involved in the etiology of the two most common oral diseases, caries, and periodontal disease. Streptococcus gordonii is one of the pioneer bacteria that initiate the formation of dental plaque on tooth surfaces. Dental plaque formation is a complex process that involves the participation of a variety of salivary components (1). Salivary ␣-amylase is the most abundant enzyme in saliva and is best known for its ability to degrade starch by hydrolyzing 1,4-glycosidic linkages with subsequent formation of maltose, maltotriose, and limit dextrins as the main products (2). Amylase binds to a number of oral streptococcal species, collectively referred to as the amylase-binding streptococci (ABS) (3-6). Once bound to streptococcal cells, amylase retains enzymatic activity to mediate the hydrolysis of starch to fermentable oligosaccharides (7-9). Thus, streptococcus-bound salivary amylase hydrolyzes dietary starch that can be further metabolized for streptococcal nutrition. It is also possible that S. gordonii and other ABS contribute to oral microbial colonization by metabolizing dietary starch and providing nutrition for non-ABS species w...

Identification of Redox Partners of the Thiol-Disulfide Oxidoreductase SdbA in Streptococcus gordonii

“…1D). The results are in agreement with a recent study showing that sgo_1180, ccdA1, sgo_1177, and sgo_1176 were cotranscribed and that sgo_1175, sgo_1174, and ccdA2 were cotranscribed (32). Based on the findings described below, we named Sgo_1171 SdbB (Streptococcus disulfide bond protein B).…”

A distinct sortase SrtB anchors and processes a streptococcal adhesin AbpA with a novel structural property

“…Such a presentation pattern not only offers a degree of mechanical strength, but would enable to the adhesive properties of AbpA to engage optimally with its host binding partner, human α-amylase. AbpA may also function as a regulator as mutation of abpA in S. gordonii down-regulates expression of a bacterial two component signal transduction system and a variety of metabolic pathways 46 . Abundant distribution of AbpA on the cell surface would assist its role as a receptor and amply signals it transduces.…”

The Role of Methionine Sulfoxide Reductases in Oxidative Stress Tolerance and Virulence of Staphylococcus aureus and Other Bacteria

“…In N. meningitidis , MSRA is part of the SigmaE regulon [ 44 ], and in the rhizobacterium Azospirillum brasilense expression of MSRA is controlled by heat-shock sigma factor RpoH2 [ 45 ]. In S. gordonii , an amylase-binding protein A (AbpA) positively upregulates the expression of peptide MSR [ 46 ].…”