RESUMEN
OBJECTIVES: Streptococcus gordonii is associated with the formation of biofilms, especially those that comprise dental plaque. Notably, S. gordonii DL1 causes infective endocarditis (IE). Colonization of this bacterium requires a mechanism that can tolerate a drop in environmental pH by producing acid via its own sugar metabolism. The ability to survive acidic environmental conditions might allow the bacterium to establish vegetative colonization even in the endocardium due to inflammation-induced lowering of pH, increasing the risk of IE. At present, the mechanism by which S. gordonii DL1 survives under acidic conditions is not thoroughly elucidated. The present study was thus conducted to elucidate the mechanism(s) by which S. gordonii DL1 survives under acidic conditions. METHODS: We analyzed dynamic changes in gene transcription and intracellular metabolites in S. gordonii DL1 exposed to acidic conditions, using transcriptome and metabolome analyses. RESULTS: Transcriptome analysis revealed upregulation of genes involved in heat shock response and glycolysis, and down regulation of genes involved in phosphotransferase systems and biosynthesis of amino acids. The most upregulated genes were a beta-strand repeat protein of unknown function (SGO_RS06325), followed by copper-translocating P-type ATPase (SGO_RS09470) and malic enzyme (SGO_RS01850). The latter two of these contribute to cytoplasmic alkalinization. S. gordonii mutant strains lacking each of these genes showed significantly reduced survival under acidic conditions. Metabolome analysis revealed that cytoplasmic levels of several amino acids were reduced. CONCLUSIONS: S. gordonii survives the acidic conditions by recovering the acidic cytoplasm using the various activities, which are regulated at the transcriptional level.
Asunto(s)
Streptococcus gordonii , Transcriptoma , Streptococcus gordonii/genética , Streptococcus gordonii/metabolismo , Transcriptoma/genética , Biopelículas , Aminoácidos/genética , Aminoácidos/metabolismo , Metaboloma/genéticaRESUMEN
OBJECTIVES: The Hsa adhesin of Streptococcus gordonii strain DL1 was previously identified as a hemagglutinin that binds specifically to sialoglycoconjugates. We recently found that among oral streptococcal species, S. gordonii strains most frequently express Hsa homologs on the bacterial cell surface. However, the effect of amino acid sequence diversity of nonrepetitive region 2 (NR2), a putative binding site of Hsa, on antigenicity and hemagglutinating (HA) properties is unclear due to difficulties in DNA sequencing the NR2 coding region. The aim of this study was to elucidate the similarity of the low NR2 antigenicity Hsa homolog of strain NDU1118 to that of strain DL1 and the association of the homolog with HA properties of the strain. METHODS: The hsa homolog of NDU1118 was sequenced using a long-read next-generation sequencer, and the Hsa homolog was assessed by alignment analysis of the deduced amino acid sequences. The hsa mutant of NDU1118 was generated by insertion of the erythromycin resistance gene. The HA properties of the wild type and the hsa mutant were assessed with human erythrocytes. RESULTS: The NR2 amino acid sequence of the NDU1118 Hsa homolog was almost identical to that of the S. gordonii M99 Hsa homolog, also known as GspB, and less similar to that of DL1 Hsa. The hsa mutation of NDU1118 induced reduction of HA activity in untreated erythrocytes, but surprisingly increased lactose-inhibitable HA activity in neuraminidase-treated erythrocytes. CONCLUSIONS: The results suggest the existence of an adhesin other than the Hsa homolog on the cell surface of NDU1118.