Foreign peptide triggers boost in pneumococcal metabolism and growth

Abstract

Background: Nonencapsulated Streptococcus pneumoniae bacteria are successful colonizers of the human nasopharynx and often possess genes aliB-like ORF 1 and 2 in place of capsule genes. AliB-like ORF 2 binds peptide FPPQSV, found in Prevotella species, resulting in enhanced colonization. How this response is mediated is so far unknown.

Results: Here we show that the peptide increases expression of genes involved in release of host carbohydrates, carbohydrate uptake and carbohydrate metabolism. In particular, the peptide increased expression of 1,5-anhydro-D-fructose reductase, a metabolic enzyme of an alternative starch and glycogen degrading pathway found in many organisms, in both transcriptomic and proteomic data. The peptide enhanced pneumococcal growth giving a competitive advantage to a strain with aliB-like ORF 2, over its mutant lacking the gene. Possession of aliB-like ORF 2 did not affect release of inflammatory cytokine CXCL8 from epithelial cells in culture and the nonencapsulated wild type strain was not able to establish disease or inflammation in an infant rat model of meningitis.

Conclusions: We propose that AliB-like ORF 2 confers an advantage in colonization by enhancing carbohydrate metabolism resulting in a boost in growth. This may explain the widespread presence of aliB-like ORF 2 in the nonencapsulated pneumococcal population in the human nasopharynx.

Keywords: Nonencapsulated; Peptide; Proteome; Streptococcus pneumoniae; Transcriptome; aliB-like ORF 2.

Fig. 1

Relative gene expression. a afr, b adhE, c nan_A3, d nanB, e yesO_2 and f ycjO expression was determined by real-time RT-PCR and is displayed relative to the value of the lowest expression, after normalization using 16S RNA gene expression. The values are the means of four (afr) or three (all other genes) separate experiments. Error bars indicate standard error., *p ≤ 0.05, **p ≤ 0.01

Fig. 2

Growth of wild type strain 110.58 and mutant ΔORF 2 in CDM with and without 0.062 mg/ml ORF2 ligand peptide FPPQSV. Curves show the mean values for three independent experiments

Fig. 3

Competition assay in the presence or absence of ORF 2 peptide. A mixture of wild type strain 110.58 and its mutant ΔORF2 was incubated in (a) the presence of 0.07 mg/ml of ORF2 ligand peptide FPPQSV or (b) the absence of peptide. At the start and at OD_600nm = 0.2 and 0.3 CFU/ml were determined to show that the wild type has a competitive advantage and that this is greater in the presence of the peptide. ****p < 0.0001, *p = 0.015. Results are the mean of three independent experiments, error bars show the standard error

Fig. 4

Effect of wild type pneumococcal strain 110.58 and its mutants ΔORF 1 + 2 and ΔORF 2 on CXCL8 induction in human nasopharyngeal Detroit 562 epithelial cells. ORF2 ligand peptide FPPQSV was either not added (open bars) or added to give a final a concentration of 0.07 mg/ml (shaded bars). No significant differences were observed between the strains under the same conditions. The bars indicate the mean of three independent experiments and error bars indicate standard error. Negative control refers to Detroit cells in the absence of bacteria