Extraction of lipoteichoic acid from Streptococcus mutants with the non-ionic detergent Triton X-114

Extracellular DNA and lipoteichoic acids interact with exopolysaccharides in the extracellular matrix of Streptococcus mutans biofilms

Streptococcus mutans-derived exopolysaccharides are virulence determinants in the matrix of biofilms that cause caries. Extracellular DNA (eDNA) and lipoteichoic acid (LTA) are found in cariogenic biofilms, but their functions are unclear. Therefore, strains of S. mutans carrying single deletions that would modulate matrix components were used: eDNA - ∆lytS and ∆lytT; LTA - ∆dltA and ∆dltD; and insoluble exopolysaccharide - ΔgtfB. Single-species (parental strain S. mutans UA159 or individual mutant strains) and mixed-species (UA159 or mutant strain, Actinomyces naeslundii and Streptococcus gordonii) biofilms were evaluated. Distinct amounts of matrix components were detected, depending on the inactivated gene. eDNA was found to be cooperative with exopolysaccharide in early phases, while LTA played a larger role in the later phases of biofilm development. The architecture of mutant strains biofilms was distinct (vs UA159), demonstrating that eDNA and LTA influence exopolysaccharide distribution and microcolony organization. Thus, eDNA and LTA may shape exopolysaccharide structure, affecting strategies for controlling pathogenic biofilms.

Anti-tumor effect of LTA combined with 5-FU on H22 tumor bearing mice

OBJECTIVE

To study the effect of lipoteichoic acid (LTA) and 5-FU on the expression of caspase-3, EGFR, TGF-α proteins of tumor tissue of H22 cancer bearing mice and its anti-tumor mechanism.

METHODS

A total of 40 SPF grade Kunming mice were selected to establish H22 liver cancer model, and then the mice were divided into 4 groups at random with ten mice in each group. Group A was given saline lavage treatment, Group B was treated with 5-FU by intraperitoneal injection, Group C was treated with LTA by lump body injection; Group D was treated with LTA by lump body injection and 5-FU by intraperitoneal injection. Two weeks after the treatment, the mice in each group were executed and the tumor tissue was stripping and weighted, and the tumor growth inhibition ratio was calculated. Then the tumor tissue was processed for conventional embedding, sectioned to observe the expression of caspase-3, EGFR, TGF-α by immunohistochemical staining method.

RESULTS

The tumor inhibitory rate o f Group D was significantly higher than Groups B and C (P < 0.05); B, the tumor inhibitory rate o f Group B had no statistical difference compared with Group C (P > 0.05). The IDO values of TGF-α, EGFR proteins in Groups B, C, D mice tumor tissue were significantly lower than that in group A (P < 0.05); while IDO value of caspase-3 in Groups B, C, D group mice tumor tissue was significantly higher than that in Group A (P < 0.05). The IDO value of TGF-α, EGFR in Group D mice tumor tissue were significantly lower than that in Groups B and C; While IDO value of aspase-3 in Group D was significantly higher than that in Groups B and C (P < 0.05).

CONCLUSIONS

LTA combined with 5-FU can effectively inhibit the tumorigenesis of H22 tumor bearing mice, increase the caspase-3 protein expression, inhibit TGF-α and EGFR protein expression, further promote tumor cell apoptosis and play a synergistic antitumor effect.

A novel glucan-binding protein with lipase activity from the oral pathogen Streptococcus mutans

Streptococcus mutans produces extracellular glucosyltransferases (GTFs) that synthesize glucans from sucrose. These glucans are important in determining the permeability properties and adhesiveness of dental plaque. GTFs and the GbpA glucan-binding protein are characterized by a binding domain containing a series of 33-amino-acid repeats, called 'A' repeats. The S. mutans genome sequence was searched for ORFs containing 'A' repeats, and one novel gene, gbpD, which appears to be unique to the mutans group of streptococci, was identified. The GbpD sequence revealed the presence of three 'A' repeats, in the middle of the protein, and a novel glucan-binding assay showed that GbpD binds to dextran with a K(D) of 2-3 nM. Construction of truncated derivatives of GbpD confirmed that the 'A' repeat region was essential for binding. Furthermore, a gbpD knockout mutant was modified in the extent of aggregation induced by polymers derived from sucrose. The N-terminus of GbpD has a signal sequence, followed by a region with no homologues in the public databases, while the C-terminus has homology to the alpha/beta hydrolase family (including lipases and carboxylesterases). GbpD contains the two regions typical of these enzymes: a GxSxG active site 'lipase box' and an 'oxyanion hole'. GbpD released free fatty acids (FFAs) from a range of triglycerides in the presence of calcium, indicating a lipase activity. The glucan binding/lipase bifunctionality suggested the natural substrate for the enzyme may be a surface macromolecule consisting of carbohydrate linked to lipid. The gbpD mutant was less hydrophobic than wild-type and pure recombinant GbpD reduced the hydrophobicity of S. mutans and another plaque bacterium, Streptococcus sanguinis. GbpD bound to and released FFA from lipoteichoic acid (LTA) of S. sanguinis, but had no effect on LTA from S. mutans. These results raise the intriguing possibility that GbpD may be involved in direct interspecies competition within the plaque biofilm.

Identification of a lipoarabinomannan-like lipoglycan in Corynebacterium matruchotii

The oral organism Corynebacterium matruchotii was investigated for the presence of lipoteichoic acid, as this common polyanionic macroamphiphilic component of Gram-positive bacteria has been implicated in phenomena related to calcium binding. Phenol-water extraction followed by a small-scale, hydrophobic-interaction chromatography step yielded carbohydrate-containing preparations that were distinguished from lipoteichoic acid by their low phosphorus content. Subsequently, large-scale phenol-water extracts from each of three strains of C. matruchotii were purified by hydrophobic-interaction chromatography and shown to contain a heterogeneous lipoglycan fraction. The major fatty acids present were the same as for the whole-cell fatty acid profiles but differed in their relative amounts. Qualitative analysis of the lipoglycan fractions revealed similarities of carbohydrate composition with a previously characterized lipoglycan fraction from C. diphtheriae and with the lipoarabinomannan/lipomannans found in the genus Mycobacterium. The carbohydrate composition and the low phosphorus content indicated that lipoteichoic acid was absent from C. matruchotii. The calcium-binding properties of C. matruchotii therefore cannot be attributed to lipoteichoic acid.