Evaluation of antibacterial properties of fluoride-containing mouth rinses differing in their acidic compound using a Streptococcus mutans biofilm.

This in vitro study assessed the antibacterial effect on Streptococcus mutans biofilms of mouth rinses with 700 ppm F- (derived from NaF) that differed only in their acid compounds (malic (A), citric (B), tartaric (C), fumaric (D), hydrochloric (E), phosphoric (F), and lactic (G) acid) used to adjust pH. S. mutans (ATCC 25175) was grown for 22 h at 37°C, harvested, resuspended in simulated body fluid and biofilm formation followed for 24 h at 37°C. Thereafter, biofilms were treated with experimental rinses for 30 s, and placed in TAM48 isothermal microcalorimeter at 37°C for 72 h. Applying Gompertz growth model parameters lag time and growth rate were determined from heatflow curves; additionally, reduction of active biofilms was calculated. Moreover, samples were live/dead stained and analyzed by confocal scanning microscopy. All mouth rinses were showing statistically significant lag time and reduction of active biofilm (p<0.05, A 19.1+/-2.3h and 58.5+/-7.7%, B 15.5+/-1.1h and 41.9+/-5.3%, C 17.6+/-1.9h and 53.1+/-7.5%, D 18.4+/-2.4h and 55.8+/-8.8%, E 20.2+/-3.3h and 61.5+/-10.0%, F 20.2+/-3.0h and 61.6+/-9.3%, and G 18.3+/-2.5h and 55.3+/-8.9%). Interestingly, there were no differences found between the treated groups (p>0.05, A 0.064+/-0.004 1/h, B 0.063+/-0.005 1/h, C 0.065+/-0.004 1/h, D 0.067+/-0.004 1/h, E 0.066+/-0.006 1/h, F 0.067+/-0.004 1/h, G 0.066+/-0.006 1/h) for the maximum growth rate. Vitality staining supported these findings.. The present investigation demonstrates that the type of acid compounds used to produce the rinses did not show any negative effect on the antimicrobial properties of the tested products as all of them exhibited a similar efficacy against S. mutans biofilms.

Antimicrobial efficacy of copper-doped titanium surfaces for dental implants.

The aim of this in vitro study was to quantify the antibacterial effect of a copper-deposited titanium surface as a model for dental implants on the peri-implantitis-associated strain Porphyromonas gingivalis (DSM 20709). A spark-assisted anodization method in a combined deposition-anodization process was applied to deposit copper on discs made of titanium. This method allows the deposition of different concentrations of copper on the surface by varying the process time. Conventional culturing was used to investigate the adhesion of P. gingivalis onto the discs over 2, 4, and 6 h as well as to study the antibacterial effect of copper released in solution. The viability of the bacterial cells is strongly inhibited on copper-deposited discs and reaches a CFU reduction of 3 log-units after 6 h in comparison to the reference. The copper released in solution causes a reduction of 4 log-units after a 6 h incubation time. With a 6 h incubation time, the CFU count decreases with increasing copper concentrations on the disc (by 2% for the 1.3 µg/disc; 32% for the 5.6 µg/disc; and 34% for the 9.5 µg/disc). However, at a higher copper concentration of 17.7 µg/disc, after 6 h, the decrease in the CFU count is less pronounced than that observed in solution, where a further decrease is observed. In conclusion, copper-functionalized titanium significantly reduces the survival of adhered bacteria and decreases the viable bacterial count in the environment surrounding the titanium. Thus, the area surrounding implants is being protected by copper released from the surface, forming a "safe zone" for improved implant healing.

Phylogenetic, structural, and functional characterization of AMT3;1, an ammonium transporter induced by mycorrhization among model grasses.

In the arbuscular mycorrhizal (AM) symbiosis, plants satisfy part of their nitrogen (N) requirement through the AM pathway. In sorghum, the ammonium transporters (AMT) AMT3;1, and to a lesser extent AMT4, are induced in cells containing developing arbuscules. Here, we have characterized orthologs of AMT3;1 and AMT4 in four other grasses in addition to sorghum. AMT3;1 and AMT4 orthologous genes are induced in AM roots, suggesting that in the common ancestor of these five plant species, both AMT3;1 and AMT4 were already present and upregulated upon AM colonization. An artificial microRNA approach was successfully used to downregulate either AMT3;1 or AMT4 in rice. Mycorrhizal root colonization and hyphal length density of knockdown plants were not affected at that time, indicating that the manipulation did not modify the establishment of the AM symbiosis and the interaction between both partners. However, expression of the fungal phosphate transporter FmPT was significantly reduced in knockdown plants, indicating a reduction of the nutrient fluxes from the AM fungus to the plant. The AMT3;1 knockdown plants (but not the AMT4 knockdown plants) were significantly less stimulated in growth by AM fungal colonization, and uptake of both 15N and 33P from the AM fungal network was reduced. This confirms that N and phosphorus nutrition through the mycorrhizal pathway are closely linked. But most importantly, it indicates that AMT3;1 is the prime plant transporter involved in the mycorrhizal ammonium transfer and that its function during uptake of N cannot be performed by AMT4.

Plant phosphorus acquisition in a common mycorrhizal network: regulation of phosphate transporter genes of the Pht1 family in sorghum and flax.

In a preceding microcosm study, we found huge differences in phosphorus (P) acquisition in sorghum (Sorghum bicolor) and flax (Linum usitatissimum) sharing a common mycorrhizal network (CMN). Is the transcriptional regulation of arbuscular mycorrhizal (AM)-induced inorganic orthophosphate (Pi) transporters responsible for these differences? We characterized and analyzed the expression of Pi transporters of the Pht1 family in both plant species, and identified two new AM-inducible Pi transporters in flax. Mycorrhizal Pi acquisition was strongly affected by the combination of plant and AM fungal species. A corresponding change in the expression of two AM-inducible Pht1 transporters was noticed in both plants (SbPT9, SbPT10, LuPT5 and LuPT8), but the effect was very weak. Overall, the expression level of these genes did not explain why flax took up more Pi from the CMN than did sorghum. The post-transcriptional regulation of the transporters and their biochemical properties may be more important for their function than the fine-tuning of their gene expression.

The largest subunit of RNA polymerase II as a new marker gene to study assemblages of arbuscular mycorrhizal fungi in the field.

Due to the potential of arbuscular mycorrhizal fungi (AMF, Glomeromycota) to improve plant growth and soil quality, the influence of agricultural practice on their diversity continues to be an important research question. Up to now studies of community diversity in AMF have exclusively been based on nuclear ribosomal gene regions, which in AMF show high intra-organism polymorphism, seriously complicating interpretation of these data. We designed specific PCR primers for 454 sequencing of a region of the largest subunit of RNA polymerase II gene, and established a new reference dataset comprising all major AMF lineages. This gene is known to be monomorphic within fungal isolates but shows an excellent barcode gap between species. We designed a primer set to amplify all known lineages of AMF and demonstrated its applicability in combination with high-throughput sequencing in a long-term tillage experiment. The PCR primers showed a specificity of 99.94% for glomeromycotan sequences. We found evidence of significant shifts of the AMF communities caused by soil management and showed that tillage effects on different AMF taxa are clearly more complex than previously thought. The high resolving power of high-throughput sequencing highlights the need for quantitative measurements to efficiently detect these effects.

Rapid nitrogen transfer in the Sorghum bicolor-Glomus mosseae arbuscular mycorrhizal symbiosis.

We have recently identified two genes coding for ammonium transporters (AMT) in Sorghum bicolor that were induced in roots colonized by arbuscular mycorrhizal (AM) fungi. To improve our understanding of the dynamics of ammonium transport in this symbiosis, we studied the transfer of soil-ammonium-derived (15)N to S. bicolor plants via the Glomus mosseae fungal mycelium in compartmented microcosms. The (15)NH (4+)-containing hyphal compartment was inaccessible to the roots in the plant compartment. (15)N label concentrations significantly increased in plant roots and leaves already 48 h after exposure of the AM fungus to the (15)NH (4+) substrate, attesting an efficient symbiotic N transfer between the symbiotic partners and further highlighting that AM symbiosis represents an important component of plant nitrogen nutrition.

The family of ammonium transporters (AMT) in Sorghum bicolor: two AMT members are induced locally, but not systemically in roots colonized by arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal (AM) fungi contribute to plant nitrogen (N) acquisition. Recent studies demonstrated the transport of N in the form of ammonium during AM symbiosis. Here, we hypothesize that induction of specific ammonium transporter (AMT) genes in Sorghum bicolor during AM colonization might play a key role in the functionality of the symbiosis. For the first time, combining a split-root experiment and microdissection technology, we were able to assess the precise expression pattern of two AM-inducible AMTs, SbAMT3;1 and SbAMT4. Immunolocalization was used to localize the protein of SbAMT3;1. The expression of SbAMT3;1 and SbAMT4 was greatly induced locally in root cells containing arbuscules and in adjacent cells. However, a split-root experiment revealed that this induction was not systemic. By contrast, a strictly AM-induced phosphate transporter (SbPt11) was expressed systemically in the split-root experiment. However, a gradient of expression was apparent. Immunolocalization analyses demonstrated that SbAMT3;1 was present only in cells containing developing arbuscules. Our results show that the SbAMT3;1 and SbAMT4 genes are expressed in root cortical cells, which makes them ready to accommodate arbuscules, a process of considerable importance in view of the short life span of arbuscules. Additionally, SbAMT3;1 might play an important role in N transfer during AM symbiosis.