F0F1-ATPase Contributes to the Fluoride Tolerance and Cariogenicity of Streptococcus mutans

Effect of Arsenic on Fluoride Tolerance in Microbacterium paraoxydans Strain IR-1

Fluoride (F) and arsenic (As) are two major contaminants of water and soil systems around the globe, causing potential toxicity to humans, plants, animals, and microbes. These contaminated soil systems can be restored by microorganisms that can tolerate toxic stress and provide rapid mineralization of soil, organic matter, and contaminants, using various tolerance mechanisms. Thus, the present study was undertaken with the arsenic hyper-tolerant bacterium Microbacterium paraoxydans strain IR-1 to determine its tolerance and toxicity to increasing doses of fluoride, either individually or in combination with arsenic, in terms of growth inhibition using a toxicity unit model. The minimum inhibitory concentration (MIC)and half maximal inhibitory concentration (IC50) values for fluoride increased, from 9 g/L to 11 g/L and from 5.91 ± 0.1 g/L to 6.32 ± 0.028 g/L, respectively, in the combination (F + As) group. The statistical comparison of observed and expected additive toxicities, with respect to toxicity unit (TU difference), using Student's t-test, was found to be highly significant (p < 0.001). This suggests the antagonistic effect of arsenic on fluoride toxicity to the strain IR-1. The unique stress tolerance of IR-1 ensures its survival as well as preponderance in fluoride and arsenic co-contaminated sites, thus paving the way for its possible application in the natural or artificial remediation of toxicant-exposed degraded soil systems.

The role of plant growth promoting rhizobacteria in strengthening plant resistance to fluoride toxicity: a review

A wide variety of bacteria are present in soil but in rhizospheric area, the majority of microbes helps plant in defending diseases and facilitate nutrient uptake. These microorganisms are supported by plants and they are known as plant growth-promoting rhizobacteria (PGPR). The PGPRs have the potential to replace chemical fertilizers in a way that is more advantageous for the environment. Fluoride (F) is one of the highly escalating, naturally present contaminants that can be hazardous for PGPRs because of its antibacterial capacity. The interactions of F with different bacterial species in groundwater systems are still not well understood. However, the interaction of PGPR with plants in the rhizosphere region reduces the detrimental effects of pollutants and increases plants' ability to endure abiotic stress. Many studies reveal that PGPRs have developed F defense mechanisms, which include efflux pumps, Intracellular sequestration, enzyme modifications, enhanced DNA repair mechanism, detoxification enzymes, ion transporter/antiporters, F riboswitches, and genetic mutations. These resistance characteristics are frequently discovered by isolating PGPRs from high F-contaminated areas or by exposing cells to fluoride in laboratory conditions. Numerous studies have identified F-resistant microorganisms that possess additional F transporters and duplicates of the well-known targets of F. Plants are prone to F accumulation despite the soil's low F content, which may negatively affect their growth and development. PGPRs can be used as efficient F bioremediators for the soil environment. Environmental biotechnology focuses on creating genetically modified rhizobacteria that can degrade F contaminants over time. The present review focuses on a thorough systemic analysis of contemporary biotechnological techniques, such as gene editing and manipulation methods, for improving plant-microbe interactions for F remediation and suggests the importance of PGPRs in improving soil health and reducing the detrimental effects of F toxicity. The most recent developments in the realm of microbial assistance in the treatment of F-contaminated environments are also highlighted.

Dynamic killing effectiveness of mouthrinses and a D-enantiomeric peptide on oral multispecies biofilms grown on dental restorative material surfaces

OBJECTIVE

To evaluate the dynamics of killing of oral multispecies biofilms grown on dental restorative materials by commercially available mouthrinses and a D-enantiomeric peptide.

METHODS

Four composite resins (3M Supreme, 3M Supreme flow, Kerr Sonicfill, and Shofu Beautifil II) and one glass ionomer (GC Fuji II) were used as restorative materials. Plaque biofilms were grown on the surfaces of restorative material discs for 1 week. The surface roughness and biofilm attachment were assessed by atomic force microscopy and scanning electron microscopy. One-week-old biofilms grown anaerobically at 37°C were exposed to each of five solutions for one minute (twice daily for seven days): Listerine Total care and Paroex Gum mouthrinses, 0.12% chlorhexidine, 0.001% D-enantiomeric peptide DJK-5, and sterile water. The dynamic variation of the biovolume of the biofilms and the percentage of dead bacteria were monitored and analyzed using confocal laser scanning microscopy.

RESULTS

All restorative materials had similar surface roughness with intact biofilm attachment. The percentage of dead bacteria and biovolume of biofilms treated by each oral rinse solution remained constant between days 1 and 7, with no statistically significant difference. DJK-5 showed the highest percentage of dead bacteria (up to 75.7%; cf. ∼20-40% for other mouthrinses) of all solutions tested within 7 days.

CONCLUSIONS

DJK-5 outperformed conventional mouthrinses in killing bacteria in oral multispecies biofilms grown on dental restorative materials.

CLINICAL SIGNIFICANCE

The antimicrobial peptide DJK-5 is effective against oral biofilms and serves as a promising candidate for the development of future mouthrinses to improve long-term oral hygiene.

Anti-biofilm and bacteriostatic effects of three flavonoid compounds on Streptococcus mutans

Streptococcus mutans (S. mutans) is the main cariogenic pathogen associated with dental caries. Orientin-2''-O-β-L-galactoside, orientin and vitexin are natural flavonoids compound. In this study, the antibacterial ability of these flavonoids and their mechanisms in inhibiting S. mutans biofilm formation were investigated. Inhibition zone and 2-fold-dilution tests showed that these flavonoids exerted inhibitory effects on S. mutans. Phenol sulfuric acid method and lactate dehydrogenase (LDH) test revealed that they could reduce EPS formation and stimulate S. mutans to release LDH. Moreover, crystal violet and live/dead bacterial staining test showed that they inhibited biofilm formation. Finally, qRT-PCR test indicated that the down-regulated the transcription levels of spaP, srtA, brpA, gtfB and luxS genes of S. mutans. In conclusion, orientin-2''-O-β-L-galactoside, orientin and vitexin had antibacterial and anti-biofilm activities.