Metagenomic investigation of bacteria associated with dental lesions : a cross-sectional study

Dental caries is considered as one of the most significant global health problem over the world. Dental caries initiates from bacterial shifts within the supragingival biofilm, then a polymicrobial biofilm is formed on the surface of tooth, and finally various bacterial species aggregate in a complex-organized manner. The exploiting variability in 16S rRNA gene sequence has been considered as a cost-efficient high-throughput characterization approach in human oral microbiome investigations. The aim of this study is to characterize bacterial species associated with superficial dental biofilm, underlying carious dentine and root caries lesion by16S rRNA gene-based metagenomic analysis. Herein, the bacterial communities in carious dentin lesion, biofilm and root canal samples of 30 subjects (aged 4?76 years) admitted to a clinic in Tehran during 2017 were investigated using a culture independent approach. Total genomic DNA of each tissue was subjected to metagenomic identification of bacteria using a nested PCR assay and 16S rRNA library construction method. 31 samples collected from 30 consenting patients (29 samples from 29 patients ant two biofilm samples from one patient). Bioinformatics analyses of a-800bp sequences of the second step of Nested-PCR revealed presence of 156 bacterial isolates in carious (n=45), biofilm (n=81) and root canal (n=30) specimens. Prevotella spp., Lactobacillus vaginalis, and streptococcus spp. showed higher prevalence in carious dentin, root and biofilm samples, respectively. Exploring the dental microbiota and comparing them in health or diseased conditions is critical step in the determination of human general health. The method applied in this study could identify bacteria related to the three dental lesions. However, due to lack of data for comparison in Genbank or because of the sequence similarity lower than 98% for most identified bacteria, the use of more powerful approaches like NGS platforms or typing of multiple loci (MLST) in future studies is recommended

Isolation and molecular identification of gamma-radiation resistant-bacteria from soil samples of a radioactive site in South Khorasan province

Background and objectives: Radiation resistance has been found widely among bacteria but little is known about the biodiversity of radiation resistant-bacteria in naturally radioactive-contaminated places in Iran. The aim of this study is to identify the radio resistant-bacteria isolated from soil samples in such locations. Materials and Methods: Samples were collected from suspected above sites and cultured on TGY agar and incubated at 300C using serial dilutions. All isolates were treated with gamma-radiation from 0 to 30 kGy doses and then plated on TGY agar medium. A radio-resistant isolate was identified by microbiological methods and verified by 16S rRNA sequencing. Results: From a total of 20 isolates which were recovered from soil samples, one isolate (F1 5kGy) could survive against gamma radiation. Phylogenetic analysis based on 16S rRNA sequencing reconfirmed the conventional identification tests showing that F1 5kG bacterium belonged to Kocuria genus with up to 5000Gy resistance to gamma radiation. Conclusion:The results showed F1 5kG bacterium would be well suited for long-term survival in naturally radioactive-contaminated sites and a suitable candidate for bioremediation of radioactive waste. Moreover, identification of proteins which involved in radio resistancy could add further application of this strain in future studies