Objective: To investigate the composition and abundance of candidate phyla radiation (CPR) in the oral cavity in caries patients and a healthy population.
Methods: The raw macrogenomic sequencing data for a total of 88 subjects were downloaded from the National Centre for Biotechnology Sequence Read Archive (NCBI SRA) public database according to the public data usage specifications. Trimmomatic (Department for Metabolic Networks, Potsdam, Germany) and Bowtie 2 (University of Maryland, College Park, MD, USA) were used to quality control and dehost the host sequences. Species annotation was made using Kraken2 (Johns Hopkins University, Baltimore, MD, USA) and Bracken (Johns Hopkins University) based on the reference database. According to the results of the species annotation, the species-significant differences and species correlation of caries and healthy oral microbiota in species composition and microbiota diversity were analysed to study the distribution and abundance differences of CPR in the oral environment.
Results: Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria and Fusobacteria were the main components. The relative abundance of TM7 (Candidatus Saccharibacteria) and GN02 (Candidatus Gracilibacteria) of CPR is second only to the aforementioned five bacteria, indicating that CPR is an important part of the oral microbiota. TM7 and GN02 were common to both the caries patients and healthy patients and were detected in all samples, suggesting that CPR is the ‘core microbiome’. There was a correlation between CPR and a variety of oral microbiota, among which the positive correlation with Capnocytophaga was the strongest, suggesting that Capnocytophaga might be the potential host bacteria of CPR.
Conclusion: CPR is an indispensable part of the oral microbiota. It is the ‘core microflora’ of the oral cavity and may play an important role in the stability and function of the oral microecological environment. Capnocytophaga may be the potential host bacteria of CPR.