Abstract
ABSTRACT Objective: It is unknown whether bacteria play a role in the collagen matrix degradation that occurs during caries progression. Our aim was to characterize the expression level of genes involved in bacterial collagenolytic proteases in root biofilms with and without caries. Method: we collected samples from active cavitated root caries lesions (RC, n = 30) and from sound root surfaces (SRS, n = 10). Total microbial RNA was isolated and cDNA sequenced on the Illumina Hi-Seq2500. Reads were mapped to 162 oral bacterial reference genomes. Genes encoding putative bacterial collagenolytic proteases were identified. Normalization and differential expression analysis was performed on all metatranscriptomes (FDR<10-3). Result: Genes encoding collagenases were identified in 113 bacterial species the majority were peptidase U32. In RC, Streptococcus mutans and Veillonella parvula expressed the most collagenases. Organisms that overexpressed collagenolytic protease genes in RC (Log2FoldChange>8) but none in SRS were Pseudoramibacter alactolyticus [HMPREF0721_RS02020; HMPREF0721_RS04640], Scardovia inopinata [SCIP_RS02440] and Olsenella uli DSM7084 [OLSU_RS02990]. Conclusion: Our findings suggest that the U32 proteases may be related to carious dentine. The contribution of a small number of species to dentine degradation should be further investigated. These proteases may have potential in future biotechnological and medical applications, serving as targets for the development of therapeutic agents.
Highlights
Root hard tissues become vulnerable to demineralization once root surfaces are exposed
We evaluated bacterial collagenolytic protease gene expression within natural biofilms from root caries (RC) compared with supragingival biofilms of RC-free individuals by RNA-seq data analysis
The higher proportion of reads assigned to the bacterial collagenolytic proteases was 0.1% of total reads (RC_7)
Summary
Root hard tissues (cementum and dentine) become vulnerable to demineralization once root surfaces are exposed. It has been suggested that host collagenases from dentine are associated with collagen matrix degradation during caries progression [9,10], representing a response of the host tissues to caries attack under acidic conditions. These proteases, which include matrix metalloproteinases (MMP-2, 3, 8, 9, and 20) and cysteine cathepsins (B and K), are present in the dentinal organic matrix and become activated once the cementum is degraded [3,9,10,11,12,13]
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