Systems biosynthesis of secondary metabolic pathways within the oral human microbiome member Streptococcus mutans

Abstract

Streptococcus mutans, a Gram-positive human commensal and pathogen, is commonly recognized as a primary causative agent in dental caries. Metabolic activity of this strain results in the creation of acids and secreted products are recognized as pathogenic factors and agents that promote immunomodulation by stimulating the release of pro-inflammatory cytokines. Products of secondary metabolic pathways of microorganisms from the human microbiome are increasingly investigated for their immunomodulatory functions. In this study, we sought to explore the metabolomic output of nonribosomal peptide pathways within the model S. mutans strain, S. mutans UA159, using a systems metabolomic approach to gain in-depth analysis on products created by this organism and probe these molecules for their immunomodulatory function. Comparative metabolomics and biosynthetic studies using wild-type and nonribosomal peptide deletion strains (within the mutanobactin biosynthetic locus), precursor feedings (fatty acid derivatives) led to the identification of 58 metabolites, 13 of which were structurally elucidated. In addition to these, an assembly line derailment product, mutanamide, was also identified and used to assess immunomodulatory properties of mutanobactins and actions relating to their previously reported functions describing hyphal inhibitory profiles in Candida albicans. The results of this study demonstrate both the complexity and the divergent roles of products stemming from this unique biosynthetic assembly line.

Streptococcus mutans Can Modulate Biofilm Formation and Attenuate the Virulence of Candida albicans

“…mutans , trans-2-decenoic acid, which suppressed morphogenesis at concentrations that do not affect fungal growth. Zvanych et al [ 30 ] tested whether mutanobactins display any immunomodulatory activity using in vitro models of macrophage cell line. Interestingly, mutanobactin B caused a significant increase in pro-inflammatory cytokines, such as IL-6 and Il-12, suggesting that mutanobactins may play an important role in modulating immune response.…”

Caries-Associated Biosynthetic Gene Clusters in Streptococcus mutans

“…Many small molecules of bacterial origin are produced by organized genes groups called biosynthetic gene clusters (BGCs). Common types of BGCs harbored by the oral microbiota include polyketide (PKS), nonribosomal peptide synthases (NRPS), hybrid PKS/NRPS, and ribosomally synthesized and posttranslationally modified peptides (RiPPs) that are represented by bacteriocins (i.e., mutacins) as well as other small molecules with various activities, such as biofilm formation, bacterial cell signaling, stress response, and host colonization (Wu et al 2010; Merritt and Qi 2012; Zvanych et al 2015; Liu et al 2016; Aleti et al 2019). Recent studies have identified novel PKS/NRPS hybrids responsible for the production of mutanicyclin and 3 structural variants of reutericyclin (Hao et al 2019; Tang et al 2020).…”

Small molecule natural products in human nasal/oral microbiota

“…1a ). Six other structures, the mutanolins ( 12–17 ), a consequence of cysteine incorporation in the final module of the NRPS assembly line, were also found (Zvanych et al, 2015 ) (Fig. 1a ).…”

“…Zvanych et al identified and proposed partial structures for a litany of mutanobactin-like molecules through MS/MS fragmentation and isotope labeling studies. First, Zvanych et al found several other mutanobactin congeners, B2 ( 4 ) and E–J ( 6–11 ) (Zvanych et al, 2015 ) (Fig. 1a ).…”