Mutanobactin A from the human oral pathogen Streptococcus mutans is a cross-kingdom regulator of the yeast-mycelium transition

Abstract

The recent investigation of a gene cluster encoding for a hybrid PKS-NRPS metabolite in the oral pathogen Streptococcus mutans UA159 yielded evidence that this natural product might play an important role regulating a range of stress tolerance factors. We have now characterized the major compound generated from this gene cluster, mutanobactin A, and demonstrated that this secondary metabolite is also capable of influencing the yeast-mycelium transition of Candida albicans.A complex suite of cross-species interactions are anticipated to occur among the wide range of microorganisms that constitute the human microbiome. 1-3 While a variety of compounds such as peptides, lipids, and acyl-homoserine lactones have emerged as key players in the multifarious exchanges among microbes and their hosts, 4,5 the important contributions of many other families of secondary metabolites have been largely overlooked. We reported that the deletion of a gene cluster encoding for a putative hybrid polyketide synthasenonribosomal peptide synthetase (PKS-NRPS) derived metabolite in the human oral pathogenic bacteria Streptococcus mutans UA159 resulted in a loss of several resistance traits associated with oxygen and hydrogen peroxide tolerance, as well as biofilm formation. 6 Given that a variety of secondary metabolites are excreted into the extracellular environment, we suspected that the biosynthetic products of this gene cluster (which we have dubbed the mutanobactins 6 ) may have additional yet undefined functions related to the interaction of S. mutans with other members of the oral microbiome. This hypothesis recently gained support based on co-culture studies in which mutanobactin-competent S. mutans and a mutanobactin deletion mutant strain (Δmub) were grown in the presence of Candida albicans. Whereas the mutanobactin producing strain of S. mutans was capable of maintaining C. albicans in a perpetual yeast morphological state (Fig. 1A), deletion of the mutanobactin cluster permitted C. albicans to shift into a mycelial growth pattern, which is believed to be the invasive form of the fungus (Fig. 1B). We now describe the distinctive † Electronic supplementary information (ESI) available: General methods, physical data, MS and NMR ( 1 H, 13 C, 1 H-1 H COSY, 1 H-1 H TOCSY, 1 H-1 H NOESY, 1 H-13 C HSQC, 1 H-13 C HMBC, and 1 H-15 N HMBC) for 1. Analytical-scale HPLC comparison of the crude extracts generated from wild-type S. mutans UA159 and Δmub strains grown on brain-heart-infusion agar plates enabled us to identify two metabolites in the elution profile that were present only in the wild-type organism. Scale-up fermentation of the wild-type strain was performed in a bioreactor with 15 L of brain-heart-infusion broth under microaerobic conditions at 37 °C to enable the isolation and structure characterization of the major metabolite. After 48 h, the cells and broth were partitioned against ethyl acetate and the solvent removed in vacuo. The resulting extract was resuspended in methanol and the organic soluble material ...

Regulation of Bacteriocin Production and Cell Death by the VicRK Signaling System in Streptococcus mutans

“…In strain UA159, genes in TnSmu2 encode nonribosomal peptide synthetases (NRPS), polyketide synthases (PKS), and accessory proteins involved in nonribosomal peptide (NRP) and polyketide (PK) biosynthesis (56). These were shown to be necessary for the biosynthesis of a hybrid NRP/PK pigment that was referred to as mutanobactin (56), whereas the secondary metabolite generated from this cluster was isolated and characterized as mutanobactin A (17). Whereas mutanobactin A was shown to suppress the morphological transition of Candida albicans from yeast to mycelium (17), mutational analysis of genes within the mutanobactin locus was shown to modulate biofilm formation and confer oxygen and hydrogen peroxide tolerance in S. mutans (56).…”

“…These were shown to be necessary for the biosynthesis of a hybrid NRP/PK pigment that was referred to as mutanobactin (56), whereas the secondary metabolite generated from this cluster was isolated and characterized as mutanobactin A (17). Whereas mutanobactin A was shown to suppress the morphological transition of Candida albicans from yeast to mycelium (17), mutational analysis of genes within the mutanobactin locus was shown to modulate biofilm formation and confer oxygen and hydrogen peroxide tolerance in S. mutans (56). In fact, we had previously reported the involvement of the VicRK in oxidative stress tolerance in S. mutans (48).…”

Synergistic combinations of antifungals and anti-virulence agents to fight againstCandida albicans

“…An increasing number of small molecules has been reported that are able to modulate morphogenetic conversions and inhibit filamentation. These are mainly regulators of the yeast-to-hyphae transition for C. albicans such as phenazines and homoserine lactones from Pseudomonas aeruginosa, mutanobactins from Streptococcus mutans and capric acid secreted by Saccharomyces boulardii, farnesol and other autoregulatory alcohols that act as quorum sensing molecules produced by C. albicansitself, retigeric acid, and bisbibenzyls [52][53][54][55][56][57][58]. …”

Regulation of Transcription by SMU.1349, a TetR Family Regulator, in Streptococcus mutans

“…The operon that encodes this regulator is part of a genomic island acquired by the organism via horizontal gene transfer. Recently, it was shown that the operon contains a gene cluster that encodes a hybrid PKS-NRPS metabolite, mutanobactin A, which is capable of inducing the hypha-toyeast transition of Candida albicans, an opportunistic human pathogen often present in the oropharyngeal cavity (18).…”