A family of post-translationally modified threoglucins for selective antibiotic activity and dormancy induction in bacteria

Background

The field of antibiotic discovery is critical for addressing the growing threat of antimicrobial resistance and the emergence of persistent bacterial pathogens. Streptococcus suis, an important agricultural pathogen and zoonotic agent, represents a significant concern due to its ability to cause severe infections in both animals and humans. Traditional efforts to discover new antibiotics have focused on well-known producers such as actinomycetes, often overlooking human-associated streptococci as potential sources of novel natural products. However, recent advances in genome mining have revealed that streptococcal genomes harbor numerous biosynthetic gene clusters (BGCs) encoding ribosomally synthesized and post-translationally modified peptides (RiPPs). Despite this genetic potential, many of these BGCs remain cryptic or silent under standard laboratory conditions, limiting the discovery of new bioactive compounds that could address the need for species-specific antibiotics and novel mechanisms of action.

Current approaches to activating cryptic BGCs and discovering new antibiotics face several challenges. Standard laboratory cultivation often fails to induce the expression of these gene clusters, resulting in missed opportunities to identify unique natural products. Even when BGCs are expressed, the resulting compounds may not exhibit the desired selectivity or potency, and broad-spectrum antibiotics can disrupt beneficial microbiota and drive resistance. Additionally, existing antibiotics are frequently ineffective against dormant or persistent bacterial cells, which can survive treatment and lead to recurrent infections. The lack of methods to selectively induce and study species-specific antibiotics, particularly those that target pathogens like S. suis without affecting other bacteria or human cells, underscores the urgent need for innovative strategies to unlock the chemical diversity encoded in microbial genomes and to develop new solutions for combating persistent and resistant infections.

Technology

Threoglucins are a newly discovered family of ribosomally synthesized and post-translationally modified peptides (RiPPs) produced by Streptococcus suis via the tqq gene cluster. This gene cluster, typically silent under standard laboratory conditions, is activated by vitamin B3 derivatives such as niacin and nicotinamide. Upon activation, S. suis synthesizes a suite of peptides characterized by a unique 1,3-oxazinane heterocycle, which is formed through an aliphatic ether bond between a threonine sidechain and an adjacent glutamine’s α-carbon. Threoglucins display potent and highly selective antibiotic activity against S. suis, functioning as dormancy signals at low concentrations—thereby increasing antibiotic tolerance—and as bactericidal agents at higher concentrations. Structural studies have shown that both the oxazinane ring and a C-terminal tryptophan-tyrosine dyad are essential for their biological activity.

This technology is differentiated by several key features. First, the structural novelty of the 1,3-oxazinane heterocycle within the peptide backbone represents a previously unobserved motif in natural products, expanding the chemical diversity of RiPPs. Second, the dual functionality of threoglucins—as both dormancy signals and selective antibiotics—demonstrates a sophisticated mechanism for microbial self-regulation and survival, offering a new paradigm in antimicrobial strategy. Unlike broad-spectrum antibiotics, threoglucins exhibit species-specific activity, targeting only S. suis without affecting other bacteria or human cells, which minimizes collateral damage to beneficial microbiota and reduces the risk of off-target effects. The ability to induce these compounds using vitamin B3 derivatives also provides a practical approach to unlocking cryptic biosynthetic pathways in bacteria, paving the way for the discovery of additional novel therapeutics.

Benefits

• Highly selective antibiotic activity specifically targeting Streptococcus suis, minimizing impact on other bacteria and human cells.
• Dual functionality as dormancy signals at low concentrations, enhancing antibiotic tolerance and survival of S. suis.
• Bactericidal effects at higher concentrations, effectively killing S. suis cells.
• Unique structural modification (1,3-oxazinane heterocycle) essential for potent biological activity.
• Activation of cryptic biosynthetic gene cluster by vitamin B3 derivatives, enabling controlled production.
• Potential to serve as narrow-spectrum antibiotics, reducing risk of broad-spectrum resistance development.
• Insight into bacterial self-regulation mechanisms via quorum sensing and dormancy modulation.

Applications

• Narrow-spectrum S. suis antibiotics
• S. suis dormancy modulation agents
• Selective livestock infection treatments
• Diagnostic tools for S. suis

Additional info

These are a family of ribosomally synthesized and post-translationally modified peptides (RiPPs) from *Streptococcus suis*, activated by vitamin B3 derivatives. They feature a unique 1,3-oxazinane heterocycle formed by an aliphatic ether bond between threonine and glutamine residues. These peptides exhibit potent, selective antibiotic activity against *S. suis*, acting as dormancy signals at low concentrations and bactericidal agents at higher concentrations. The heterocycle and a C-terminal Trp-Tyr dyad are crucial for their function.