Research Projects

Streptomycetes are a group of filamentous soil bacteria known for producing commercially important natural products, including antibiotics and antifungal compounds. Natamycin (NTM) is a polyene macrolide and the only important antifungal compound with generally regarded as safe (GRAS) status. NTM has been used as an antifungal compound in more than 150 countries. NTM is a broad-spectrum antifungal compound and does not kill bacteria; hence, it is less likely to cause antibacterial resistance. The mechanism of NTM action is via the interaction with ergosterol, altering the structure and permeability of the fungal membrane. Compared to other antifungal compounds like amphotericin and nystatin, NTM displays low mammalian cell toxicity and is made safe to be used in food preservation. Additionally, NTM is used to treat fungal diseases like mycotic keratitis and bronchopulmonary aspergillosis. Major natural sources for NTM are Streptomyces chattanogenesis, S. natalensis, S. gilvosporeus, and S. lydicus. Production of NTM is catalysed by multi-modular enzymes coded by the biosynthesis gene cluster (BGC), which is under tight control of transcription regulators (TRs) responding to signalling molecule(s). TRs are often categorised as pathway-specific and global regulators based on their function, with the former being in a general cluster situated. Furthermore, these TRs are sub-classified as positive (activator) and negative (repressor) regulators, with the latter being placed at the top of the regulatory cascade responding to diffusible signalling molecules (SMs). Although NTM BGC contains two pathway-specific activators, ScnRI and ScnRII, the structural underpinnings of activation are unknown. Moreover, the negative regulator of NTM biosynthesis remains unidentified. Based on literature and bioinformatics studies, we hypothesise that ScgR, a TetR family transcription regulator (TFTR) responding to γ-butyrolactone (GBL, a SM), might negatively control NTM biosynthesis. The TFTRs have DNA and SM-binding domains on a single polypeptide chain at N- and C-termini, respectively. SM binding induces allostery in the DNA binding domain (DBD), which eventually derepresses the promoter of BGC activator(s). As mentioned above, ScnRI and ScnRII are the activators, and ScgR is the putative repressor for NTM biosynthesis. We aim to identify the SM for ScgR, followed by characterising its regulatory role in NTM biosynthesis to underpin the molecular basis of repression. Insights from the NTM synthesis repressor enable us to uncover the mechanism of transcription regulation, which can be exploited for enhanced NTM biosynthesis.