Understanding and manipulating a conserved and essential transcription factor to activate antibiotic production in Streptomyces species

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Almost all the antibiotics used in human medicine were discovered >50 years ago and most disease-causing bacteria are now resistant to one or more of these drugs. This means humans are facing a return to the pre-antibiotic era, an alarming situation that has been described as 'antibiotic Armageddon'. The government commissioned O'Neill review on AntiMicrobial Resistance (AMR) estimates that if we do not kick-start antibiotic discovery efforts now then by 2050 drug resistant infections will kill more people than cancer, an estimated 10 million a year. Most of the antibiotics we currently use are natural products derived from the secondary metabolites of soil bacteria and the most important group are called Streptomyces, which make 50% of all known antibiotics. Streptomyces are incredibly important to humans and although scientists have already discovered lots of antibiotics from these bacteria we now know that they only found the really easy to find compounds, the low hanging fruit. Genome sequencing over the last 15 years has revealed that Streptomyces bacteria only make about 25% of their secondary metabolites under laboratory conditions which means that from 1940-60, the so-called golden age of antibiotic discovery, scientists were barely sampling their capability. The rest are called 'silent' secondary metabolites because they do not make them in the lab. The good news is this means we have a big advantage over scientists working in the 20th century - if we can find ways to switch on production of all the silent secondary metabolites in the >600 known species we will find lots of new antibiotics that can enter the clinical trials pipeline. This is the earliest stage in antibiotic discovery and it is vital that we increase our efforts now because it takes 10-15 years to get drugs through clinical trials and approved for use in humans. Probably <1% of antibiotics will be suitable for treating disease so the more natural products we can discover from Streptomyces in the next few decades the better. One way to activate the production of silent secondary metabolites is to understand the natural signals and signalling pathways that control their production in the soil and this is the focus of our research. If we can manipulate those signalling pathways we can force the bacteria to make all of their antibiotics in the laboratory. Ideally we want to identify signalling pathways which effect antibiotic production in all 600+ known Streptomyces species and this is the subject of our proposal. We have identified a signalling pathway consisting of two proteins called MtrA and MtrB and found this is the only conserved and essential pathway in the genus Streptomyces. This means this MtrAB two-component system is found in every single sequenced Streptomyces strain! MtrA is a DNA binding protein and its activity is controlled by the signal sensing protein MtrB. If we disrupt the pathway by deleting the mtrA gene it is lethal. If we delete the mtrB gene it removes the need for an environmental signal to activate the pathway and results in over-production of active MtrA protein which switches on production of antibiotics that are usually silent in the wild-type strains. However, simply over-producing MtrA does not work, we HAVE to remove MtrB as well. In this project we will analyse MtrAB in two model species called S. coelicolor and S. venezuelae. We will determine how MtrB controls MtrA activity, why MtrA is active in the absence of MtrB and why and how MtrA activates the production of silent secondary metabolites. We will also try to make gain of function MtrA proteins that are always active and see if we can use them to switch on antibiotic production in our model strains and in two new talented Streptomyces species that we have isolated and genome sequenced. We call them talented because they appear to encode many novel secondary metabolites and MtrA may allow us to discover new antibiotics from these strains.