A genome-scale census of virulence factors in the major mould pathogen of human lungs

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Infectious diseases caused by fungi are a worldwide problem causing at least as many deaths as malaria and tuberculosis. For infections caused by spore-forming moulds there is only one available class of oral drug, the azoles. Azole resistance amongst clinical mould isolates is increasing and one possible cause of this problem is the widespread use of azoles in the environment as agricultural fungicides. There is therefore a desperate need to develop new antifungal treatments.Fungal particles (or spores), which are continually present in the air that we breathe, are able to survive in the human lung. Usually, this occurs when the immune system of the infected individual is not functioning optimally. Always, it involves the germination of the fungal spore (rather like a plant seed) and growth of long fungal cells called hyphae. Hyphae penetrate and dissolve lung tissues by secreting enzymes. The major fungal pathogen in the air we breathe is called Aspergillus fumigatus and people affected by cancer, or requiring organ transplants, are particularly at risk of fatal infections caused by it. Unfortunately our lack of understanding of A. fumigatus, and the technical difficulties encountered when working with it, has limited progress in this field. We do not fully understand why Aspergillus is able to survive inside the lung environment. We urgently need more basic information about this pathogen so we can begin to design future therapies. When scientists try to figure out how cellular processes work, a first port of call is often transcription factors. Transcription factors control the activity of many genes simultaneously so they command great power over cellular processes. If a transcription factor is important for a particular process, one will then look at which genes it regulates and this will give clues to the biology underlying that process. If a transcription factor is not involved then it, and all of the genes it regulates, can be eliminated from the investigation. By asking which transcription factors control the ability of A. fumigatus to cause disease, we can achieve a global view of the regulatory network which drives infection. We intend to couple this approach to a state of the art DNA sequencing technology to gain maximal insight on A. fumigatus pathogenicity, with minimal usage of mice. We have searched the A. fumigatus genome for transcription factor genes and created a collection of 401 A. fumigatus mutants, each one lacking a transcription factor. To ask which of the transcription factors is important for mammalian lung infection we will infect mice with the collection of mutants and see which are unable to survive inside the lung. We have devised a method which will allow us to test many mutants at the same time. This involves infecting all of the mutants into a single mouse, and after sacrifice, sequencing the DNA extracted from the lung to tell us which mutants have managed to survive. We will use this method to reveal all of the transcription factors driving pathogenicity (P-TFs) in A. fumigatus. Thus the lowest possible number of animals will be utilised. When we have identified all of the P-TFs we will then work to identify the genes which are regulated by each P-TF. In order to do this we will use two approaches. First we will chemically fix the transcription factor to A. fumigatus DNA to identify the binding sites of each transcription factor. Second we will look at gene expression in mutants lacking P-TFs and work out which genes become deregulated. The success of this investigation will 1) Redress the meagre progress made in recent decades in defining the molecular basis of pathogenicity of Aspergillus fumigatus 2) Lead us directly to the fungal processes we need to target with new drugs 3) Hugely reduce the number of animal infection studies performed by other scientists on A. fumigatus 4) Help us to optimise high throughput manipulation of A. fumigatus for future drug screens.