Steve Diggle

Position:   Royal Society University Research Fellow
Tel:   +44(0)115 846 7949
Fax:   +44(0)115 846 7951
Email:   steve.diggle@nottingham.ac.uk 

Links:   Full list of publications; Funding; Twitter: @stevediggle

About me
I graduated in Biological Sciences (B.Sc, University of Salford, 1997, 1st Class) prior to undertaking a Ph.D in molecular microbiology studying quorum sensing in Pseudomonas aeruginosa (University of Nottingham, 2001). I worked as a Postdoctoral Fellow on both EU and BBSRC funded grants before obtaining a personal fellowship from the Royal Society in 2006. I served on the editorial board of FEMS Microbiology Letters from 2008-2012 and currently I am an editor for Microbiology Open. In my spare time I play bass guitar in The Unusual Suspects.

Awards
I was awarded the 2010 Fleming Prize by the Society of General Microbiology.

Current Research Interests: Social evolution theory in microbes
This is an extremely exciting time for researchers interested in the social behaviour of microbes. It is being increasingly realised that bacteria communicate and cooperate to perform a wide range of multicellular behaviours such as dispersal, foraging, biofilm formation, chemical warfare, and quorum sensing. These behaviours are provoking interest both in their own right, but also because of the applied implications that follow from many of them being involved with parasite virulence. I am using microbial systems to investigate two major fundamental questions of evolutionary biology, namely those of cooperation and communication. This is work funded by the Royal Society, NERC and the Human Frontier Science Program (HFSP).

Teaching
I currently give lectures on the School of Molecular Medical Sciences BMedSci course.

Previous main research findings 
My first research post focused on the effects of UV-irradiation on unscheduled DNA synthesis in human skin samples (Chadwick et al. 1996). I was also involved in the study of radiation treated gut epithelial tissue. During my post-graduate studies and future post-doctoral positions, I have studied cell-to-cell communication via diffusible signal molecules (quorum sensing) in the opportunistic pathogen Pseudomonas aeruginosa. This problematic organism, which is a leading cause of death in patients with Cystic Fibrosis, utilises three intertwined quorum sensing systems, two N-acyl homoserine lactone (AHL)-based and the Pseudomonas quinolone signal (PQS) to regulate virulence factor production.

Previously we demonstrated that the cytotoxic lectin (LecA) is strictly dependent on AHLs (Winzer et al. 2000) and PQS (Diggle et al. 2003). To unravel the increasing complexity of the quorum sensing genetic circuitry in P. aeruginosa, I constructed a lecA::luxCDABE fusion in P. aeruginosa and subjected it to random transposon mutagenesis. This set of experiments revealed a novel negative regulator of lecA expression, MvaT, previously undescribed in P. aeruginosa, which was subsequently shown to influence AHL and virulence factor levels (Diggle et al. 2002). A search of the available microbial genomes revealed that MvaT was restricted to the Pseudomonad's and many of these species contained at least one homologue (Vallet et al. 2004). In collaboration with Alain Filloux at the CNRS in Marseille, we found that a mutation in mvaT results in enhanced biofilm formation due to up-regulation of the fimbrial cup gene cluster (Vallet et al. 2004). Furthermore we showed (in collaboration with Abdul Hamood, Texas) that MvaT binds directly to the promoter region of ptxS, a gene involved in the regulation of exotoxin A (Westfall et al. 2004), a major virulence determinant. A microarray analysis revealed that a mutation in mvaT resulted in the transcriptional change of over 200 genes (Vallet et al. 2004). It therefore appears that MvaT is involved in many cellular processes and indeed, it has recently been shown by other workers that MvaT proteins are HN-S like in nature and these proteins regulate a variety of functions in other species of bacteria.

My work has also revealed that the galactophilic lectin LecA is involved in the formation of mature P. aeruginosa biofilms. Interestingly, such biofilms can be prevented and even dispersed by the addition of hydrophobic galactosides to the growth medium (Diggle et al. 2006). It is assumed that these sugars compete with sugars on the cell surface for LecA binding and so prevent cell to cell interactions. This work may lead to simple yet effective methods to eradicate P. aeruginosa biofilms which are economically important in the medical environment where they colonise catheters and other in-dwelling devices, and also are important in the cystic fibrosis lung being the leading cause of mortality. Furthermore, biofilms remain problematic in industry where they often grow in industrial pipes. Treating pipes with sugars offers a cheap and safe solution to such problems. Recently we have shown that inhibitors designed against the fucose-specific lectin LecB can significantly reduce biofilm formation (Johansson et al. 2009). Another way of disrupting biofilms may come from interrupting quorum sensing signalling (quorum quenching). We recently described an AHL acylase (PA2385) which degrades long chain AHLs (Sio et al. 2006). When overexpressed, this acylase significantly reduced virulence factor production. Its potential role in biofilm development remains to be elucidated.

P. aeruginosa also produces over 50 2-alkyl-4-quinolones (AQs), some of which were originally identified from their antibacterial properties (Diggle et al. 2006; Dubern & Diggle 2008; Heeb et al. 2011). One of these compounds, 2-heptyl-3-hydroxy-4-quinolone was discovered to function as a diffusible signal molecule and termed the pseudomonas quinolone signal (PQS). I demonstrated that PQS is essential for the production of several key virulence factors including LecA (Diggle et al. 2003). In collaboration with Pierre Cornelis from the University of Brussels I was involved in the identification of an efflux pump which facilitates cell-to-cell communication, antibiotic susceptibility and growth of P. aeruginosa (Aendekerk et al. 2005). Interestingly, addition of PQS to pump mutants completely restored growth, antibiotic susceptibility and virulence although the exact mechanism remains a mystery (Aendekerk et al. 2005). Microarray analysis performed in Nottingham has also revealed that PQS has a dual role as both an iron chelator and a signal molecule, and that the PQS precursor HHQ can also function as a direct signal (Diggle et al. 2007). The PQS-Fe complex plays an important role in the P. aeruginosa killing of C. elegans (Zaborin et al. 2009).

To date, PQS has not been identified in any other species of bacteria. However, I constructed a biosensor capable of detecting PQS and other related AQs from P. aeruginosa (Fletcher et al. 2007a; Fletcher et al. 2007b; Diggle et al. 2011). A screen of a number of Pseudomonas and Burkholderia species (including the important human pathogen Burkholderia pseudomallei) revealed that several made the immediate PQS precursor molecule HHQ (Diggle et al. 2006). This data is significant as it demonstrates for the first time a role for AQs in bacterial cell-to-cell communication beyond P. aeruginosa. Other work with B. pseudomallei has identified a number of AHLs produced by this organism and a role for QS in the response to oxidative stress (Lumjiaktase et al. 2006).

 
Other microbial interests

Historical and epidemiological aspects of plague. Always happy to give a talk on this and I have spoken on the subject at schools including Fettes College (Edinburgh), Manchester Grammar School and Oakham School (Rutland).