Dr Martin Day
Figure 1 - The colonial morphology of an indigenous rhizosphere isolate on a selective medium
Bacteria are ubiquitous microorganisms that can sometimes be cultured in isolation on selective media (Figure 1). My research interests are broad in the sense I have looked at gene exchange in Gram-positives and Gram-negatives, in clinical and ‘ecological’ sites (Figure 2).
Figure 2 - An electron microscope image of an indigenous plasmid and phage-host bacterium
However the theme is really encompassed by a desire to understand how genetic interactions (of gene flow and exchange) and selection drivemicrobial evolution. All bacteria participate in gene exchange and the three recognised mechanisms that have evolved are designed to do so. One of which is termed transduction. This process is driven by bacteriophage (Figures 3 to 5). When these phage plate on their host (Figure 1) they produce distinctive plaque morphologies (Figures 6 and 7). Of many questions you could ask, it is interesting to ask how and why three have evolved? Is any one more significant than any other?
Figure 3 - Phage 1
Figure 4 - Phage 3
Figure 5 - Phage 4
I have also participated in various clinically based research projects and have looked at gene exchange by conjugation and transduction in MRSA and vancomycin resistant streptococci. I have also participated in various clinically based research projects and have looked at gene exchange by conjugation and transduction in MRSA and vancomycin resistant streptococci. More recently this work has examined SCV (small colony variant) formation in MRSA staphylococci. SCVs show different sensitivities to antimicrobials and appear to be a survival strategy as when environmental conditions for the wild type cells become adverse, then SCVs are sometimes more viable. The ecologically-based work until recently was been done in collaboration with Prof Fry and this reflected the importance of seamlessly combining ecological and genetical approaches in order to achieve success. Thus over the past 15 years we have looked at gene movement in biofilms, such as the epilithon and rhizosphere. We have through this work shown indigenous plasmids and phage to be capable of movement and together with transformation shown transfer of chromosomal genes too. Parallel microcosm and laboratory experiments have resolved some the limiting factors as well as identifying those that promote transfer. After a sabbatical in USA we isolated a phage with an extremely large genome. This phage came from an extremophile isolated from the Great Salt Plains, Oklahoma. It is about to be sequenced and we expect the sequence data will reveal characteristics important to survival in environments naturally subject to intense temperature and salinity changes.
Figure 6 - Plaque morphologies of phage 1
Figure 7 - Plaque morphologies of phage 4
Thus the research work aims to bridge gaps in genetic and ecological information by doing experiments in the field and in microcosm, and comparing these data with those from laboratory work.
Funding in recent years has come from MAFF, NERC, NERC / BBSRC and Ciby-Giegy.
Much of this work has been done in association with others. Collaboration has been with staff within the University, in the Schools of Biosciences and Pharmacy, and outside at CEC, Oxford and the Department of Microbiology, Oklahoma State University.