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Dr Martin Day 


The colonial morphology of an indigenous rhizosphere isolate on a selective medium

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).

An electron microscope image of an indigenous plasmid and phage-host bacterium

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?

Phage 1

Figure 3 - Phage 1

Phage 3

Figure 4 - Phage 3

Phage 4

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 projects were done in collaboration with ecologists and clinically related microbiologists and their success lay seamlessly combining ecological or clinical studies with a genetical ‘hat’. Thus 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.  This was done in situ in aquatic and rhizosphere.  Parallel microcosm and laboratory experiments have resolved some the limiting factors as well as identifying those that promote transfer. After a sabbatical period in the USA we isolated a phage with an extremely large genome – over 350 kb, the second largest known. This phage came from an extremophile isolated from the Great Salt Plains, Oklahoma.

The main theme of my research interest is in gene exchange and mutational events that contribute to bacterial evolution.  In summary my  interests/projects (present and past) are -

Small colony variants in staphylococci We have examined a range of characteristics, such as their mutation rates, modifications to gene expression levels, alterations in heat and antibiotic sensitivity.  This has examined the evolution of antimicrobial insensitivity as opposed to resistance.

Genome sequencing of small colony variants This work identified novel gene target sites for the generation of the SCV phenotype.

Plasmid and phage gene exchange in the environment This work was mostly done in situ ‘in a local river’ with indigenous aquatic bacteria.

Antibiotic and antiseptic resistance gene exchange between clinical isolates of staphylococci and streptococci.

Microbial genetics in extreme environments. Phage distribution in sea water stations in the Antartic and part way up the west coast of south America were studied.  In a separate study We isolated the second largest phage so far found from an inland salt lake (Oklahoma) from an indigenous halophile.

Plaque morphologies of phage 1

Figure 6 - Plaque morphologies of phage 1

Plaque morphologies of phage 4

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.

Grants

Funding in recent years has come from MAFF, NERC, NERC / BBSRC and Ciby-Giegy.

Collaborations

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.

Affiliated Staff

Paul Seaman