Emeritus Professor John Pemberton

Emeritus Professor

School of Chemistry and Molecular Biosciences
Faculty of Science

Overview

My research interests have concentrated on the molecular genetic analysis of multigene phenotypes of bacteria encompassing the degradation of man-made environmental pollutants, synthesis of antitumour antibiotics, photosynthesis and the secretion of extracellular enzymes. My research was the first to identify, isolate and clone genes responsible for the degradation of a man-made molecule providing an explanation of how microorganisms rapidly evolve the ability to degrade and recycle a vast array of worldwide environmental pollutants which cause a range of diseases from cancer to birth defects. (Pemberton & Fisher,1977). The man made molecule used in these studies was the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), the most widely used pesticide in the world. One of these 2,4-D degradation genes (tfdA) confers resistance to the herbicide 2,4-D. Plants genetically engineered with tfdA show resistance to the herbicide 2,4-D. A range of plants including corn, soya, cotton and grapes have been genetically engineered for resistance to the herbicide 2,4-D.Bacteria play a major role in the degradation of environmental pollutants and the most widely studied is the bacterium Ralstonia eutropha JMP134 which has an extraordinary ability to degrade and recycle the most complex and most toxic man made molecules( Don and Pemberton, 1981:Schmidt et.al.,2011. Catabolic Plasmids.Encyclopedia of Life Sciences).Famously more recent studies have shown that there are catabolic genes and catabolic gene clusters encoding the degradation of explosives and chemical weapons of war. Detailed studies of the catabolic activities of bacteria show that catabolic genes and catabolic gene clusters play a major role in the worldwide carbon cycle.

Research in bacterial photosynthesis lead to the first genetic map of a photosynthetic bacterium (Bowen and Pemberton.1981). Photosynthesis is considered the most important biological process on earth and the discovery of the long sought master regulator(PPSR) of bacterial photosynthesis (Penfold and Pemberton,1991&1994) provided the first detailed insight of how bacterial photosynthesis is regulated at the molecular level. This research also led to the first cloning and heterologous expression of a carotenoid gene cluster(Pemberton&Harding,1986 & 1987).Subsequent heterologous expression of carotenoid genes in an increasing variety of plants led to the production of foods enriched in the precursors of vitamin A. My research was the first to clone and express an antibiotic biosynthesis pathway in E.coli K12 (Pemberton et.al.,1991). This was a gene cluster from Chromobacterium violaceum which encodes the strikingly purple pigmented anti-tumour antibiotic violacein. Sequence analysis and functional characterisation of the violacein biosynthetic pathway was carried out by August and co-workers(2000). Subsequent studies led to the development of techniques and vectors that should allow cloning and stable, high level expression of more antibiotic biosynthesis pathways in E.coli K12, particularly pathways from the prolific antibiotic producers the Streptomycetes ( Sarovich and Pemberton,2007; Philip, Sarovich and Pemberton,2008 & 2009; Ahmetagic & Pemberton, 2010 & 2011; Ahmetagic,Philip ,Sarovich,Kluver and Pemberton,2011).An article published in June 2013 by Stevens and co-workers PLoS ONE 8(5) showed that a native gene cluster from Streptomyces rimosus encoding tetracycline can be directly expressed in E.coli.

For the first time researchers have showed the expression of the violacein gene cluster in a eukaryote-the yeast Saccharomyces cerevisiae (Lee et al., 2013). Such a discovery may indicate that the violacein gene cluster can be expressed in organisms which range from microbes to man. It may also indicate that major pathways from microorganisms can be engineered and expressed in a range of eukaryotes.Since violacein is a potent anticancer agent it is of interest to determine if eukaryotes carrying bacteria engineered to produce violacein have reduced cancer rates. In addition, it may be possible to engineer the violacein pathway into organisms that do get cancer and observe if such organisms have lower cancer rates.In view of the purported prokaryotic ancestry of eukaryoyic organelles such as mitochondria and chloroplasts ,one possible way of boosting violacein synthesis in eukaryotic cells could be to integrate the violacein gene cluster into organelle DNA.

Finally, violacein is chemically related to the well known anti-cancer drug staurosporine and possesses anticancer, antifungal, antiparasite, antibacterial and antiviral activities. Indeed it is now known that violacein producing bacteria associated with certain frogs provides some protection against extinction by the worldwide spread of ‘chytrid’ fungus(Harris et.al., 2009). Since the violacein gene cluster is expressed in a wide range of bacteria ( Dr D S Philip, personal communication;D.S/Philip.PhD Thesis 2010) and has potent activity against the malarial parasite Plasmodium falciparum and other mosquito borne parasites, there is the possibility that mosquitoes engineered to carry the violacein gene cluster might be resistant to parasite infection. The cluster could be stably incorporated in the genomes of bacteria normally inhabiting the surface or the gut of the mosquito.

Qualifications

  • Fellow of the Australian Society for Microbiology
  • Fellow of the American Academy of Microbiology
  • GDipEd, University of Southern Queensland
  • Doctor of Philosophy, Monash University
  • BAgrSc, University of Melbourne

Publications

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Publications

Journal Article

Conference Publication

PhD and MPhil Supervision

Completed Supervision