Simmonds Lab Research
Dr Simmonds’ major research interest is in the use of heterotrophic bacteria to bioconvert agricultural waste into useful product or industrial feedstock.
Rhodococcus opacus strain PD630 has been shown to accumulate triacylglycerol (TAG) to very high levels both in laboratory culture (87%) and at pilot-plant scale (38%). Four enzymes are involved in the TAG biosynthesis pathway. These enzymes all draw on the cellular pool of acyl-CoA intermediates and sequentially attach the acyl units to the glycerol backbone. Diacylglycerol acyltransferase (DGAT) is the last enzyme in the pathway and its presence or absence is critical to the formation of TAG containing intracellular inclusion bodies. Accumulation of TAG in this strain (and others) seems to be a survival mechanism and occurs in response to growth under starvation conditions, characterized by low nitrogen levels in the presence of excess carbohydrate. In most respects R. opacus PD630 is an admirable industrial producer strain, but its inability to accumulate lipids under condition of high nitrogen limits its potential industrial use to growth on substrates of relatively high purity (expensive). The mechanism by which nitrogen level controls TAG accumulation in R. opacus PD630 is not well understood and it is the focus of Dr Simmonds’ current research to understand this process at the molecular level.
Xiong, X., X. Wang and S. Chen. (2012). Engineering of a xylose-metabolic pathway in Rhodococcus strains. Appl. Environ. Microbiol. 78:5483-5491.
Holder, J.W. et al. (2011) Comparative and functional genomics of Rhodococcus opacus PD630 for Biofuels development. PLoS Genetics. 7 (9):e1002219.
Kurosawa K., K. Boccassi, N. de Almeida and A.J. Sinskey. (2010). High-cell-density batch fermentation of Rhodococcus opacus PD630 using a high glucose concentration for triacylglycerol production. J. Biotech. 147:212-218.
Alvarez H.M. and A. Steinbuchel. (2002). Triacylglycerols in prokaryotic microorganisms. Appl. Microbiol. Biotechnol. 60:367-376.
Voss, I. and A. Steinbuchel. (2001). High cell density cultivation of Rhodococcus opacus for lipid production at a pilot-plant scale. Appl. Microbiol. Biotechnol. 55:457-555.
Projects in Dr Simmonds’ lab are:
Physiological and chemical testing of lipids. In association with Dr John Birch, Department of Food Science. The lipids produced by R. opacus PD630 when grown on glucose have a composition that is different from those produced by eukaryotic organisms. This project seeks to understand the functional characteristics of these lipids and their potential uses in the food industry.
Production of novel FAs. In association with Dr Jason Ryan, Industrial Research Limited. This project seeks to determine if the expression of non-host fatty acid biosynthesis genes in R. opacus PD630 will lead to the accumulation of TAGs with novel FA compositions.
Understanding the regulation of FA biosynthesis genes. The accumulation of TAG in R. opacus PD630 is highly regulated, but the mechanism by which this is achieved is unknown. This project seeks to understand the genetic mechanisms involved in the accumulation of TAG in R. opacus PD630.
Applications for postgraduate study in Dr Simmonds’ lab are welcome. A major in microbiology or microbial technology is essential, and university level papers in chemistry and mathematics are highly desirable. It is essential for students to hold a University scholarship (or equivalent) before they undertake project work. Applications for scholarships can be found at: http://www.otago.ac.nz/postgraduate/index.html
Dr Simmonds has enjoyed a long standing collaboration with professors Gary Sloan and Russell Timkovich of the University of Alabama at Tuscaloosa which has resulted in ten joint publications and the exchange of PhD students between their respective laboratories.
Lester, K. and R. S. Simmonds. 2012. Zoocin A and lauricidin in combination reduce Streptococcus mutans growth in a multi-species biofilm. Caries Research.46:185-193.
Dufour, M., F.S.A. McLeod and R.S. Simmonds. 2011. Zoocin A facilitates the entry of antisense constructs into Streptococcus mutans. FEMS Microbiology Letters.317:93-99.
Gargis, S. R., H. E. Heath, P. A. LeBlanc, L. Dekker, R. S. Simmonds and G. L. Sloan. 2010. Inhibition of the activity of both domains of lysostaphin through peptidoglycan modification by the lysostaphin immunity protein. Applied and Environmental Microbiology. 76:6944-6946.
Gargis, S. R., A .S. Gargis, H. E. Heath, L. S. Heath, P. A. LeBlanc, M. Senn, B. Berger-Bächi, R. S. Simmonds and G. L. Sloan. 2009. Zif, the zoocin A immunity factor, is a FemABX-like immunity protein with a novel mode of action. Applied and Environmental Microbiology. 75:6205-6210.
Gargis, A., A-L. O’Rourke, A-L., G. Sloan and R. S. Simmonds. 2009. Prevalence and acquisition of the genes for zoocin A and zoocin A resistance in Streptococcus equi subsp. zooepidemicus. Journal of Molecular Evolution. 68:498-505.
Gargis, S. R., H. E. Heath, L. S. Heath, P. A. LeBlanc, R. S. Simmonds, R. Timkovich and G. L. Sloan. 2009. Use of 4-sulfophenyl isothiocyanate labeling and mass spectrometry to determine the site of action of the streptococcolytic peptidoglycan hydrolase zoocin A. Applied and Environmental Microbiology. 75:72-77.