Nematode Genetics Laboratory
In 2010 I took early retirement from my teaching position to focus full-time on research as an emeritus professor. Research in my laboratory concentrates on the molecular genetics of anhydrobiosis and cryobiosis in nematodes. Cellular water is generally essential for the maintenance of living systems, yet some organisms can survive in a desiccated state for indefinite periods. This remarkable ability, called anhydrobiosis (“life without water”), is found across all biological kingdoms, including bacteria, fungi, animals and plants. Anhydrobiotic organisms have evolved mechanisms which enable them to survive conditions in which there is no continuous aqueous phase in the cytoplasm and where the hydration shell of biomolecules is lost. In the anhydrobiotic state, metabolism and life processes come to a halt, but they resume again on rehydration. For example a viable culture of the nematode Panagrolaimus sp. PS443 was isolated from dry soil which had been stored in the laboratory for 8 years1, embryonated egg cysts of the brine shrimp Artemia salina can survive in an anhydrobiotic state for 15 years2 and plant seeds have been shown to survive for up to 300 years in herbaria3 and seed collections4.
Nematodes of the genus Panagrolaimus, offer many advantages as a system for the study of anhydrobiosis because they contain members with diverse anhydrobiotic phenotypes, have a short generation time and can readily cultured in large quantities in the laboratory with Esherichia coli as a food source, using methods developed for Caenorhabditis elegans. We have assembled a collection of species and strains of Panagrolaimus from various ecosystems worldwide and we have investigated their anhydrobiotic phenotypes. Our data show that within the genus Panagrolaimus there is a continuum of phenotypes. These range from desiccation sensitive strains, to strains which are unable to survive exposure to low relative humidity (RH) without prior preconditioning at high RH (slow desiccation strategists), to strains which can readily survive immediate exposure to severe desiccation over activated silica gel (fast desiccation strategists)5. We have also found that strongly anhdyrobiotic strains of Panagrolaimus are capable of surviving freezing to -80 0C in water. It seems likely that some of the adaptations that protect anhydrobiotic strains of Panagrolaimus from cellular dehydration overlap with adaptations which protect the nematodes during freezing. Freezing causes severe damage to cells by withdrawing water into ice, resulting in dehydration. In addition, ice crystals cause mechanical damage to cell organelles and membranes. Microrganisms, invertebrates and plants that experience subfreezing temperatures in nature can prevent or reduce freezing damage by synthesizing osmotically active antifreeze molecules such as glycerol or other polyols5,6 and/or synthesizing antifreeze proteins (AFPs) which bind to ice and inhibit its growth7,8,9,10. We also find that tissue extracts of the freezing tolerant strains of Panagrolaimus are able to inhibit the growth of ice crystals, which is very strong evidence that these nematodes are synthesizing an ice binding protein.
Recent developments in high-throughput sequencing11,12 represent a major breakthrough for genome and transcriptome studies of non-model organisms such as Panagrolaimus. In collaboration with Prof. Mark Blaxter, Institute of Evolutionary Biology, The University of Edinburgh, we are currently sequencing and annotating the genome and transcriptome of the Arctic nematode P. superbus, which is both freezing and desiccation tolerant. We are also characterising ice binding proteins from this nematode and carrying out a functional screen to identify anhydrobiotic genes. We expect that these projects will lead to the discovery of several novel genes and may ultimately lead to the development of new methods of preserving biological materials that do not normally survive drying.
Science Foundation Ireland, Enterprise Ireland, The Wellcome Trust, IRCSET (Irish Research Council for Science, Engineering and Technology), NUI Maynooth Research Enhancement Fund, Departmental Funding.
Burnell, A.M. and Tunnacliffe A. (2010). Gene induction and desiccation stress in nematodes. In: Perry R.N and Wharton D. (eds.) Molecular and Physiological Basis of Nematode Survival. CABI. Wallingford Oxfordshire UK ISBN:m978 1 84593 687 7 (in press).
Regeai, S.O., Dolan, K.M., Fitzpatrick, D.A., Browne, J.A., Jones, J.T. and Burnell A.M. (2009). Novel primers for the amplification of nuclear DNA introns in the entomopathogenic nematode Heterorhabditis bacteriophora and their cross-amplification in seven other Heterorhabditis species. Molecular Ecology Resources 9, 421–424.
Shannon, A.J., T. Tyson, I. Dix, J. Boyd and A.M. Burnell (2008). Systemic RNAi mediated gene silencing in the anhydrobiotic nematode Panagrolaimus superbus' BMC EVOLUTIONARY BIOLOGY 9 pp 58.
Tyson, T., W. Reardon, J.A. Browne and A.M. Burnell (2007). Gene induction by desiccation stress in the entomopathogenic nematode Steinernema carpocapsae reveals parallels with drought tolerance mechanisms in plants. International Journal of Parasitology, 37:763–776.
Fitzpatrick, D.A, O'Halloran, D.M. and Burnell, A.M. (2006). Multiple lineage specific expansions within the guanylyl cyclase gene family. BMC Evolutionary Biology 6, 26.
O'Halloran, D.M., Fitzpatrick, D.A, McCormack, G.P, McInerney, J.O and Burnell, A.M. (2006). The molecular phylogeny of a nematode specific clade of heterotrimeric G-protein a subunit genes. Journal of Molecular Evolution 63, 87-94.
Goyal, K. Walton, L.J. Browne, J.A., Burnell, A.M. and Tunnacliffe, A. (2005). Molecular anhydrobiology: identifying molecules involved in invertebrate anhydrobiosis. Integrative and Comparative Biology 45, 702-709.
Goyal, K., Browne, J.A., Burnell, A.M. and Tunnacliffe, A. (2005). Dehydration induced tps transcripts from an anhydrobiotic nematode contain novel spliced leaders and encode atypical GT-20 family proteins. Biochimie 87, 565-574.
Burnell, A.M., Houthoofd, K., O'Hanlon, K. and Vanfleteren, J.R. (2005). Alternate metabolism during the dauer stage of the nematode Caenorhabditis elegans. Experimental Gerontology 40, 850-856.
Shannon, A.J., Browne, J.A., Boyd, J. Fitzpatrick D.A. and Burnell, A.M. (2005). The anhydrobiotic potential and molecular phylogenetics of species and strains of Panagrolaimus (Nematoda, Panagrolaimidae). Journal of Experimental Biology 208, 2433-2445.
Browne, J.A., Dolan, K.M., Tyson, T., Goyal, K., Tunnacliffe, A. & Burnell, A.M. (2004). Dehydration-specific induction of hydrophilic protein genes in the anhydrobiotic nematode Aphelenchus avenae. Eukaryotic Cell 3, 966-975.
O'Halloran, D.M. and Burnell, A.M. (2003). An investigation of chemotaxis in the insect parasitic nematode Heterorhabditis bacteriophora. Parasitology 127, 375-385.
Goyal, K., Tisi, L., Basran, A., Browne, J., Burnell, A., Zurdo, J. and Tunnacliffe, A. (2003). Transition from natively unfolded to folded state induced by desiccation in an anhydrobiotic nematode protein. Journal of Biological Chemistry 278, 12977 - 12984.
Dolan, K.M. Jones J.T. and Burnell, A.M. (2002). Detection of changes occurring during recovery from the dauer stage in Heterorhabditis bacteriophora. Parasitology 125, 71-81.
Browne, J., Tunnacliffe A. and Burnell A. (2002). Plant desiccation gene found in nematode. Nature 416, 38.
Stock, S.P. Griffin, C.T. and Burnell, A.M. (2002). Morphological characterisation of Heterorhabditis isolates from the “Irish group” (Rhabditida, Heterorhabditidae), additional evidence supporting their recognition as a distinct species Heterorhabditis downesi, n. sp. Systematic Parasitology 51, 95-106.
Kakouli-Duarte, T. Casey, D.G. and Burnell, A.M. (2001). Development of a diagnostic DNA probe for the fruit flies Ceratitis capitata and Ceratitis rosa (Diptera: Tephritidae) using AFLP. Journal of Economic Entomology 94, 989-997.
Casey, D.G. and Burnell, A.M. (2001). The isolation of microsatellite loci in the Mediterranean fruitfly Ceratitis capitata (Diptera: Tephritidae) using a biotin/streptavidin enrichment technique. Molecular Ecology Notes 1, 120-122.
O'Leary, S.A. Power, A.P., Stack C.M. and. Burnell, A.M. (2001). Behavioural and physiological responses of infective juveniles of the entomopathogenic nematode Heterorhabditis to desiccation. BioControl 46, 345-362.
Ehlers, R.-U., Niemann, I., Hollmer, S., Strauch, O., Jende, D., Shanmugasundaram, M., Mehta, U.K., Easwaramoorthy, S. K. and Burnell, A.M. (2000). Mass production potential of the bacto-helminthic biocontrol complex Heterorhabditis indica-Photorhabdus luminescens. Biocontrol Science and Technology 10, 607-616.
Stack, C.M., Easwaramoorthy, S.G., Metha, U.K., Downes, M.J., Griffin, C.T., and Burnell, A.M. (2000). Molecular characterisation of Heterorhabditis indica isolates from India, Kenya, Indonesia and Cuba. Nematology 2, 477-487.
Burnell, A.M. and Stock, P. (2000). Heterorhabditis, Steinernema and their bacterial symbionts - lethal pathogens of insects. Nematology 2, 31-42.