Koval, Susan - University of Western Ontario - Department of Microbiology and Immunology

研究领域

Research in our lab is focussed on a group of predatory prokaryotes, Bdellovibrio-and-like organisms (BALOs). These microorganisms are important components in the control of Gram-negative bacterial populations (both free-living and pathogenic species) in aquatic and terrestrial ecosystems. BALOs are one of only a few prokaryotes with a developmental life cycle. This life cycle alternates between an extracellular, flagellated, nongrowing phase (the attack phase) and an intracellular, periplasmic phase in the prey cell after the formation of an osmotically stable body termed the bdelloplast (the growth phase). In the growth phase, the predator hydrolyses for nutrients the cytoplasmic macromolecules of the prey cell, and grows into a single, elongating, spiral cell with unseptated cytoplasm. Upon some unknown signal, multiple septa are formed simultaneously and progeny cells formed. Synthesis of the single, polar sheathed flagellum begins and continues after the progeny cells are released from the bdelloplast. It is important to note that DNA replication occurs only in the growth phase. Thus BALOs are obligate predators. Bdellovibrio bacteriovorus was first described in 1963 by Stolp and Starr. To date, there are four recognized genera of BALOs (Bdellovibrio, Bacteriovorax, Peredibacter and Bacteriolyticum) whose species are able to utilize Gram-negative bacteria as prey cells. The best-characterized of these predators is Bdellovibrio bacteriovorus and hence the term ‘Bdellovibrio-and-like-organisms’. All the described species exhibit the periplasmic life cycle traits described above. Our lab isolated a Bdellovibrio-like organism with a different life cycle, termed epibiotic (Shemesh et al. 2003). This organism does not enter the periplasm of the prey cell, but remains attached on the outside from where it utilizes nutrients from the prey cell. Phylogenetic studies showed that this isolate belongs to the genus Bdellovibrio (Davidov and Jurkevitch, 2004). We have designed a 16S rRNA-targeted oligonucleotide probe for detection of the genus Bdellovibrio by fluorescence in situ hybridization (Mahmoud et al. 2007). This probe is useful not only for ecological studies but also to assist in identification of new isolates of BALOs. Recent studies have focussed on the role of type IV pili in the attachment and invasion stages of the life cycle of BALOs (Mahmoud and Koval, 2010). Our current research objectives are: (1) to determine the components of predator and prey surfaces that dictate attachment and penetration; (2) to characterize the life cycle of epibiotic predators and compare it with the details of the periplasmic life cycle that have been investigated. Our studies will contribute towards an understanding of the dynamics of microbial populations in freshwater and terrestrial environments. Major Research Interests: life cycle, diversity and detection of Bdellovibrio-and-like organisms; structure and function of bacterial surface components; microbial ultrastructure.

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Chanyi, R.M., S.F. Koval and J.S. Brooke. 2016. Stenotrophomonas maltophilia biofilm reduction by Bdellovibrio exovorus. Environmental Microbiology Reports 8: 343-351. doi:10.1111/1758-2229.12384 Chanyi, R.M. and S.F. Koval. 2014. Role of Type IV pili in predation by Bdellovibrio bacteriovorus. PLoS One Nov 19;9(11):e113404. doi: 10.1371/journal.pone.0113404. Koval, S.F., H.N. Williams and O.C. Stine. 2014. Reclassification of Bacteriovorax marinus as Halobacteriovorax marinus gen. nov., comb. nov. and Bacteriovorax litoralis as Halobacteriovorax litoralis comb. nov.; description of Halobacteriovoraceae fam. nov. in the class Deltaproteobacteria. International Journal of Systematic and Evolutionary Microbiology Nov 18. pii: ijs.0.070201-0. doi: 10.1099/ijs.0.070201-0. [Epub ahead of print] Pasternak, Z., M. Njagi, Y. Shani, R. Chanyi, O. Rotem, M.N. Lurie-Weinberger, S. Koval, S. Pietrokovski, U. Gophna and E. Jurkevitch. 2013. In and out: an analysis of epibiotic vs. periplasmic bacterial predators. ISME J. doi:10.1038/ismej.2013.164 Chanyi, R.M., C. Ward, A. Pechey, and S.F. Koval. 2013. To invade or not to invade: two approaches to a prokaryotic predatory life cycle. Canadian Journal of Microbiology 59:273-279. Koval, S.F., S.H. Hynes, R.S. Flannagan, Z. Pasternak, Y. Davidov and E. Jurkevitch. 2013.Bdellovibrio exovorus. sp. nov., a novel predator of Caulobacter crescentus. International Journal of Systematic and Evolutionary Microbiology. 63:146-151. Mahmoud, K.K. and S.F. Koval. 2010.Characterization of type IV pili in the life cycle of the predator bacterium Bdellovibrio. Microbiology 156:1040-1051 Mahmoud, K.K., D. McNeely, C. Elwood and S.F. Koval. 2007. Design and performance of a 16S rRNA-targeted oligonucleotide probe for detection of members of the genus Bdellovibrio by fluorescence in situ hybridization. Applied and Environmental Microbiology. 73:7488-7493 Koval , S.F. and G.D. Sprott. 2007. Cell fractionation. In: Methods for General and Molecular Microbiology. American Society for Microbiology Press p. 108-137 Koval, S.F. 2007. The Search for Hunters: culture-dependent and -independent methods for analysis of Bdellovibrio and like organisms. In: Predatory Prokaryotes - Biology, Ecology and Evolution. E. Jurkevitch (ed.) Springer Microbiology Monographs. p.191-211. (Published online: 27 October 2006) Davidov, Y., D. Hutchon, S.F. Koval, and E. Jurkevitch. 2006. A new α-proteobacterial clade of Bdellovibrio-like predators: implications for the mitochondrial endosymbiotic theory. Environmental Microbiology 8:2179-2188 Flannagan , R.S., M.A. Valvano and S.F. Koval 2004. Downregulation of the motA gene delays the escape of the obligate predator Bdellovibrio bacteriovorus 109J from bdelloplasts of bacterial prey cells. Microbiology 150:649-656 Shemesh , Y., Y. Davidov , S. Koval and E. Jurkevitch. 2003. Small eats big: Ecology and diversity of Bdellovibrio and like organisms, and their dynamics in predator-prey interactions. Agronomie 23:1-7 Koval , S.F. and M.E. Bayer 1997. Bacterial capsules: no barrier to Bdellovibrio . Microbiology 143:749-753