Academic and Professional Awards

1992	The Michael Landau award for research in microbiology
1993 - 1995	The Clore scholarship for academic excellence, for Ph.D. students
1996 - 1998	EMBO long term fellowship, for Post Doctoral studies
1998 - 1999	Stephen Morse fellowship, for Post Doctoral studies
1999 - 2002	The "Alon" fellowship for outstanding young researchers. Awarded by the Israeli Ministry of Education

The research in the lab is focused on the study of microbial pathogenesis systems. Our goal is to understand the molecular mechanisms by which these systems function, the ways in which they are regulated and the evolutionary events that facilitate their establishment as pathogenesis systems. We have chosen to study two bacterial pathogens: Legionella pneumophila – the causative agent of a sever pneumonia in humans known as Legionnaires’ disease and the potential bio-terrorism agent Coxiella burnetii – the causative agent of Q-fever. Both these pathogens utilize a conserved type-IV secretion system, the Icm/Dot system, to modulate host cellular functions by the translocation of effector proteins into host cells. The components of the type-IV secretion system itself and the large collection of effectors which are translocated into host cells during infection are the primary pathogenesis determinants of these bacteria.

The projects carried out in the lab focus on different aspects of microbial pathogenesis:
- Co-evolution between pathogens and their host cells that leads to gene variation
- Modulation of host cell processes by bacterial pathogens
- Host-pathogen lateral gene transfer and its contribution to pathogenesis
- The regulatory network that control the expression of pathogenesis related genes
- Functional sub-complexes in type-IV secretion systems

Some examples of our research are shown below

1. Identification and characterization of Legionella and Coxiella effector proteins
In order to find new effector encoding genes we performed a genomic analysis using the consensus sequence of pathogenesis related regulators as a signature and identified thirty-five Legionella and sixty-eight Coxiella unique genes that contain the PmrA regulatory element. Few of these genes from Legionella were already found to be new icm/dot effectors. The characterization of the function of these PmrA regulated genes in both Legionella and Coxiella and their involvement in pathogenesis is currently studied in the lab.

Model of the Icm/Dot Type-IV secretion system

                                     Trends Microbiol. 6:253-255.

Identification of new Icm/Dot effector proteins

Mol. Microbiol. (2007) 63:1508-1523.

2. Study of hyper-variable genomic regions encoding for effector proteins
The number of effector encoded by the Legionella pneumophila genome was found to be very high. Some of the effectors are encoded from genomic regions enriched with effector encoding genes. Genomic analysis of these regions revealed that some of them are hyper-variable in their gene content, probably reflecting the on going arm race between Legionella and different amoeba species that serve as their environmental hosts.

Comparison of a hyper-variable genomic region from 4 Legionella pneumophila strains

Translocation analysis of proteins encoded from the hyper-variable genomic region

Infect. Immun. (2008) 76: 4581-4591.

3. Study of effectors horizontally transferred from amoebae to Legionella
The LegS2 of Legionella pneumophila is a homologue of the highly conserved eukaryotic enzyme sphingosine-1-phosphate lyase (SPL). Phylogenetic analysis revealed that it was most likely acquired from a protozoan organism early during Legionella evolution. The LegS2 protein was found to translocate into host cells using a C-terminal translocation domain absent in its eukaryotic homologues. LegS2 was found to complement the sphingosine-sensitive phenotype of the yeast Saccharomyces serevisia SPL-null mutant and this complementation depended on evolutionary conserved residues in the LegS2 catalytic domain. Interestingly, unlike the eukaryotic SPL that localizes to the endoplasmic reticulum, LegS2 was found to be targeted mainly to host cell mitochondria.

The Legionella effector LegS2 was most likely acquired from a protozoan organism

The Legionella effector LegS2 is localized to the host cell mitochondria

Cell. Microbiol. (2009) 11:1219-1235.

4. Two-component systems controls the expression of the Legionella pathogenesis system
Bacterial two-component systems are important regulatory machineries that control gene expression in response to environmental changes. It is well documented that such systems participate in the regulation of pathogenesis genes expression in many bacterial pathogens such as Salmonella enterica, Agrobacterium tumefaciens, Bordetella pertussis and others. A genetic screen performed in the lab identified the CpxR two-component response regulator, as an activator of the L. pneumophila icmR gene and additional icm/dot genes. Another two-component response regulator that was identified using a bioinformatic approach is PmrA that was found to control the expression of effector encoding genes. Moreover, both these regulators (CpxR and PmrA) were found to activate together the expression of the fir genes describe above. The central role of these two-component response-regulators in the regulation of Legionella pathogenesis might indicte that environmental signals sensed by their cognate sensor-kinases are critical for bacterial pathogenesis.

Screen for pathogenesis related regulators identified CpxR

J. Bacteriol. (2003) 185:4908-4919.

The regulators PmrA and CpxR bind directly and independently to the FIR regulatory region

J. Bacteriol. (2007) 189:3382-3391.

Model of the regulatory network of the Legionella Icm/Dot pathogenesis system

The PmrA-PmrB story - Mol. Microbiol. (2007) 63:1508-1523.

The CpxR-CpxA story - J. Bacteriol. (2008) 190:1985-1996.

The LetAS-RsmYZ-CsrA story - Mol. Microbiol. (2009) 72:995-1010.

1. Biran, D., Michaeli, S., Segal, G., and E. Z. Ron. 1992. Location of the metA gene on the physical map of Escherichia coli. J. Bacteriol. 174:5753-5754.

2. Segal, G., and E. Z. Ron. 1993. Cloning, sequencing, and transcriptional analysis of the vegetative sigma factor of Agrobacterium tumefaciens. J. Bacteriol. 175:3026-3030.

3. Segal, G., and E. Z. Ron. 1993. Heat shock transcription of the groESL operon of Agrobacterium tumefaciens may involved a hairpin-loop structure. J. Bacteriol. 175:3083-3088.

4. Segal, G., and E. Z. Ron. 1995. The groESL operon of Agrobacterium tumefaciens, evidence for heat shock-dependent mRNA cleavage. J. Bacteriol. 177:750-757.

5. Segal, G., and E. Z. Ron. 1995. The dnaKJ operon of Agrobacterium tumefaciens: transcriptional analysis and evidence for a new heat shock promoter. J. Bacteriol. 177:5952-5958.

6. Segal, G., and E. Z. Ron. 1996. Heat shock activation of the groESL operon of Agrobacterium tumefaciens and the roles of the inverted repeat. J. Bacteriol. 178:3634-3640.

7. Segal, G. and H. A. Shuman. 1997. Characterization of a new region, required for macrophage killing by Legionella pneumophila. Infect. Immun. 65:5057-5066.

8. Segal, G., Purcell, M., and H. A. Shuman. 1998. Host cell killing and bacterial conjugation require overlapping sets of genes within a 22-kb region of the Legionella pneumophila genome. Proc. Natl. Acad. Sci. USA. 95:1669-1674.

9. Segal, G. and H. A. Shuman. 1998. Intracellular multiplication and human macrophage killing by Legionella pneumophila are inhibited by conjugal components of IncQ plasmid RSF1010. Mol. Microbiol. 30:197-208.

10. Segal, G., and H. A. Shuman. 1999. Legionella pneumophila utilize the same genes for intracellular multiplication in Acanthamoeba castellanii and human macrophages. Infect. Immun. 67:2117-2124.

11. Segal, G., and H. A. Shuman. 1999. Possible origin of the Legionella pneumophila virulence genes and their relation to Coxiella burnetii. Mol. Microbiol. 33:669-670.

12. Segal, G., J. J. Russo and H. A. Shuman. 1999. Relationships between a new type-IV secretion system and the icm/dot virulence system of Legionella pneumophila. Mol. Microbiol. 34:799-809.

13. Hilbi, H., G. Segal and H. A. Shuman. 2001. Icm/Dot-dependent upregulation of phagocytosis by Legionella pneumophila. Mol. Microbiol. 42:603-618.

14. Zusman, T., O. Gal-Mor and G. Segal. 2002. Characterization of a Legionella pneumophila relA insertion mutant and the role of RelA and RpoS in virulence gene expression. J. Bacteriol. 184:67-75.

15. Toren, A., G. Segal, E. Z. Ron, and E. Rosenberg. 2002. Structure-function studies of the recombinant protein bioemulsifier AlnA. Environ. Microbiol. 4:257-261.

16. Gal-Mor, O., T. Zusman and G. Segal. 2002. Analysis of DNA regulatory elements required for the expression of the Legionella pneumophila icm and dot virulence genes. J. Bacteriol. 184:3823-3833.

17. Gal-Mor, O., and G. Segal. 2003. The Legionella pneumophila GacA homolog (LetA) is involved in the regulation of icm virulence genes and is required for intracellular multiplication in A. castellanii. Microb. Pathog. 34:187-194.

18. Zusman, T., G. Yerushalmi and G. Segal. 2003. Functional similarities between the icm/dot pathogenesis system of Coxiella burnetii and Legionella pneumophila. Infect. Immun. 71: 3714-3723.

19. Gal-Mor, O., and G. Segal. 2003. Identification of CpxR as a positive regulator of the icm/dot virulence genes of Legionella pneumophila. J. Bacteriol. 185:4908-4919.

20. Chen, J., K. Suwwan de Felipe, M. Clarke, H. Lu, R. Anderson, G. Segal and H. A. Shuman. 2004. Legionella effectors that promote non-lytic release from protozoa. Science. 303:1358-1361.

21. Zusman, T., M. Feldman, E. Halperin and G. Segal. 2004. Characterization of the icmH and icmF genes required for Legionella pneumophila intracellular growth, genes that are present in many bacteria associated with eukaryotic cells. Infect. Immun. 72:3398-3409.

22. Feldman, M., and G. Segal. 2004. A specific genomic location within the icm/dot pathogenesis region of different Legionella species encodes for functionally similar nonhomologous virulence proteins. Infect. Immun. 72:4503-4511.

23. Chien, M., I. Morozova, S. Shi, H. Sheng, J. Chen, S. M. Gomez, G. Asamani, K. Hill, J. Nuara, M. Feder, J. Rineer, J. J. Greenberg, V. Steshenko, S. H. Park, B. Zhao, E. Teplitskaya, J. R. Edwards, S. Pampou, A. Georghiou, I. Chou, W. Iannuccilli, M. E. Ulz, D. H. Kim, A. Geringer-Sameth C. Goldsberry, P. Morozov, S. G. Fischer, G. Segal, X. Qu, A. Rzhetsky, P. Zhang, E. Cayanis, P. J. De Jong, J. Ju, S. Kalachikov, H. A. Shuman, and J. J. Russo. 2004. The genomic sequence of the accidental pathogen Legionella pneumophila. Science. 305: 1966-1968.

24. Bekerman, R., G. Segal, E.Z. Ron and E. Rosenberg. 2005. The AlnB protein of the bioemulsan alasan is a peroxiredoxin. Appl. Microbiol. Biotechnol. 66:635-641.

25. Feldman, M., T. Zusman, S. Hagag and G. Segal. 2005. Coevolution between non-homologous but functionally similar proteins and their conserved partners in the Legionella pathogenesis system. Proc. Natl. Acad. Sci. USA. 102:12206-12211.

26. Yerushalmi, G., T. Zusman and G. Segal. 2005. Additive effect on intracellular growth by Legionella pneumophila Icm/Dot proteins containing a Lipobox motif. Infect. Immun. 73:7578-7587.

27. Zusman, T., G. Aloni, E. Halperin, H. Kotzer, E. Degtyar, M. Feldman and G. Segal. 2007. The Response Regulator PmrA is a Major Regulator of the icm/dot type-IV secretion system in Legionella pneumophila and Coxiella burnetii. Mol. Microbiol. 63:1508-1523.

28. Feldman, M., and G. Segal. 2007. A pair of highly conserved two-component systems participates in the regulation of the hyper variable FIR proteins in different Legionella species. J. Bacteriol. 189:3382-3391.

29. Altman E. and G. Segal. 2008. The response regulator CpxR directly regulates the expression of several Legionella pneumophila icm/dot components as well as new translocated substrates. J. Bacteriol. 190:1985-1996.

30. Zusman, T., E. Degtyar and G. Segal. 2008. Identification of a hypervariable region containing new Legionella pneumophila Icm/Dot translocated substrates using the conserved icmQ regulatory signature. Infect. Immun. 76: 4581-4591.

31. Rasis, M., and G. Segal. 2009. The LetA-RsmYZ-CsrA regulatory cascade, together with RpoS and PmrA, post-transcriptionally regulates stationary phase activation of Legionella pneumophila Icm/Dot effectors. Mol. Microbiol. 72:995-1010.

32. Degtyar, E., T. Zusman, M. Ehrlich and G. Segal. 2009. A Legionella effector acquired from protozoa is involved in sphingolipids metabolism and is targeted to the host cell mitochondria. Cell. Microbiol. 11:1219-1235.

33. Burstein, D., T. Zusman, E. Degtyar, R. Viner, G. Segal and T. Pupko. 2009. Genome-scale identification of Legionella pneumophila effectors using a machine learning approach. PLoS Pathog. 5(7): e1000508.

34. Hurtado-Guerrero, R., T. Zusman, S. Pathak, A. F. M. Ibrahim, S. Shepherd, A. Prescott, G. Segal and D. M. F. van Aalten. 2010. Molecular mechanism of elongation factor 1A inhibition by a Legionella pneumophila glycosyltransferase. Biochem. J. 426(3):281-292.

B. CHAPTERS IN BOOKS

1. Segal, G. and H. A. Shuman. Intracellular multiplication of Legionella pneumophila in human and environmental hosts. In: Microbial ecology of infectious disease, ed.: E. Rosenberg. Washington, ASM Press, 1999, pp. 170-186.

2. Ron, E. Z., Segal, G., Robinson, M., and D. Graur. Control elements in the regulation of bacterial heat shock response. In: Microbial ecology of infectious disease, ed.: E. Rosenberg. Washington, ASM Press, 1999, pp. 143-152.

3. Segal, G. and H. A. Shuman. Genetic analysis of Legionella pneumophila intracellular multiplication in human and protozoan hosts. In: Legionella, ed.: R. Marre et al. Washington, ASM Press, 2001, pp. 90-96.

4. Segal, G. The Evolution of the Legionella pneumophila Icm/Dot pathogenesis system. In: Introduction to the Evolutionary Biology of Bacterial and Fungal Pathogens, ed.: Baquero, César Nombela, Gail H. Cassell and José A. Gutiérrez. Washington, ASM Press, 2007, pp. 455-464.

C. REVIEWS

1. Segal, G., and E. Z. Ron. 1996. Regulation and organization of groE and dnaK operons in eubacteria. FEMS Microbiol. Lett. 138:1-10.

2. Segal, G., and E. Z. Ron. 1998. Heat shock response in bacteria. In: Stress of life from molecules to man, ed.: P. Csermely. Ann. N. Y. Acad. Sci. vol. 851:147-151.

3. Shuman, H. A., Purcell, M., Segal, G., Hales, L., and L. A. Wiater. 1998. Intracellular multiplication of Legionella pneumophila: Human pathogen or accidental tourist? In: Bacterial Infections: Close encounters at the Host Pathogen Interface, ed.: P. K. Vogt and M. J. Mahan. Springer, New York. Curr. Top. Microbiol. Immunol. 225:99-112.

4. Segal, G. and H. A. Shuman. 1998. How is the intracellular fate of the Legionella pneumophila phagosome determined? Trends Microbiol. 6:253-255.

5. Segal, G., M. Feldman, and T. Zusman. 2005. The Icm/Dot type-IV secretion system of Legionella pneumophila and Coxiella burnetii. FEMS Microbiol. Rev. 29:65-81.