Mainly the latter considerably lowers the DCl
energy levels for vibrationally excited states (for
details, see section IV in the supplementary materials), resulting in a shallow well on the DCl
(v2 = 0, v3 = 2)–H VAP around the peak position
of the ground VAP, which supports one resonance state as shown in Fig. 4B. The resonance
state b has the same origin as the state a, except
on the bending excited state.
Both resonance states a and b are shape resonances on the DCl (v3 = 2) VAP, and they enhance the overall reactivity as shown in Fig. 3B.
They decay either through tunneling over the
barrier to yield DCl (v′ = 2) product or through
coupling with the DCl (v3 = 0,1) VAP to form DCl
(v′ = 0,1) products (Fig. 4B). Hence, these two
resonance states are also Feshbach resonances.
Because the state b is a bending excited (122)
state, it produces DCl with a bimodal rotational
distribution, in contrast with a Gaussian distribution from the state a (fig. S9). At EC = 4. 3 kcal/mol,
the low–partial-wave contribution of the state b
yields DCl with bimodal rotational distributions
in the backward scattering hemisphere, whereas
the contribution from high partial waves of resonance a generates broad peaks in the forward
scattering hemisphere with a rotationally cold
DCl product (fig. S10).
Quantum reactive scattering calculations showed
that similar dynamical resonances also exist in
the Cl + HD (v = 1) → HCl + D reaction channel
(see supplementary materials for details). However, because of the considerably smaller cross
sections of this reaction channel as compared
with the DCl channel, which are due to the strong
effect of the van der Waals interaction in the
entrance channel as has been observed for the
ground HD reaction ( 21), it is extremely difficult
to perform crossed-beam experiments on this reaction channel.
From the above studies, we have demonstrated that extremely short-lived resonances
in the Cl + HD (v = 1) reaction can be clearly
probed with the backward scattering spectroscopy method. These resonances are supported
by shallow wells on the DCl (v′ = 2) VAP caused
by chemical bond softening in the transition
state region. Because chemical bond softening
in the transition state region always occurs in
reactions with energetic barriers and can result in potential wells on highly excited VAPs, we
anticipate the existence of similar resonances
in many other chemical reactions involving
vibrationally excited reagents. Therefore, reaction dynamics studies with vibrationally excited
reagents open the door to probe resonances in
many direct chemical reactions.
REFERENCES AND NOTES
1. G. C. Schatz, Science 288, 1599–1600 (2000).
2. F. Fernández-Alonso, R. N. Zare, Annu. Rev. Phys. Chem. 53,
3. K. Liu, Adv. Chem. Phys. 149, 1– 46 (2012).
4. R. D. Levine, S.-F. Wu, Chem. Phys. Lett. 11, 557–561 (1971).
5. G. C. Schatz, J. M. Bowman, A. Kuppermann, J. Chem. Phys.
58, 4023–4025 (1973).
6. D. M. Neumark, A. M. Wodtke, G. N. Robinson, C. C. Hayden,
Y. T. Lee, Phys. Rev. Lett. 53, 226–229 (1984).
7. R. T. Skodje et al., Phys. Rev. Lett. 85, 1206–1209 (2000).
8. M. Qiu et al., Science 311, 1440–1443 (2006).
9. T. Wang et al., Science 342, 1499–1502 (2013).
10. I. M. Waller, T. N. Kitsopoulos, D. M. Neumark, J. Phys. Chem.
94, 2240–2242 (1990).
11. B. Zhang, K. Liu, J. Chem. Phys. 122, 101102 (2005).
12. J. G. Zhou, J. J. Lin, K. P. Liu, Mol. Phys. 108, 957–968 (2010).
13. J. Zhou, J. J. Lin, K. Liu, J. Chem. Phys. 121, 813–818 (2004).
14. R. Otto et al., Science 343, 396–399 (2014).
15. S. C. Althorpe, D. C. Clary, Annu. Rev. Phys. Chem. 54,
16. J. Hirschfelder, H. Eyring, B. Topley, J. Chem. Phys. 4,
17. H. S. Johnston, Gas Phase Reaction Rate Theory (Ronald,
New York, 1966).
18. K. P. Kumaran, S. S. Lim, J. V. Michael, J. Chem. Phys. 101,
19. J. Srinivasan, T. C. Allison, D. W. Schwenke, D. G. Truhlar,
J. Phys. Chem. A 103, 1487–1503 (1999).
20. M. Alagia et al., Science 273, 1519–1522 (1996).
21. D. Skouteris et al., Science 286, 1713–1716 (1999).
22. D. Skouteris et al., J. Chem. Phys. 114, 10662 (2001).
23. M. J. Ferguson, G. Meloni, H. Gomez, D. M. Neumark, J. Chem.
Phys. 117, 8181–8184 (2002).
24. D. E. Manolopoulos et al., Science 262, 1852–1855 (1993).
25. D. M. Neumark, Science 272, 1446–1447 (1996).
26. S. A. Kandel et al., J. Chem. Phys. 112, 670–685 (2000).
27. M. H. Alexander, G. Capecchi, H. J. Werner, Science 296,
28. E. Garand, J. Zhou, D. E. Manolopoulos, M. H. Alexander,
D. M. Neumark, Science 319, 72–75 (2008).
29. X. Wang et al., Science 322, 573–576 (2008).
30. Z. F. Ren et al., Rev. Sci. Instrum. 77, 016102 (2006).
31. T. Wang, T. Yang, C. Xiao, D. Dai, X. Yang, J. Phys. Chem. Lett.
4, 368–371 (2013).
32. N. Mukherjee, R. N. Zare, J. Chem. Phys. 135, 184202
33. N. Mukherjee, W. Dong, J. A. Harrison, R. N. Zare, J. Chem.
Phys. 138, 051101 (2013).
34. L. Schnieder, K. Seekamp-Rahn, E. Wrede, K. H. Welge,
J. Chem. Phys. 107, 6175–6195 (1997).
35. M. H. Qiu et al., Rev. Sci. Instrum. 76, 083107 (2005).
36. H. J. Werner et al., MOLPRO, version 2012.1, A package of ab
initio programs (2012); see www.molpro.net.
37. Z. Sun, H. Guo, D. H. Zhang, J. Chem. Phys. 132, 084112
This work was supported by the National Natural Science Foundation
of China, the Ministry of Science and Technology of China, and the
Key Research Program of the Chinese Academy of Sciences.
Figs. S1 to S13
Tables S1 and S2
References ( 38–45)
28 August 2014; accepted 17 November 2014
The type VI secretion system of Vibrio
cholerae fosters horizontal
Sandrine Borgeaud, Lisa C. Metzger, Tiziana Scrignari, Melanie Blokesch*
Natural competence for transformation is a common mode of horizontal gene transfer
and contributes to bacterial evolution. Transformation occurs through the uptake of
external DNA and its integration into the genome. Here we show that the type VI secretion
system (T6SS), which serves as a predatory killing device, is part of the competence
regulon in the naturally transformable pathogen Vibrio cholerae. The T6SS-encoding gene
cluster is under the positive control of the competence regulators TfoX and QstR and is
induced by growth on chitinous surfaces. Live-cell imaging revealed that deliberate killing
of nonimmune cells via competence-mediated induction of T6SS releases DNA and
makes it accessible for horizontal gene transfer in V. cholerae.
Vibrio cholerae is a well-studied human path- ogen that causes severe and potentially fatal diarrhea in humans. V. cholerae is primarily an aquatic bacterium that is often found in association with zooplankton (1). The
molted exoskeletons of planktonic crustaceans
are primarily composed of the polymer chitin.
When growing on chitinous surfaces, V. cholerae
initiates a developmental program known as
natural competence (2, 3), which allows the
bacterium to take up free DNA from the envi-
ronment ( 4) using a competence-specific DNA
uptake machinery ( 5, 6). The competence pro-
gram is dependent on the regulatory protein
TfoX, which is produced in the presence of
chitin and chitin degradation products ( 4, 7–9)
(fig. S1). Natural competence is also co-regulated
by carbon catabolite repression ( 10) and quorum
sensing (QS) ( 7). QS requires autoinducers [chol-
era autoinducer 1 (CAI-1) and autoinducer 2] and
a master regulator (HapR) ( 11). We recently dem-
onstrated that only a subset of the known com-
petence genes (e.g., comEA and comEC) (fig. S1)
are co-regulated by QS and in a CAI-1–dependent
manner ( 12, 13), and we suggested that CAI-1 acts
as a competence pheromone ( 12). The QS and
TfoX-dependent regulator QstR links QS and
TfoX activity in the induction of competence
genes ( 14) (fig. S1). In this study, we demon-
strate that the type VI secretion system (T6SS)
SCIENCE sciencemag.org 2 JANUARY 2015 • VOL 347 ISSUE 6217 63
Laboratory of Molecular Microbiology, Global Health Institute,
School of Life Sciences, Ecole Polytechnique Fédérale de
Lausanne, CH-1015 Lausanne, Switzerland.
*Corresponding author. E-mail: email@example.com
RESEARCH | REPORTS