Modification of essential bacterial peptidoglycan (PG)-containing cell walls can lead to antibiotic resistance; for example, β-lactam resistance by l,d-transpeptidase activities. Predatory Bdellovibrio bacteriovorus are naturally antibacterial and combat infections by traversing, modifying and finally destroying walls of Gram-negative prey bacteria, modifying their own PG as they grow inside prey. Historically, these multi-enzymatic processes on two similar PG walls have proved challenging to elucidate. Here, with a PG-labelling approach utilizing timed pulses of multiple fluorescent d-amino acids, we illuminate dynamic changes that predator and prey walls go through during the different phases of bacteria:bacteria invasion. We show formation of a reinforced circular port-hole in the prey wall, l,d-transpeptidaseBd-mediated d-amino acid modifications strengthening prey PG during Bdellovibrio invasion, and a zonal mode of predator elongation. This process is followed by unconventional, multi-point and synchronous septation of the intracellular Bdellovibrio, accommodating odd- and even-numbered progeny formation by non-binary division.
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We thank D. Kearns and his laboratory (Indiana University, USA) for facilities and hospitality to culture B. bacteriovorus, A. Lovering (University of Birmingham, UK) for insights and assistance with the alignment of l,d-transpeptidase protein sequences in B. bacteriovorus, T. Pilizota (University of Edinburgh, UK) for advice on osmotic stress conditions, and R. Lowry (University of Nottingham, UK) for assistance in image acquisition. One of the 3D SIM microscopes used for this research was supported by Medical Research Council UK grant (MR/K015753/1) to S. Foster, University of Sheffield, UK, and we thank C. Walther and S. Foster for the access and their kind help with this. This work was supported by BBSRC grant [BB/M010325/1] to C.L., a Leverhulme Trust (UK) Research Leave Fellowship RF-2013-348 to R.E.S., NIH GM113172 grant to M.V.N. and Y.V.B. and R35GM122556 and GM51986 to Y.V.B. A.De. was supported by an EMBO long-term fellowship, and W.V. was supported by funds from the Wellcome Trust (101824/Z/13/Z).
The authors declare no competing financial interests.
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A correction to this article is available online at https://doi.org/10.1038/s41564-017-0087-1.
Electronic supplementary material
Supplementary Figures 1–9, Supplementary Tables 1–3, Supplementary References.
3D-project of 3D-SIM scan of BADA-labelled Bdellovibrio cells (false coloured in red) preying upon E. coli cells pulse-labelled with HADA (false coloured in cyan), 15 minutes post-mixing.
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Kuru, E., Lambert, C., Rittichier, J. et al. Fluorescent D-amino-acids reveal bi-cellular cell wall modifications important for Bdellovibrio bacteriovorus predation. Nat Microbiol 2, 1648–1657 (2017). https://doi.org/10.1038/s41564-017-0029-y
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