Multifunctional magnetic nanoparticle cloud assemblies for in situ capture of bacteria and isolation of microbial DNA

Suspended magnetic nanoparticle assemblies forming between magnetized micropillars are used as a multifunctional capture matrix for Escherichia coli O157:H7 and in-flow extraction of microbial DNA released upon bacterial lysis.

Intramolecular synergism and bacterial lysis regulation can explain the complex multi-domain architecture of the bacteriophage endolysin PlySK1249

Endolysins are peptidoglycan hydrolases produced at the end of the bacteriophage (phage) replication cycle to lyse the host cell. Gram-positive phages endolysins come in a variety of multi-modular forms that combine different catalytic domains and may have evolved to adapt to their bacterial hosts. However, the reason why phage can adopt endolysin with such complex multidomain architecture is for the moment not well understood.We used the Streptococcus dysgalactiae phage endolysin PlySK1249 as a model to study the implication of multi-domain architecture in phage-induced bacterial lysis and lysis regulation. The activity of the enzyme relied on a bacteriolytic amidase (Ami), a non-bacteriolytic L-Ala-D-Ala endopeptidase (CHAP) acting as a de-chaining enzyme and central LysM cell wall binding domain (CBD).Ami and CHAP synergized for peptidoglycan digestion and bacteriolysis in the native enzyme or when expressed individually and reunified in vitro. This cooperation could be modulated by bacterial cell wall-associated proteases, which specifically cleaved the two linkers connecting the different domains. While both catalytic domains were observed to act coordinately to optimize bacterial lysis, the CBD is expected to delay diffusion of the enzyme until proteolytic inactivation is achieved.As for certain autolysins, PlySK1249 cleavage by bacterial cell wall associated proteases might be an example of dual phage-bacterial regulation and mutual coevolution. In addition, understanding more thoroughly the multidomain interplay of PlySK1249 opens new perspectives on the ideal architecture of therapeutic antibacterial endolysins.

Coordination of cohabiting phage elements supports bacteria–phage cooperation

Bacterial pathogens often carry multiple prophages and other phage-derived elements within their genome, some of which can produce viral particles in response to stress. Listeria monocytogenes 10403S harbors two phage elements in its chromosome, both of which can trigger bacterial lysis under stress: an active prophage (ϕ10403S) that promotes the virulence of its host and can produce infective virions, and a locus encoding phage tail-like bacteriocins. Here, we show that the two phage elements are co-regulated, with the bacteriocin locus controlling the induction of the prophage and thus its activity as a virulence-associated molecular switch. More specifically, a metalloprotease encoded in the bacteriocin locus is upregulated in response to stress and acts as an anti-repressor for CI-like repressors encoded in each phage element. Our results provide molecular insight into the phenomenon of polylysogeny and its intricate adaptation to complex environments.

Investigation of the calcium-induced activation of the bacteriophage T5 peptidoglycan hydrolase promoting host cell lysis

Bacteriophage T5 endolysin could be activated by Ca2+ in the periplasm of the host cell, thereby promoting bacterial lysis.