John Thomas Beatty
  • Department of Microbiology and Immunology, University of British Columbia, Vancouver
Endolysin Expression, Purification and Activity Determination by Zymography
Authors:  Alexander B. Westbye, Paul C. Fogg and John Thomas Beatty, date: 08/20/2014, view: 14763, Q&A: 0
Endolysins are peptidoglycan-degrading (muralytic) enzymes produced by many bacteriophages for cell lysis of the host bacterium. The enzymatic activity of muralytic enzymes can be assayed qualitatively using a zymogram containing incorporated peptidoglycan. This protocol describes the expression of a recombinant 6x His-tagged endolysin using an Escherichia coli (E. coli) expression system and native affinity purification of the protein using Ni-NTA agarose. For the zymogram, the protocol details isolation of crude peptidoglycan from the Gram-negative bacterium Rhodobacter capsulatus and the zymography of purified protein and crude cell lysate. Construction of an E. coli BL21 (DE3) pET28-a(+)-derived endolysin-expression system is briefly described.

The protocol described here was developed and optimized for the endolysin 555 utilized by the Rhodobacter capsulatus bacteriophage-like gene transfer agent (RcGTA) (Westbye et al., 2013) and to study the muralytic activities of protein P14 of RcGTA (Fogg et al., 2012), but should be transferrable as a general protocol to express and study a variety of endolysins.
Surface Polysaccharide Extraction and Quantification
Authors:  Cedric Arthur Brimacombe and John Thomas Beatty, date: 10/20/2013, view: 18625, Q&A: 8
Gram-negative bacterial cells possess two membranes - the inner cytoplasmic membrane and the outer membrane. The two membranes are distinct in their composition; the inner membrane is composed of a phospholipid bilayer, whereas the outer membrane (OM) is composed of an asymmetrical bilayer, with the outer leaflet containing lipopolysaccharide (LPS) (Raetz and Whitfield, 2002). Surface polysaccharides, such as LPS O-antigen, or capsular polysaccharide, are often tightly associated with the OM (Whitfield, 2006). This tight association can be used to generate a rough quantification of surface polysaccharides of Gram-negative bacterial cells, as the OM can easily be dissociated from cells without associated cell lysis (Brimacombe et al., 2013). The following method describes how to quickly extract and quantify OM-associated polysaccharides.
Bacterial Conjugation in Rhodobacter capsulatus
Authors:  Molly M. Leung and John Thomas Beatty, date: 07/05/2013, view: 12489, Q&A: 1
Bacterial conjugation of plasmids is the common method of introducing foreign DNA into Rhodobacter capsulatus because transformational systems have not been shown as efficient methods of introducing DNA to R. capsulatus. For R. capsulatus bacterial conjugation using an Escherichia coli donor can be used to introduce replicating vectors, and non-replicating vectors for targeted chromosomal modifications.
Rhodobacter capsulatus Gene Transfer Agent Transduction Assay
Authors:  Molly M. Leung and John Thomas Beatty, date: 02/20/2013, view: 10340, Q&A: 0
The gene transfer agent (GTA) is a bacteriophage-like particle that transfers genomic DNA from a donor to a recipient bacterium. The Rhodobacter capsulatus GTA (RcGTA) was the first to be studied and this protocol has been optimized for RcGTA transduction, although it could be modified for other bacteria containing a GTA. The RcGTA transduction assay can be used to determine transduction efficiencies, to create gene knock-outs, or to create new strains by transferring alleles from one strain to another.
Construction of Chromosomal In-Frame Deletion Mutants in Rhodobacter capsulatus
Authors:  Molly M. Leung and John Thomas Beatty, date: 02/20/2013, view: 12599, Q&A: 0
Markerless chromosomal in-frame deletion mutants are often used to avoid polar effects, conserve antibiotic resistance markers or make multiple mutations. This protocol capitalizes on the sacB gene (lethal in the presence of sucrose), for selection against a single cross-over event, on a suicide vector (contains no Rhodobacter capsulatus compatible origin of replication). The bacterial strains, media and suicide vectors in this protocol are specific for R. capsulatus, but the concepts can be applied to other species.
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