Performance of wild, tailed, humidity-robust phage on a surface-scanning magnetoelastic biosensor for Salmonella Typhimurium detection

A wild, tailed phage (TST) was compared with a genetically modified, filamentous phage (FST) for S. Typhimurium (ST) detection. When both phages were introduced into oppositely charged MUA and MUAM sensors, the RU values of TST showed an obvious increase on the MUAM sensor. The sensitivity of TST [54.78 ΔRU/(log PFU/mL)] was greater than that of FST [48.05 ΔRU/(log PFU/mL)]. The binding affinity (K_D = 1.75 × 10^-13 M) of TST on MUAM sensor was greater than that of FST. Both phages were specific to only ST, and TST exhibited a persistent binding capability at 50 % RH. When each phage-immobilized sensor was employed on chili pepper, the sensitivity [880.80 Hz/(log CFU/mL)] and detection limit (1.31 ± 0.27 log CFU/mL) of TST were significantly greater than those of FST. The orientation of TST on sensor promoted the uniform capture of bacteria and enhanced the reliable performance of a surface-scanning magnetoelastic biosensor.

Evaluating the effect of silver nanoparticles on bacteriophage lytic infection cycle-a mechanistic understanding

Bacteriophages and engineered nano-material (AgNPS) interactions is a relatively unexplored area of research. To answer the fundamental question whether bacteriophage lytic growth cycle is affected by the presence of AgNPs, laboratory experiments were performed with phages of Klebsiella pneumoniae, Delftia tsuruhatensis, Salmonella typhimurium, and Shigella flexneri using silver nanoparticles (AgNPs) with coating materials. One-step growth curves of bacteriophages indicated that the presence of these nanoparticles, and the associated ions of silver, produced pronounced effects on the lytic infection of certain bacteriophages. Effects included 96% reductions in post-infection phage yield in terms of plaque forming units (PFUs) after phages were incubated with silver nanoparticles and 28%-43% reductions from the presence of Ag⁺ alone. However, when Klebsiella pneumonia phage KL and Salmonella typhimurium phage Det7 were exposed to silver nanoparticles coated with poly-N-vinyl-2 pyrrolidone (PVP), an increase in final phage yield by as much as 250% was observed compared with the same phage not incubated with nanoparticles. A proposed mechanism, observed by transmission electron microscopy and verified using synthetic biology by which the nanoparticle binding phenotype can be produced, is that the binding of metal nanomaterial to phage virions results in potentially inhibitory effects. This binding was found to be dependent on the presence of exposed positively charged C-terminal amino-acid residues on the phage capsid surface, implied at first by amino-acid sequence comparisons between capsid proteins of the different phages used in this study. This was then proven experimentally using targeted DNA editing methods to fuse positive charged amino-acid residues to the coat protein C-terminus of non-binding phage. This induced the AgNP binding phenotype, as observed by TEM, DLS size measurements, and growth curve data that show the mutant constructs to be functionally inhibited after exposure to AgNPs. This research sets up a first platform for further research in the unexplored area of phage and AgNP interactions and provides useful findings.

Contributions of P2- and P22-like prophages to understanding the enormous diversity and abundance of tailed bacteriophages

We identified 9371 tailed phage prophages of 20 known types in reported complete genome sequences of 3298 bacteria in the Salmonella genus. These include 4758 P2 type and 744 P22 type prophages. The latter prophage types were found in the genome sequences of 127 and 24 bacterial host genera, increasing the known host ranges of phages in these groups by 114 and 20 genera, respectively. These prophage nucleotide sequences displayed much more diversity than was previously known from the 48 P2 and 24 P22 type authentic phages whose genomes have been sequenced. More detailed analysis of these prophage sequences indicated that major capsid protein (MCP) gene exchange between tailed phage clusters or types is extremely rare and that P22 prophage-encoded tailspikes correspond perfectly with their hosts' surface polysaccharide structure; thus, MCP and tailspike sequences accurately predict tailed phage type (and thus lifestyle) and host cell surface polysaccharide structure, respectively.