The adventure of bacteriophage adsorption to the bacteria and the brownian motion

How do phages adsorb to bacteria?
Did you know that phage adsorption to bacterial cells involves Brownian motion?
If no, then you are just a second to the answer.
Bacteriophages are viruses that infect bacterial cells as their hosts in an extremely efficient manner that made them be regarded as an antibiotics alternative. A successful phage infection involves a number of stages with adsorption being the first step and thus its understanding is fundamental in exploring the mechanisms of eating up bacteria. This represents the initial point of contact between virus and host and is vital in host range specificity determination.
A bacteriophage attaches to a bacteria. Photo by Tyler J. Ford

What is bacteriophage adsorption?

Bacteriophage adsorption refers to the adhesion (attachment) of phage to a bacterial cell. This process occurs naturally although scientists have also tried to modify it to fit their needs. This article will enlight on how it happens naturally

How does phage adsorption happen

There are mainly three steps involved in phage adsorption: initial contact, reversible binding and irreversible attachment. Initial contact involves random collisions between the phage and host usually brought about by Brownian motion, flow, dispersion, or diffusion. Reversible binding was discovered by by Garen and Puck (1951), involves binding and detachment from the cells, and was shown to keep the phage in close proximity to the bacterial cell surface as it searches for the specific receptor that can enable irreversible attachment. Reversible binding is sometimes mediated by an enzymatic cleavage which allows for conformational rearrangements in the phage molecules resulting into release of the genetic material into the host.

What happens during phage binding to the bacteria?

During adsorption, phages target an extensive range of receptors found on the cell wall of bacteria from peptide sequences to polysaccharide moieties, slime, biofilms, capsules, pili and flagella. Due to a wide range of receptors, phages end up adsorbing to more than one site, and sometimes, the receptors involved in reversible binding are not the ones involved in irreversible binding. The two receptor mechanism is beneficial in that it increases the stability and probability of finding receptors for irreversible binding in phages. Because of the difference in cell wall composition in the Gram-positive and Gram-negative bacteria, different receptors are involved in phage adsorption.

In Gram-positive bacteria, the receptors involved are usually teichoic acid, peptidoglycans or murein and or their residues. whereas In Gram-negative, the receptors involved are usually; Lipopolysaccharides (Lipid A, the core polysaccharide, O-polysaccharide), pili, flagella, and capsule. 

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