2023-04-26 10:00:19
Brods or spheres, spirals or commas, bacterial cells can adopt a wide variety of shapes. The typical morphology of each species is imposed by a rigid structure, made up of polymers assembled around the cells: the cell wall. In addition to its reinforcement role, the composite wall exerts a counter-pressure on the cellular contents, otherwise the bacteria would swell like balloons until they burst, due to their internal pressure. With each division, significant rearrangements of the wall guide the partition through the middle of a mother cell into two identical daughter cells.
By virtue of its position as an interface between the cell and the outside, the wall certainly constitutes a protective structure, but also a privileged target of antibacterial attacks, both by certain antibiotics such as penicillin and by bacteria viruses, called “phages”. “. The latter, following having infected a bacterium and having multiplied there, produce molecules which break the wall; the explosion of their host under the effect of osmotic pressure (due to a difference in concentration between the inside and the outside) then leads to their release.
In 1935, microbiologist Emmy Klieneberger-Nobel discovered that certain bacteria can, under protective osmotic conditions, live in a form without a wall, which she named “L-form”. In this form, spherical in the absence of architectural constraints, the bacteria multiply much more slowly and must free themselves from the well-regulated mechanisms which usually ensure cell division. The new bacteria then bud on the surface, or assemble inside the older ones, like those soap bubbles that skilful blowers manage to inflate inside a first bubble. One of the advantages of this L-form, despite its fragility and slow growth, is that it is insensitive to antibiotics which target the cell wall.
A barrier to phage therapy
In review Nature Microbiology Of March, researchers from the Swiss Federal Institute of Technology in Zurich (Switzerland) have studied the transition to the L form during a phage attack. By observing under the microscope bacteria of the species Listeria monocytogenes in the presence of phages, they observed the appearance of L forms of the bacterium, characterized by their typical morphology and mode of growth. During this process, it is not the infected bacteria themselves that are converted into L-forms, but part of their bath neighbors, which thus become resistant to infection. Only to survive the attack, these bacteria continue to multiply, while the others die. If they are replaced in an environment devoid of phages, they then resume their normal mode of growth.
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