Original ideas that categorized filamentous bacteria as the stressed and dying members of a population are apparently wrong. This is not a terribly unusual finding since scientists are always correcting ideas; assigning roles to presumably defunct systems and finding mechanisms for what were thought to be random processes.

Filamentation in bacteria occur when the cell continues to grow after its chromosomes have been copied, but the cell doesn’t divide. Filamentous cells are characterized by their elongated shape, which can be 10-50 times longer than normal. Certain bacteria have genes that encode proteins which can make alterations to cell length for the purpose of becoming filamentous, but random mutations can cause deletions in components controlling cell division with a similar affect.

In uropathogenic Escherichia coli (UPEC), bacteria adhere to urinary tract walls, invade and multiply within epithelium cells (see figure below). A fraction of UPEC become filamentous within these cells. Being filamentous allows these cells, upon efflux, to avoid phagocytosis (getting ‘eaten’) by neutrophils (white blood cells). Moreover, it seems as if bacteria become filamentous in direct response to various receptors on host innate immune cells. This suggests that filamentation in this system evolved as a response to selection pressures from the host immune system, an advantage is conferred which allows the pathogen to reenter ‘fresh’ epithelial and sustain infection.

This type of system is used in various other bacteria and infection models to avoid host immune response, evade predators and even to confer antibiotic resistance. Filamentous bacteria responding to environmental stressors in order to obtain greater fitness is known as ‘morphological plasticity.’ In other words, cues from the external environment activate genes (plasticity) which change the shape of the bacteria (morphology). Studying this type of organism behavior can lead to better a understanding of pathogen-host interactions, letting us develop better medicines, especially if it turns out that bacteria filamentation is a widely used process among microscopic organisms, bacteria and fungi.

reference: Justice SS, Hunstad DA, Cegelski L, Hultgren SJ. (2008) Morphological plasticity as a bacterial survival strategy. Nat Rev Microbiol. 6(2):162-8

This entry was posted on Tuesday, March 18th, 2008 at 10:48 pm and is filed under evolution, microbiology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.