Filamentation is the anomalous growth of certain
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a Bacte ...
, such as ''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet st ...

Escherichia coli
'', in which cells continue to elongate but do not divide (no septa formation). The cells that result from elongation without division have multiple chromosomal copies. In the absence of
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokary ...
s or other stressors, filamentation occurs at a low frequency in bacterial populations (4-8% short filaments and 0-5% long filaments in 1- to 8-hour cultures), the increased cell length protecting bacteria from
protozoa Protozoa (also protozoan, plural protozoans) is an informal term for a group of single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris. Historically, ...
predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
and neutrophil
by making ingestion of the cells more difficult. Filamentation is also a virulence factor thought to protect bacteria from antibiotics, and is associated with other aspects of bacterial virulence such as formation. The number and length of filaments within a bacterial population increases when the bacteria are treated with various chemical and physical agents (e.g. DNA synthesis-inhibiting antibiotics, UV light). Some of the key genes involved in filamentation in ''E. coli'' include ''sulA'' and ''minCD''.

Filament formation

Antibiotic-induced filamentation

Some peptidoglycan synthesis inhibitors (e.g. cefuroxime, ceftazidime) induce filamentation by inhibiting the penicillin binding protein, penicillin binding proteins (PBPs) responsible for crosslinking peptidoglycan at the septal wall (e.g. PBP3 in ''E. coli'' and ''P. aeruginosa''). Because the PBPs responsible for lateral wall synthesis are relatively unaffected by cefuroxime and ceftazidime, cell elongation proceeds without any cell division and filamentation is observed. DNA synthesis-inhibiting and DNA damaging antibiotics (e.g. metronidazole, mitomycin C, the fluoroquinolones, novobiocin) induce filamentation via the SOS response. The SOS response inhibits septum formation until the DNA can be repaired, this delay stopping the transmission of damaged DNA to progeny. Bacteria inhibit septation by synthesizing protein SulA, an FtsZ inhibitor that halts Z-ring formation, thereby stopping recruitment and activation of PBP3. If bacteria are deprived of the nucleobase thymine by treatment with folate, folic acid synthesis inhibitors (e.g. trimethoprim), this also disrupts DNA synthesis and induces SOS-mediated filamentation. Direct obstruction of Z-ring formation by SulA and other FtsZ inhibitors (e.g. berberine) induces filamentation too. Some protein synthesis inhibitors (e.g. kanamycin), Transcription (biology), RNA synthesis inhibitors (e.g. bicyclomycin) and membrane disruptors (e.g. daptomycin, polymyxin B) cause filamentation too, but these filaments are much shorter than the filaments induced by the above antibiotics.

Ultraviolet light-induced filamentation

UV light damages bacterial DNA and induces filamentation via the SOS response.

Nutrition-induced filamentation

Nutritional changes may also cause bacterial filamentation. For example, if bacteria are deprived of the nucleobase thymine by starvation, this disrupts DNA synthesis and induces SOS-mediated filamentation.

See also

* Bacterial morphological plasticity * Segmented filamentous bacteria


{{Reflist, 2 Cellular processes Microbiology