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Cholera Grows, Diversifies on Crustacean Shell Compound

Chitin triggers natural competence in V. cholerae

MONDAY, Dec. 19 (HealthDay News) -- Vibrio cholera was previously thought to mutate and diversify only through conjugation or by naturally induced DNA mutations. Now a study in Science suggests that the bacteria can take up exogenous DNA through "natural competence" while growing on chitin, the carbohydrate that makes up the shell of crustaceans and is found in the natural habitat of cholera.

Aquatic environments typically hold a diversity of organisms and can provide for a wide array of genetic material for horizontal gene transfer in naturally competent bacteria. Karin Meibom, Ph.D., and colleagues from Stanford University in Stanford, Calif., found that chitin from crab shells can induce cholera to take up antibiotic resistance genes, which permit them to grow in antibiotic containing media.

Chitin induces a type of pili in cholera that can gather and release DNA. Chitin also activates regulatory cascades and a suspected DNA binding protein, which may be important for the acquisition of "natural competence."

"This model highlights the importance of natural competence, occurring in chitin-attached bacterial communities in the aqua sphere, as a powerful driver of the evolution of V. cholerae," the authors conclude. "It further suggests that environmental events giving rise to copepod blooms likely foster the rapid evolution of this pathogen."

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