The Role Of SpeG In Vibrio Cholerae Biofilm Formation

Vibrio cholerae is a Gram-negative, aquatic bacterium responsible for the human disease cholera. Illness typically results from ingestion of the bacterium in its biofilm form. It is known that polyamines regulate biofilm formation. V. cholerae can uptake polyamine norspermidine, as well as sense it extracellularly, and synthesize it by the enzyme NspC, encoded by the nspC gene. Mutants overexpressing nspC have been shown to form significantly more biofilms than the wild-type strain; however internal norspermidine levels do not show any increase. Norspermidine can be toxic to cells; therefore, cells could secrete norspermidine extracellularly to mitigate toxicity. However, previous work suggests that this polyamine is not being secreted as is. Norspermidine toxicity could be mitigated by the enzyme SpeG, encoded by the speG gene. SpeG modifies some polyamines by acetylating the primary amine group and facilitating its transport extracellularly. I hypothesized that an acetylated form of norspermidine could be sensed extracellularly and lead to an increase in biofilm formation. The objective of this study was to elucidate the role of SpeG in biofilm formation. My data suggests that a secreted signal from the speG overexpression strain is enhancing biofilm formation through the a signaling complex in V. cholerae.