Microbial Physiology notes lec22 11-17-10

Microbial Physiology notes lec22 11-17-10 - Microbial...

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Microbial Physio Lecture 22: Bacterial Chemical Communication November 17, 2010 Bacterial Chemical Communication (Quorum Sensing) In bacterial quorum sensing, have to have a certain # of bacterium to accumulate external concentrations of these pheromones/chemical communication molecules, so that you can get a response Usually what happens is in order to get a high enough concentration of the molecule which the bacteria is synthesizing and then responding to, you have to have enough bacteria in the solution to get a high enough concentration that will be recognized by the bacterium and it can be a single bacterium, that can both send the signal and get the signal (respond to the signal)—usually it’s a whole population of bacteria, all one species that recognizes the presence of the signal, which in the case of the molecule that we’re going to talk about to day is Acyl homoserine lactones (AHSL) 1. History: a. Bacteria were not discovered by God, he knew nothing of them b. 1684: Bacteria discovered by Van Leeuwenhoek i. called them deaf mutes because they weren’t paying any attention to him, regardless of him making loud noises, and they weren’t making noises themselves c. 1880: Bacterial communication discovered by Engelman i. chemotaxis by bacterial swarms one swarm attracting another swarm ii. i.e one swarm can be going in one direction and another swarm going in another direction, and when they get a sense of the products that the other bacteria are producing, which is still unknown, then they would swim towards each other and form a much larger swarm d. 1965: bacterial sex pheromones for competence(DNA transfer) and conjugation (Tomasz i. sex pheromones are small peptides in many peptide signaling mechanism, it’s the C-terminal part, because of the originally synthesized polypeptide chain, because you make something that is substantially larger, you use that protein, to signal that the protein has to go outside, and then you cleave off that signal, and then you further process that molecule 1. so you start out w/ something large in the sense that is has maybe 40-50 amino acids, and then you process it so that you’re down to a tripeptide, or a pentapeptide, or a decapeptide, and then there are the signaling molecules 2. so many of the signaling molecules proved to be the C- terminus of the pro-signaling molecule that the bacteria make
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3. In other cases, it’s the N-terminus, these are the sex pheromones, which are used to communicate female and male e. 1970: quorum sensing by acyl homoserine lactones (Nealson) Power point slides: Coordinating the Raucous crowd: Quorum sensing signals affecting microbial social fxn 1. Quorum sensing signals are used as chemical signals in order to coordinate the activity of all the members of the species, even when they’re living in the planktonic state(swimming around freely) and the signaling molecule are also used in biofilms when the bacteria are coordinated and living together a. There are some activating signals which tend to create more cohesion w/in
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Microbial Physiology notes lec22 11-17-10 - Microbial...

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