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Team:Imperial College London/Project/Chemotaxis/Overview
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| + | Movement performed by bacteria based on attraction or repulsion of chemicals in the environment is known as chemotaxis. In our project we are using this mechanism for location of plant root by modified bacteria, which will be attracted to the root and will actively swim towards it.<br><br> | ||
| + | Chemotaxis in Escherichia coli is well documented. E. Coli can perform two types of movement, tumbling or smooth swimming. The difference between the two is in flagellar movement. During tumbling movement,flagella move clockwise due to the formation of complex between CheY-P and FliM ,one of the flagellum associated proteins. During smooth swimming, CheY is not phosphorylated and therefore cannot associate with flagellar proteins, which causes flagellum to move counterclockwise. Smooth swimming is the movement performed by bacteria, while the bacteria are being attracted towards localised chemical source. The control of smooth swimming is done by a number of chemotaxis proteins, which together concise a signalling pathway.<br><br> | ||
| + | At the start of the signalling pathway there is a receptor which is associated with CheW and CheA, when no attractant is bound. This complex leads to phosphorylation of CheY, which then carries on to be associated with flagellar proteins. When ligand (attractant or repellent) binds to receptor, CheW & CheA dissociates from the receptor and leads to inability to phosphorylate CheY that leads to flagellar FliM protein not being associated with CheY and that leads to counterclockwise flagellar movement. Also there is CheZ a phosphatase, which removes phosphate group from CheY. Another aspect of bacterial chemotaxis is a simple memory that bacteria use to move up the concentration gradient. This is achieved by protein CheR a methyltransferase, which methylates MCP (methyl accepting chemotaxis protein) and this way affect the capability of receptor to form association with CheW & CheA. CheW & CheA dissociation from the chemoreceptor depends on the rising concentration of attractant, which in turn depends on the bacterium moving towards the source of attraction. Also there is CheB, which acts as a methylesterase and can remove methyl groups from MCP receptor (Chelsky & Dahlquist, 1980). <br><br> | ||
| + | We have identified malate and other root exudates to act as chemotactic attractants in a number of other bacteria. For our project we are therefore rewiring chemotaxis in E. coli, by adding a chemoreceptor mcpS from Pseudomonas putida KT2440 strain. McpS is a receptor, which responds to a number of TCA cycle intermediates such as malate, fumarate, oxaloacetate, succinate, citrate, isocitrate and butyrate (Lacal et al, 2010). P. putida uses chemotaxis proteins in a different way to control its chemotactic response, however structurally are very similar to Che proteins in E. coli. Therefore the idea is that mcpS domain that interacts with Che proteins is sufficiently similar to native chemoreceptors, so that upon malate binding to the mcpS receptor, E. coli with expressed mcpS will exhibit chemotactic response towards malate. In a similar way we are also utilising chemotaxis receptor PA2652 from Pseudomonas aeruginosa PA01 strain, which also uses malate as attractant ligand. Therefore we can also compare which of the two introduced chemoreceptors responds more efficiently in terms of concentration of malate attractant. <br><br> | ||
| + | This way we can show that foreign chemoreceptors are compatible with e. coli chemotaxis system, provided the parts integrated share substantial structural similarity. Also we are capable of increasing a number of attractants to which e. coli is attracted, by addition of compatible chemoreceptors. | ||
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Revision as of 15:34, 10 August 2011
Chemotaxis Overview
Movement performed by bacteria based on attraction or repulsion of chemicals in the environment is known as chemotaxis. In our project we are using this mechanism for location of plant root by modified bacteria, which will be attracted to the root and will actively swim towards it.Chemotaxis in Escherichia coli is well documented. E. Coli can perform two types of movement, tumbling or smooth swimming. The difference between the two is in flagellar movement. During tumbling movement,flagella move clockwise due to the formation of complex between CheY-P and FliM ,one of the flagellum associated proteins. During smooth swimming, CheY is not phosphorylated and therefore cannot associate with flagellar proteins, which causes flagellum to move counterclockwise. Smooth swimming is the movement performed by bacteria, while the bacteria are being attracted towards localised chemical source. The control of smooth swimming is done by a number of chemotaxis proteins, which together concise a signalling pathway.
At the start of the signalling pathway there is a receptor which is associated with CheW and CheA, when no attractant is bound. This complex leads to phosphorylation of CheY, which then carries on to be associated with flagellar proteins. When ligand (attractant or repellent) binds to receptor, CheW & CheA dissociates from the receptor and leads to inability to phosphorylate CheY that leads to flagellar FliM protein not being associated with CheY and that leads to counterclockwise flagellar movement. Also there is CheZ a phosphatase, which removes phosphate group from CheY. Another aspect of bacterial chemotaxis is a simple memory that bacteria use to move up the concentration gradient. This is achieved by protein CheR a methyltransferase, which methylates MCP (methyl accepting chemotaxis protein) and this way affect the capability of receptor to form association with CheW & CheA. CheW & CheA dissociation from the chemoreceptor depends on the rising concentration of attractant, which in turn depends on the bacterium moving towards the source of attraction. Also there is CheB, which acts as a methylesterase and can remove methyl groups from MCP receptor (Chelsky & Dahlquist, 1980).
We have identified malate and other root exudates to act as chemotactic attractants in a number of other bacteria. For our project we are therefore rewiring chemotaxis in E. coli, by adding a chemoreceptor mcpS from Pseudomonas putida KT2440 strain. McpS is a receptor, which responds to a number of TCA cycle intermediates such as malate, fumarate, oxaloacetate, succinate, citrate, isocitrate and butyrate (Lacal et al, 2010). P. putida uses chemotaxis proteins in a different way to control its chemotactic response, however structurally are very similar to Che proteins in E. coli. Therefore the idea is that mcpS domain that interacts with Che proteins is sufficiently similar to native chemoreceptors, so that upon malate binding to the mcpS receptor, E. coli with expressed mcpS will exhibit chemotactic response towards malate. In a similar way we are also utilising chemotaxis receptor PA2652 from Pseudomonas aeruginosa PA01 strain, which also uses malate as attractant ligand. Therefore we can also compare which of the two introduced chemoreceptors responds more efficiently in terms of concentration of malate attractant.
This way we can show that foreign chemoreceptors are compatible with e. coli chemotaxis system, provided the parts integrated share substantial structural similarity. Also we are capable of increasing a number of attractants to which e. coli is attracted, by addition of compatible chemoreceptors.
