Quorum sensing in Escherichia coli and Salmonella typhimurium - Essay Example

1. What is the possible role of quorum sensing in Escherichia coli and Salmonella typhimurium? The possible role of E.coli and S. typhimurium in quorum sensing is shown to be the production of a signaling substance that stimulates one particular quorum-sensing system which is a species non-specific system in Vibrio harveyi. The signal produced by E.coli and S. typhimurium was seen to be potent and equal to that of V. harveyi. The results also showed that the quorum sensing in these two bacteria differs from other quorum sensing bacteria in a way that it is tuned for a lower cell-density community as the signal is degraded before it enters the stationary phase.

The influence of environmental factors on quorum sensing as seen by the influence of glucose metabolism on the production and degradation of the signal shows that through quorum sensing the cells communicate their growth phase as well as the metabolic potential of their environment.2. E. coli AB1157 and S. typhimurium LT2 cell-free culture fluids contain a signaling substance that induces luminescence in V. harveyi (Fig. 1), please describe this phenotype.Strain AB 1157 of E. coli and strain LT2 of S.

typhimurium grown in 0.5% glucose containing LB broth for the assay was removed from the medium and checked for activity that resulted in expression of luminescence in V. harveyi. 10% cell-free culture fluids from the two strains demonstrated maximal induction of luminescence in the V. Harveyi reporter strain BB170 which has the phenotype for quorum sensing, sensor 1-, sensor 2+ which induces luminescence exclusively through the signaling system 2 detector. The response was similar to that from V.

harveyi BB152 culture fluid with E. Coli showing 106% and S. typhimurium showing 237% activity of the control activity. The signaling factor was not produced and the luminescence expression not induced when the bacterial strains were cultured in LB broth without added glucose and substitution of 10% LB medium containing glucose respectively. Candidates for signal including glucose, cAMP, amino acids, acetate, α-ketogluterate, homoserine lactone and other keto acids also produced no activity suggesting V.

Harveyi BB170 respond to some signaling substance secreted by E. coli AB1157 and S. typhimurium LT2 grown on glucose containing LB medium.An analogous experiment performed with V. Harveyi reporter strain BB886 (sensor 1+ , sensor 2-) which is a wild type strain that do not act in response to signaling molecules that function through the signaling system 2 detector. Addition of E. coli AB1157 and S. typhimurium LT2 cell-free culture fluids showed only a respective 1% and 5% increase above control level (control used V.

harveyi BB120 spent cultures which produces system 1 autoinducer).These results shows that E. coli AB1157 and S. typhimurium LT2 cell-free culture fluids contain a signaling substance that induces luminescence in V. harveyi must specifically act through the 2nd signaling system. Hence the phenotype of the signaling substance of E. coli AB1157 and S. typhimurium LT2 cell-free culture fluids can be designated as inducer 1-, inducer 2+.3. Please explain what is glucose effect on the production and degradation of the signaling activity by S.

typhimurium LT2.The production and degradation of the signaling factor by S. typhimurium LT2 is regulated by glucose. The cell-free culture fluids with glucose added did not show activity indicating the significance of glucose metabolism in the process. Also testing for activity with glucose and other carbohydrates also showed the highest activity when glucose was present. Testing S. typhimurium LT2 with limiting glucose concentration of 0.1% and non-limiting concentration of 0.5% showed that S.

typhimurium LT2 produces the signal in midexponential phase and stops production on depletion of glucose from the medium, when the glucose concentration is limiting whereas when it is non-limiting the signaling activity is greater and continues throughout exponential phase. The activity is degraded by the time the stationary phase is reached with limiting conditions of glucose showing no activity and non-limiting conditions showing 24% activity in stationary phase. The results showed no changes on increasing the glucose concentration of the growth medium.4. Please use your own words to write a summary based on what you learn from this paperThe paper discusses the results of experiments designed to assay the role of Escherichia coli and Salmonella typhimurium in quorum sensing.

The species non-specific signaling system 2 of Vibrio harveyi was used to detect and determine the signaling substance produced by E. coli and Salmonella. E. coli AB1157 and S. typhimurium LT2 strains were grown in Luria Bertani broth containing glucose and cell-free culture fluids were prepared for the assay. Similarly cell-free culture fluids of two strains of V. harveyi BB152 (auto inducer 1-, auto inducer 2+) and V. harveyi BB120 (auto inducer 1+, auto inducer 2+) were also prepared for autoinducers 2 and 1 respectively.

10% cell-free culture fluids from the two strains demonstrated maximal induction of luminescence in the V. harveyi reporter strain BB170 which has the phenotype for quorum sensing, sensor 1-, sensor 2+ which induces luminescence exclusively through the signaling system 2 detector. The response of E. coli AB1157 and S. typhimurium cell free culture fluid was similar to that from V. harveyi BB152 culture fluid. An analogous experiment performed with V. harveyi reporter strain BB886 (sensor 1+ , sensor 2-) which is a wild type strain that do not act in response to signaling molecules that function through the signaling system 2 detector.

Addition of E. coli AB1157 and S. typhimurium LT2 cell-free culture fluids showed almost no response above the control level .These results shows that E. coli AB1157 and S. typhimurium LT2 cell-free culture fluids contain a signaling substance that induces luminescence in V. harveyi must specifically act through the 2nd signaling system. The assay results showed the possible role of E. coli and S. typhimuriumin quorum sensing is shown to be the production of a signaling substance that stimulates one particular quorum-sensing system in Vibrio harveyi.

The signal was seen to be produced only in the presence of glucose showing the influence of glucose metabolism on the synthesis and degradation of the signal with the production of signal in the midexponential phase and its degradation by the stationary phase. This suggests the role of quorum sensing in E. coli and S. typhimurium in pathogenesis communicating not only the cell density information but also information regarding the presence of metabolites.