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Indian Institute of Science

1. Srinivasa Sandeep, S. Testing the Hypothesis of Quorum Sensing in Vibrio fischeri : Luminescence, Motility, and Biofilm.

Degree: 2017, Indian Institute of Science

The individual behaviour of prokaryotic organisms such as bacteria often gives rise to complexity that is commonly associated with multicellular behaviour. The transition from unicellular to multicellular behaviour occurs in response to chemical signals, called autoinducers, which bacteria generate and receive internally within a given population. These autoinducers control the gene expression necessary for the emergence of group-behaviour-phenotype. This phenomenon is called quorum sensing (QS). An example of the quorum sensing control of gene regulation has been the luminescence (lux) operon in Vibrio fischeri. The luxI and ainS quorum signalling systems work in conjunction to regulate luminescence in V. fischeri. LuxI and AinS are acyl-synthases that catalyse the production of the autoinducers C6-HSL and C8-HSL respectively. These autoinducers bind to LuxR, a transcriptional activator of the lux operon, which activates expression of the lux genes causing an increase in luminescence. It was shown that quorum signalling also affects motility and biofilm formation in bacteria. However, the evidence with respect to these phenotypes is conflicting and inconclusive, the reason being the state of quorum is ambiguously defined. It is not properly known whether the observed collective behaviour is purely a result of physical crowding of bacteria, or that both chemical signalling and crowding contribute to this phenomenon. This work attempts to address these issues by studying luminescence, motility, and biofilm, a diverse set of behaviours, yet closely linked to each other in V. fischeri-squid symbiosis. We studied the luminescence response of V. fischeri to both endogenous and externally added signals at per-cell and population level. Experiments with ES114, a wild-type strain of V. fischeri, and ainS mutant showed that (i) luminescence per cell does not mutually correlate with the cell-density, indicating that bacteria do not show greater response to the signal at higher densities; (ii) the activity of the lux signalling circuit shows a strong dependence on the growth stage, (iii) the cells do not show enhanced growth, i.e., they do not derive fitness benefits at higher densities in response to the signal. We anticipated that the culture with a higher cell-density should exhibit greater per-cell-luminescence. However, we found that the luminescence curve of the culture with lower density crosses that of the cultures with higher densities during the exponential phase. Kinetic modelling of the luxI mRNA expression showed that the expression profile qualitatively agrees with the luminescence trend observed in the cultures, supporting the observation that growth-phase plays a major role in regulating the luminescence gene expression. We also studied the effect of autoinducers on motility of V. fischeri. V. fischeri uses flagella to move into the inner crypts of the light organ of the squid. The bacterium secretes autoinducers, encounters secretions of the light organ, and slows down during the final stage of colonization… Advisors/Committee Members: Nott, Prabhu R.

Subjects/Keywords: Quorum Sensing (QS); Prokaryotic Organisms - Multi-cellular Behavior; Quorum Signalling Circuits - Vibrio Fischeri; LuxI, C6-HSL; LuxR Protein; Vibrio fischeri; V. fischeri; Quorum Signalling; Autoinducers; Chemical Engineering

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APA (6th Edition):

Srinivasa Sandeep, S. (2017). Testing the Hypothesis of Quorum Sensing in Vibrio fischeri : Luminescence, Motility, and Biofilm. (Thesis). Indian Institute of Science. Retrieved from http://hdl.handle.net/2005/3270

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Srinivasa Sandeep, S. “Testing the Hypothesis of Quorum Sensing in Vibrio fischeri : Luminescence, Motility, and Biofilm.” 2017. Thesis, Indian Institute of Science. Accessed September 16, 2019. http://hdl.handle.net/2005/3270.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Srinivasa Sandeep, S. “Testing the Hypothesis of Quorum Sensing in Vibrio fischeri : Luminescence, Motility, and Biofilm.” 2017. Web. 16 Sep 2019.

Vancouver:

Srinivasa Sandeep S. Testing the Hypothesis of Quorum Sensing in Vibrio fischeri : Luminescence, Motility, and Biofilm. [Internet] [Thesis]. Indian Institute of Science; 2017. [cited 2019 Sep 16]. Available from: http://hdl.handle.net/2005/3270.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Srinivasa Sandeep S. Testing the Hypothesis of Quorum Sensing in Vibrio fischeri : Luminescence, Motility, and Biofilm. [Thesis]. Indian Institute of Science; 2017. Available from: http://hdl.handle.net/2005/3270

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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