Question

V. fischeri have the ability to bioluminesce. This ability is encoded by an operon. Including the I gene that encodes the autoinducer, this operon contains 8 genes. Draw out the operon and label each gene in this operon. Indicate which gene encodes the regulatory protein that induces transcription of the rest of the operon

What is an autoinducer and what class of molecules act as autoinducers for V. fischeri and other bacteria that share its gram status?

Answer 1

Qorum sensing upregulates the synthesis of surfactant molecules. Biofilmdevelopment and quorum sensing (QS) are closely interconnected processes.Biofilm formation is a cooperative group behaviour that involves bacterial populations living embedded in a self-produced extracellular matrix.

The bioluminescence emitted by the marine bacterium Vibrio fischeri is a particularly striking result of individual microbial cells co-ordinating a group behaviour. The genes responsible for light production are principally regulated by the LuxR-LuxI quorum-sensing system. In addition to LuxR-LuxI, numerous other genetic elements and environmental conditions control bioluminescence production. Efforts to mathematically model the LuxR-LuxI system are providing insight into the dynamics of this autoinduction behaviour.

1. molecular characterization of naturally occurring, non-bioluminescent strains of Vibrio fischeri. These 'dark' V. fischeri strains remained non-bioluminescent even after treatment with both autoinducer and aldehyde, substrate additions that typically maximize light production in dim strains of luminous bacteria. Surprisingly, the entire lux locus (eight genes) was absent in over 97% of these dark V. fischeri strains. Although these strains were all collected from a Massachusetts (USA) estuary in 2007, phylogenetic reconstructions allowed us to reject the hypothesis that these newly described non-bioluminescent strains exhibit monophyly within the V. fischeri clade. These dark strains exhibited a competitive disadvantage against native bioluminescent strains when colonizing the light organ of the model V. fischeri host, the Hawaiian bobtail squid Euprymna scolopes. Significantly, we believe that the data collected in this study may suggest the first observation of a functional, parallel locus-deletion event among independent lineages of a non-pathogenic bacterial species.

2. Quorum sensing (QS) is a mechanism by which bacteria communicate through the secretion and detection of extracellular signaling molecules known as autoinducers. This research focuses on the quorum sensing regulated bioluminescence of Vibrio fischeri, a marine bacterium that lives in symbiosis with certain fish and squid species. Previous studies of V. harveyi, a close relative of V. fisheri, indicate that a strong magnetic field has a positive effect on V.harveyi bioluminescence. However the effect of magnetic fields on quorum sensing-regulated luminescence is in general poorly understood. We grew V. fischeri in solid and liquid growth media, subject to strong static magnetic fields, and imaged the bioluminescence over a period of forty-eight hours. Luminescence patterns were analyzed in both the spatial and time dimensions. We find no indication that a magnetic field influences Vibrio fischeri luminescence either positively or negatively.
3. In negative regulation a repressor protein binds to an operator to prevent a genefrom being expressed. In positive regulation a transcription factor is required to bind at the promoter in order to enable RNA polymerase to initiate transcription
4. genetic regulation. …operon is controlled by a regulator gene, which produces a small protein molecule called a repressor. The repressor binds to the operator gene and prevents it from initiating the synthesis of the protein called for by the operon.
5. Autoinducers are signaling molecules that are produced in response to changes in cell-population density. As the density of quorum sensing bacterial cells increases so does the concentration of the autoinducer. Detection of signal molecules by bacteria acts as stimulation which leads to altered gene expression once the minimal threshold is reached
6. The term "autoinduction" was first coined in 1970, when it was observed that the bioluminescent marine bacterium Vibrio fischeri produced a luminescent enzyme (luciferase) only when cultures had reached a threshold population densityThe term "autoinduction" was first coined in 1970, when it was observed that the bioluminescent marine bacterium Vibrio fischeri produced a luminescent enzyme (luciferase) only when cultures had reached a threshold population density--
7. Whereas Gram-negative bacteria primarily use acylated homoserine lactones, Gram-positive bacteria generally use oligopeptides as autoinducers for quorum sensing.
8. In Vibrio fischeri, the synthesis of N-3-oxohexanoyl-L-homoserine lactone, the autoinducer for population density-responsive induction of the luminescence operon (the lux operon, luxICDABEG), is dependent on the autoinducer synthase gene luxI. Gene replacement mutants of V. fischeri defective in luxI, which had been expected to produce no autoinducer, nonetheless exhibited lux operon transcriptional activation. Mutants released into the medium a compound that, like N-3-oxohexanoyl-L-homoserine lactone, activated expression of the lux system in a dose-dependent manner and was both extractable with ethyl acetate and labile to base. The luxI-independent compound, also like N-3-oxohexanoyl-L-homoserine lactone, was produced by V. fischeri cells in a regulated, population density-responsive manner and required