Biolumininiscence of bacteria

DEFINATION:

Bio  means  “living”  in Greek  and  lumen  means  “light”  in  Latin.

“Bioluminescence is the production and emission of light by a living organism”. It is a form of chemiluminescence. During this process, chemical energy is converted into light energy.

 HABITAT:

 It is present mostly in sea water, marine sediments, surface of decomposing fish and in gut of marine animals.

OCCURANCE:

These bacteria may live free (example, Vibrio harveyi) or in symbiosis (example, Vibrio fischeri) with animals such as the Hawaiian Bobtail squid or terrestrial nematodes (example ,Xenorhabdus luminescens) .

QUORAM  SENSING:

“Quorum sensing is a system of stimulae and response correlated to population density”. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population.

MECHANISM:

Bacteria that use quorum sensing constitutively produce and secrete certain signaling molecules (called autoinducers or pheromones). These bacteria also have a receptor that can specifically detect the signaling molecule (inducer). When the inducer binds the receptor, it activates transcription of certain genes, including those for inducer synthesis. There is a low likelihood of a bacterium detecting its own secreted inducer. Thus, in order for gene transcription to be activated, the cell must encounter signaling molecules secreted by other cells in its environment.

BIOCHEMISTRY  OF BIOLUMINISCENT  BACTERIA:

Light emission in bacteria is catalyzed by a uniquely bacterial kind of luciferase, a heterodimeric protein of approximately 80 kD, composed of alpha (40 kDa) and beta (37 kDa) subunits, with homology to long-chain alkane  monooxygenases. The enzyme mediates the oxidation of reduced flavin mononucleotide (FMNH2) and a long-chain aliphatic (fatty) aldehyde (RCHO) by O2 to produce blue-green light according to the following reaction:

 Where

 FMNH2  =  Reduced flavin mononucleotide

 BACTERIAL  LUX  GENES:

While the regulation of the lux operon, the set of genes responsible for the production of the correct enzymes needed to drive the luciferase reaction. The lux operon is bidirectional and encodes seven genes (luxR, I, C, D, A, B, and E) needed for bioluminescence.  The luxI gene encodes the autoinducer, which is secreted by the bacterium and enters a neighboring cell and induces the transcription of the operon.  The luxR gene encodes the protein that responds to the autoinducer. Three genes, luxC, D, and E, are involved in the production of the aldehyde substrate.  Finally, luxA and B encode for the alpha and beta subunits of the luciferase enzyme.

 

BIOLUMINISCENT  BACTERIA  IN  BOBTAIL  SQUID:

Bobtail squid have a symbiotic relationship with bioluminescent bacteria (Vibrio fischeri), which inhabit a special light organ in the squid's mantle. The bacteria are fed a sugar and amino acid solution by the squid and in return hide the squid's silhouette when viewed from below by matching the amount of light hitting the top of the mantle. The organ contains filters which may alter the wavelength of luminescence closer to that of downwelling moonlight and starlight; a lens with biochemical similarities to the squid's eye to diffuse the bacterial luminescence; and a reflector which directs the light ventrally.

 

USES  OF  BIOLUMINISCENT  BACTERIA:

The uses of bioluminescent bacteria are as follows:

·         ANAEROBIC  BACTERIA:

      Anaerobic bacteria may have developed bioluminescence to use up toxic oxygen.

·         DNA  REPAIRING:

       It helps in stimulation of DNA repair .

·         QOURAM  SENSING:

       Qouram sensing helps to attract animals to feed à dispersal of population.

·         WATER  CONTAMINATION:

        Bioluminiscence bacteria are use to detect water contamination.

·         CAMOUFLAGE:

        Bioluminiscent bacteria helps in camouflaging of prey for different speices.

·         COMMUNICATION:

         Bioluminiscence helps bacteria to communicate within colony.

·         MATING:

          Bioluminescence bacteria helps to attract mates for different speices.