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Morphology and physiology

The morphology and physiology researches showed that luminescent bacteria are very similar to enteric bacteria.

It is possible to observe the shape of luminescent bacteria cells using popular light microscope. The bacterial cells are more visible when special method of staining is used. There are many methods of staining. I used the Gram staining method and the negative staining method. Click on the link below to see some photos of luminescent bacteria cells.

SOME PHOTOS OF LUMINESCENT BACTERIA CELLS

Every luminescent bacteria are Gram-negative. Bacterial cells have motion organs - flagella (they are visible in light microscope only when special method of staining is used). In the case of Vibrio genus polar flagella are enclosed in a sheath continuous with the outer membrane of the cell wall. In the case of Photobacterium genus only unsheathed flagella are present.

On the basis of my photos and other data (electron micrographs, phase contrast micrographs) we can create the simplified pictures of luminous bacteria.

This picture shows the cells of luminescent bacterium Photobacterium phosphoreum. The cells of this bacterium are motile by one to three unsheathed polar flagella. a - bacterial cell b - unsheathed flagella

This picture shows the cells of luminescent bacterium Vibrio fischeri. The cells of this bacterium are motile by two to eight sheathed polar flagella. a - bacterial cell b - sheathed flagella

On the constant media luminous bacteria (like other bacteria) can form the colonies. Colonies are visible aggregations of bacterial cells (about 2-8 mm in diameter). Colony can be created by one bacterial cell in the way of multiple cell divisions. On the photo on the left colonies of the luminescent bacterium Photobacterium luciferum are shown. The photo on the right shows the colonies of the luminescent bacterium Vibrio fischeri.

The luminescence ability is in strict dependence on the medium composition. The light generating reactions require oxygen. The luminescence process is something like the offshoot of the aerobic respiration. The main difference is that the final product of aerobic respiration is ATP and the final product of luminescence reactions is excited luciferase (chemical compound) which can generate light.

SCHEME OF THE LUMINESCENCE REACTIONS

On the photo near the colonies of luminescent bacterium - Photobacterium luciferum are shown. I was applying the long-time exposure (1min.) In the case of these bacteria the light is emitted particularly in the casting parts of colonies. (click on the photo to see it better)

Interesting is the fact, that luminescent bacteria do not produce light (or produce it very weakly) when their cells are in considerable dispersion (e.g. in the sea-water). In contrast, when many cells are in condensed suspensions (e.g. cultures growing in the liquid, microbiological mediums) they produce light very efficiently.
The researches show that luminescent bacteria produce specific chemical compound - autoinducer which can induce bioluminescence reactions in bacterial cells if present in environment in actual concentration.
When many bacterial cells are present in the environment, the concentration of autoinducer grows and luminescence is induced very efficiently.
Similarly, luminescent bacteria cells which live in sea-water do not produce light but the cells which live in luminous organs of marine animals produce it very effectively. It is possible because the quantity of bacterial cells in these organs reach 10¹⁰ cells/ml.

Other chemical compounds similar to autoinducer were isolated from other bacteria species which do not produce light. Perhaps in this case their role is informational. On the base of concentration of these compounds bacterial cell "knows" how many other cells are in close nearness.

1.

2.

The photos above show colonies of luminescent bacterium - Vibrio fischeri on the medium "BOSS". This bacterium is most intensively light-producing bacteria in my collection. Photo 1 was taken in the normal light terms and photo 2 was taken in the dark. I was applying the long-time exposure (40 sec.).
(click on the photo to see it better)

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