Photobacterium phosphoreum

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Photobacterium phosphoreum
Scientific classification
Kingdom: Bacteria Phylum: Proteobacteria Class: Gammaproteobacteria Order: Vibrionales Family: Vibrionaceae Genus: Photobacterium Species: P. phosphoreum
Binomial name
Photobacterium phosphoreum

Description and significance

Photobacterium phosphoreum is a luminescent bacterium. They are gram-negative, straight rod, plump and large (0.8-1.3 um in diameter and 1.8-2.4 um in length). They can be motile or non-motile. Those that are motile have 1-3 unsheathed polar flagella. It can grow at low temperature, 4˚C, but no at 35˚C. They emit the brightest light from all bacteria [1]. Their optimum temperature is 18-25˚C [2]. They emit a blue-green light due to the catalytic activity of luciferase. They are oxidase positive because they can use D-glucose as their principle carbon source (Prescott, Harley and Klein 557). They can be cultivated in Long and Hammer Agar (1% NaCl). It is known as a symbiotic bacterium that lives in the light organ of some marine fishes. It can also live freely in seawater, saprophytically and parasitically [3].

Their major significance is their symbiotic relationship with some marine animals like fishes and squids. They have light organs that provide P. phosphoreum microorganisms with a safe place to inhabit and food; while these animals use the light that the bacteria provide for camouflage and even for attracting mates or escape from predators. Another role that P. phosphoreum has is their ability of signaling the relative toxicity of a substance. This can happen due to the connection of the light producing process with the cellular metabolism. If the toxins disrupt the cellular metabolism, then the strength of the light produced decreases [4].

Cell structure and metabolism

P. phosphoreum is a chemoorganotroph which is capable of respiratory and fermentative metabolism [5]. It is a facultative anaerobe that can grow in the absence of oxygen when appropriate electron-acceptors are present. It doesn’t denitrify; in other word, it cannot use nitrogen molecules [6].

P. phosphoreum can produce blue-green light with the help of an enzyme called luciferase. “Luciferase catalyzes the reaction and uses reduced flavin mononucleotide, molecular oxygen, and a long-chain aldehyde as substrate” (Prescott, Harley and Klein 559).

Equation FMNH₂ + O₂ + RCHO + luciferase &rarr FMH + H₂ + RCOOH + light

When the excited flavin intermediate (FMN) moves to ground state, it emits the light which is one of the products of the reaction [7].

Ecology

P. phosphoreum is mostly considered a marine bacterium because sodium ions are required for its growth. It lives in the depth of the ocean, seawater, marine sediments, in the guts of marine animals, and on the surface of decomposing fish. Inside of the marine organisms, it can act as a parasite.

References

http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=659

http://www.microbiologyatlas.kvl.dk/biologi/english/showmorf.asp?articleid=44

http://www.disknet.com/indiana_biolab/b203.htm

http://www.biology.pl/bakterie_sw/index_en.html

http://cibt.bio.cornell.edu/programs/archive/0608alum/lumos.pdf

http://web.mst.edu/~microbio/BIO221_2005/P_phosphoreum.htm

http://www.microbelibrary.org/ASMOnly/Details.asp?ID=552