PHOTOBACTERIUM - An Overview

This page describes, in brief, the Genus of bacteria known as Photobacterium. It encompasses characteristics, isolation, Taxanomic description, and mentions references for this page and related links.

IDENTIFYING CHARACTERISTICS

• Striaght and Plump Rods
• Gram Negative
• Sodium Required for Growth
• One to Three Polar Flagella; some Nonmotile
• Luminescent
• 40 - 44% Gaunine and Cytosine (GC)
• Do not form Spores
• Diameter: 0.8-1.3 um; Length: 1.8-2.4 um
• Facultatively Anaerobic
• Chemoorganotrophs
• Optimal Growth Temperatures Range from 18-25 C
• Metabolism is Fermentative and Respiratory

TAXONOMIC DESCRIPTION

Photobacterium is a genus within the Family Vibrionaceae. Photobacterium can be distinguished from other genera of bacteria by the characteristics mentioned above and also utilization of Carbon sources. To distinguish between species of Photobacterium, the following characteristics can be determined: Luminescence; Growth at 4 C and 35 C; Presence of the enzymes Gelatinase and Lipase; and untilization of Proline, Xylose, pyruvate, maltose, glycerate,acetate, etc. There are many species including Photobacterium phosphoreum, Ph. leiognathi, Ph. angustum, and Ph. profundum. Many species were classified as belonging to other genera of bacteria, until the recent development of 16S RNA sequencing. Due to this protocol researchers suggest such species as Pastuella damselae (a fish pathogen), Vibro iliopiscarius, and others be reclassified as Photobacterium sp.

ISOLATION AND ECOLOGY

Photobacterium are primarily marine organisms, hence the requirement of sodium for growth. They may be free-living in the water, or found associated with fish. These associations may be symbiotic growth in light organs of fish, as an agent of disease, as a neutral entity on the surface or intestines of fish, or as decomposers of dead fish. Some species may also be found at considerable oceanic depth, and are barophilic.

Photobacterium can be isolated and cultured with the following media: Glycerol Chalk Media, Luminous Media, Photobacterium agar and broth, Photobacterium MPY Medium, and Seawater Agar. Photobacterium contain no pigmentation, therefore colonies may be white or colorless. Because in colonies the cells are at high density, they will exhibit flourescence in the dark. Flourescence is based upon accumulation of an autoinducer in the environment by the cells. Accumulation only occurs under high cell density, therefore free-living Photobacterium do not flouresce. Light genreation is an oxygen-requiring process, therefore, no luminescence will be seen in anaerobically grown Photobacterium. Also, isolation can result from incubating a dead fish for 1-2 days at 10-20 C.

ADDITIONAL SOURCES OF INFORMATION

• Atlas, R.M. 1997. Handbook of Microbiological Media, 2nd. ed. CRC Press, Inc. NY.
  
  
• Holt, J.G., N.R. Krieg, P.H.A. Sneath, J.T. Staley, and S.T. Williams. 1994. Bergey's Manual of Determinative Bacteriology, 9th ed. Williams and Wilkins. Baltimore, Maryland.
  
  
• Line, L., 1980. The Audubon Society Book of Marine Wildlife. Harry N. Abrams, Inc. NY.
  
  
• Madigan, M.T., J.M. Marinko, J. Parker. 1997. Brock Biology of Microorganisms, 8th ed. Prentice Hall, Inc. Upper Saddle River, NJ.
  
  

LINKS TO OTHER SITES ON PHOTOBACTERIUM

• AMERICAN TYPE CULTURE COLLECTION - online database of bacterial cultures currently held by the ATCC. Includes numerous Photobacterium strains.
  
  
• PHOTOBACTERIUM FORUM - Discussion group primarily aimed at using Photobacterium as toxicity indicator assays.
  
  
• BACTERIAL NAMES - List of some Photobacterium Species as given by the International Code of Nomenclature of Bacteria (Bacteriological Code)