Introduction to Isolation of Luminescent
Bacteria
The intention of this experiment was to use enrichment cultures and develop
a protocol that would provide for isolation and the maintenance of growth
of luminescent bacteria.
Luminescent bacteria are found in marine environments but are occasionally
found in freshwater or soil. Bioluminescent species found in marine
environments are members of the genera Vibrio or Photobacterium.
A squid was chosen as the environment from which the bacteria
would be isolated because luminescent bacteria are ubiquitous in the marine
environment while they are rare in freshwater and soil. It was hypothesized
that after a period of incubation in 3% salt solution, glowing colonies would
be observed on the squid. From these colonies,
luminescent bacteria, either of the genus Vibrio or Photobacterium
, both from the family Vibrionaceae, could be isolated and maintained.
A protocol was designed based on known characteristics
of marine luminescent bacteria. Past tests have proven that species
of the genus Vibrio and Photobacterium are Gram-negative,
straight or curved rods, that require salt for growth and are facultative
anaerobes. Most species are also motile (Holt 1984). Enrichment
procedures focused on the dependence of bacteria on salt for growth and therefore,
NaCl Agar provided a media on which these luminescent bacteria could colonize.
Luminous media was chosen to support growth of luminescent bacteria. This
recipe also contains a high concentration of salt and thus is ideal for growth.
The seawater complete liquid medium was used based on previous findings,
which have concluded that both Vibrio and Photobacterium can
be supported in this medium (Farmer and Hickman-Brenner).
Distinguishing between Vibrio and Photobacterium
is difficult due to the many similar characteristics they possess. However,
several tests based on differences can be performed in an attempt to classify
the isolated organism in either genus. A Gram stain, motility test, oxidase
test, and carbohydrate utilization test will provide information helpful for
the classification of the bacteria.
Figure 1. Squid from which luminescent bacteria were
isolated.
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