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Microbiology in Drug Discovery by Dr. Peter McCarthy and Kathleen Janda Division of Biomedical Marine Research Harbor Branch Oceanographic Institution Marine invertebrates, such as sponges, are hosts to a large community of microorganisms including bacteria and fungi. In some cases as much as 50% of the mass of the sponge may consist of microorganisms. These symbiotic microbes produce 
some chemicals with the potential to fight disease found in marine organisms and are therefore a very valuable resource
for drug discovery. In order to study these bacteria and fungi they must first be cultured, a process that starts at sea
and continues for many months after they are returned to the main laboratories.
Immediately after the submersible returns to the ship, samples that were collected during the dive are taken into the shipboard "wet lab." Microbiologists take a small sample of each organism (e.g., sponge, gorgonian, tunicate) to be used for this microbial culturing work. At the same time a small sample of the organism is cryopreserved at -80°C, using a solution of glycerol and seawater as a cryoprotectant (to prevent ice crystal damage to the cells). These samples will be used for isolation of microbes back at our laboratories at HARBOR BRANCH Oceanographic Institution. 
The sample that was taken for microbial isolation at sea is ground with sterile seawater and then diluted. A small volume
(50 microliters) of this suspension is then dispensed, or plated, onto the surface of growth media in Petri dishes, which
allows colonies of microbes to grow. Many types of growth media are used depending on the type of microbe we want to isolate.
The Petri dishes are sealed to prevent drying out of this growth media, and incubated at room temperature for anywhere from
2 weeks to several months. After the incubation period, dozens of colonies may grow on each plate. These are then "picked"
and streaked onto another plate until we obtain a single type of microorganism growing on a plate-a pure culture.
The culture is then characterized using properties such as the color, size and shape of specific colonies, the size and shape of individual cells, and properties of the cells such as their motility, or movement. Once a pure culture has been characterized, it is preserved as a part of HARBOR BRANCH Marine Microbial Culture Collection which at this time contains approximately 16,000 isolates. Cultures are frozen at -80°C for long-term storage, which will ensure that these microbes are available for study for many years. Additional cultures are stored at 25°C as "working stocks" for ongoing research. 
With these cultures in hand, the process of drug discovery can then begin. The isolates are used to inoculate flasks containing
growth media designed to allow both growth of these unusual microbes and their production of bioactive compounds. After a growth
period (which can be anywhere between three days and two weeks), during which the cultures are shaken to allow oxygen to reach
the cells, the cultures are extracted using an organic solvent such as ethyl acetate. Many of the compounds produced by the microbes
are more soluble in the solvent than in the growth medium and are therefore "extracted." These extracts are then tested for their
biological activity using a variety of assays designed to identify potential drugs to treat cancer and infectious diseases.
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