BALTIMORE, Md. Calif.–In research aimed at finding natural compounds from the sea for drugs and other products, a team of scientists report in the journal Marine Biology on a bacterium that seems to be an indicator for health of a marine sponge.
The team found that a type of sponge living along the Great Barrier Reef near Australia contains a "culturable" population of almost entirely one strain of bacteria, living in a close relationship with the porous sea animals but not in surrounding waters. There are also many "uncultured" bacteria in the sponge that scientists cannot yet grow.
"We have found that the culturable microbe population is very stable," reports Russell Hill of the University of Maryland Biotechnology Institute (UMBI). "The presence of this bacterium seems to be related to the health of the sponge and is a good model for our work." Some unhealthy specimens of the same type of sponge, Rhopaloeides odorabile, did not contain the bacterial strain, report Hill, a molecular microbiologist at UMBI’s Center of Marine Biotechnology, and colleagues at the Australian Institute of Marine Science (AIMS).
Understanding the symbiosis of such microbes and sponges is a critical step in studying potential biologically active, possibly medicinal, compounds in such bacteria. Sponges are recognized as rich sources of new compounds with biologically active ingredients that could qualify as new medicinal drug candidates. In some cases the bioactive compounds are likely to come from bacteria rather than the sponges themselves..
A January 2001 study, published by the COMB/AIMS team, opened the possibility that bacteria living in marine sponges may be a rich source of future drugs. In the earlier study, they identified by gene sequencing studies that many of the uncultured bacteria from sponges surveyed were in a bacterial family Actinomycetes. For many decades, soil borne members of the microbe family have been the sources of 60 to 70 percent of today’s naturally occurring antibiotics.
In the current study, the team has cultured several new actinomycetes in the laboratory for further studies. "Isolating the compound-producing microbes or its genes is obviously a much better approach than trying to harvest and grow sponges, which is extremely difficult," comments Hill.
The finding of the predominance of newly discovered bacterial strain (of the family, alpha Proteobacteria, very common to coastal waters) is also somewhat of a scientific departure. Previous cultivation studies of such bacterial-sponge associations showed that bacterial populations in sponges could be very diverse.
"This provides an excellent opportunity to assess temporal and geographic variations in this component of the community as well as variations between individual Rhopaloeides odorabile at a single location," Hill suggests. "The stability of microbial communities associated with sponges has not been study widely and has important implications for production of symbiont-derived bioactive compounds and for use of sponges as source materials for microbial diversity in programs screening for natural products. We think this shows that it is a true symbiont of this sponge."
The R. odorabiles sponge is common throughout the Great Barrier Reef region and reflects the typical ecological conditions. The team studied the microbes of the sponge collected from ten different areas of the coral reefs near Australia. The bacteria may play a role in food intake.
The scientists found that the microbes surrounding the sponge’s food ingesting chambers, sort of a multiple mouth system of such animals. But they are not actually food for the sponge. Because they could not find the strain of bacterium in water around the sponges, the scientists say it likely the two have a specific and intimate relationship.
There is growing interest that in some cases the compounds are being synthesized by bacteria living on and in the sponges and playing roles in keeping the animals healthy and nourished.
University of Maryland Biotechnology Institute. July 2001.