Ernesto J. Quintero

Professor of Biology

In the last few years, marine microorganisms have been recognized as an important and unexploited source of novel bioactive compounds. Natural products have been a major source of new drugs for medicine; close to 60% of the compounds commercially available or in late stages of clinical trials for the treatment of infectious diseases or cancer have been derived from this source. Recently, the rate of discovery of new molecules from terrestrial sources has decreased. The oceans cover greater than 70% of the earth's surface and, taking this into account by volume, represent better than 95% of the biosphere. Given this fact, the oceans present themselves as an unexplored area of opportunity for the discovery of pharmacologically active compounds.

Bacteria and other microorganisms are often found living in close association with higher organisms in the marine environment. Associations of bacteria with sponges are among the most interesting and complex examples. These interactions have created considerable interest in recent years, because the production of biological active substances. It has recently been demonstrated that in many cases, microorganisms associated with these animals are responsible for the biosynthesis of active compounds, which was initially attributed to the invertebrate. It has been proposed that they contribute to the integrity of their hosts and their defense by the excretion of antibiotic and other biologically active substances. In particular sessile marine organisms like sponges are considered to depend on chemical defense mechanisms against predatory animals, but also against attacks of pathogenic microorganisms. If these bacteria can be isolated and cultured, or if their biosynthetic gene clusters can be cloned into suitable expression hosts, the compound can be produced by bacterial fermentation rather than relying on harvesting of the invertebrate, which may deplete its natural population.

I have broad interests in marine microbial ecology and in the application of molecular techniques to this field. A major research interest in my laboratory is the study of the biochemical ecology of marine microbes and invertebrates for the identification and isolation of bioactive compounds, particularly the ecology and molecular biology of actinomycete bacteria from the marine environment. Actinomycetes are important sources of bioactive compounds and more than two-thirds of naturally occurring antibiotics come from this single group of bacteria. The isolation, distribution and biodiversity of marine actinomycetes is under investigation to facilitate screening of these organisms for novel antibacterial, anticancer and antiviral compounds.

We are currently isolating actinomycetes from marine sediments and invertebrates found in different marine and estuarine ecosystem found in Southwest Florida, particularly from the Rookery Bay National Estuarine Research Reserve. In this process we are utilizing different types of culture media and conditions in order to obtain new strains of microbes never cultured before. The isolates are tested to ascertain if they are producing secondary metabolites with antibiotic, antiviral or cytotoxic properties. The isolates are characterized using Restriction Fragment Length Polymorphism (RFLP) and sequencing of their 16S ribosomal RNA genes.

Marine Actinomycetes tested for production of metabolites active against methicillin-resistant Staphylococcus aureus

Other research interests include the isolation of marine bacteria that produce polysaccharides with adhesive properties of commercial value. Polysaccharides consist of a chain of sugar residues that can impart a wide range of chemical and structural properties to the polymer through various combinations of sugar subunits with varying degrees of branching and functional group substitutions. Many polysaccharides produced by bacteria in nature are excreted to form the scaffolding that physically link cells to each other and anchors them to surfaces. The extracellular polysaccharides protect the cells from antimicrobial agents and sequester nutrients for the cells from the surrounding environment. The bacteria excrete this adhesive polysaccharide to form a biofilm in aqueous environments. Some of these polymers have been developed into specialty adhesives that satisfy specific industrial requirements.