California Sea Grant College Program

Microbial inhabitants of the marine environment are poorly understood in terms of chemical interaction. Tremendous taxonomic diversity exists among these microorganisms, encompassing adaptations to the wide range of physical parameters found in marine habitats. Production of secondary metabolites has been studied in several marine bacteria and fungi, primarily isolated from shallow, near-shore sediments. However, most resources for the discovery of new natural products from marine microorganisms remain unexploited, and little is known of the function of microbial secondary metabolites in situ.

The study described in  this dissertation had two major goals: 1) to identify novel compounds produced by microbial isolates from extreme marine environments, and 2) to identify antibiotic compounds which might act in situ. The first investigation resulted in the isolation and structure elucidation of several novel compounds from deep-sea isolates of the genus Bacillus. These compounds included guaymasol and epiguaymasol and the iturin class acylpeptide, surfactamide.

In the research focussed on microbial antibiosis, estuaries were chosen as collecting sites, since these environments are rich in nutrients and, thus, high in concentration of microorganisms. In preliminary work, one estuarine isolate produced a series of novel bicyclic depsipeptides, the salinamides, which exhibited moderate activity against Gram(+) bacteria and  potent anti-inflammatory activity. Based on the  salinamide results and  the desire to investigate ecologically-relevant chemical competition, a project was designed to isolate and  identify compounds which inhibited growth of microorganisms from the  same environment as the producing organism.

The study sites included one tropical mangrove swamp in Belize, Central America, and one temperate lagoon in San Diego County. The antibiotic compounds produced by the lagoon isolates included piericidin, chloramphenicol, nonactin, valinomycin, fumitremorgin C, and  the diketopiperazine cyc/o(L-trans-(4- hydroxyprolinyl)-L-Phe). The Belizean mangrove isolates produced one novel compound, cis-cascarillic acid, as well as the known antibiotic compounds: cycloheximide, tirandamycin, o-hydroxybenzamide, and  several nucleotide bases. Several known secondary metabolites with no recorded bioactivity were also isolated and identified. Culture of the  microorganism, isolation and  identification of each compound, and the significance of production of the compounds by a marine microorganism are discussed for each isolate.