| Although many bacteria have the ability to produce antimicrobial compounds in culture, it is not clear whether bacterial metabolites have an adaptive function in microbial competition. The work described in this thesis represents a new approach to microbial chemical ecology.; Three examples are described where antimicrobial compounds produced by epibiotic bacteria protect the host from encroachment by other microorganisms. Embryos of the caridean shrimp Palaemon macrodactylus are protected against infection by the pathogenic fungus Lagenidium callinectes by at least one strain of epibiotic bacteria. This strain produces 2,3-indolinedione, a strong antifungal agent. The American lobster, Homarus americanus, uses a similar strategy of defense against the fungus. Healthy embryos are covered by a dense layer formed by a bacterial monoculture. These bacteria produce the compound p-hydroxyphenyl ethanol, which also inhibits fungal growth. Three strains of pigmented bacteria which occur in exclusive association with Microcoleus lyngbyaceus, a filamentous species of cyanobacteria, produce a potent antimicrobial compound. The compound, which had not been described previously, has considerable inhibitory activity against a number of fungi and bacteria.; The results of this research indicate that antimicrobial secondary metabolites indeed mediate microbial competition and strongly influence the establishment of associations between antimicrobial-producing bacteria and a variety of hosts. |
