ABSTRACT
Marine fungi (including marine-derived strains) are rich sources of biologically active secondary metabolites and interesting research objects for chemical ecological studies. This chapter describes chemical ecology of filamentous fungi emphasizing the defensive functions of secondary metabolites. New antimicrobial and cytotoxic metabolites of fungi isolated from marine organisms that may have ecological roles in protection mechanisms of marine organisms and the results on a probable implication of filamentous fungi in the indirect chemical protection mechanism of marine sponges are described.
A possible role of antimicrobial metabolites produced by fungi isolated from marine organisms is suggested to be a negative cue against fouling, settlement, colonization, adhesion, and infection by potentially harmful microorganisms. Cytotoxic metabolites may be deterrents against larvae and potential predators.
Our study demonstrated the possibility that fungi associated with marine sponges may participate in the indirect chemical defense system of the hosts in providing antibacterial metabolites. Bioassay-guided isolation afforded three new and five known antibacterial metabolites 82against a marine bacterium Ruegeria atlantica, a common fouling species. Penicillic acid, a well known mycotoxin first reported in 1936, may be a ubiquitous antibiotic of marine fungi because this antibiotic strongly inhibited the growth of R. atlantica with high selectivity from terrestrial bacteria and the producing fungi have been isolated from a wide area of the North Pacific Ocean.
Chemical ecological studies on marine fungi and their association with the hosts provide a better understanding of the importance of fungi in the marine environment. Chemical relationships between fungi and their host organisms are very interesting studies not only in understanding the marine fungal ecology but also in searching for new biologically active metabolites.
