Insecticidal compounds of the biofilm-forming cyanobacterium Fischerella sp (ATCC 43239)

Cyanobacterial biofilms are grazed by many different benthic invertebrates. In particular, larvae of insects are often. present in great numbers and exert strong grazing pressure on cyanobacteria. Along with morphological adaptations, allelochemicals may have been developed as defense mechanisms against insect larvae. To investigate the chemical defense of biofilm-forming cyanobacteria, larvae of Chironornus sp., a widely distributed genus in this habitat, were used. Ten artificial biofilms of axenic and nonaxenic cyanobacteria were screened for insecticidal activity against Chironomus sp. Fischerella 43239 was the cyanobacterium that exhibited the highest acute toxicity. A bioassay-guided isolation procedure was used to study the compounds responsible for toxicity in more detail. A toxic fraction was obtained when the 60% methanolic extract of Fischerella 43239 was separated on a C18 HPLC column. Electrospray mass spectrometry indicated the presence of several compounds in this fraction. The successful separation into individual compounds was achieved by HPLC on a cyanopropyl column. The heavily clustered quasimolecular ions observed on an electrospray mass spectrometer and the absorption spectra of the separated compounds were indicative of indole derivatives. The existence in the benthic cyanobacterium Fischerella 43239 of strong insecticidal metabolites that serve as chemical protection agents against insect larvae is supported by the data. (c) 2005 Wiley Periodicals, Inc.