Antifungal cyclic peptides from the terrestrial blue-green alga Anabaena laxa. I. Isolation and biological properties.

Abstract

Laxaphycins are responsible for the antifungal and cytotoxic activity of crude ethanolic extracts from the cultured blue-green alga Anabaena laxa. These cyclic peptides exhibit an unusual biological synergism when tested for antifungal or cytotoxic effects. The isolation procedure for the peptides, their characterization and biological activities are described here along with experiments demonstrating synergism between the two major laxaphycins. 1451Blue-green algae (cyanobacteria) have been recognized in the last several years as a source of novel cytotoxic and antifungal metabolites. Someof these metabolites are providing potential leads for the development of new pharmaceutical compounds. Knownantifungal compoundsare frequently toxic when used at levels high enough to be reliably therapeutic, especially for the systemic infections encountered in immunocompromisedpatients. New families of compounds that exhibit synergism either with one another or with known antifungal drugs offer the potential for reducing required dosages, thereby mitigating toxicity and providing more effective antifungal treatment regimens.Wereport here the isolation of a group of cyclic peptides from a cyanophyte that act synergistically with one another to inhibit the growth of fungi and yeasts. These cyclic peptides also show synergistic cytotoxic effects. Isolation and CharacterizationThe cyclic peptides were isolated from the methanol-soluble portion of a crude 7 : 3 ethanol -water extract of the cyanophyte Anabaena laxa Rabenhorst (UH strain FK-1-2) by reversed-phase chromatography. The total yield ofpeptides based on the dried weight of the alga was 1.3%. The complexity of the mixture of peptides is indicated by the HPLCchromatogram shown in Fig. 1. All marked peaks correspond to cyclic peptides with molecular weights ranging from 1,150 to 1,400 daltons as determined by FABmass spectrometry. Unmarkedpeaks probably correspond to additional cyclic peptides that have not yet been characterized. Table 1 lists the yield, relative abundance in the crude extract, and the molecular weight for the individual laxaphycins isolated.Laxaphycins A, B, C, D, and E have been purified by reversed-phase HPLC, while the remaining characterized peptides have been only partially purified. Peaks marked H, I, and P are known to be mixtures. The two peaks markedN correspond to a laxaphycin in the expected mass range and to another compoundwhich is probably not a cyclic peptide. All the peptides isolated were found to fall into two groups-those related to laxaphycin A with

Antifungal activity improved by coproduction of cyclodextrins and anabaenolysins in Cyanobacteria

“…Discussion Synergistic Antifungal Activity. Cyanobacteria are known to produce lipopeptides with antifungal activity, such as nostofungicidine (18), laxaphycins (19)(20)(21), lobocyclamides (22), and hassallidins (14,23,24). In this study, we show that anabaenolysins have a weak antifungal activity (Fig.…”

Synergistic allelochemicals from a freshwater cyanobacterium

“…These, however, display distinct peptidic sequences. A similar situation was described in the synergistic antifungal activity of two classes of cyclic peptides obtained from the freshwater cyanobacterium Anabaena laxa (48). Other examples include the proteic "binary toxin" systems of several gram-positive bacteria, most notably the anthrax toxin (49).…”

Modulation of biocidal activity of Calothrix sp. and Anabaena sp. by environmental factors

“…The production of toxins and qualitative and quantitative information on the regulation of genes involved in toxin synthesis have revealed that a differential expression occurs in response to light quality and quantity, growth phase and chemical stressors (Carmichael 1994). Terrestrial cyanobacteria such as Anabaena laxa produce antifungal cyclic peptides such as laxaphycin A and B (Frankmolle et al 1992). Kulik (1995) reported that extracts from the cyanobacterium Nostoc muscorum Agardh inhibited the in vitro growth of the fungal plant pathogens such as Sclerotinia sclerotiorum (Cottony rot of vegetables and flowers) and Rhizoctonia solani (root and stem rots).…”