Allelopathic activity of cyanobacteria isolated from Lake Tuzkol.

Allelopathy plays a crucial role in shaping phytoplankton community dynamics and diversity. It influences competition between photoautotrophs for resources and affects species succession in aquatic ecosystems. This article evaluates the allelopathic activity of cyanobacteria isolated from Lake Tuzkol, Kazakhstan. The allelopathic effects, including growth inhibition or stimulation, were assessed by adding cell-free filtrates of the cyanobacteria Oscillatoria sp. SS-9, Nostoc sp. CZS 2205, Synechococcus sp. SS-5, or Anabaena sp. SS-8 to the tested microalgae. The most pronounced effect was observed with Nostoc sp. CZS 2205, which reduced the cell counts of Chlorella vulgaris SP BB-2 and Chlamydomonas reinhardtii CC-124 by 60% and 57%, respectively, and Scenedesmus quadricauda CC-1 and Ankistrodesmus falcatus CB-2 by 55% and 53%, respectively. Synechococcus sp. SS-5, in contrast, stimulated the growth of Chlorella vulgaris SP BB-2 and Scenedesmus quadricauda CC-1 by 11% and 8.8%, respectively. Filtrates from Oscillatoria sp. SS-9 and Anabaena sp. SS-8 had no significant impact on microalgal growth. Considering the significant allelopathic activity of Nostoc sp. CZS 2205, an agar diffusion test using biomass extracts confirmed a significant inhibitory effect, with the biomass extracts showing stronger activity than cell-free filtrates. A detailed analysis of the cell-free filtrates revealed eight compounds, including methyl heptadecanoate, methyl eicosanoate, tricosane, methyl octadeca-9,12-dienoate, methyl 13,16-octadecadienoate, and 2,2-dimethoxybutane. Additionally, nostocyclamide, a cyclic peptide, was identified in the biomass extract. The detection of nostocyclamide emphasizes its ecological importance and potential evolutionary role. These results enhance our understanding of the role of cyanobacteria in aquatic ecosystems and lay the groundwork for future research into their ecological applications.