Isolation and identification of compounds from biofilms in eutrophic water and their allelopathic effects on cyanobacterial growth

That allelochemicals from land plants and macrophytes inhibit cyanobacterial growth has been confirmed. However, there is little information available on allelochemicals from biofilms. This study focused on the extraction, isolation and identification of compounds from photoautotrophic biofilms.Ethyl acetate and ethanol extracted 44 compounds, much more quantity of allelochemicals than dichloromethane, and water did (17 compounds), implying that solvents with polarity index from 4.4 to 5.1 could be suitable extractants for extracting more allelochemicals from biofilms. Total of 22 known and 5 unknown compounds were isolated from the ethyl acetate extract of the biofilms, and 12 known and 5 unknown compounds from methanol, four known and 3 unknown from dichloromethane, and 7 known and 3 unknown from water. The 3,4,5-trihydroxybenzoic acid was the highest amount compounds extracted from biofilms by methanol, which was considered as a potential allelochemical on cyanobacterium because the compound was also an putative allelochemical from land plants and macrophytes.Growth of the cyanobacterium Microcystis aeruginosa was significantly inhibited by 3,4,5-trihydroxybenzoic acid with concentrations from 0.1 mg/L to 0.3 mg/L'and the allelopathic effect increased with time. The known allelopathic compound ethyl-2-methylacetoacetate was also identified. It was concluded therefore that some of the suite of compounds extracted from biofilms were the same as those extracted from land plants or macrophytes. Additionally, currently unidentified compounds extracted from biofilm require bioassay to determine their allelopathic potential for the inhibition of cyanobacterial growth.