title: Biomedicine in the environment: cyclotides constitute potent natural toxins in plants and soil bacteria.
abstract: Bioactive compounds produced by plants are easily transferred to soil and water and may cause adverse ecosystem effects. Cyclotides are gene-encoded, circular, cystine-rich mini-proteins produced in Violaceae and Rubiaceae in high amounts. Based on their biological activity and stability, cyclotides have promising pharmaceutical and agricultural applications. We report the toxicity of the cyclotides: kalata B1, kalata B2, and cycloviolacin O2 extracted from plants to green algae (Pseudokirchneriella subcapitata), duckweed (Lemna minor L.), lettuce (Lactuca sativa L.), and bacteria extracted from soil measured as [³H]leucine incorporation. Quantification by liquid chromatography-mass spectrometry demonstrated up to 98% loss of cyclotides from aqueous solutions because of sorption to test vials. Sorption was prevented by adding bovine serum albumin (BSA) to the aqueous media. Cyclotides were toxic to all test organisms with EC50 values of 12 through 140 µM (algae), 9 through 40 µM (duckweed), 4 through 54 µM (lettuce), and 7 through 26 µM (bacteria). Cycloviolacin O2 was the most potent cyclotide in all assays examined. This report is the first to document toxic effects of cyclotides in plants and soil bacteria and to demonstrate that cyclotides are as toxic as commonly used herbicides and biocides. Hence, cyclotides may adversely affect soil and aquatic environments, which needs to be taken into account in future risk assessment of cropping systems for production of these highly bioactive compounds.
authors.affiliation: Department of Basic Sciences and Environment, University of Copenhagen, Copenhagen, Denmark. rgo@life.ku.dk
authors.forename: Rikke Gleerup
authors.initials: RG
authors.lastname: Ovesen
authors.forename: Kristian Koefoed
authors.initials: KK
authors.lastname: Brandt
authors.forename: Ulf
authors.initials: U
authors.lastname: Göransson
authors.forename: John
authors.initials: J
authors.lastname: Nielsen
authors.forename: Hans Christian Bruun
authors.initials: HC
authors.lastname: Hansen
authors.forename: Nina
authors.initials: N
authors.lastname: Cedergreen
mesh_terms: D029064:Araceae / Q000187:drug effects; D001419:Bacteria / Q000187:drug effects*; D001688:Biological Products / Q000633:toxicity; D000460:Chlorophyta / Q000187:drug effects; D047169:Cyclotides / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D018545:Lactuca / Q000187:drug effects; D010936:Plant Extracts / Q000633:toxicity*; D012988:Soil Microbiology; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D001688:Biological Products; D047169:Cyclotides; D010936:Plant Extracts; D014874:Water Pollutants, Chemical; C091930:kalata B1; C473355:cycloviolacin O2