The study of allelochemicals from Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju
Date Issued
2008
Date
2008
Author(s)
Huang, Yu-Chi
Abstract
Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju is a filamentous freshwater cyanobacterium. It has been widely distributed in the tropical and subtropical regions and widespread to temperate climate regions during last few decades. It often formed algal bloom or predominated in phytoplankton assemblages in certain water reservoirs and thus affected seriously the water quality. The conditions for its massive growth are not very different from those of common cyanobacteria or chlorophytes in the eutrophic environment. Thus, it is speculated that the outgrowth of C. raciborskii might be related to an allelopathic effect. The present study is done to verify this.he strain of C. raciborskii used for this study was isolated from the water reservoir of Kinmen. After mass-culture in the laboratory, the cells were harvested and extracted with 80% ethanol solution. The extract was separated by liquid-liquid partitioning to get organic and water-soluble extracts. The growth inhibition test with Chlorella vulgaris, Anabaena sp. and Microcystis aeruginosa showed that positive inhibitory effect was observed in both the organic and water-soluble extracts. Analyses with GC-MS and bioassay indicated that active compounds in organic extract were palmitic acid (PA, 16:0), palmitoleic acid (PTA, 16:1), linoleic acid (LA, 18:2), and a-linolenic acid (ALA, 18:3). For the water-soluble extract, a partial purification with a C18 liquid-solid-partition column was done. Positive inhibitory effect was detected for the eluted fractions of 0%, 75%, 90% and 100% methanol. Nevertheless, analysis with GC-MS showed that all of these fractions contained a common fatty acid, palmitic acid. In addition to this, there was an highly polar, unknown active compound which needed to be further studied. he treatment of C. vulgaris or M. aeruginosa cells with both the PTA and ALA would cause a remarkable K+-leakage from cells to extracellular medium, while no significant effect was observed by treating with PA. In response to the treatment with fatty acids, M. aeruginosa displayed higher tolerance than C. vulgaris, in the time course as well as in the magnitude of K+-leakage. Observation under transmission electron microscope showed that ALA would result in ultrastructural changes of M. aeruginosa, causing a shrinkage in intracellular membranes to give rise to spaces between cell wall and membranes. The resultant space increased in size and number over time after ALA treatment.n conclusion, this study verified that C. raciborskii might produce fatty acids as the allelochemicals to inhibit the growth of other algae in the aquatic environment. The fatty acids, particularly of polyunsaturated species, would exert cytotoxic effects on the target cells, causing ultrastructural changes and damages in cell membranes. As a result, leakage of potassium from the intracellular to extracellular medium as a symptom of cell damages was observed
Subjects
Cylindrospermopsis raciborskii
allelochemicals
fatty acid
K+-leakage
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