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要旨:
Massive growth of single species of cyanobacteria is a common phenomenon in many eutrophicated waters
worldwide. Allelopathic growth control of phytoplankton species
is one suggested mechanism, but still controversially
discussed. The fact that the synthesis of biological active compounds
requires high energy costs and carbon investment for a
single cell in contrast to high dilution rates in natural systems
questions the universal validity of allelopathic mechanisms,
even more as high concentrations of allelopathic substances
are often needed in several experiments to cause biological
effects. In this study, it was tested, if growth inhibition is
induced by chemical signaling alone or via direct cell–cell
interaction. As a test system, we used a co-culture of the green
algae Oocystis marsonii (Trebouxiophyceae) with the cyanobacterium
Microcystis aeruginosa which is known to strongly
reduce the growth of the green algal competitor. In this study,
direct co-culturing as well as membrane-separated growth
chambers were used to test for chemical and contactmediated
interactions. In the membrane-separated chambers,
both species can be co-cultivated and a membrane allows the
exchange of metabolites. Growth of O. marsonii was only
affected in the direct co-cultivation situation, where direct
cell-to-cell contact was possible. During direct co-cultivation,
deviating cellular traits, namely cell cycle pattern and large
cell-aggregate formation of both species, could be detected.
These data strongly support the hypothesis of a direct cell-cellcontact
necessary for allelopathic growth control in this model
system. Such direct contact would allow targeting allelopathic
metabolites directly towards the competitor and thereby minimizing
dilution effects.
