Abstract
Cylindrospermopsin (CYN) is a toxic secondary metabolite produced by filamentous cyanobacteria which could work as an allelopathic substance, although its ecological role in cyanobacterial-algal assemblages is mostly unclear. The competition between the CYN-producing cyanobacterium Chrysosporum (Aphanizomenon) ovalisporum, and the benthic green alga Chlorococcum sp. was investigated in mixed cultures, and the effects of CYN-containing cyanobacterial crude extract on Chlorococcum sp. were tested by treatments with crude extracts containing total cell debris, and with cell debris free crude extracts, modelling the collapse of a cyanobacterial water bloom. The growth inhibition of Chlorococcum sp. increased with the increasing ratio of the cyanobacterium in mixed cultures (inhibition ranged from 26% to 87% compared to control). Interestingly, inhibition of the cyanobacterium growth also occurred in mixed cultures, and it was more pronounced than it was expected. The inhibitory effects of cyanobacterial crude extracts on Chlorococcum cultures were concentration-dependent. The presence of C. ovalisporum in mixed cultures did not cause significant differences in nutrient content compared to Chlorococcum control culture, so the growth inhibition of the green alga could be linked to the presence of CYN and/or other bioactive compounds.
Highlights
Despite many studies addressing toxicological aspects of cyanobacterial metabolites, their physiological role remains largely unclear, some authors suggested that these metabolites may play a crucial role in allelopathy [1]
This study focuses on the interspecific interactions of the filamentous CYN-producing cyanobacterium, Chrysosporum ovalisporum and the benthic green alga, Chlorococcum sp
Based on the showed results we suggest that the decrease of the cell number of the green alga in mixed cultures occurred due to the presence of other bioactive compounds than only CYN
Summary
Despite many studies addressing toxicological aspects of cyanobacterial metabolites, their physiological (ecological) role remains largely unclear, some authors suggested that these metabolites may play a crucial role in allelopathy [1]. Allelopathy can be an important factor in the organization and formation of both planktonic and benthic algal assemblages in rivers and especially in lakes [1]. Allelopathic effects can appear in planktonic or in benthic assemblages, and between planktonic and benthic taxa [2,3,4]. The interspecific relations between planktonic and benthic algal/cyanobacterial organisms are much more pronounced in shallow lakes with extended littoral regions, than in deep lakes or rivers [4]. Planktonic species can negatively affect the benthic assemblages both by their presence (e.g., by shading and nutrient uptake) and by allelopathic compounds. Extrapolation of detailed data from co-culturing experiments could lead one step closer to the understanding of these interspecific relations
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