In recent years, decline of freshwater resources has been recognized as one of the main environmental problems on global level. In addition to the increasing extent of primary salinization due to climate change, secondary salinization caused by human interventions is also a significantly increasing problem, therefore, the development of various chemical-free, biological desalination and removal procedures will become increasingly important. In the present study, the salinity tolerance, salinity, and nutrient reducing ability of nine common freshwater microalgae species from the genera Chlorella, Chlorococcum, Desmodesmus, Scenedesmus, and Monoraphidium were investigated. Our results proved that the studied green microalgae species are halotolerant ones, which are able to proliferate in environments with high salt concentrations. Furthermore, most of the species were able to reduce conductivity and remove significant amounts of chloride (up to 39%) and nutrients (more than 90% nitrate). The results proved that nitrate removal of the studied species was not influenced by salt concentration, only indirectly via growth inhibition. However, the results also highlighted that N:P ratio of the medium has primarily importance in satisfactory phosphorous removal. It can be concluded that assemblages of the studied microalgae species could be able to adapt to changing conditions even of salt-rich wastewaters and improve water quality during bioremediation processes.
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.
Non-steroidal anti-inflammatory drugs initiate morphological changes but inhibit carotenoid accumulation in Haematococcus pluvialis.
A few literature data suggest that one of the possible roles of the cyanotoxin cylindrospermopsin (CYN) is forcing other phytoplankton species in the environment to produce alkaline phosphatase, which enables the cyanobacterium to take up the enzymatically liberated phosphate. In this study, cultures of a planktonic green alga Scenedesmus obtusus (Chlorophyta, Sphaeropleales) were treated with CYN producer Aphanizomenon (Cyanobacteria, Nostocales) crude extract (C+), with non-CYN producer Aphanizomenon crude extract (C-), and with non-CYN producer Aphanizomenon crude extract supplemented with CYN (C-+C). The results showed that C+ treatment induced both acidic and alkaline phosphatases of the studied cosmopolitan green alga, which otherwise was neither sensitive to the relatively high CYN concentration, nor to phosphate limitation. In cases of C-and C-+C treatments, these phenomena were not observed. Several studies suggest that additional compounds may support CYN action. The results presented here suggest in a more direct way, that other components present in the cellular matrix of the producer organism itself are involved in the effects of CYN, activation of phosphatases (not only alkaline ones) among them. These other components are absent in C-crude extract, or can not actively contribute to the effects of exogenously added CYN.
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