Interspecies interplay between cyanobacteria and green algae - the first step to know why cyanobacteria produce what we call “Toxins”

Over the past decades, cyanobacteria have attracted the researcher’s attention due to their ability to produce cyanotoxins. Among cyanotoxins, microcystins (MCs) are the most commonly studied. However, their significance for the producing species beyond their toxicity is still mysterious (was reviewed in Paper I). In the present study, the interactions between a common bloom-forming cyanobacterium “Microcystis aeruginosa” and a green alga “Desmodesmus subspicatus” were studied to provide more insights into the ecological importance of the algal secondary metabolites concerning MCs. To achieve this, a dialysis co-cultivation system was established. First, M. aeruginosa PCC 7806 and D. subspicatus were co-cultured (1:1) at different phases of growth (Paper II). Second, D. subspicatus was co-cultured with M. aeruginosa PCC 7806 and PCC 7005 (toxic and non-toxic strains, respectively) that were grown to the stationary phase of growth (Paper III). As a result, the concentration of intracellular and extracellular (inner and outer membrane) MC-LR was quantified using liquid chromatography-tandem mass spectrometry and the cell density was monitored using a haemocytometer under the light microscopy. The growth of M. aeruginosa PCC 7806 and D. subspicatus in the culture filtrates of each other and the effects of toxic M. aeruginosa crude extracts on the growth of D. subspicatus were studied as well (Paper II). The results provided clues to the involvement of the algal secondary metabolites in the interspecies interplay. The growth of the two species was inhibited in the culture filtrates of one another (˃ 25% exudates). The MC-containing crude extracts (˃ 140 µg/L) inhibited the growth of green alga. Moreover, the co-cultured species influenced the growth of each other negatively depending on the stages of the growth. During the exponential phase of growth, the green alga inhibited the growth and MC production but has not influenced the MC release. While, at the stationary phase of growth, MC production and release were enhanced, coinciding with the inhibition of the growth of green alga (Paper II). Moreover, MC-producing strain excluded the green alga greater and earlier compared to non-toxic strain. The MC-producing M. aeruginosa benefited from MC, in addition to or rather than the other secondary metabolites, to improve its fitness and the greater exclude of the green alga. However, inhibition of the growth of green alga at the concentrations of MC-LR above the environmental levels may explain the frequent co-existence of the green algae with cyanobacterial blooms. Moreover, the results indicated that the diffusion rate of extracellular MC-LR across the dialysis membrane was positively related to the time and negatively to the concentration of extracellular MC-LR.

Author dc:creator

• Omidi, Azam

Advisor dc:contributor.advisor

• Pflugmacher Lima, Stephan

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Identifier URI

http://dx.doi.org/10.14279/depositonce-9921

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/11033