Contrasting effects of the cyanobacterium Microcystis aeruginosa on the growth and physiology of two green algae, Oocystis marsonii and Scenedesmus obliquus, revealed by flow cytometry

Abstract

Summary Aquatic photosynthetic productivity is influenced by resource availability, resource use efficiency and interspecific interactions. In hypertrophic environments, interspecific interference is known to influence species succession. The effect of interference by phytoplankton on biomass production is very poorly understood. One hypothesis is that the development of cyanobacterial blooms is triggered by the excretion of allelopathic substances that inhibit the growth of other phytoplankton species. In this study, we analysed how the co‐cultivation of the cyanobacterium Microcystis aeruginosa with two green algae (Oocystis marsonii and Scenedesmus obliquus) influences the resource use efficiency of each partner under nutrient‐replete conditions. Using single‐cell technologies, it was possible to quantify the efficiency of light use and the biomass gain for all three species under hypertrophic (non‐limiting nutrient) conditions. The presence of M. aeruginosa resulted in growth inhibition, reduced metabolic activity and an increased quantum requirement for biomass assimilation in O. marsonii, whereas no changes were observed in S. obliquus. M. aeruginosa, on the other hand, showed an increased cell size in mixed cultures with O. marsonii. However, with respect to biomass production, M. aeruginosa did not profit from the growth inhibition of O. marsonii in the experimental period of 8 days. By contrast, the co‐cultivation of M. aeruginosa with S. obliquus did not affect the physiological activity of either species. This study highlights the potential of flow cytometry to determine species‐specific basic growth parameters, light‐use efficiency and biomass gain during co‐cultivation of different algal strains. It is further demonstrated that sorted cells can be used to analyse their macromolecular composition. The results of this study reveal very different species‐specific patterns of growth kinetics and light‐use‐efficiency of green algae in co‐cultivation experiments with a cyanobacterium.

Chemically mediated interactions between Microcystis and Planktothrix: impact on their growth, morphology and metabolic profiles

“…Direct cultivation of strains/species allowing cell‐to‐cell interaction is a more realistic approach to mimic interspecific interaction. Recent studies have shown stronger growth inhibition in green algae and diatoms in direct co‐cultivation with M. aeruginosa than in membrane‐separated co‐culture or with cyanobacteria exudates (Dunker et al ., ; ; Wang et al ., ). However, direct co‐cultivation does not as easily allow for monitoring the respective physiological and metabolic responses of both interacting organisms.…”

Toxic and non-toxic strains of Microcystis aeruginosa induce temperature dependent allelopathy toward growth and photosynthesis of Chlorella vulgaris

“…It has been reported that green algae Quadrigula chodatii grew significantly better than nontoxic M. aeruginosa PCC7820 under co-cultured conditions (Zhang et al, 2013b). Furthermore, green algae Scenedesmus obliquus was observed to benefit from the competition with toxic M. aeruginosa strains (Dunker et al, 2013;Harel et al, 2013). It has been suggested that allelopathy and competition to affect algal predominance during cyanobacteria bloom-forming, especially the dominance of Microcystis species (Chen et al, 2003;Yamamoto and Nakahara, 2009).…”

Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients

“…Alternatively, unfavorable and sub-optimal conditions reducing photosynthetic efficiency and growth may arise from direct interactions between phytoplankters. For example, some green algae and cyanobacteria produce secondary metabolites that inhibit photosynthesis and growth of their competitors (e.g., Dunker et al 2013, Harel et al 2013, Zhang et al 2013. The detection of such allelopathic interactions was beyond the scope of our study.…”

“…In general, a reduction of photosynthetic efficiency and growth can be interpreted as a reaction to sub-optimal, resource-limiting conditions (c.f. Morris 1976, Spijkerman 2010 thesis and growth of their competitors (e.g., Dunker et al 2013, Harel et al 2013, Zhang et al 2013. In response, species may adjust their biochemical composition.…”