Alteration of Cylindrospermopsin Content of <i>Aphanizomenon ovalisporum</i> (Cyanobacteria, Nostocales) due to Step-Down from Combined Nitrogen to Dinitrogen

Abstract

In this study we show that cylindrospermopsin (a cyanotoxin) content of filaments of Aphanizomenon ovalisporum ILC164 depended on growth on combined nitrogen or nitrogen fixation. Our results also demonstrated that the shift down of cyanobacterial filaments from combined nitrogen to dinitrogen fixing condition resulted in a significant decrease of cylindrospermopsin pool size which resumed a growth rate dependent manner as the heterocyst and nitrogenase formation appeared. The current study indicated that alteration of nitrogen metabolism of Aphanizomenon ovalisporum (Forti) induced changes in cyanotoxin (cylindrospermopsin) metabolism. In addition, this is the first report that isolated heterocysts, the differentiated anaerobic cells for nitrogen fixation of cyanobacteria, did not contain cylindrospermopsin.

Effects of Cylindrospermopsin Producing Cyanobacterium and Its Crude Extracts on a Benthic Green Alga—Competition or Allelopathy?

“…Furthermore, intracellular CYN decreased in mixed cultures. These decreases are in accordance with our previous findings about CYN content changes of the used Chrysosporum strain under nutrient limitation [ 44 , 45 ]. The other potential reason of measuring low amount of extracellular CYN could be that due to the rich matrix particulate (but otherwise effective) CYN [ 17 ] occurred, which was not detectable by our capillary electrophoretic method developed for free dissolved CYN measurements.…”

“…The effects of abiotic factors on the production of CYN are quite well-known both from field studies [ 40 , 41 , 42 ], and from laboratory experiments (temperature [ 43 ]; phosphate-, sulphate-, and nitrate starvation [ 44 , 45 ]; and temperature and light intensity [ 46 , 47 ]. It seems, that extracellular CYN-content could change in a wide range due to different abiotic factors ( Cylindrospermopsis raciborskii : 39 × 10 −3 μg·mL −1 [ 48 ]; Chrysosporum ( Aphanizomenon ) gracile and C .…”

Nitrogen Limitation Promotes Accumulation and Suppresses Release of Cylindrospermopsins in Cells of Aphanizomenon Sp.

“…While −N and +N cultures produced similar amounts of CYNs during their exponential growth phase, cells in −N cultures contained at least two times higher total CYNs at the end of the experiment. Our results contrast with findings for Aphanizomenon ovalisporum where the CYN content first decreased and then increased during exponential growth in cultures free of nitrogen, but never reached the content of cultures grown under combined nitrogen conditions [ 34 ]. One reason for this discrepancy could be that this study had not considered the extracellular CYN fraction, which can amount to 20%−50% on total CYN depending on strain and growth phase, as shown for Aphanizomenon ovalisporum strains as well as C. raciborskii [ 15 , 35 ].…”

“…An impact of nitrogen availability was observed in several Australian C. raciborskii strains with highest intracellular CYN contents in batch cultures free of nitrogen and intracellular CYN contents (per unit dry weight) varying at maximum by a factor of 2 [ 33 ]. In contrast, CYN content in Aphanizomenon ovalisporum was lower in cultures free of nitrogen compared to growth under combined nitrogen supply [ 34 ].…”

Low cobalt limits cyanobacteria heterocyst frequency in culture but potential for cobalt limitation of frequency in nitrogen-limited surface waters is unclear

“…We know that heterocyst frequency differs among species (perhaps because of differences in cell size as discussed above) and among strains grown under controlled conditions (this study and Nayak et al, 2007;Ahad et al, 2015). Frequency also varies with environmental factors such as incubation time (Vasas et al, 2013;Zulkefli and Hwang, 2020), calcium (Smith et al, 1987;Torecilla et al, 2004), Fe (Aly and Andrews, 2016), Ni (Rai and Raizada, 1986), inorganic N (Fogg, 1949;Ogawa and Carr, 1969;Rother and Fay 1979;Brown and Rutenberg, 2012;Mohlin et al, 2012;Zulkefli and Hwang, 2020), CO2 (Kulasooriya et al,1972;Kang et al, 2004;Masukawa et al, 2017), O2 (Kangatharalingam et al, 1992), light (Fogg, 1949) and temperature (Zakrisson and Larsson, 2014). This large number of known confounding variables (there may be others) makes it very difficult to assign relative importance to variables known to affect heterocyst frequencies.…”