Dissolved nitrogen form mediates phycocyanin content in cyanobacteria

Abstract

Chemically reduced nitrogen forms are increasing in aquatic systems and beginning to reach concentrations not previously measured. Despite this, little research has examined the potential of reduced nitrogen forms to encourage excess nitrogen storage and promote algal bloom longevity compared to oxidised forms. A 2‐week field, pulse‐application experiment was carried out using 1,100‐L plastic limnocorrals to examine cyanobacterial community response to three nitrogen forms, including nitrate, ammonium, and urea (added as 600 µg N/L). Cell pigments and counts were used to calculate cell‐specific pigment concentrations, and cell‐associated microcystin concentrations were also measured to examine toxin response to a shift in nitrogen source. Results showed that, upon nitrogen introduction, extracellular nitrogen quickly decreased in accordance with an increase in cellular phycocyanin 72 hr after fertilisation. Ammonium and urea treatments had more phycocyanin/cell than nitrate or control treatments at 72 hr. After 72 hr, phycocyanin content quickly decreased, consistent with the use of nitrogen from phycobiliproteins. Despite the decrease in light‐harvesting pigments, the total number of cyanobacterial cells increased in the ammonium and urea treatments after 2 weeks. Cyanobacterial particulate toxin (microcystin) quotas were not affected by nitrogen additions. Results show that reduced nitrogen forms encourage greater nitrogen storage as pigments and increase bloom longevity compared to oxidised forms. Findings support previous studies that suggest reduced nitrogen forms encourage greater cell density and algal bloom persistence. Results further point to excess nitrogen storage as another mechanism that allows cyanobacteria to dominate freshwater systems despite variable environmental conditions.

Uncovering the Differential Growth of Microcystis aeruginosa Cultivated under Nitrate and Ammonium from a Photophysiological Perspective

“…The generation of Chl a was not apparently affected by different N supplies (Figure A), which is consistent with observations from an outdoor pond experiment . However, from day 6 onward, carotenoid production significantly increased in M.…”

“…The generation of Chl a was not apparently affected by different N supplies (Figure 2A), which is consistent with observations from an outdoor pond experiment. 13 However, from day 6 onward, carotenoid production significantly increased in M. aeruginosa grown in media containing NH 4 + -N (Figure 2C), resulting in a relatively high ratio of carotenoid-to-Chl a of cells (Figure S4). Carotenoid plays a significant role in photoprotection.…”

“…The growth inhibition of M. aeruginosa with high NH 4 + -N supply significantly reduced its PBP synthesis. Gladfelter et al 13 demonstrated that NH 4 + -N encourages greater N storage as PC and increases the longevity of the blooms than NO 3 − -N. In this study, the contents of PC, APC, and PE per unit of M. aeruginosa biomass under NH 4 + -N-only and NO 3 − -N + NH 4 + -N were significantly higher than that of cells under NO 3 − -Nonly after incubation of 2 days (Figure 2D−F), which were similar to the observations at a low N level 13 and consistent with the results of specific growth rate between different treatments. Thereafter, the synthesis of pigments was significantly inhibited by the supply of NH 4 + -N-only, where the average amounts of PC, APC, and PE from day 6 to day 10 were only 74, 69, and 83% of NO 3 − -N-only supply, respectively.…”

“…The available amount of NH 4 + -N is increasing due to the rapid development of intensive aquaculture and the massive global use of urea as a N fertilizer. 13 Because of its low energy cost during transmembrane transport and subsequent assimilation, NH 4 + is considered as the favored form of N for uptake and utilization by cyanobacteria. 14 As observed in many field studies, the dominance of HAB species becomes increasingly evident with the increasing proportion of NH 4 + in the N pool.…”

Enhanced phycocyanin production of Arthrospira maxima by addition of mineral elements and polypeptides using response surface methodology

“…The types of nitrogen sources also had an impact on phycocyanin accumulation. Gladfelter et al (2022) discovered that compared to nitrate, the reduced nitrogen forms (ammonium/ammonia and urea) can much more promote algae growth and phycocyanin accumulation. In addition, in a research on improving the sources of nitrogen in the culture medium, the phycocyanin content was increased by 23% after optimizing the medium that included soda ash production wastes, NaNO 3 , KCl and KH 2 PO 4 (Xie and Wang, 2017).…”