Cyanophycin accumulated under nitrogen-fluctuating and high-nitrogen conditions facilitates the persistent dominance and blooms of Raphidiopsis raciborskii in tropical waters
Cyanophycin accumulated under nitrogen-fluctuating and high-nitrogen conditions facilitates the persistent dominance and blooms of Raphidiopsis raciborskii in tropical waters
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DOI：
10.1016/j.watres.2022.118215
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发表时间：
2022-02-25
期刊：
影响因子：
12.8
通讯作者：
Paerl, Hans W.
中科院分区：
文献类型：
--
作者：
Lu, Zhe;Ye, Jinmei;Paerl, Hans W.
营养盐储存被认为是藻类物种适应营养盐供应波动的关键策略。过量的磷（P）进入聚磷酸盐的储存延长了蓝藻优势的持续时间和磷缺乏下的水华。然而，目前还不清楚是否氮（N）存储在蓝藻素的形式支持持久的蓝藻优势或水华在热带地区，氮缺乏通常发生在夏季。在这项研究中，我们研究了蓝藻素的合成和降解的Raphidiopsis raciborskii，在热带沃茨，一个广泛和占主导地位的蓝藻的基因，并检测蓝藻素积累波动下的N浓度和其生态作用的种群动态的物种。蓝藻素合成基因（cphA）和降解基因（cphB）在23株针藻属菌株中有21株高度保守。这表明，蓝藻素的合成和降解是进化保守的，以支持R。raciborskii在N波动和/或缺乏条件。同位素N-15-NaNO_3标记实验表明，R.无论外源氮是否缺乏，raciborskii QDH 7总是在波动的氮条件下开始合成和积累蓝藻素。当NO_3~--N浓度超过1.2mg（L~（-1））时，R. raciborskii主要通过吸收N-15-NaNO3合成蓝藻素。然而，当NO3--N浓度低于1.0 mg L-1，蓝藻素为基础的N是来自未标记的N-2，证明了增加二氮酶活性。细胞生长在NO3--N 1.2 mg L-1。< 1.0 mg L-1 had lower cyanophycin accumulation rates than cells grown under NO3--N >我们在大型热带水库的实地调查强调了藻蓝素含量与R.拉齐波斯基。蓝藻素含量在氮素充足（NO3--N> 0.45 mg L-1）时期较高，在氮素缺乏的夏季有所下降。夏季，R. raciborskii维持相对高的生物量，产生很少的异形胞（<1%）。这些结果表明，蓝藻素释放的N，而不是固定的N，支持持久的R。在氮素缺乏的季节里，刺槐开花。我们的研究表明，在N-2固定蓝藻物种的高度适应性的策略，使减轻其开花比以前假设的更困难。
Nutrient storage is considered a critical strategy for algal species to adapt to a fluctuating nutrient supply. Luxury phosphorus (P) uptake into storage of polyphosphate extends the duration of cyanobacterial dominance and their blooms under P deficiency. However, it is unclear whether nitrogen (N) storage in the form of cyanophycin supports persistent cyanobacterial dominance or blooms in the tropics where N deficiency commonly occurs in summer. In this study, we examined genes for cyanophycin synthesis and degradation in Raphidiopsis raciborskii, a widespread and dominant cyanobacterium in tropical waters; and detected the cyanophycin accumulation under fluctuating N concentrations and its ecological role in the population dynamics of the species. The genes for cyanophycin synthesis (cphA) and degradation (cphB) were highly conserved in 21 out of 23 Raphidiopsis strains. This suggested that the synthesis and degradation of cyanophycin are evolutionarily conserved to support the proliferation of R. raciborskii in N-fluctuating and/or deficient conditions. Isotope N-15-NaNO3 labeling experiments showed that R. raciborskii QDH7 always commenced to synthesize and accumulate cyanophycin under fluctuating N conditions, regardless of whether exogenous N was deficient. When the NO3--N concentration exceeded 1.2 mg (L-1), R. raciborskii synthesized cyanophycin primarily through uptake of N-15-NaNO3. However, when the NO3--N concentration was below 1.0 mg L-1, cyanophycin-based N was derived from unlabeled N-2, as evidenced by increased dinitrogenase activity. Cells grown under NO3--N < 1.0 mg L-1 had lower cyanophycin accumulation rates than cells grown under NO3--N > 1.2 mg L-1. Our field investigation in a large tropical reservoir underscored the association between cyanophycin content and the population dynamics of R. raciborskii. The cyanophycin content was high in N-sufficient (NO3--N > 0.45 mg L-1) periods, and decreased in N-deficient summer. In summer, R. raciborskii sustained a relatively high biomass and produced few heterocysts (< 1%). These findings indicated that cyanophycin-released N, rather than fixed N, supported persistent R. raciborskii blooms in N-deficient seasons. Our study suggests that the highly adaptive strategy in a N-2-fixing cyanobacterial species makes mitigating its bloom more difficult than previously assumed.