Shenzhen Public Platform for Screening and Application of Marine Microbial Resources, Tsinghua Shenzhen International Graduate School, Shenzhen, Guangdong Province, PR China.
National Innovation Center for Molecular Drug, Shenzhen, Guangdong Province, PR China.
Nat Commun. 2024 Nov 9;15(1):9716. doi: 10.1038/s41467-024-53978-9.
Diazotrophic cyanobacteria can fix nitrogen gas (N) but are usually scarce in nitrogen-limited coastal waters, which poses an apparent ecological paradox. One hypothesis is that high salinities (> 10 g/L NaCl) may inhibit cyanobacterial N fixation. However, here we show that N fixation in a unicellular coastal cyanobacterium exclusively depends on sodium ions and is inhibited at low NaCl concentrations (< 4 g/L). In the absence of Na, cells of Cyanothece sp. ATCC 51142 (recently reclassified as Crocosphaera subtropica) upregulate the expression of nifHDK genes and synthesise a higher amount of nitrogenase, but do not fix N and do not grow. We find that the loss of N-fixing ability in the absence of Na is due to insufficient ATP supply. Additional experiments suggest that N fixation in this organism is driven by sodium energetics and mixed-acid fermentation, rather than proton energetics and aerobic respiration, even though cells were cultured aerobically. Further work is needed to clarify the underlying mechanisms and whether our findings are relevant to other coastal cyanobacteria.
固氮蓝藻可以固定氮气（N），但在氮限制的沿海水域通常很少见，这构成了一个明显的生态悖论。一种假设是，高盐度（>10 g/L NaCl）可能会抑制蓝藻的固氮作用。然而，在这里我们表明，一种单细胞沿海蓝藻的固氮作用完全依赖于钠离子，并且在低 NaCl 浓度（<4 g/L）下受到抑制。在没有 Na 的情况下，Cyanothece sp. ATCC 51142（最近重新分类为 Crocosphaera subtropica）的细胞上调 nifHDK 基因的表达并合成更多的固氮酶，但不固定 N 也不生长。我们发现，在没有 Na 的情况下，失去固氮能力是由于 ATP 供应不足所致。额外的实验表明，该生物体中的固氮作用是由钠离子能量学和混合酸发酵驱动的，而不是质子能量学和需氧呼吸，即使细胞是在好氧条件下培养的。需要进一步的工作来阐明潜在的机制，以及我们的发现是否与其他沿海蓝藻有关。
