Gao Guang, Liu Wei, Zhao Xin, Gao Kunshan
State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen, China.
Department of Technology and Resource Management, Guangdong Jiangmen Chinese White Dolphin Provincial Nature Reserve Management Bureau, Jiangmen, China.
Front Microbiol. 2021 Mar 16;12:651567. doi: 10.3389/fmicb.2021.651567. eCollection 2021.
The diatom is cosmopolitan and forms algal blooms in coastal waters, being exposed to varying levels of solar UV radiation (UVR) and reduced levels of carbon dioxide (CO). While reduced CO availability is known to enhance CO concentrating mechanisms (CCMs) in this diatom and others, little is known on the effects of UV on microalgal CCMs, especially when CO levels fluctuate in coastal waters. Here, we show that upregulated its CCMs in response to UVR (295-395 nm), especially to UVA (320-395 nm) in the presence and absence of photosynthetically active radiation (PAR). The intensity rise of UVA and/or UVR alone resulted in an increase of the activity of extracellular carbonic anhydrase (CAe); and the addition of UVA enhanced the activity of CCMs-related CAe by 23-27% when PAR levels were low. Such UV-stimulated CCMs activity was only significant at the reduced CO level (3.4 μmol L). In addition, UVA alone drove active HCO uptake although it was not as obvious as CAe activity, another evidence for its role in enhancing CCMs activity. In parallel, the addition of UVA enhanced photosynthetic carbon fixation only at the lower CO level compared to PAR alone. In the absence of PAR, carbon fixation increased linearly with increased intensities of UVA or UVR regardless of the CO levels. These findings imply that during blooming period when CO and PAR availability becomes lower, solar UVR (mainly UVA) helps to upregulate its CCMs and thus carbon fixation, enabling its success of frequent algal blooms.
硅藻分布广泛，在沿海水域形成藻华，会受到不同水平的太阳紫外线辐射（UVR）和降低的二氧化碳（CO）水平影响。虽然已知二氧化碳可利用性降低会增强这种硅藻及其他硅藻的二氧化碳浓缩机制（CCMs），但关于紫外线对微藻CCMs的影响却知之甚少，尤其是当沿海水域的二氧化碳水平波动时。在此，我们表明，在有和没有光合有效辐射（PAR）的情况下，该硅藻会响应UVR（295 - 395纳米），特别是UVA（320 - 395纳米）而上调其CCMs。单独UVA和/或UVR强度的增加导致细胞外碳酸酐酶（CAe）活性增加；当PAR水平较低时，添加UVA可使CCMs相关的CAe活性提高23 - 27%。这种紫外线刺激的CCMs活性仅在降低的二氧化碳水平（3.4微摩尔/升）时才显著。此外，单独的UVA驱动了活跃的HCO₃⁻吸收，尽管不如CAe活性明显，这是其在增强CCMs活性中作用的另一个证据。同时，与单独的PAR相比，添加UVA仅在较低的二氧化碳水平下增强了光合碳固定。在没有PAR的情况下，无论二氧化碳水平如何，碳固定都随UVA或UVR强度的增加而线性增加。这些发现表明，在藻华期，当二氧化碳和PAR的可利用性降低时，太阳UVR（主要是UVA）有助于上调其CCMs，从而促进碳固定，使其能够成功频繁形成藻华。
