Differences in the Formation Mechanism of Giant Colonies in Two Phaeocystis globosa Strains.

Dayong Liang,Shaoshan Li,Xiaodong Wang,Yan Wang,Yiping Huo

doi:10.3390/ijms21155393

Dayong Liang, Shaoshan Li + Show 3 more

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https://doi.org/10.3390/ijms21155393

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Abstract

Phaeocystis globosa has become one of the primary causes of harmful algal bloom in coastal areas of southern China in recent years, and it poses a serious threat to the marine environment and other activities depending upon on it (e.g., aquaculture, cooling system of power plants), especially in the Beibu Gulf. We found colonies of P. globosa collected form Guangxi (China) were much larger than those obtained from Shantou cultured in lab. To better understand the causes of giant colonies formation, colonial cells collected from P. globosa GX strain (GX-C) and ST strain (ST-C) were separated by filtration. Morphological observations, phylogenetic analyses, rapid light-response curves, fatty acid profiling and transcriptome analyses of two type cells were performed in the laboratory. Although no differences in morphology and 18S rRNA sequences of these cells were observed, the colonies of GX strain (4.7 mm) are 30 times larger than those produced by the ST strain (300 μm). The rapid light-response curve of GX-C was greater than that of ST-C, consistent with the upregulated photosynthetic system, while the fatty acid content of GX-C was lower than that of ST-C, also consistent with the downregulated synthesis of fatty acids and the upregulated degradation of fatty acids. In summary, the increased energy generated by GX-C is allocated to promote the secretion of extracellular polysaccharides for colony formation. We performed a physiological and molecular assessment of the differences between the GX-C and ST-C strains, providing insights into the mechanisms of giant colonies formation in P. globosa.

Highlights

The genus Phaeocystis (Prymnesiophyceae) is globally distributed in the marine environment, ranging from tropical to polar oceans, and plays important roles in the global carbon and sulfur cycles and in regional food webs [1]
SEM observations showed that the flagella and a short haptonema are replaced by two short appendages (0.15–0.45 μm), inserted into the center of the apical pole between the two plastids, and these have a smooth surface without scales (Figure 1b,e)
The phylogeny shows that ST and GX strains belong to the same sub-group within the P. globosa clade

Summary

Introduction

The genus Phaeocystis (Prymnesiophyceae) is globally distributed in the marine environment, ranging from tropical to polar oceans, and plays important roles in the global carbon and sulfur cycles and in regional food webs [1]. Among the six species to have been identified, P. globosa is a common cause of harmful algal blooms that often produces red tides by forming colonies in temperate and trophic zones [2,3]. P. globosa has been reported along the coast since the 1990s in China [4]. During the period 2001–2007, blooms of P. globosa were frequently reported throughout the year, including extensive areas from the Bohai Sea (the North China Sea) to the coast of the Hainan Province (the South China Sea), strongly impacting on local fisheries [5,6]. From 2010-2019, outbreaks of P. globosa affected the local aquaculture and coastal environment, and posed a potential threat to nuclear power cooling systems in coastal areas. Blooms of P. globosa have become an important environmental problem requiring urgent mitigation

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