Abstract
Life history (life cycle) plays a vital role in the ecology of some microalgae; however, the well-known brown-tide-causing pelagophyte Aureococcus anophagefferens has been barely investigated in this regard. Recently, based mainly on detections in marine sediments from China, we proved that this organism has a resting stage. We, therefore, conducted a follow-up study to characterize the resting stage cells (RSCs) of A. anophagefferens using the culture CCMP1984. The RSCs were spherical, larger than the vegetative cells, and smooth in cell surface and contained more aggregated plastid but more vacuolar space than vegetative cells. RSCs contained a conspicuous lipid-enriched red droplet. We found a 9.9-fold decrease in adenosine triphosphate (ATP) content from vegetative cells to RSCs, indicative of a "resting" or dormant physiological state. The RSCs stored for 3 months (at 4 °C in darkness) readily reverted back to vegetative growth within 20 days after being transferred to the conditions for routine culture maintenance. Our results indicate that the RSCs of A. anophagefferens are a dormant state that differs from vegetative cells morphologically and physiologically, and that RSCs likely enable the species to survive unfavorable conditions, seed annual blooms, and facilitate its cosmopolitan distribution that we recently documented.
Highlights
The non-motile, picoplanktonic (2–3 μm) pelagophyte Aureococcus anophagefferens Hargraves et Sieburth has caused numerous ecosystem disruptive algal blooms (EDABs), commonly known as "brown tides", in U.S estuaries since 1985 [1,2]
As a novel brown-tide-forming species in China, whether A. anophagefferens was an alien species recently introduced to China via anthropogenic transport processes or has been an indigenous species existing with a background abundance prior to the first reported bloom has become a question of ecological significance
In our recently published work [29], we proved that A. anophagefferens has a resting stage in its life history via germination experiments of a sediment sample collected from the coast of Qinhuangdao, China, where blooms of this species occurred, and found that this species has an extremely wide geographic distribution and a more than 1500-year presence in China and is not an alien species
Summary
The non-motile, picoplanktonic (2–3 μm) pelagophyte Aureococcus anophagefferens Hargraves et Sieburth has caused numerous ecosystem disruptive algal blooms (EDABs), commonly known as "brown tides", in U.S estuaries since 1985 [1,2]. This species lacked morphological features distinguishing it from other similar sized forms under light microscopy, but ultrastructural observations exhibited that each cell has a single chloroplast, nucleus, and mitochondrion and an unusual exocellular polysaccharide-like layer [2]. A comparison of nearly the entire length of the 18S ribosomal RNA (rRNA) gene sequences of A. anophagefferens from Qinhuangdao, China with that from the USA has shown that there was relatively little genetic variability (0–6 bp differences) [9], which suggested that A. anophagefferens was possibly an alien species in China [10,14]
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