Abstract
Harmful algal blooms (HABs) cause significant economic and ecological
damage worldwide. Despite considerable efforts, a comprehensive
understanding of the factors that promote these blooms
has been lacking, because the biochemical pathways that facilitate
their dominance relative to other phytoplankton within specific
environments have not been identified. Here, biogeochemical
measurements showed that the harmful alga Aureococcus anophagefferens
outcompeted co-occurring phytoplankton in estuaries
with elevated levels of dissolved organic matter and turbidity
and low levels of dissolved inorganic nitrogen. We subsequently
sequenced the genome of A. anophagefferens and compared its
gene complement with those of six competing phytoplankton species
identified through metaproteomics. Using an ecogenomic approach,
we specifically focused on gene sets that may facilitate
dominance within the environmental conditions present during
blooms. A. anophagefferens possesses a larger genome (56 Mbp)
and has more genes involved in light harvesting, organic carbon
and nitrogen use, and encoding selenium- and metal-requiring
enzymes than competing phytoplankton. Genes for the synthesis
of microbial deterrents likely permit the proliferation of this species,
with reduced mortality losses during blooms. Collectively,
these findings suggest that anthropogenic activities resulting in
elevated levels of turbidity, organic matter, and metals have
opened a niche within coastal ecosystems that ideally suits the
unique genetic capacity of A. anophagefferens and thus, has facilitated
the proliferation of this and potentially other HABs.
