HABs have increasingly occurred and impacted human health, aquatic ecosystems, and coastal economies. Despite great efforts, the factors that drive the development and termination of a bloom are poorly understood, largely due to inadequate
in situ
data about the physiology and metabolism of the causal species and the community.
Lineage-wise physiological activities of plankton communities in the ocean are important but challenging to characterize. Here we conducted whole-assemblage metatranscriptomic profiling at continental shelf and slope sites of South China Sea to investigate carbon fixation in different lineages. We catalogued 4.4 million unique genes, ~37% being annotatable and mainly involved in microbial metabolism, photosynthesis, amino acid synthesis, oxidative phosphorylation, and two-component systems. With RuBisCO expression as proxy, Calvin carbon fixation (CCF) was mainly contributed by Bacillariophyta, Chlorophyta, Cyanobacteria, Haptophyta andnon-diatom Stramenopiles, which was differentially affected by environmental factors among lineages. CCF exhibited positive or negative correlations with phagotrophy gene expression depending on lineages, suggesting phagotrophy enhances (Bacillariophyta, Haptophyta, and Chlorophyta) or complements (Dinophyta) CCF. Our data reveal significant potential of non-Calvin carbon fixation (NCF), mainly contributed by Flavobacteriales, Alteromonadales, Oceanospirillales and Rhodobacterales. Furthermore, in Flavobacteriales, Alteromonadales, Pelagibacterales and Rhodobacterales, NCF potential was positively correlated with proteorhodopsin expression, suggesting that NCF is energetically supported by proteorhodopsin. The novel insights into lineage-dependent potential of carbon fixation, widespread mixotrophy, and proteorhodopsin as energy source for NCF lay a methodological and informational foundation for further research to understand the carbon fixation and trophic landscape in the ocean.
Ocean warming can cause injury and death in mussels and is believed to be one of the main reasons for extensive die-offs of mussel populations worldwide. However, the biological processes by which mussels respond to heat stress are still unclear. In this study, we conducted an analysis of enzyme activity and TMT-labelled based proteomic in the digestive gland tissue of Mytilus coruscus after exposure to high temperatures. Our results showed that the activities of superoxide dismutase, acid phosphatase, lactate dehydrogenase, and cellular content of lysozyme were significantly changed in response to heat stress. Furthermore, many differentially expressed proteins involved in nutrient digestion and absorption, p53, MAPK, apoptosis, and energy metabolism were activated post-heat stress. These results suggest that M. coruscus can respond to heat stress through the antioxidant system, the immune system, and anaerobic respiration. Additionally, M. coruscus may use fat, leucine, and isoleucine to meet energy requirements under high temperature stress via the TCA cycle pathway. These findings provide a useful reference for further exploration of the response mechanism to heat stress in marine mollusks.
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