Project description:Emiliania huxleyi: Cellular cascades induced by bacterial algicides Interactions between phytoplankton and bacteria play a central role in mediating oceanic biogeochemical cycling and microbial trophic structure in the ocean. The intricate relationships between these two domains of life are mediated via excreted molecules that facilitate communication and determine competitive outcomes. Yet, despite their predicted importance, identifying these secreted compounds and understanding their ecological significance has remained a challenge. Research in the Whalen Lab endeavors to (i) identify those bacterially-derived chemical signaling compounds (i.e. infochemicals) that mediate phytoplankton population dynamics, and (ii) determine the underlying physiological processes that contribute to phytoplankton tolerance or susceptibility to these compounds. Recently, the Whalen lab isolated an alkylquinolone-signaling molecule with known quorum sensing function from the globally distributed marine γ-proteobacteria, Pseudoalteromonas sp. capable of inducing species-specific phytoplankton mortality. This research was the first to suggest quorum sensing compounds have expanded and previously unrecognized ecological roles in regulating primary production and phytoplankton bloom dynamics. We are now investigating in how this alkylquinolone induces phytoplankton mortality via transcriptomic profiling and diagnostic biochemical analysis. Complementary to this transcriptomic examination, we will complete whole-cell proteomic approach to identify those phytoplankton proteins crucial in competitive interactions with bacterial infochemicals, but whose functions may not yet be known. With this proteomic approach in parallel to our transcriptomic investigation, we can establish a better understanding of the eukaryotic macromolecular targets and cellular cascades induced in response to bacterial algicides like alkylquinolones. With the knowledge gained from both approaches we can begin to address how these ?keystone molecules? influence population dynamics and community composition of phytoplankton and bacteria in field-based experiments with the goal of defining a new mechanistic framework for how bacterially derived signaling molecules influence biogeochemical cycles. D= DMSO - control treatment L= low 1 nm HHG additions M= medium 10 nm HHG additions H= high 100 nm HHG additions Each treatment had 4 biological replicates A-D

Project description:Marine phytoplankton are a diverse group of photoautotrophic organisms and key mediators in the global carbon cycle. Phytoplankton physiology and biomass accumulation are closely tied to mixed layer depth, but the intracellular metabolic pathways activated in response to changing mixed layer depths remain unexplored. Here, metatranscriptomics was used to characterize the phytoplankton community response to a mixed layer shallowing from 233 meters to 5 meters over the course of two days during the late spring in the Northwest Atlantic. Most phytoplankton genera downregulated core photosynthesis, carbon storage, and carbon fixation genes as the system transitioned from a deep to a shallow mixed layer and shifted towards catabolism of stored carbon ic pathways supportive of rapid cell growth. In contrast, phytoplankton genera exhibited divergent transcriptional strategies for photosystem light harvesting complex genes during this transition. Active infection, taken as the ratio of virus to host transcripts, increased in the Bacillariophyta (diatom) phylum and decreased in the Chlorophyta (green algae) phylum upon mixed layer shallowing. A conceptual model is proposed to provide ecophysiological context for our findings, in which light limitation during deep mixing induces populations into a transcriptional state which maximizes interrupts the oscillating levels of transcripts related to photosynthesis, carbon storage, and carbon fixation found in shallow mixed layers with relatively higher growth rates. We propose that upon sensing high light levels during mixed layer shallowing, phytoplankton resume diel oscillation of core sets of genes enabling photoprotection, biosynthesis and cell replication. Our findings highlight the shared and unique transcriptional response strategies within phytoplankton communities acclimating to the dynamic light environment associated with transient deep mixing and shallowing events during the annual North Atlantic bloom.

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Karenia brevis allelopathy compromises the lipidome, membrane integrity, and photosynthetic efficiency of competitors

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