Significance Microscopic marine algae (phytoplankton) are responsible for much of Earth's photosynthesis, serving as the base of a massive food web supporting fisheries. Phytoplankton compete for limiting resources, with some species producing noxious compounds that kill competitors or inhibit their growth. The red-tide dinoflagellate Karenia brevis is one such allelopathic species, causing growth suppression of other phytoplankton and negatively impacting coastal ecosystems. Metabolomic and proteomic approaches were used to characterize the sublethal physiological impacts of K. brevis allelopathy on two competing phytoplankton, providing insights into the physiological mechanisms by which allelopathy occurs and the metabolic pathways that enable resistance in co-occurring competitors.

Members of the resistance nodulation cell division (RND) of efflux pumps play essential roles in multidrug resistance (MDR) in Gram-negative bacteria. Here, we describe the search for new small molecules from marine microbial extracts to block efflux and thus restore antibiotic susceptibility in MDR bacterial strains. We report the isolation of 3,4-dibromopyrrole-2,5-dione (1), an inhibitor of RND transporters, from Enterobacteriaceae and Pseudomonas aeruginosa, from the marine bacterium Pseudoalteromonas piscicida. 3,4-Dibromopyrrole-2,5-dione decreased the minimum inhibitory concentrations (MICs) of two fluoroquinolones, an aminoglycoside, a macrolide, a beta-lactam, tetracycline, and chloramphenicol between 2- and 16-fold in strains overexpressing three archetype RND transporters (AcrAB-TolC, MexAB-OprM, and MexXY-OprM). 3,4-Dibromopyrrole-2,5-dione also increased the intracellular accumulation of Hoechst 33342 in wild-type but not in transporter-deficient strains and prevented H33342 efflux (IC50 = 0.79 μg/mL or 3 μM), a hallmark of efflux pump inhibitor (EPI) functionality. A metabolomic survey of 36 Pseudoalteromonas isolates mapped the presence of primarily brominated metabolites only within the P. piscicida phylogenetic clade, where a majority of antibiotic activity was also observed, suggesting a link between halogenation and enhanced secondary metabolite biosynthetic potential. In sum, 3,4-dibromopyrrole-2,5-dione is a potent EPI and deserves further attention as an adjuvant to enhance the effectiveness of existing antibiotics.

A review of chemically mediated interactions in planktonic marine environments covering new studies from January 2015 to December 2017.

No abstract

The formation, propagation, and maintenance of harmful algal blooms are of interest due to their negative effects on marine life and human health. Some bloom-forming algae utilize allelopathy, the release of compounds that inhibit competitors, to exclude other species dependent on a common pool of limiting resources. Allelopathy is hypothesized to affect bloom dynamics and is well established in the red tide dinoflagellate Karenia brevis. K. brevis typically suppresses competitor growth rather than being acutely toxic to other algae. When we investigated the effects of allelopathy on two competitors, Asterionellopsis glacialis and Thalassiosira pseudonana, using nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS)-based metabolomics, we found that the lipidomes of both species were significantly altered. However, A. glacialis maintained a more robust metabolism in response to K. brevis allelopathy whereas T. pseudonana exhibited significant alterations in lipid synthesis, cell membrane integrity, and photosynthesis. Membrane-associated lipids were significantly suppressed for T. pseudonana exposed to allelopathy such that membranes of living cells became permeable. K. brevis allelopathy appears to target lipid biosynthesis affecting multiple physiological pathways suggesting that exuded compounds have the ability to significantly alter competitor physiology, giving K. brevis an edge over sensitive species.

The bloom-forming dinoflagellate Karenia brevis produces a suite of allelopathic compounds that inhibit the growth of several phytoplankton competitors in laboratory experiments. However, it is less clear how allelopathy affects competition in the field, including whether allelopathic compounds impact K. brevis bloom dynamics. We investigated the extent to which phytoplankton species typically found offshore in the Gulf of Mexico, where K. brevis blooms initiate, are sensitive to K. brevis allelopathy. Natural assemblages of offshore phytoplankton dominated by diatoms were largely resistant to K. brevis allelopathy, even experiencing slight stimulation of growth from exposure to K. brevis exudates. When tested in pair-wise laboratory experiments, four diatom species often found offshore in the Gulf of Mexico exhibited varying degrees of resistance to K. brevis similar to that observed with field assemblages, although some competitors displayed a trend toward growth inhibition. In concurrent pair-wise laboratory experiments, four diatom species whose nearshore habitats frequently experience dense K. brevis blooms also demonstrated a range of responses to K. brevis allelopathy, from strong sensitivity to resistance. Overall, Gulf of Mexico phytoplankton that co-occur with K. brevis blooms in both nearshore and offshore environments respond variably to K. brevis allelopathy.

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Editors are often described as gatekeepers of scientific publishing, as they are responsible for maintaining journal standards, deciding what is published, and ultimately guiding discourse. Scientists who are journal editors gain career benefits, yet these are rarely described to early career researchers, much less how to prepare for such a role. Additionally, disparities at the editorial level could impact which scientists receive benefits of filling these roles. To better characterize the demographics and professional experiences of current associate editors, while also highlighting the benefits and potential challenges to this position, we conducted a survey of associate editors for the Association for the Sciences of Limnology & Oceanography society journals. Our results highlight potential demographic disparities present in the editorial pool, including that non‐native English speaking editors assume the role after obtaining more experience serving as a peer reviewer than native English speaking editors. Our results also highlight several rewards along with challenging components of being an editor. We hope our results can inform early career researchers on steps they can take to prepare themselves for editorial work, as well as provide strategies for scientific societies to minimize editorial board disparities.