@article {syhapanha_transcriptomicsguided_2023, title = {Transcriptomics-guided identification of an algicidal protease of the marine bacterium Kordia algicida OT-1}, journal = {MicrobiologyOpen}, volume = {12}, number = {5}, year = {2023}, pages = {e1387}, abstract = {In recent years, interest in algicidal bacteria has risen due to their ecological importance and their potential as biotic regulators of harmful algal blooms. Algicidal bacteria shape the plankton communities of the oceans by inhibiting or lysing microalgae and by consuming the released nutrients. Kordia algicida strain OT-1 is a model marine algicidal bacterium that was isolated from a bloom of the diatom Skeletonema costatum. Previous work has suggested that algicidal activity is mediated by secreted proteases. Here, we utilize a transcriptomics-guided approach to identify the serine protease gene KAOT1_RS09515, hereby named alpA1 as a key element in the algicidal activity of K. algicida. The protease AlpA1 was expressed and purified from a heterologous host and used in in vitro bioassays to validate its activity. We also show that K. algicida is the only algicidal species within a group of four members of the Kordia genus. The identification of this algicidal protease opens the possibility of real-time monitoring of the ecological impact of algicidal bacteria in natural phytoplankton blooms., Algicidal bacteria shape the plankton communities of the oceans by lysing microalgae and consuming the released nutrients. Kordia algicida is an environmentally relevant marine bacterium whose algicidal activity is mediated by secreted proteases. In this study, we utilize a transcriptomics-guided approach to identify the secreted serine protease AlpA1 as a key factor in the algicidal process. This discovery offers new approaches for the real-time monitoring and manipulation of algicidal bacteria in algal blooms.}, keywords = {RCC75}, issn = {2045-8827}, doi = {10.1002/mbo3.1387}, url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10565126/}, author = {Syhapanha, Kristy S. and Russo, David A. and Deng, Yun and Meyer, Nils and Poulin, Remington X. and Pohnert, Georg} } @article {meyer_pronounced_2022, title = {Pronounced Uptake and Metabolism of Organic Substrates by Diatoms Revealed by Pulse-Labeling Metabolomics}, journal = {Frontiers in Marine Science}, volume = {9}, year = {2022}, pages = {821167}, abstract = {Diatoms contribute as a dominant group of microalgae to approximately 20\% of the global carbon fixation. In the plankton, these photosynthetic algae are exposed to a plethora of metabolites, especially when competing algae are lysed. It is well established that diatoms can take up specific metabolites, such as vitamins, amino acids as nitrogen source, or dimethylsulfoniopropoionate to compensate for changes in water salinity. It is, however, unclear to which extent diatoms take up other organic resources and if these are incorporated into the cell{\textasciiacute}s metabolism. Here, we explore the general scope of uptake of metabolites from competitors. Using labeled metabolites released during lysis of algae grown under a 13CO2 atmosphere, we show that the cosmopolitan diatom Chaetoceros didymus takes up even dilute organic substrates from these lysates with little bias for molecular weight or polarity. This is reflected by a high degree of labeling in the metabolome of the exposed cells. The newly developed pulse label/mass spectrometry metabolomics approach reveals that polarity and molecular weight has no detectable influence on uptake. We further show that the taken-up metabolites are partly maintained without metabolic modification within the cells, but also a substantial part is subject to catabolic and anabolic transformation. One of the most dominant phytoplankton groups thus has the potential to compete with heterotrophs, suggesting that the observed osmotrophy may substantially impact organic material fluxes in the oceans. Our findings call for the refinement of our understanding of competition in the plankton.}, keywords = {RCC75}, issn = {2296-7745}, doi = {10.3389/fmars.2022.821167}, url = {https://www.frontiersin.org/articles/10.3389/fmars.2022.821167/full}, author = {Meyer, Nils and Rydzyk, Aljoscha and Pohnert, Georg} }