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1. Functional annotation and importance of marine bacterial transporters of plankton exometabolites

   https://doi.org/10.1038/s43705-023-00244-6  

   Schroer, William F.; Kepner, Hannah E.; Uchimiya, Mario; Mejia, Catalina; Rodriguez, Lidimarie Trujillo; Reisch, Christopher R.; Moran, Mary Ann (April 2023, ISME Communications)

   Abstract Metabolite exchange within marine microbial communities transfers carbon and other major elements through global cycles and forms the basis of microbial interactions. Yet lack of gene annotations and concern about the quality of existing ones remain major impediments to revealing currencies of carbon flux. We employed an arrayed mutant library of the marine bacterium Ruegeria pomeroyi DSS-3 to experimentally annotate substrates of organic compound transporter systems, using mutant growth and compound drawdown analyses to link transporters to their cognate substrates. Mutant experiments verified substrates for thirteen R. pomeroyi transporters. Four were previously hypothesized based on gene expression data (taurine, glucose/xylose, isethionate, and cadaverine/putrescine/spermidine); five were previously hypothesized based on homology to experimentally annotated transporters in other bacteria (citrate, glycerol, N-acetylglucosamine, fumarate/malate/succinate, and dimethylsulfoniopropionate); and four had no previous annotations (thymidine, carnitine, cysteate, and 3-hydroxybutyrate). These bring the total number of experimentally-verified organic carbon influx transporters to 18 of 126 in the R. pomeroyi genome. In a longitudinal study of a coastal phytoplankton bloom, expression patterns of the experimentally annotated transporters linked them to different stages of the bloom, and also led to the hypothesis that citrate and 3-hydroxybutyrate were among the most highly available bacterial substrates. Improved functional annotation of the gatekeepers of organic carbon uptake is critical for deciphering carbon flux and fate in microbial ecosystems. 

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2. Penicillium molds impact the transcriptome and evolution of the cheese bacterium Staphylococcus equorum

   https://doi.org/10.1128/msphere.00047-23  

   Ye, Ruby; Tomo, Christopher; Chan, Neal; Wolfe, Benjamin E. (January 2023, mSphere)

   Mitchell, Aaron P. (Ed.)

   Fungi and bacteria are commonly found co-occurring both in natural and synthetic microbiomes, but our understanding of fungal–bacterial interactions is limited to a handful of species. Conserved mechanisms of interactions and evolutionary consequences of fungal–bacterial interactions are largely unknown. Our RNA sequencing and experimental evolution data with Penicillium species and the bacterium S. equorum demonstrate that divergent fungal species can elicit conserved transcriptional and genomic responses in co-occurring bacteria. Penicillium molds are integral to the discovery of novel antibiotics and production of certain foods. By understanding how Penicillium species affect bacteria, our work can further efforts to design and manage Penicillium -dominated microbial communities in industry and food production. 

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3. Heterotrophic bacteria trigger transcriptome remodelling in the photosynthetic picoeukaryote Micromonas commoda

   https://doi.org/10.1111/1758-2229.13285  

   Hamilton, Maria; Ferrer‐González, Frank Xavier; Moran, Mary Ann (June 2024, Environmental Microbiology Reports)

   Abstract Marine biogeochemical cycles are built on interactions between surface ocean microbes, particularly those connecting phytoplankton primary producers to heterotrophic bacteria. Details of these associations are not well understood, especially in the case of direct influences of bacteria on phytoplankton physiology. Here we catalogue how the presence of three marine bacteria (Ruegeria pomeroyiDSS‐3,Stenotrophomonassp. SKA14 andPolaribacter dokdonensisMED152) individually and uniquely impact gene expression of the picoeukaryotic algaMicromonas commodaRCC 299. We find a dramatic transcriptomic remodelling byM. commodaafter 8 h in co‐culture, followed by an increase in cell numbers by 56 h compared with the axenic cultures. Some aspects of the algal transcriptomic response are conserved across all three bacterial co‐cultures, including an unexpected reduction in relative expression of photosynthesis and carbon fixation pathways. Expression differences restricted to a single bacterium are also observed, with the FlavobacteriiaP. dokdonensisuniquely eliciting changes in relative expression of algal genes involved in biotin biosynthesis and the acquisition and assimilation of nitrogen. This study reveals thatM. commodahas rapid and extensive responses to heterotrophic bacteria in ways that are generalizable, as well as in a taxon specific manner, with implications for the diversity of phytoplankton‐bacteria interactions ongoing in the surface ocean. 

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4. Growth phase proteomics of the heterotrophic marine bacterium Ruegeria pomeroyi

   https://doi.org/10.1038/s41597-019-0308-y  

   Krayushkina, Dasha; Timmins-Schiffman, Emma; Faux, Jessica; May, Damon H.; Riffle, Michael; Harvey, H. Rodger; Nunn, Brook L. (December 2019, Scientific Data)

   Abstract The heterotrophic marine bacterium,Ruegeria pomeroyi, was experimentally cultured under environmentally realistic carbon conditions and with a tracer-level addition of¹³C-labeled leucine to track bacterial protein biosynthesis through growth phases. A combination of methods allowed observation of real-time bacterial protein production to understand metabolic priorities through the different growth phases. Over 2000 proteins were identified in each experimental culture from exponential and stationary growth phases. Within two hours of the¹³C-labeled leucine addition,R.pomeroyisignificantly assimilated the newly encountered substrate into new proteins. This dataset provides a fundamental baseline for understanding growth phase differences in molecular physiology of a cosmopolitan marine bacterium. 

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5. Bacterial transcriptional response to labile exometabolites from photosynthetic picoeukaryote Micromonas commoda

   https://doi.org/10.1038/s43705-023-00212-0  

   Ferrer-González, Frank X.; Hamilton, Maria; Smith, Christa B.; Schreier, Jeremy E.; Olofsson, Malin; Moran, Mary Ann (December 2023, ISME Communications)

   Abstract Dissolved primary production released into seawater by marine phytoplankton is a major source of carbon fueling heterotrophic bacterial production in the ocean. The composition of the organic compounds released by healthy phytoplankton is poorly known and difficult to assess with existing chemical methods. Here, expression of transporter and catabolic genes by three model marine bacteria ( Ruegeria pomeroyi DSS-3, Stenotrophomonas sp. SKA14, and Polaribacter dokdonensis MED152) was used as a biological sensor of metabolites released from the picoeukaryote Micromonas commoda RCC299. Bacterial expression responses indicated that the three species together recognized 38 picoeukaryote metabolites. This was consistent with the Micromonas expression of genes for starch metabolism and synthesis of peptidoglycan-like intermediates. A comparison of the hypothesized Micromonas exometabolite pool with that of the diatom Thalassiosira pseudonana CCMP1335, analyzed previously with the same biological sensor method, indicated that both phytoplankton released organic acids, nucleosides, and amino acids, but differed in polysaccharide and organic nitrogen release. Future ocean conditions are expected to favor picoeukaryotic phytoplankton over larger-celled microphytoplankton. Results from this study suggest that such a shift could alter the substrate pool available to heterotrophic bacterioplankton. 

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