Taxonomic difference in marine bloom-forming phytoplanktonic species affects the dynamics of both bloom-responding prokaryotes and prokaryotic viruses

ABSTRACTThe production of dissolved organic matter during phytoplankton blooms and consumption by heterotrophic prokaryotes promote marine carbon biogeochemical cycling. Although prokaryotic viruses presumably affect this process, their dynamics during blooms are not fully understood. Here, we investigated the effects of taxonomic difference in bloom-forming phytoplankton on prokaryotes and their viruses. We analyzed the dynamics of coastal prokaryotic communities and viruses under the addition of dissolved intracellular fractions from taxonomically distinct phytoplankton, the diatom Chaetoceros sp. (CIF) and the raphidophycean alga Heterosigma akashiwo (HIF), using microcosm experiments. Ribosomal RNA gene amplicon and viral metagenomic analyses revealed that particular prokaryotes and prokaryotic viruses specifically increased in either CIF or HIF, indicating that taxonomic difference in bloom-forming phytoplankton promotes distinct dynamics of not only the prokaryotic community but also prokaryotic viruses. Furthermore, combining our microcosm experiments with publicly available environmental data mining, we identified both known and novel possible host-virus pairs. In particular, the growth of prokaryotes associating with phytoplanktonic organic matter, such as Bacteroidetes (Polaribacter and NS9 marine group), Vibrio spp., and Rhodobacteriales (Nereida and Planktomarina), was accompanied by an increase in viruses predicted to infect Bacteroidetes, Vibrio, and Rhodobacteriales, respectively. Collectively, our findings suggest that changes in bloom-forming species can be followed by an increase in a specific group of prokaryotes and their viruses and that elucidating these tripartite relationships among specific phytoplankton, prokaryotes, and prokaryotic viruses improves our understanding of coastal biogeochemical cycling in blooms.IMPORTANCEThe primary production during marine phytoplankton bloom and the consumption of the produced organic matter by heterotrophic prokaryotes significantly contribute to coastal biogeochemical cycles. While the activities of those heterotrophic prokaryotes are presumably affected by viral infection, the dynamics of their viruses during blooms are not fully understood. In this study, we experimentally demonstrated that intracellular fractions of taxonomically distinct bloom-forming phytoplankton species, the diatom Chaetoceros sp. and the raphidophycean alga Heterosigma akashiwo, promoted the growth of taxonomically different prokaryotes and prokaryotic viruses. Based on their dynamics and predicted hosts of those viruses, we succeeded in detecting already-known and novel possible host-virus pairs associating with either phytoplankton species. Altogether, we propose that the succession of bloom-forming phytoplankton would change the composition of the abundant prokaryotes, resulting in an increase in their viruses. These changes in viral composition, depending on bloom-forming species, would alter the dynamics and metabolism of prokaryotes, affecting biogeochemical cycling in blooms

Multiplexed bioluminescence imaging of cancer cell response to hypoxia and inflammation in the caudal-artery injection model of bone metastasis during zoledronic acid treatment

Aim: Therapeutic agents suppressing bone remodeling have been clinically approved to delay metastatic progression and skeletal-related events in patients with bone metastasis. However, therapeutic agents including zoledronic acid (ZA) are insufficient to regress established bone metastasis. Therefore, new treatment strategies are desired, and unraveling the status of cancer cells during bone metastatic progression will help develop therapeutic strategies.Methods: We developed a unique multiplexed reporter system for bioluminescent imaging (MRS-BLI) using three luciferase reporter genes. This system allows for the noninvasive and quantitative monitoring of tumor growth and activities of nuclear factor-kappa B (NF-κB) and hypoxia-inducible factor (HIF), which are the key transcriptional factors in response to inflammation and hypoxia, respectively. PC-3/MRS-BLI, a human prostate cancer cell line that stably retains the MRS-BLI reporter genes, was applied to the caudal-artery injection model of bone metastasis to observe the status of cancer cells during bone metastasis development and ZA treatment (< 1 month).Results: MRS-BLI reveals key events during the bone metastasis development: NF-κB and HIF are activated in cancer cells after migration to the bone marrow and are transiently reduced, followed by rapid activation before proliferation begins. ZA treatment suppresses the growth of metastasized cancer cells by suppressing NF-κB and HIF activities that may be indirectly induced by osteoclast activation.Conclusion: By visualizing the NF-κB and HIF activities of PC-3/MRS-BLI in bone, MRS-BLI has enabled new discoveries regarding the regulation of bone metastases. Further analysis of the progression of bone metastases using MRS-BLI may provide important information for developing new therapeutic strategies

Year-round dynamics of amplicon sequence variant communities differ among eukaryotes, Imitervirales , and prokaryotes in a coastal ecosystem

International audienceAbstract Coastal microbial communities are affected by seasonal environmental change, biotic interactions, and fluctuating nutrient availability. We investigated the seasonal dynamics of communities of eukaryotes, a major group of double-stranded DNA viruses that infect eukaryotes (order Imitervirales; phylum Nucleocytoviricota), and prokaryotes in the Uranouchi Inlet, Kochi, Japan. We performed metabarcoding using ribosomal RNA genes and viral polB genes as markers in 43 seawater samples collected over 20 months. Eukaryotes, prokaryotes, and Imitervirales communities characterized by the compositions of amplicon sequence variants (ASVs) showed synchronic seasonal cycles. However, the community dynamics showed intriguing differences in several aspects, such as the recovery rate after a year. We also showed that the differences in community dynamics were at least partially explained by differences in recurrence/persistence levels of individual ASVs among eukaryotes, prokaryotes, and Imitervirales. Prokaryotic ASVs were the most persistent, followed by eukaryotic ASVs and Imitervirales ASVs, which were the least persistent. We argue that the differences in the specificity of interactions (virus–eukaryote vs. prokaryote–eukaryote) as well as the niche breadth of community members were at the origin of the distinct community dynamics among eukaryotes, their viruses, and prokaryotes