Summary Phytoplankton communities within the photic zones of the oceans and lakes are characterised by highly complex assemblages of unicellular microalgae and associated bacteria. The interconnected evolutionary history of algae and bacteria allowed the formation of a wide spectrum of associations defined by orchestrated nutrient exchange, mutual support with growth factors, quorum sensing mediation, and episodic killing of the partners to obtain more resources. In this review, we discuss how these cross‐kingdom interactions shape plankton communities that undergo annual, seasonal switching between alternative states with balanced multispecies consortia. We illustrate how these microscopic interactions can have consequences that scale up to influence global element cycling.

Benthic diatoms are the main primary producers in shallow freshwater and coastal environments, fulfilling important ecological functions such as nutrient cycling and sediment stabilization. However, little is known about their evolutionary adaptations to these highly structured but heterogeneous environments. Here, we report a reference genome for the marine biofilm-forming diatom Seminavis robusta, showing that gene family expansions are responsible for a quarter of all 36,254 protein-coding genes. Tandem duplications play a key role in extending the repertoire of specific gene functions, including light and oxygen sensing, which are probably central for its adaptation to benthic habitats. Genes differentially expressed during interactions with bacteria are strongly conserved in other benthic diatoms while many species-specific genes are strongly upregulated during sexual reproduction. Combined with re-sequencing data from 48 strains, our results offer insights into the genetic diversity and gene functions in benthic diatoms.

Highlights d Proteomes of aged MuSCs and skeletal muscles reveal altered communication d 183 extracellular proteins change abundance in different skeletal muscles during aging d FAPs are the main source of niche proteins affected during aging d Injection of Smoc2 into regenerating muscle of young mice hampers regeneration

Diatoms are unicellular algae with a fundamental role in global biogeochemical cycles as major primary producers at the base of aquatic food webs. In recent years, chemical communication between diatoms and associated bacteria has emerged as a key factor in diatom ecology, spurred by conceptual and technological advancements to study the mechanisms underlying these interactions. Here, we use a combination of physiological, transcriptomic, and metabolomic approaches to study the influence of naturally co-existing bacteria, Maribacter sp. and Roseovarius sp., on the sexual reproduction of the biofilm inhabiting marine pennate diatom Seminavis robusta . While Maribacter sp. severely reduces the reproductive success of S. robusta cultures, Roseovarius sp. slightly enhances it. Contrary to our expectation, we demonstrate that the effect of the bacterial exudates is not caused by altered cell-cycle regulation prior to the switch to meiosis. Instead, Maribacter sp. exudates cause a reduced production of diproline, the sexual attraction pheromone of S. robusta . Transcriptomic analyses show that this is likely an indirect consequence of altered intracellular metabolic fluxes in the diatom, especially those related to amino acid biosynthesis, oxidative stress response, and biosynthesis of defense molecules. This study provides the first insights into the influence of bacteria on diatom sexual reproduction and adds a new dimension to the complexity of a still understudied phenomenon in natural diatom populations.

Marine biofilms are complex multi-species communities where chemical signaling regulates a substantial share of interactions. The involved natural products represent targets for competition strategies by signal interference. Diatoms, that often dominate biofilms, rely on a complex pheromone system during sexual reproduction, involving synchronizing and attracting metabolites. The present study addresses the effect of bacteria on sexual reproduction of the model pennate diatom Seminavis robusta. We observe that sexual reproduction is most efficient under axenic conditions. Bacteria isolated from field collected biofilms modulate sexual reproduction in the algae. A species-specific effect on the diatom mating efficiency could be observed, with Maribactersp. and Marinobactersp. significantly reducing the sexual reproduction rate. Spent medium from these bacteria has the same effect, demonstrating that chemically mediated cross kingdom interactions take place. In contrast, proportion of auxospores. We further observed a lower concentration of the diatom attraction pheromone diproline in the presence of bacteria compared to axenic conditions. In agreement, the Seminavis-associated bacterial community as well as isolated bacterial strains degraded the pheromone over time. Our results highlight that the pheromone system of diatoms is subject to interference strategies of the associated bacterial community by modulation of the signal landscape.