Trade-offs of lipid remodeling in a marine predator-prey interaction in response to phosphorus limitation

The microbial phosphorus cycle in aquatic ecosystems

Phosphorus is an essential element for life, and phosphorus cycling is crucial to planetary habitability. In aquatic environments, microorganisms are a major component of phosphorus cycling and rapidly transform the diverse chemical forms of phosphorus through various uptake, assimilation and release pathways. Recent discoveries have revealed a more dynamic and complex aquatic microbial phosphorus cycle than previously understood. Some microorganisms have been shown to use and produce new phosphorus compounds, including those in reduced forms. New findings have also raised numerous unanswered questions that warrant further investigation. There is an expanding influence of human activity on aquatic ecosystems. Advancements in understanding the phosphorus biogeochemistry of evolving aquatic environments offer a unique opportunity to comprehend, anticipate and mitigate the effect of human activities. In this Review, I discuss the wealth of new aquatic phosphorus cycle research, spanning disciplines from omics and physiology to global biogeochemical modelling, with a focus on the current comprehension of how aquatic microorganisms sense, transport, assimilate, store, produce and release phosphorus. Of note, I delve into cellular phosphorus allocation, an underexplored topic with wide-ranging implications for energy and element flux in aquatic ecosystems.

Divergent impacts of fertilization regimes on below-ground prokaryotic and eukaryotic communities in the Tibetan Plateau

Chemical nutrient amendment by human activities can lead to environmental impacts contributing to global biodiversity loss. However, the comprehensive understanding of how below- and above-ground biodiversity shifts under fertilization regimes in natural ecosystems remains elusive. Here, we conducted a seven-year field experiment (2011-2017) and examined the effects of different fertilization on plant biodiversity and soil belowground (prokaryotic and eukaryotic) communities in the alpine meadow of the Tibetan Plateau, based on data collected in 2017. Our results indicate that nitrogen addition promoted total plant biomass but reduced the plant species richness. Conversely, phosphorus enrichment did not promote plant biomass and exhibited an unimodal pattern with plant richness. In the belowground realm, distinct responses of soil prokaryotic and eukaryotic communities were observed under fertilizer application. Specifically, soil prokaryotic diversity decreased with nitrogen enrichment, correlating with shifts in soil pH. Similarly, soil eukaryotic diversity decreased with increased phosphorous inputs, aligning with the equilibrium between soil available and total phosphorus. We also established connections between these soil organism communities with above-ground plant richness and biomass. Overall, our study contributes to a better understanding of the sustainable impacts of human-induced nutrient enrichment on the natural environment. Future research should delve deeper into the long-term effects of fertilization on soil health and ecosystem functioning, aiming to achieve a balance between agricultural productivity and environmental conservation.

New insights in bacterial organophosphorus cycling: From human pathogens to environmental bacteria

In terrestrial and aquatic ecosystems, phosphorus (P) availability controls primary production, with consequences for climate regulation and global food security. Understanding the microbial controls on the global P cycle is a prerequisite for minimising our reliance on non-renewable phosphate rock reserves and reducing pollution associated with excessive P fertiliser use. This recognised importance has reinvigorated research into microbial P cycling, which was pioneered over 75 years ago through the study of human pathogenic bacteria-host interactions. Immobilised organic P represents a significant fraction of the total P pool. Hence, microbes have evolved a plethora of mechanisms to transform this fraction into labile inorganic phosphate, the building block for numerous biological molecules. The 'genomics era' has revealed an extraordinary diversity of organic P cycling genes exist in the environment and studies going 'back to the lab' are determining how this diversity relates to function. Through this integrated approach, many hitherto unknown genes and proteins that are involved in microbial P cycling have been discovered. Not only do these fundamental discoveries push the frontier of our knowledge, but several examples also provide exciting opportunities for biotechnology and present possible solutions for improving the sustainability of how we grow our food, both locally and globally. In this review, we provide a comprehensive overview of bacterial organic P cycling, covering studies on human pathogens and how this knowledge is informing new discoveries in environmental microbiology.

Predation in a Microbial World: Mechanisms and Trade-Offs of Flagellate Foraging

Heterotrophic nanoflagellates are the main consumers of bacteria and picophytoplankton in the ocean and thus play a key role in ocean biogeochemistry. They are found in all major branches of the eukaryotic tree of life but are united by all being equipped with one or a few flagella that they use to generate a feeding current. These microbial predators are faced with the challenges that viscosity at this small scale impedes predator-prey contact and that their foraging activity disturbs the ambient water and thus attracts their own flow-sensing predators. Here, I describe some of the diverse adaptations of the flagellum to produce sufficient force to overcome viscosity and of the flagellar arrangement to minimize fluid disturbances, and thus of the various solutions to optimize the foraging-predation risk trade-off. I demonstrate how insights into this trade-off can be used to develop robust trait-based models of microbial food webs.

Aminolipids in bacterial membranes and the natural environment

Our comprehension of membrane function has predominantly advanced through research on glycerophospholipids, also known as phosphoglycerides, which are glycerol phosphate-based lipids found across all three domains of life. However, in bacteria, a perplexing group of lipids distinct from glycerol phosphate-based ones also exists. These are amino acid-containing lipids that form an amide bond between an amino acid and a fatty acid. Subsequently, a second fatty acid becomes linked, often via the 3-hydroxy group on the first fatty acid. These amide-linked aminolipids have, as of now, been exclusively identified in bacteria. Several hydrophilic head groups have been discovered in these aminolipids including ornithine, glutamine, glycine, lysine, and more recently, a sulfur-containing non-proteinogenic amino acid cysteinolic acid. Here, we aim to review current advances in the genetics, biochemistry and function of these aminolipids as well as giving an ecological perspective. We provide evidence for their potential significance in the ecophysiology of all major microbiomes, i.e. gut, soil, and aquatic as well as highlighting their important roles in influencing biological interactions.

Nutrient availability and grazing influence the strength of priority effects during freshwater bacterial community coalescence

When bacterial communities mix, immigration history can fundamentally affect the community composition as a result of priority effects. Priority effects arise when an early immigrant exhausts resources and/or alters habitat conditions, thereby influencing the establishment success of the late arriver. The strength of priority effects is context-dependent and expected to be stronger if environmental conditions favour the growth of the first arriver. In this study, we conducted a two-factorial experiment testing the importance of nutrient availability and grazing on the strength of priority effects in complex aquatic bacterial communities. We did so by mixing two dissimilar communities, simultaneously, and with a 38 h time-delay. Priority effects were measured as the invasion resistance of the first community to the invading second community. We found stronger priority effects in treatments with high nutrient availability and absence of grazing, but in general, the arrival timing was less important than the selection by nutrients and grazing. At the population level, the results were complex, but priority effects may have been driven by bacteria belonging to for example, the genera Rhodoferax and Herbaspirillum. Our study highlights the importance of arrival timing in complex bacterial communities, especially if environmental conditions favour rapid community growth.

Aminolipids elicit functional trade-offs between competitiveness and bacteriophage attachment in Ruegeria pomeroyi

Lipids play a crucial role in maintaining cell integrity and homeostasis with the surrounding environment. Cosmopolitan marine roseobacter clade (MRC) and SAR11 clade bacteria are unique in that, in addition to glycerophospholipids, they also produce an array of amino acid-containing lipids that are conjugated with beta-hydroxy fatty acids through an amide bond. Two of these aminolipids, the ornithine aminolipid (OL) and the glutamine aminolipid (QL), are synthesized using the O-acetyltransferase OlsA. Here, we demonstrate that OL and QL are present in both the inner and outer membranes of the Gram-negative MRC bacterium Ruegeria pomeroyi DSS-3. In an olsA mutant, loss of these aminolipids is compensated by a concurrent increase in glycerophospholipids. The inability to produce aminolipids caused significant changes in the membrane proteome, with the membrane being less permeable and key nutrient transporters being downregulated while proteins involved in the membrane stress response were upregulated. Indeed, the import of ¹⁴C-labelled choline and dimethylsulfoniopropionate, as a proxy for the transport of key marine nutrients across membranes, was significantly impaired in the olsA mutant. Moreover, the olsA mutant was significantly less competitive than the wild type (WT) being unable to compete with the WT strain in co-culture. However, the olsA mutant unable to synthesize these aminolipids is less susceptible to phage attachment. Together, these data reveal a critical role for aminolipids in the ecophysiology of this important clade of marine bacteria and a trade-off between growth and avoidance of bacteriophage attachment.