Laboratory evolution and characterization of nitrate-resistant phosphite dehydrogenase (PtxD) for enhanced cyanobacterial cultivation

Phosphite dehydrogenase (PtxD) catalyzes NAD+-dependent oxidation of phosphite (Pt) to phosphate (Pi), offering various biotechnological applications, such as the creation of Pt-dependency for the biological containment of genetically modified organisms. Previously, we established a Pt-dependent cyanobacterial strain (RH714) by expressing PtxD and a reduced phosphorous compound-specific transporter (HtxBCDE) in Synechococcus elongatus PCC 7942 devoid of its endogenous Pi transporters. This strain demonstrated strict Pt dependency but failed to grow in unbuffered BG-11 medium supplemented with 2 % CO2 owing to medium acidification below approximately pH 6.5. The present study aimed to overcome this limitation by passaging the RH714 strain in an unbuffered growth medium, resulting in mutants capable of growing without buffering. The mutant strains carried a Gly157Ser mutation in the Rossmann fold domain of PtxD, leading to approximately five- and eight-fold higher Km values for NAD+ and Pt, respectively, compared with the wild-type enzyme. Interestingly, PtxDG157S exhibited enhanced resistance to nitrate, a major component of BG-11, suggesting that reduced substrate affinity mitigates nitrate inhibition at lower pH levels. Further kinetic analysis revealed that nitrate inhibits wild-type PtxD through an uncompetitive mechanism, targeting the enzyme-substrate complex at an allosteric site. Consequently, the PtxDG157S mutation reduces nitrate binding, facilitating sustained growth of Pt-dependent strains under conditions without pH buffering. These findings imply that PtxDG157S could significantly enhance the applicability of Pt-dependent cyanobacterial strain.

Bioavailable phosphite in the surface ocean during the Great Oxidation Event

Phosphorus availability has influenced the co-evolution of life and Earth's environments. While phosphate was likely the main phosphorus source for life during the Archean, phosphite (HPO32-) gained importance leading up to the Great Oxidation Event (GOE). However, the concentration of phosphite in seawater at that time, and the processes driving this shift in P utilization, remain poorly constrained. Using lab experiments and phosphite data from banded iron formations (BIFs), we show that hydrous ferric oxides (HFO) preferentially remove phosphate over phosphite. This suggests that shallow seawater at the onset of the GOE could have contained up to 0.17 µM phosphite, comprising 5-88% of total dissolved inorganic phosphorus. We propose that phosphate depletion driven by HFO adsorption and microbial competition may have promoted the use of phosphite as an alternative P source.

The functional mechanisms of phosphite and its applications in crop plants

Phosphite (Phi), the reduced form of phosphate (Pi), is characterized by its stability, high solubility, efficient transport, resistance to fixation in soil, and widespread occurrence in natural environments. Although Phi exhibits greater suitability than Pi as a soil fertilizer, it cannot be metabolized by plants. In agricultural applications, Phi serves as a bio-stimulant, fungicide, herbicide, and has other purposes. As a bio-stimulant, Phi has been shown to promote plant growth, enhance stress resistance, and improve fruit quality. Additionally, when used as a fungicide or pesticide, it effectively inhibits the growth of phytopathogens in various crop species. The discovery of the phosphite dehydrogenase (ptxD) gene in microorganisms has significantly expanded the potential applications of Phi, including its use as a herbicide, phosphatic fertilizer, and a selectable chemical for generating marker-free transgenic plants. Therefore, the dual fertilization and weed control system of ptxD/Phi facilitates the utilization of Phi as the sole phosphorus source while concurrently suppressing the evolution of herbicide-resistant weeds in the future. Notably, ptxD also acts as an ideal selectable marker because its resistant is specific to Phi, thereby eliminating the risk of false positive clones. The application of Phi provides a promising strategy for addressing phosphorus resource shortages and improving the efficiency of phosphatic fertilizers in agriculture. Furthermore, Phi is considered an environmentally friendly fertilizer, as it contributes to the mitigation of eutrophication. In prospect, Phi is anticipated to play a significant role as a chemical fertilizer that promotes the sustainable development of agriculture. In this review, we provide a comprehensive analysis of the functional mechanisms of Phi and its current applications in agriculture, with the aim of offering deeper insights into its potential benefits and practical utility.

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.

Evaluating Serpentinization as a Source of Phosphite to Microbial Communities in Hydrothermal Vents

Previous studies have documented the presence of phosphite, a reduced and highly soluble form of phosphorus, in serpentinites, which has led to the hypothesis that serpentinizing hydrothermal vents could have been an important source of bioavailable phosphorus for early microbial communities in the Archean. Here, we test this hypothesis by evaluating the genomic hallmarks of phosphorus usage in microbial communities living in modern hydrothermal vents with and without influence from serpentinization. These genomic analyses are combined with results from a geochemical model that calculates phosphorus speciation during serpentinization as a function of temperature, water:rock ratio, and lithology at thermodynamic equilibrium. We find little to no genomic evidence of phosphite use in serpentinizing environments at the Voltri Massif or the Von Damm hydrothermal field at the Mid Cayman Rise, but relatively more in the Lost City hydrothermal field, Coast Range Ophiolite Microbial Observatory, The Cedars, and chimney samples from Old City hydrothermal field and Prony Bay hydrothermal field, as well as in the non-serpentinizing hydrothermal vents at Axial Seamount. Geochemical modeling shows that phosphite production is favored at ca 275°C-325°C and low water:rock ratios, which may explain previous observations of phosphite in serpentinite rocks; however, most of the initial phosphate is trapped in apatite during serpentinization, suppressing the absolute phosphite yield. As a result, phosphite from serpentinizing vents could have supported microbial growth around olivine minerals in chimney walls and suspended aggregates, but it is unlikely to have fueled substantial primary productivity in diffusely venting fluids during life's origin and evolution in the Archean unless substrates equivalent to dunites (composed of > 90 wt% olivine) were more common.

The impact of organic matter and iron/calcium coupling on phosphorus retention in the hyporheic zone of the Danjiangkou area tributary: Evidence from bonding recognition

The coupling between organic matter (OM) and minerals considerably influences the phosphorus (P) cycle within the hyporheic zone, but the role of different geological mineral-organic complexes (MOCs) on P burial during hyporheic exchange remains under-explored. This study investigates the effects of OM and iron (Fe)/calcium (Ca) coupling on P migration within the hyporheic zone of an agricultural tributary to the Danjiangkou Reservoir. These relationships were explored by measuring hyporheic flow (q), organic and inorganic P forms, and sediment PO4-P adsorption capacity [following treatment with fulvic acid (FA), Fe-OM, or Ca-OM]. Multivariate statistical analysis, X-Ray Diffraction, Fourier-transform Infrared Spectroscopy, and X-ray Photoelectron Spectroscopy were employed to elucidate the underlying mechanisms. Results indicate that upward hyporheic flow transports dissolved porewater P into surface water, contributing 11.27-12.13 % of the total P flux. MOCs associated with Fe(III)/Ca silicate minerals, along with FA and labile OM, were identified as key OM fractions influencing P migration, contributing 5-24 %, 10-11.7 %, and 6-14.9 % to the overall flux, respectively. FA and labile OM facilitate P release, whereas MOCs enhance P retention. Ca-OM is the most efficient PO4-P adsorption [adsorption capacity (AC): 0.8980-0.9524 mg/g], followed by Fe-OM (AC: 0.5120-0.7020 mg/g), original sediment (AC: 0.4368-0.5596 mg/g), and FA (AC: 0.2657-0.2769 mg/g). Cation bridges, primarily formed by -OH and -NH2 groups within Ca-OM (outer-sphere complexes), promote greater P adsorption than Fe-OM (inner-sphere complexes, mainly associated with -COOH). However, Fe-OM-P exhibits a more stable structure. In high P environments, P adsorption onto Ca-OM may induce the release of labile OM, temporarily retaining P through resorption onto labile OM. Hyporheic flow with higher pH and Eh values promotes MOC formation, underscoring their significant P retention capacity. Therefore, strategic MOC use within the hyporheic zone is crucial for mitigating surface water eutrophication.

Adaptive Responses of Cyanobacteria to Phosphate Limitation: A Focus on Marine Diazotrophs

Phosphorus is an essential component of numerous macromolecules and is vital for life. Its availability significantly influences primary production, particularly in oligotrophic environments. Marine diazotrophic cyanobacteria, which play key roles in biogeochemical cycles through nitrogen fixation (N2 fixation), have adapted to thrive in phosphate (Pi)-poor areas. However, the molecular mechanisms that facilitate their adaptation to such conditions remain incompletely understood. Bacteria have evolved various strategies to cope with Pi limitation, including detecting Pi availability, utilising high-affinity Pi transporters, and hydrolyzing dissolved organic phosphorus (DOP) with various enzymes. This review synthesises current knowledge regarding how cyanobacteria adapt to Pi scarcity, with particular emphasis on subtropical marine free-living diazotrophs and their ability to utilise diverse DOP molecules. Omics approaches, such as (meta)genomics and (meta)transcriptomics, reveal the resilience of marine diazotrophs in the face of Pi scarcity and highlight the need for further research into their molecular adaptive strategies. Adaptation to Pi limitation is often intertwined with the broader response of cyanobacteria to multiple limitations and stresses. This underscores the importance of understanding Pi adaptation to assess the ecological resilience of these crucial microorganisms in dynamic environments, particularly in the context of global climate change.

Different fates of particulate matters driven by marine hypoxia: A case study of oxygen minimum zone in the Western Pacific

The oxygen minimum zone (OMZ) is an important representative of marine hypoxia in the open ocean, and it is developing rapidly under the context of global warming. However, the research on OMZ in the Western Pacific is still deficient. This study focused on its basic characteristics and impact on the degradation of particulate matters in the M4 seamount of Western Pacific. The results showed that the OMZ is located at 290-1100 m, just below the high-salinity area and thermocline. The M4 seamount has a weak impact on the OMZ, and only the bottom waters contacting with the seamount have a weak decrease in dissolved oxygen (DO). With the increase of water depth, particulate nitrogen and phosphorus decrease first above and in the OMZ and then increase below the OMZ, while particulate organic carbon (POC) gradually decreases. The low-DO environment in the OMZ is not conducive to the degradation of particulate matters, which promotes the transport of particulate matters to the deep sea, and most particulate matters have the lowest degradation rate here. The waters above the OMZ have the fastest change rate of particulate matters, in which particulate organic phosphorus (POP) and particulate inorganic phosphorus (PIP) are preferentially degraded, and the degradation rate of them is significantly higher than particulate organic nitrogen (PON) and particulate inorganic nitrogen (PIN). The particulate nitrogen and phosphorus in the waters below the OMZ continue to increase, while PON/total particulate nitrogen (TPN) and POP/total particulate phosphorus (TPP) increase significantly, and the increase rate of PIN and PIP is far lower than PON and POP, indicating that the increase of organic matters in particulate matters is more significant. It is speculated that this phenomenon might be related to the input of Antarctic Bottom Water or the in-situ production by microorganisms. This study revealed the relationship between OMZ and different particulate matters, which may provide a valuable pathway for the biogeochemical effects of OMZ in the Western Pacific.

Enhanced nutrient supply promotes mutualistic interactions between cyanobacteria and bacteria in oligotrophic ocean

Cyanobacteria can form complex interactions with heterotrophic microorganisms, but this relationship is susceptible to nutrient concentrations. Disentangling the cyanobacteria-bacteria interactions in relation to nutrient supply is essential to understanding their roles in geochemical cycles under global change. We hypothesize that enhanced nutrient supply in oligotrophic oceans can promote interactions among cyanobacteria and bacteria. Therefore, we investigated the planktonic bacteria and their interactions with cyanobacteria in relation to elevated nutrients caused by enhanced upwelling around a shallow and a deep seamount in the tropical western Pacific Ocean. We found obviously higher complexity of network occurred with significantly more cyanobacteria in the deep chlorophyll maximum layer of the shallow seamount when compared with that of the deep seamount. Cyanobacteria can shape bacterial interaction and community evenness in response to relatively high nutrient concentrations. The effects of the nutrients on cyanobacteria-related networks were further estimated based on the Tara Oceans data. Statistical analyses further showed a facilitative effect of nitrate concentrations on cyanobacteria-bacteria mutualistic interactions in the global oligotrophic ocean. By analysing the Tara Ocean macrogenomic data, we detected functional genes related to cyanobacteria-bacteria interactions in all samples, indicating the existence of a mutualistic relationship. Our results reveal cyanobacteria-bacteria interaction in response to nutrient elevation in oligotrophic ocean and highlight the potentially negative effects of global change on the bacterial community from the view of the bio-interaction.

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.

New insights into estimation of bioavailable inorganic phosphorus in natural coastal seawater

Considering the impact of the high salinity and high turbidity of coastal seawater on phosphorus forms, a new method was proposed to determine bioavailable inorganic phosphorus (BIP). The phosphorus most relevant to eutrophication is BIP, and traditional analysis methods may underestimate the degree of eutrophication. In this study, a microelectrode of multigold (AuμE) was fabricated for direct voltammetric determination of BIP without filtration, and BIP environmental characteristics including distribution and correlation relationships with environmental factors in typical coastal seawater of Northern China were analyzed. The proposed AuμE showed a low detection limit of 0.03 μM. The surface and bottom BIP concentrations ranged from 1.00 to 2.13 and from 0.88 to 2.05 μM, respectively. BIP dominated the total P (TP) accounting for 48.5-67.5 % in the surface layer samples, and 32.6-92.7 % in the bottom layer samples, respectively. The concentrations of BIP were obviously higher than those of DIP, indicating that DIP may underestimate the probability of eutrophication occurring. And BIP was positively correlated with dissolved oxygen (DO) (P < 0.05). BIP may be a promising indicator of eutrophication potential in coastal areas with high salinity and high turbidity. The proposed reliable voltammetry method provides a new indicator for environmental assessment and represents a significant step in the comprehensive analysis of P species.

Taxonomic distribution of metabolic functions in bacteria associated with Trichodesmium consortia

IMPORTANCE

Colonies of the cyanobacteria Trichodesmium act as a biological hotspot for the usage and recycling of key resources such as C, N, P, and Fe within an otherwise oligotrophic environment. While Trichodesmium colonies are known to interact and support a unique community of algae and particle-associated microbes, our understanding of the taxa that populate these colonies and the gene functions they encode is still limited. Characterizing the taxa and adaptive strategies that influence consortium physiology and its concomitant biogeochemistry is critical in a future ocean predicted to have increasingly resource-depleted regions.

Methylphosphonate-driven methane formation and its link to primary production in the oligotrophic North Atlantic

Methylphosphonate is an organic phosphorus compound used by microorganisms when phosphate, a key nutrient limiting growth in most marine surface waters, becomes unavailable. Microbial methylphosphonate use can result in the formation of methane, a potent greenhouse gas, in oxic waters where methane production is traditionally unexpected. The extent and controlling factors of such aerobic methane formation remain underexplored. Here, we show high potential net rates of methylphosphonate-driven methane formation (median 0.4 nmol methane L-1 d-1) in the upper water column of the western tropical North Atlantic. The rates are repressed but still quantifiable in the presence of in-situ or added phosphate, suggesting that some methylphosphonate-driven methane formation persists in phosphate-replete waters. The genetic potential for methylphosphonate utilisation is present in and transcribed by key photo- and heterotrophic microbial taxa, such as Pelagibacterales, SAR116, and Trichodesmium. While the large cyanobacterial nitrogen-fixers dominate in the surface layer, phosphonate utilisation by Alphaproteobacteria appears to become more important in deeper depths. We estimate that at our study site, a substantial part (median 11%) of the measured surface carbon fixation can be sustained by phosphorus liberated from phosphonate utilisation, highlighting the ecological importance of phosphonates in the carbon cycle of the oligotrophic ocean.

Phototransformation of phosphite induced by zinc oxide nanoparticles (ZnO NPs) in aquatic environments

Phosphite, an essential component in the biogeochemical phosphorus cycle, may make significant contributions to the bioavailable phosphorus pool as well as water eutrophication. However, to date, the potential impacts of coexisting photochemically active substances on the environmental fate and transformation of phosphite in aquatic environments have been sparsely elucidated. In the present study, the effect of zinc oxide nanoparticles (ZnO NPs), a widely distributed photocatalyst in aquatic environments, on phosphite phototransformation under simulated solar irradiation was systematically investigated. The physicochemical characteristics of the pristine and reacted ZnO NPs were thoroughly characterized. The results showed that the presence of ZnO NPs induced the indirect phototransformation of phosphite to phosphate, and the reaction rate increased with increasing ZnO NPs concentration. Through experiments with quenching and trapping free radicals, it was proved that photogenerated reactive oxygen species (ROS), such as hydroxyl radical (•OH), superoxide anion (O2•-), and singlet oxygen (1O2), made substantial contributions to phosphite phototransformation. In addition, the influencing factors such as initial phosphite concentration, pH, water matrixes (Cl-, F-, Br-, SO42-, NO3-, NO2-, HCO3-, humic acid (HA) and citric acid (CA)) were investigated. The component of generated precipitates after the phosphite phototransformation induced by ZnO NPs was still dominated by ZnO NPs, while the presence of amorphous Zn3(PO4)2 was identified. This work explored ZnO NPs-mediated phosphite phototransformation processes, indicating that nanophotocatalysts released into aquatic environments such as ZnO NPs may function as photosensitizers to play a beneficial role in the transformation of phosphite to phosphate, thereby potentially mitigating the toxicity of phosphite to aquatic organisms while exacerbating eutrophication. The findings of this study provide a novel insight into the comprehensive assessment of the environmental fate, potential ecological risk, and biogeochemical behaviors of phosphite in natural aquatic environments under the condition of combined pollution.

The Microbial Degradation of Natural and Anthropogenic Phosphonates

Phosphonates are compounds containing a direct carbon-phosphorus (C-P) bond, which is particularly resistant to chemical and enzymatic degradation. They are environmentally ubiquitous: some of them are produced by microorganisms and invertebrates, whereas others derive from anthropogenic activities. Because of their chemical stability and potential toxicity, man-made phosphonates pose pollution problems, and many studies have tried to identify biocompatible systems for their elimination. On the other hand, phosphonates are a resource for microorganisms living in environments where the availability of phosphate is limited; thus, bacteria in particular have evolved systems to uptake and catabolize phosphonates. Such systems can be either selective for a narrow subset of compounds or show a broader specificity. The role, distribution, and evolution of microbial genes and enzymes dedicated to phosphonate degradation, as well as their regulation, have been the subjects of substantial studies. At least three enzyme systems have been identified so far, schematically distinguished based on the mechanism by which the C-P bond is ultimately cleaved-i.e., through either a hydrolytic, radical, or oxidative reaction. This review summarizes our current understanding of the molecular systems and pathways that serve to catabolize phosphonates, as well as the regulatory mechanisms that govern their activity.

Role of phosphite in the environmental phosphorus cycle

In modern geochemistry, phosphorus (P) is considered synonymous with phosphate (Pi) because Pi controls the growth of organisms as a limiting nutrient in many ecosystems. The researchers therefore realised that a complete P cycle is essential. Limited by thermodynamic barriers, P was long believed to be incapable of redox reactions, and the role of the redox cycle of reduced P in the global P cycling system was thus not ascertained. Nevertheless, the phosphite (Phi) form of P is widely present in various environments and participates in the global P redox cycle. Herein, global quantitative evidences of Phi are enumerated and the early origin and modern biotic/abiotic sources of Phi are elaborated. Further, the Phi-based redox pathway for P reduction is analysed and global multienvironmental Phi redox cycle processes are proposed on the basis of this pathway. The possible role of Phi in controlling algae in eutrophic lakes and its ecological benefits to plants are proposed. In this manner, the important role of Phi in the P redox cycle and global P cycle is systematically and comprehensively identified and confirmed. This work will provide scientific guidance for the future production and use of Phi products and arouse attention and interest on clarifying the role of Phi in the environmental phosphorus cycle.

Enrichment of geogenic phosphorus in a coastal groundwater system: New insights from dissolved organic matter characterization

High concentrations of geogenic phosphorus (P) in coastal aquifer systems pose a serious and continuous threat to the health of marine ecosystems. A major source for geogenic P enrichment in aquifer systems is the mineralization of P-containing organic matter. However, the mechanisms that drive the enrichment remain unclear. Therefore, our study sought to characterize the occurrence, sources, and enrichment mechanisms of geogenic P in a coastal confined aquifer system of the Pearl River Delta, southern China. To achieve this, we conducted Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and fluorescence excitation-emission-matrix spectra (EEMs) as well as hydrochemistry and stable carbon isotope analyses. Our findings indicated that intense degradation of P-containing organic matter produced up to 8.07 mg/L of geogenic P in a reducing environment with abundant organic matter. The dissolved organic matter (DOM) of high-P groundwater (P > 1 mg/L) contained more humic-like fluorophores and exhibited higher humification. Groundwater with high P concentrations contained more aliphatic compounds and highly unsaturated-low O compounds, and the enrichment of P was mostly associated with CHOP compounds in the region of aliphatic compounds and CHON2P compounds in the region of highly unsaturated-low O compounds. Different types of dissolved organic phosphorus (DOP) can be mineralized into P, and even the mineralization of phosphonates takes precedence over the more unstable phosphate esters. P produced by the metabolism of different types of DOP was assimilated by marine microorganisms (e.g., heterotrophic bacteria and archaea), and the newly synthesized organic P compounds by chemosynthesis were subsequently released into the groundwater. Over time, P continues to be enriched in the aquifer system. This study provides new insights into subsurface P cycling in coastal aquatic systems.

Bacterial catabolism of membrane phospholipids links marine biogeochemical cycles

In marine systems, the availability of inorganic phosphate can limit primary production leading to bacterial and phytoplankton utilization of the plethora of organic forms available. Among these are phospholipids that form the lipid bilayer of all cells as well as released extracellular vesicles. However, information on phospholipid degradation is almost nonexistent despite their relevance for biogeochemical cycling. Here, we identify complete catabolic pathways for the degradation of the common phospholipid headgroups phosphocholine (PC) and phosphorylethanolamine (PE) in marine bacteria. Using Phaeobacter sp. MED193 as a model, we provide genetic and biochemical evidence that extracellular hydrolysis of phospholipids liberates the nitrogen-containing substrates ethanolamine and choline. Transporters for ethanolamine (EtoX) and choline (BetT) are ubiquitous and highly expressed in the global ocean throughout the water column, highlighting the importance of phospholipid and especially PE catabolism in situ. Thus, catabolic activation of the ethanolamine and choline degradation pathways, subsequent to phospholipid metabolism, specifically links, and hence unites, the phosphorus, nitrogen, and carbon cycles.

Assessment of Seasonal Variability in Phosphorus Biodynamics by Cosmogenic Isotopes 32P, 33P around Balaklava Coast

The sorption efficiency of phosphorus from seawater by aluminum oxide and sorbents based on Fe(OH)₃ obtained by various methods (using prepared sodium ferrate or precipitation of Fe(OH)₃ with ammonia) was assessed. It was shown that phosphorus was recovered most efficiently at a seawater flow rate of one-to-four column volumes per minute with a sorbent based on hydrolyzed polyacrylonitrile fiber with a precipitation of Fe(OH)₃ with ammonia. Based on the results obtained, a method for phosphorus isotopes recovery with this sorbent was suggested. Using this method, the seasonal variability of phosphorus biodynamics in the Balaklava coastal area was estimated. For this purpose, the short-lived isotopes of cosmogenic origin ³²P and ³³P were used. Volumetric activity profiles of ³²P and ³³P in particulate and dissolved forms were obtained. Based on ³²P and ³³P volumetric activity, indicators of phosphorus biodynamics were calculated: the time, rate, and degree of phosphorus circulation to inorganic and particulate organic forms. In spring and summer, elevated values of phosphorus biodynamic parameters were determined. This is explained by the peculiarity of the economic and resort activities of Balaklava, which negatively affect the state of the marine ecosystem. The results obtained can be used to assess the dynamics of changes in the content of forms of dissolved and suspended phosphorus, and the biodynamic parameters when performing a comprehensive environmental assessment of the state of coastal waters.

Organophosphorus Compound Formation Through the Oxidation of Reduced Oxidation State Phosphorus Compounds on the Hadean Earth

Reduced oxidation state phosphorus compounds may have been brought to the early Earth via meteorites or could have formed through geologic processes. These compounds could have played a role in the origin of biological phosphorus (P, hereafter) compounds. Reduced oxidation state P compounds are generally more soluble in water and are more reactive than orthophosphate and its associated minerals. However, to date no facile routes to generate C-O-P type compounds using reduced oxidation state P compounds have been reported under prebiotic conditions. In this study, we investigate the reactions between reduced oxidation state P compounds-and their oxidized products generated via Fenton reactions-with the nucleosides uridine and adenosine. The inorganic P compounds generated via Fenton chemistry readily react with nucleosides to produce organophosphites and organophosphates, including phosphate diesters via one-pot syntheses. The reactions were facilitated by NH₄⁺ ions and urea as a condensation agent. We also present the results of the plausible stability of the organic compounds such as adenosine in an environment containing an abundance of H₂O_2. Such results have direct implications on finding organic compounds in Martian environments and other rocky planets (including early Earth) that were richer in H₂O₂ than O₂. Finally, we also suggest a route for the sink of these inorganic P compounds, as a part of a plausible natural P cycle and show the possible formation of secondary phosphate minerals such as struvite and brushite on the early Earth.

Oyster culture changed the phosphorus speciation in sediments through biodeposition

Phosphorus speciation in the sediments is regulated by a series of physicochemical and microbial processes, and directly affects water phosphorus pool. However, the influence of culture activities and microbial metabolism on the sedimentary phosphorus speciation is poorly studied. In this study, we compared the abundance of distinguishable phosphorus phases and other physicochemical properties of sediments from oyster-farming areas and reference areas. The Geochip 5.0 technique was introduced to reveal the microbiological mechanisms of phosphorus metabolic alteration. The results showed that oyster culture enhanced the bioavailability of phosphorus in sediments. The free organic phosphorus was reduced significantly, whereas the free inorganic phosphorus and iron-bound phosphorus greatly increased in the oyster culture area (P ≤ 0.05). Moreover, the results of Geochip showed that the oyster culture reshaped the microbial network structure in sediments, with typical phosphate-solubilizing and phosphorus-accumulating microbes being enriched by 17.76% and 10.60%. The abundance of functional genes related to the main phosphorus cycle pathways were also significantly increased (P ≤ 0.05) in the culture area compared to the reference area. This work suggested that oyster culture can greatly improve the microbial phosphorus metabolism and provided insights into the environmental recovery and reconstruction from marine aquaculture activities.

New insights into the growth response of the macrophyte Vallisneria natans exposed to phosphite

Renewed interest in phosphite, an analog of phosphate, has increased due to its widespread distribution and increasing abundance in many waterbodies. However, up until recently very little is known about their ecological effects on aquatic organisms. Herein we studied the effects of phosphite via root and foliar exposure on the growth responses of the dominant pioneer macrophyte V. natans. Overall, both exposures of phosphite to V. natans resulted in significant reductions in the leaf length, root length, relative growth rate (RGR) and photosynthetic pigments, suggesting phosphite had an inhibitory effect on the plant growth. Our results further confirmed phosphite could induce the oxidative stresses in the V. natans cells, as indicated by the significantly increased intracellular enzyme activities i.e. superoxide dismutase activity (SOD) and malondialdehyde (MDA). Microscopic evidence also showed phosphite penetrated the cell membrane and destroyed membrane integrity under high phosphite stress. Besides, V. natans leaves exhibited intuitive deterioration symptoms, which seemed to be more sensitive to phosphite toxicity than roots. It is concluded that the increased abundance of phosphite in waterbodies cannot be utilized as a bioavailable P source but impose adverse physiological and metabolic limitations to plant growth, which should be receive more attention in the ecological risk assessment. Our result is necessary to build a comprehensive understanding of phosphite biogeochemical behaviors in aquatic ecosystems.

Physical and Chemical Regularities of Phosphorus and Beryllium Recovery by the Sorbents Based on Acrylic Fiber Impregnated by Iron Hydroxide (III)

The paper investigates the physicochemical regularities (kinetics and isotherm) of phosphorus and beryllium recovery by sorbents based on polyacrylonitrile (PAN) fiber and Fe(OH)3 obtained by various methods: PAN or pre-hydrolyzed PAN with precipitation of FeCl3 with ammonia, using ready-made or electrochemically generated Na2FeO4, pre-hydrolyzed PAN treated with an alkaline solution of Na2FeO4, as well as their comparison with granular aluminum oxide. The Langmuir, Freudlich and Dubinin–Radushkevich models show high performance of materials for sorption of stable P and Be used as tracers for the release of 7Be, 32P, and 33P from seawater. The obtained kinetic data are processed using kinetic models of intraparticle diffusion and the pseudo-first-order, pseudo-second-order, and Elovich models. Optimal conditions for obtaining sorbents are established, namely, the effect of NaOH concentration at the stages of preparation on the properties of sorbents based on the PAN fiber and Fe(OH)3 obtained by various methods.

Global and seasonal variation of marine phosphonate metabolism

Marine microbial communities rely on dissolved organic phosphorus (DOP) remineralisation to meet phosphorus (P) requirements. We extensively surveyed the genomic and metagenomic distribution of genes directing phosphonate biosynthesis, substrate-specific catabolism of 2-aminoethylphosphonate (2-AEP, the most abundant phosphonate in the marine environment), and broad-specificity catabolism of phosphonates by the C-P lyase (including methylphosphonate, a major source of methane). We developed comprehensive enzyme databases by curating publicly available sequences and then screened metagenomes from TARA Oceans and Munida Microbial Observatory Time Series (MOTS) to assess spatial and seasonal variation in phosphonate metabolism pathways. Phosphonate cycling genes were encoded in diverse gene clusters by 35 marine bacterial and archaeal classes. More than 65% of marine phosphonate cycling genes mapped to Proteobacteria with production demonstrating wider taxonomic diversity than catabolism. Hydrolysis of 2-AEP was the dominant phosphonate catabolism strategy, enabling microbes to assimilate carbon and nitrogen alongside P. Genes for broad-specificity catabolism by the C-P lyase were far less widespread, though enriched in the extremely P-deplete environment of the Mediterranean Sea. Phosphonate cycling genes were abundant in marine metagenomes, particularly from the mesopelagic zone and winter sampling dates. Disparity between prevalence of substrate-specific and broad-specificity catabolism may be due to higher resource expenditure from the cell to build and retain the C-P lyase. This study is the most comprehensive metagenomic survey of marine microbial phosphonate cycling to date and provides curated databases for 14 genes involved in phosphonate cycling.

Rethinking the biotic and abiotic remineralization of complex phosphate molecules in soils and sediments

Phosphorus (P) is an essential macronutrient for all living organisms. Despite a diversity of P compounds in the environment, orthophosphate is the most bioavailable form of P. Remineralization of complex P molecules (e.g., organic P and phosphoanhydrides) into orthophosphate is traditionally considered to be carried out primarily by enzymes. Natural minerals are recently viewed to be abiotic catalysts (as compared to the organic phosphatases) to facilitate the cleavage of terminal P-O-C/P bonds and remineralization of complex P compounds. However, quantitative comparison between biotic and abiotic remineralization pathways of complex P molecules is still missing, impeding our capability to assess the importance and contribution of abiotic P remineralization in the environment. This study compares the hydrolysis rates of six organic phosphates and three inorganic phosphoanhydrides by representative enzymes (acid and alkaline phosphatases) and natural oxide minerals (hematite, birnessite, and boehmite). The results show that enzymes and minerals have different substrate preferences. Specifically, alkaline phosphatase hydrolyzes phosphate monoesters faster than phosphoanhydrides, whereas acid phosphatase and minerals show higher hydrolysis rates toward phosphoanhydrides than phosphate monoesters. Although the hydrolysis rates by enzymes (~μM hr^-1) are orders of magnitude higher than those by minerals (~μM d^-1), normalization of the rates by the natural abundance of enzymes and minerals leads to comparable contributions of both processes in soils and sediments. These results highlight the significance of natural minerals in the remineralization of complex P compounds, a process that was traditionally overlooked but with important implications for constraining P biogeochemical cycling in the environment.

Phosphonate production by marine microbes: Exploring new sources and potential function

SignificancePhosphonates are a class of phosphorus metabolites characterized by a highly stable C-P bond. Phosphonates accumulate to high concentrations in seawater, fuel a large fraction of marine methane production, and serve as a source of phosphorus to microbes inhabiting nutrient-limited regions of the oligotrophic ocean. Here, we show that 15% of all bacterioplankton in the surface ocean have genes phosphonate synthesis and that most belong to the abundant groups Prochlorococcus and SAR11. Genomic and chemical evidence suggests that phosphonates are incorporated into cell-surface phosphonoglycoproteins that may act to mitigate cell mortality by grazing and viral lysis. These results underscore the large global biogeochemical impact of relatively rare but highly expressed traits in numerically abundant groups of marine bacteria.

Ignored effects of phosphite (P+III) on the growth responses of three typical algae species

Nowadays, the ubiquitous distribution and increasing abundance of P^+III in waterbodies have caused serious concerns regarding its bioavailability and potential toxicity. However, our knowledge on these issues is relatively limited. We addressed previously unknown effects of P^+III on three dominate algae species i.e. Microcystic aeruginosa (M. aeruginosa), Chlorella pyrenoidesa (C. pyrenoidesa) and Cyclotella. sp in eutrophic waterbodies in China. Remarkable declines in biomass, specific growth rate and Chl-a of algae cells treated with 0.01-0.7 mg/L P^+III as sole or an alternative P source were observed, indicating P^+III had an inhibitory effect on the algal growth. Besides, the intracellular enzyme activities e.g superoxide dismutase (SOD) and malondialdehyde (MDA) were significantly increased with P^+III stress. M. aeruginosa and Cyclotella. sp cells seemed to be more sensitive to P^+III toxicity than C. pyrenoidesa since cell membrane suffered more serious stress and destruction. These findings combined, it confirmed P^+III could not be utilized as bioavailable P, but had certain toxicity to the tested algae. It indicated that the increased P^+III abundance in eutrophic waterbodies would accelerate the algal cell death, which could have a positive effect against algal blooms. Our results provide new insights into assessing the ecological risks of P^+III in aquatic environments.

Sorption methods in marine radiochemistry

The review presents the general methodology of using sorption methods to solve problems of marine radiochemistry, including sampling, preconcentration and radiochemical preparation and methods for measuring the activity of radionuclides. The possible methodological errors at various stages of sampling and sample concentration are discussed. The most widely used artificial (90Sr, 134Cs, 137Cs, 239Pu, 240Pu), natural (210Pb, 210Po; radium quartet: 223Ra, 224Ra, 226Ra, 228Ra; thorium isotopes, mainly 234Th) and cosmogenic (7Be, 32P, 33P) radiotracers are considered. The sorption of uranium from seawater is not addressed, since its concentration in seawater is usually calculated from the known dependence of uranium concentration on seawater salinity.

The bibliography includes 200 references.

Bottom-up controls, ecological revolutions and diversification in the oceans through time

Animals originated in the oceans and evolved there for hundreds of millions of years before adapting to terrestrial environments. Today, oceans cover more than two-thirds of Earth and generate as much primary production as land. The path from the first macrobiota to modern marine biodiversity involved parallel increases in terrestrial nutrient input, marine primary production, species' abundance, metabolic rates, ecotypic diversity and taxonomic diversity. Bottom-up theories of ecosystem cascades arrange these changes in a causal sequence. At the base of marine food webs, nutrient fluxes and atmosphere-ocean chemistry interact with phytoplankton to regulate production. First-order consumers (e.g., zooplankton) might propagate changes in quantity and quality of phytoplankton to changes in abundance and diversity of larger predators (e.g., nekton). However, many uncertainties remain about the mechanisms and effect size of bottom-up control, particularly in oceans across the entire history of animal life. Here, we review modern and fossil evidence for hypothesized bottom-up pathways, and we assess the ramifications of these processes for four key intervals in marine ecosystems: the Ediacaran-Cambrian (635-485 million years ago), the Ordovician (485-444 million years ago), the Devonian (419-359 million years ago) and the Mesozoic (252-66 million years ago). We advocate for a clear articulation of bottom-up hypotheses to better understand causal relationships and proposed effects, combined with additional ecological experiments, paleontological documentation, isotope geochemistry and geophysical reconstructions. How small-scale ecological change transitions into large-scale evolutionary change remains an outstanding question for empirical and theoretical research.

Trace-Level Sensing of Phosphate for Natural Soils by a Nano-Screen-Printed Electrode

Phosphate as one of the most essential components of living systems, robust analytical techniques available for phosphate sensing in natural waters and soils are essential for monitoring and predicting water quality and agronomic evaluation of phosphate. Using cyclic voltammetry, a point-of-use electrochemical sensor zirconium dioxide/zinc oxide/multiple-wall carbon nanotubes/ammonium molybdate tetrahydrate/screen printed electrode (ZrO₂/ZnO/MWCNTs/AMT/SPE) was applied to explore the electro-redox reaction of phosphomolybdate complexes on the surface of electrode, which produced a quantitative electrochemical response of phosphate anions. The modification of the electrode surface with ZrO₂/ZnO/MWCNTs nanocomposites is able to generate the electroactive species via chemical reaction between molybdenum (Mo(VI)) and the targeted phosphate anions, leading to a sensitive detection technique for trace phosphate with a lower detection limit (LOD = 2.0 × 10^-8 mol L^-1), higher reproducibility, anti-interference, and precision in different soil sources. This system will be of great potential to advance the trace-level understanding of phosphate especially in field environmental analysis.

Transporter characterisation reveals aminoethylphosphonate mineralisation as a key step in the marine phosphorus redox cycle

The planktonic synthesis of reduced organophosphorus molecules, such as alkylphosphonates and aminophosphonates, represents one half of a vast global oceanic phosphorus redox cycle. Whilst alkylphosphonates tend to accumulate in recalcitrant dissolved organic matter, aminophosphonates do not. Here, we identify three bacterial 2-aminoethylphosphonate (2AEP) transporters, named AepXVW, AepP and AepSTU, whose synthesis is independent of phosphate concentrations (phosphate-insensitive). AepXVW is found in diverse marine heterotrophs and is ubiquitously distributed in mesopelagic and epipelagic waters. Unlike the archetypal phosphonate binding protein, PhnD, AepX has high affinity and high specificity for 2AEP (Stappia stellulata AepX Kd 23 ± 4 nM; methylphosphonate Kd 3.4 ± 0.3 mM). In the global ocean, aepX is heavily transcribed (~100-fold>phnD) independently of phosphate and nitrogen concentrations. Collectively, our data identifies a mechanism responsible for a major oxidation process in the marine phosphorus redox cycle and suggests 2AEP may be an important source of regenerated phosphate and ammonium, which are required for oceanic primary production.

Redox-induced mobilization of phosphorus in groundwater affected arable soil profiles

Mobilization of phosphorus (P) in arable soils might be affected by groundwater fluctuations and the associated changes in redox potential (E_H). However, the impact of systematic changes of E_H on P mobilization in redoximorphic arable soils along a catena has not been studied so far. Therefore, we investigated P mobilization under different redox conditions in top- and sub-soil horizons of three groundwater affected arable soils along a slight slope (toe-, mid-, and upper-slope position) in Northern Germany using an automated biogeochemical microcosm system. The impact of pH, Al, Fe, Mn, and dissolved organic carbon (DOC) on P mobilization was also studied. The initial E_H (+351 to +431 mV) and pH (6.5-7.0) decreased in all soil samples (E_H = -280 mV; pH = 4.4) when creating a slurry. Thereafter, the pH increased to 7.1 and 6.4 with increasing E_H in the mid-and toe-slope soil, respectively. Concentrations of dissolved P ranged between 20.8 mg L^-1 under low E_H in the toe slope topsoil and 0.69 mg L^-1 under high E_H in the toe- and mid-slop subsoil. Concentrations (mg L^-1) of dissolved Fe (0.31-13.3) and DOC (92-2651) increased under low E_H and decreased under high E_H. The increase of P mobilization under low E_H and pH in the soils might be due to the release of P via the reductive and acidic dissolution of Fe-(oxhydr)oxides and/or due to soil organic matter mineralization. The high mobilization of P under reducing conditions may increase its bioavailability; however, it may increase its loss in the soils, particularly in the toe slope profile.

The Role of Phosphorus Limitation in Shaping Soil Bacterial Communities and Their Metabolic Capabilities

Phosphorus (P) is an essential nutrient that is often in limited supply, with P availability constraining biomass production in many terrestrial ecosystems. Despite decades of work on plant responses to P deficiency and the importance of soil microbes to terrestrial ecosystem processes, how soil microbes respond to, and cope with, P deficiencies remains poorly understood. We studied 583 soils from two independent sample sets that each span broad natural gradients in extractable soil P and collectively represent diverse biomes, including tropical forests, temperate grasslands, and arid shrublands.

Phosphorus (P) is an essential nutrient that is often in limited supply, with P availability constraining biomass production in many terrestrial ecosystems. Despite decades of work on plant responses to P deficiency and the importance of soil microbes to terrestrial ecosystem processes, how soil microbes respond to, and cope with, P deficiencies remains poorly understood. We studied 583 soils from two independent sample sets that each span broad natural gradients in extractable soil P and collectively represent diverse biomes, including tropical forests, temperate grasslands, and arid shrublands. We paired marker gene and shotgun metagenomic analyses to determine how soil bacterial and archaeal communities respond to differences in soil P availability and to detect corresponding shifts in functional attributes. We identified microbial taxa that are consistently responsive to extractable soil P, with those taxa found in low P soils being more likely to have traits typical of oligotrophic life history strategies. Using environmental niche modeling of genes and gene pathways, we found an enriched abundance of key genes in low P soils linked to the carbon-phosphorus (C-P) lyase and phosphonotase degradation pathways, along with key components of the high-affinity phosphate-specific transporter (Pst) and phosphate regulon (Pho) systems. Taken together, these analyses suggest that catabolism of phosphonates is an important strategy used by bacteria to scavenge phosphate in P-limited soils. Surprisingly, these same pathways are important for bacterial growth in P-limited marine waters, highlighting the shared metabolic strategies used by both terrestrial and marine microbes to cope with P limitation.

Nonenzymatic Metabolic Reactions and Life's Origins

Prebiotic chemistry aims to explain how the biochemistry of life as we know it came to be. Most efforts in this area have focused on provisioning compounds of importance to life by multistep synthetic routes that do not resemble biochemistry. However, gaining insight into why core metabolism uses the molecules, reactions, pathways, and overall organization that it does requires us to consider molecules not only as synthetic end goals. Equally important are the dynamic processes that build them up and break them down. This perspective has led many researchers to the hypothesis that the first stage of the origin of life began with the onset of a primitive nonenzymatic version of metabolism, initially catalyzed by naturally occurring minerals and metal ions. This view of life's origins has come to be known as "metabolism first". Continuity with modern metabolism would require a primitive version of metabolism to build and break down ketoacids, sugars, amino acids, and ribonucleotides in much the same way as the pathways that do it today. This review discusses metabolic pathways of relevance to the origin of life in a manner accessible to chemists, and summarizes experiments suggesting several pathways might have their roots in prebiotic chemistry. Finally, key remaining milestones for the protometabolic hypothesis are highlighted.

Carbon recycling efficiency and phosphate turnover by marine nitrifying archaea

Thaumarchaeotal nitrifiers are among the most abundant organisms in the ocean, but still unknown is the carbon (C) yield from nitrification and the coupling of these fluxes to phosphorus (P) turnover and release of metabolites from the cell. Using a dual radiotracer approach, we found that Nitrosopumilus maritimus fixed roughly 0.3 mol C, assimilated 2 mmol P, and released ca. 10^-2 mol C and 10^-5 mol P as dissolved organics (DOC and DOP) per mole ammonia respired. Phosphate turnover may influence assimilation fluxes by nitrifiers in the euphotic zone, which parallel those of the dark ocean. Collectively, marine nitrifiers assimilate up to 2 Pg C year^-1 and 0.05 Pg P year^-1 and thereby recycle roughly 5% of mineralized C and P into marine biomass. Release of roughly 50 Tg DOC and 0.2 Tg DOP by thaumarchaea each year represents a small but fresh input of reduced substrates throughout the ocean.

Quantifying nutrient throughput and DOM production by algae in continuous culture

Freshwater and marine algae can balance nutrient demand and availability by regulating uptake, accumulation and exudation. To obtain insight into these processes under nitrogen (N) and phosphorus (P) limitation, we reanalyze published data from continuous cultures of the chlorophyte Selenastrum minutum. Based on mass budgets, we argue that much of the non-limiting N and P had passed through the organisms and was present as dissolved organic phosphorus or nitrogen (DOP or DON). We construct a model that describes the production of biomass and dissolved organic matter (DOM) as a function of the growth rate. A fit of this model against the chemostat data suggests a high turnover of the non-limiting N and P: at the highest growth rates, N and P atoms spent on average only about 3 h inside an organism, before they were exuded as DON and DOP, respectively. This DOM exudation can explain the observed trends in the algal stoichiometric ratios as a function of the dilution rate. We discuss independent evidence from isotope experiments for this apparently wasteful behavior and we suggest experiments to quantify and characterize DON and DOP exudation further.

Phosphine as a Biosignature Gas in Exoplanet Atmospheres

A long-term goal of exoplanet studies is the identification and detection of biosignature gases. Beyond the most discussed biosignature gas O₂, only a handful of gases have been considered in detail. In this study, we evaluate phosphine (PH₃). On Earth, PH₃ is associated with anaerobic ecosystems, and as such, it is a potential biosignature gas in anoxic exoplanets. We simulate the atmospheres of habitable terrestrial planets with CO₂- and H₂-dominated atmospheres and find that PH₃ can accumulate to detectable concentrations on planets with surface production fluxes of 10¹⁰ to 10¹⁴ cm^-2 s^-1 (corresponding to surface concentrations of 10s of ppb to 100s of ppm), depending on atmospheric composition and ultraviolet (UV) irradiation. While high, the surface flux values are comparable to the global terrestrial production rate of methane or CH₄ (10¹¹ cm^-2 s^-1) and below the maximum local terrestrial PH₃ production rate (10¹⁴ cm^-2 s^-1). As with other gases, PH₃ can more readily accumulate on low-UV planets, for example, planets orbiting quiet M dwarfs or with a photochemically generated UV shield. PH₃ has three strong spectral features such that in any atmosphere scenario one of the three will be unique compared with other dominant spectroscopic molecules. Phosphine's weakness as a biosignature gas is its high reactivity, requiring high outgassing rates for detectability. We calculate that tens of hours of JWST (James Webb Space Telescope) time are required for a potential detection of PH₃. Yet, because PH₃ is spectrally active in the same wavelength regions as other atmospherically important molecules (such as H₂O and CH₄), searches for PH₃ can be carried out at no additional observational cost to searches for other molecular species relevant to characterizing exoplanet habitability. Phosphine is a promising biosignature gas, as it has no known abiotic false positives on terrestrial planets from any source that could generate the high fluxes required for detection.

Phosphite binding by the HtxB periplasmic binding protein depends on the protonation state of the ligand

Phosphorus acquisition is critical for life. In low phosphate conditions, some species of bacteria have evolved mechanisms to import reduced phosphorus compounds, such as phosphite and hypophosphite, as alternative phosphorus sources. Uptake is facilitated by high-affinity periplasmic binding proteins (PBPs) that bind cargo in the periplasm and shuttle it to an ATP-binding cassette (ABC)-transporter in the bacterial inner membrane. PtxB and HtxB are the PBPs responsible for binding phosphite and hypophosphite, respectively. They recognize the P-H bond of phosphite/hypophosphite via a conserved P-H...π interaction, which confers nanomolar dissociation constants for their respective ligands. PtxB also has a low-level binding affinity for phosphate and hypophosphite, whilst HtxB can facilitate phosphite uptake in vivo. However, HtxB does not bind phosphate, thus the HtxBCDE transporter has recently been successfully exploited for biocontainment of genetically modified organisms by phosphite-dependent growth. Here we use a combination of X-ray crystallography, NMR and Microscale Thermophoresis to show that phosphite binding to HtxB depends on the protonation state of the ligand, suggesting that pH may effect the efficiency of phosphite uptake by HtxB in biotechnology applications.

Synthetic Phosphorus Metabolic Pathway for Biosafety and Contamination Management of Cyanobacterial Cultivation

Recent progress in genetic engineering and synthetic biology have greatly expanded the production capabilities of cyanobacteria, but concerns regarding biosafety issues and the risk of contamination of cultures in outdoor culture conditions remain to be resolved. With this dual goal in mind, we applied the recently established biological containment strategy based on phosphite (H₃PO₃, Pt) dependency to the model cyanobacterium Synechococcus elongatus PCC 7942 ( Syn 7942). Pt assimilation capability was conferred on Syn 7942 by the introduction of Pt dehydrogenase (PtxD) and hypophosphite transporter (HtxBCDE) genes that allow the uptake of Pt, but not phosphate (H₃PO₄, Pi). We then identified and disrupted the two indigenous Pi transporters, pst (Synpcc7942_2441 to 2445) and pit (Synpcc7942_0184). The resultant strain failed to grow on any media containing various types of P compounds other than Pt. The strain did not yield any escape mutants for at least 28 days with a detection limit of 3.6 × 10^-11 per colony forming unit, and rapidly lost viability in the absence of Pt. Moreover, growth competition of the Pt-dependent strain with wild-type cyanobacteria revealed that the Pt-dependent strain could dominate in cultures containing Pt as the sole P source. Because Pt is rarely available in aquatic environments this strategy can contribute to both biosafety and contamination management of genetically engineered cyanobacteria.

Archean phosphorus liberation induced by iron redox geochemistry

The element phosphorus (P) is central to ecosystem growth and is proposed to be a limiting nutrient for life. The Archean ocean may have been strongly phosphorus-limited due to the selective binding of phosphate to iron oxyhydroxide. Here we report a new route to solubilizing phosphorus in the ancient oceans: reduction of phosphate to phosphite by iron(II) at low (<200 °C) diagenetic temperatures. Reduction of phosphate to phosphite was likely widespread in the Archean, as the reaction occurs rapidly and is demonstrated from thermochemical modeling, experimental analogs, and detection of phosphite in early Archean rocks. We further demonstrate that the higher solubility of phosphite compared to phosphate results in the liberation of phosphorus from ferruginous sediments. This phosphite is relatively stable after its formation, allowing its accumulation in the early oceans. As such, phosphorus, not as phosphate but as phosphite, could have been a major nutrient in early pre-oxygenated oceans.

Phosphorus is presumed to have been a limiting nutrient in the Archean ocean due to binding to iron oxides. Here, the authors show the heating of iron with phosphate results in the reduction of phosphate to the ion phosphite, which is solubilized and ameliorates the issue of a low Archean phosphorus supply.

Seawater toilet flushing sewage treatment and nutrients recovery by marine bacterial-algal mutualistic system

Seawater toilet flushing sewage with excess eutrophic and high salinity brought a great barrier on the municipal wastewater treatment plants. Nutrients recovery and biomass production as potential biofuel feedstock with less energy consumption will be a key challenge in wastewater treatment. In the optimal inoculation of algae and bacteria, a marine bacterial-algal mutualistic system was established to treat synthetic seawater toilet flushing sewage without extra carbon and O₂ addition. It was showed that 85.5% of total nitrogen (TN) (from 200 mg/L), 91.0% of total phosphorus (TP) (from 40 mg/L) and 98.7% of chemical oxygen demand (COD) (from 1600 mg/L) were removed with 4.28 g/L of biomass yield (biomass productivity 159.3 mg/L/d) containing 16.3% lipid and 62.6% protein, which performance mainly achieved by bacteria during first six days and algae functioned subsequently. Both nitrogen and phosphorus removal of the system were mainly assimilation/accumulation. Algal facultative heterotrophia ensured dissolved organic carbon for bacterial utilization and avoiding excessive organic matter produced. The established algal-bacterial system provided a potential energy-efficient and eco-friendly approach for seawater blackwater treatment and nutrients recovery simultaneously.

Transcriptional patterns identify resource controls on the diazotroph Trichodesmium in the Atlantic and Pacific oceans

The N₂-fixing cyanobacterium Trichodesmium is intensely studied because of the control this organism exerts over the cycling of carbon and nitrogen in the low nutrient ocean gyres. Although iron (Fe) and phosphorus (P) bioavailability are thought to be major drivers of Trichodesmium distributions and activities, identifying resource controls on Trichodesmium is challenging, as Fe and P are often organically complexed and their bioavailability to a single species in a mixed community is difficult to constrain. Further, Fe and P geochemistries are linked through the activities of metalloenzymes, such as the alkaline phosphatases (APs) PhoX and PhoA, which are used by microbes to access dissolved organic P (DOP). Here we identified significant correlations between Trichodesmium-specific transcriptional patterns in the North Atlantic (NASG) and North Pacific Subtropical Gyres (NPSG) and patterns in Fe and P biogeochemistry, with the relative enrichment of Fe stress markers in the NPSG, and P stress markers in the NASG. We also observed the differential enrichment of Fe-requiring PhoX transcripts in the NASG and Fe-insensitive PhoA transcripts in the NPSG, suggesting that metalloenzyme switching may be used to mitigate Fe limitation of DOP metabolism in Trichodesmium. This trait may underpin Trichodesmium success across disparate ecosystems.

Phosphate insensitive aminophosphonate mineralisation within oceanic nutrient cycles

Many areas of the ocean are nutrient-poor yet support large microbial populations, leading to intense competition for and recycling of nutrients. Organic phosphonates are frequently found in marine waters, but require specialist enzymes for catabolism. Previous studies have shown that the genes that encode these enzymes in marine systems are under Pho regulon control and so are repressed by inorganic phosphate. This has led to the conclusion that phosphonates are recalcitrant in much of the ocean, where phosphorus is not limiting despite the degradative genes being common throughout the marine environment. Here we challenge this paradigm and show, for the first time, that bacteria isolated from marine samples have the ability to mineralise 2-aminoethylphosphonate, the most common biogenic marine aminophosphonate, via substrate-inducible gene regulation rather than via Pho-regulated metabolism. Substrate-inducible, Pho-independent 2-aminoethylphosphonate catabolism therefore represents a previously unrecognised component of the oceanic carbon, nitrogen and phosphorus cycles.

Molecular Mechanisms of Acclimatization to Phosphorus Starvation and Recovery Underlying Full-Length Transcriptome Profiling in Barley (Hordeum vulgare L.)

A lack of phosphorus (P) in plants can severely constrain growth and development. Barley, one of the earliest domesticated crops, is extensively planted in poor soil around the world. To date, the molecular mechanisms of enduring low phosphorus, at the transcriptional level, in barley are still unclear. In the present study, two different barley genotypes (GN121 and GN42)-with contrasting phosphorus efficiency-were used to reveal adaptations to low phosphorus stress, at three time points, at the morphological, physiological, biochemical, and transcriptome level. GN121 growth was less affected by phosphorus starvation and recovery than that of GN42. The biomass and inorganic phosphorus concentration of GN121 and GN42 declined under the low phosphorus-induced stress and increased after recovery with normal phosphorus. However, the range of these parameters was higher in GN42 than in GN121. Subsequently, a more complete genome annotation was obtained by correcting with the data sequenced on Illumina HiSeq X 10 and PacBio RSII SMRT platform. A total of 6,182 and 5,270 differentially expressed genes (DEGs) were identified in GN121 and GN42, respectively. The majority of these DEGs were involved in phosphorus metabolism such as phospholipid degradation, hydrolysis of phosphoric enzymes, sucrose synthesis, phosphorylation/dephosphorylation and post-transcriptional regulation; expression of these genes was significantly different between GN121 and GN42. Specifically, six and seven DEGs were annotated as phosphorus transporters in roots and leaves, respectively. Furthermore, a putative model was constructed relying on key metabolic pathways related to phosphorus to illustrate the higher phosphorus efficiency of GN121 compared to GN42 under low phosphorus conditions. Results from this study provide a multi-transcriptome database and candidate genes for further study on phosphorus use efficiency (PUE).