Nutrient Acquisition Strategies Research Articles

The fate of siderophores: antagonistic environmental interactions in exudate-mediated micronutrient uptake.

Organisms acquire metals from the environment by releasing small molecules that solubilize and promote their specific uptake. The best known example of this nutrient uptake strategy is the exudation of siderophores, which are a structurally-diverse class of molecules that are traditionally viewed as being integral to iron uptake. Siderophores have been proposed to act through a variety of processes, but their effectiveness can be mitigated by a variety of chemical and physical processes of both biotic and abiotic origin. Processes that occur at the surface of minerals can degrade or sequester siderophores, preventing them from fulfilling their function of returning metals to the organism. In addition, biotic processes including enzymatic degradation of the siderophore and piracy of the metal or of the siderophore complex also disrupt iron uptake. Some organisms have adapted their nutrient acquisition strategies to address these potential pitfalls, producing multiple siderophores and other exudates that take advantage of varying kinetic and thermodynamic factors to allow the continued uptake of metals. A complete understanding of the factors that contribute to metal uptake in nature will require a concerted effort to study processes identified in laboratory systems in the context ofmore complicated environmental systems.

Mineral nutrition of campos rupestres plant species on contrasting nutrient-impoverished soil types.

In Brazil, the campos rupestres occur over the Brazilian shield, and are characterized by acidic nutrient-impoverished soils, which are particularly low in phosphorus (P). Despite recognition of the campos rupestres as a global biodiversity hotspot, little is known about the diversity of P-acquisition strategies and other aspects of plant mineral nutrition in this region. To explore nutrient-acquisition strategies and assess aspects of plant P nutrition, we measured leaf P and nitrogen (N) concentrations, characterized root morphology and determined the percentage arbuscular mycorrhizal (AM) colonization of 50 dominant species in six communities, representing a gradient of soil P availability. Leaf manganese (Mn) concentration was measured as a proxy for carboxylate-releasing strategies. Communities on the most P-impoverished soils had the highest proportion of nonmycorrhizal (NM) species, the lowest percentage of mycorrhizal colonization, and the greatest diversity of root specializations. The large spectrum of leaf P concentration and variation in root morphologies show high functional diversity for nutritional strategies. Higher leaf Mn concentrations were observed in NM compared with AM species, indicating that carboxylate-releasing P-mobilizing strategies are likely to be present in NM species. The soils of the campos rupestres are similar to the most P-impoverished soils in the world. The prevalence of NM strategies indicates a strong global functional convergence in plant mineral nutrition strategies among severely P-impoverished ecosystems.

Leaf manganese accumulation and phosphorus-acquisition efficiency.

Plants that deploy a phosphorus (P)-mobilising strategy based on the release of carboxylates tend to have high leaf manganese concentrations ([Mn]). This occurs because the carboxylates mobilise not only soil inorganic and organic P, but also a range of micronutrients, including Mn. Concentrations of most other micronutrients increase to a small extent, but Mn accumulates to significant levels, even when plants grow in soil with low concentrations of exchangeable Mn availability. Here, we propose that leaf [Mn] can be used to select for genotypes that are more efficient at acquiring P when soil P availability is low. Likewise, leaf [Mn] can be used to screen for belowground functional traits related to nutrient-acquisition strategies among species in low-P habitats.

The reallocation of carbon in P deficient lupins affects biological nitrogen fixation

It is not known how phosphate (P) deficiency affects the allocation of carbon (C) to biological nitrogen fixation (BNF) in legumes. The alteration of the respiratory and photosynthetic C costs of BNF was investigated under P deficiency. Although BNF can impose considerable sink stimulation on host respiratory and photosynthetic C, it is not known how the change in the C and energy allocation during P deficiency may affect BNF. Nodulated Lupinus luteus plants were grown in sand culture, using a modified Long Ashton nutrient solution containing no nitrogen (N) for ca. four weeks, after which one set was exposed to a P-deficient nutrient medium, while the other set continued growing on a P-sufficient nutrient medium. Phosphorus stress was measured at 20 days after onset of P-starvation. During P stress the decline in nodular P levels was associated with lower BNF and nodule growth. There was also a shift in the balance of photosynthetic and respiratory C toward a loss of C during P stress. Below-ground respiration declined under limiting P conditions. However, during this decline there was also a shift in the proportion of respiratory energy from maintenance toward growth respiration. Under P stress, there was an increased allocation of C toward root growth, thereby decreasing the amount of C available for maintenance respiration. It is therefore possible that the decline in BNF under P deficiency may be due to this change in resource allocation away from respiration associated with direct nutrient uptake, but rather toward a long term nutrient acquisition strategy of increased root growth.

Genomic characterization and transcriptional studies of the starch-utilizing strain Bifidobacterium adolescentis 22L.

Bifidobacteria are members of the gut microbiota, but the genetic basis for their adaptation to the human gut is poorly understood. The analysis of the 2,203,222-bp genome of Bifidobacterium adolescentis 22L revealed a nutrient acquisition strategy that targets diet/plant-derived glycans, in particular starch and starch-like carbohydrates. Starch-like carbohydrates were shown to support the growth of B. adolescentis 22L. Transcriptome profiling of 22L cultures grown under in vitro conditions or during colonization of the murine gut by RNA sequencing and quantitative real-time PCR assays revealed the expression of a set of chromosomal loci responsible for starch metabolism as well as for pilus production. Such extracellular structures include so-called sortase-dependent and type IVb pili, which may be involved in gut colonization of 22L through adhesion to extracellular matrix proteins.

Influence of daylight surface aggregation behavior on nutrient cycling during a Karenia brevis (Davis) G. Hansen & Ø. Moestrup bloom: Migration to the surface as a nutrient acquisition strategy

The toxic HAB dinoflagellate Karenia brevis (Davis) G. Hansen & Ø. Moestrup (formerly Gymnodinium breve) exhibits a migratory pattern atypical of dinoflagellates: cells concentrate in a narrow (∼0–5cm) band at the water surface during daylight hours due to phototactic and negative geotactic responses, then disperse downward at night via non-tactic, random swimming. The hypothesis that this daylight surface aggregation behavior significantly influences bacterial and algal productivity and nutrient cycling within blooms was tested during a large, high biomass (chlorophyll a >19μgL−1) K. brevis bloom in October of 2001 by examining the effects of this surface layer aggregation on inorganic and organic nutrient concentrations, cellular nitrogen uptake, primary and bacterial productivity and the stable isotopic signature (δ15N, δ13C) of particulate material. During daylight hours, concentrations of K. brevis and chlorophyll a in the 0–5cm surface layer were enhanced by 131% (±241%) and 32.1% (±86.1%) respectively compared with an integrated water sample collection over a 0–1m depth. Inorganic (NH4, NO3+2, PO4, SiO4) and organic (DOP, DON) nutrient concentrations were also elevated within the surface layer as was both bacterial and primary productivity. Uptake of nitrogen (NH4+, NO3−, urea, dissolved primary amines, glutamine and alanine) compounds by K. brevis was greatest in the surface layer for all compounds tested, with the greatest enhancement evident in urea uptake rates, from 0.08×10−5ngN K. brevis cell−1h−1 to 3.1×10−5ngN K. brevis cell−1h−1. These data suggests that this surface aggregation layer is not only an area of concentrated cells within K. brevis blooms, but also an area of increased biological activity and nutrient cycling, especially of nitrogen. Additionally, the classic dinoflagellate migration paradigm of a downward migration for access to elevated NO3− concentrations during the dark period may not apply to certain dinoflagellates such as K. brevis in oligotrophic nearshore areas with no significant nitricline. For these dinoflagellates, concentration within a narrow surface layer in blooms during daylight hours may enhance nutrient supply through biological cycling and photochemical nutrient regeneration.

Is nitrogen transfer among plants enhanced by contrasting nutrient‐acquisition strategies?

Nitrogen (N) transfer among plants has been found where at least one plant can fix N2 . In nutrient-poor soils, where plants with contrasting nutrient-acquisition strategies (without N2 fixation) co-occur, it is unclear if N transfer exists and what promotes it. A novel multi-species microcosm pot experiment was conducted to quantify N transfer between arbuscular mycorrhizal (AM), ectomycorrhizal (EM), dual AM/EM, and non-mycorrhizal cluster-rooted plants in nutrient-poor soils with mycorrhizal mesh barriers. We foliar-fed plants with a K(15) NO3 solution to quantify one-way N transfer from 'donor' to 'receiver' plants. We also quantified mycorrhizal colonization and root intermingling. Transfer of N between plants with contrasting nutrient-acquisition strategies occurred at both low and high soil nutrient levels with or without root intermingling. The magnitude of N transfer was relatively high (representing 4% of donor plant N) given the lack of N2 fixation. Receiver plants forming ectomycorrhizas or cluster roots were more enriched compared with AM-only plants. We demonstrate N transfer between plants of contrasting nutrient-acquisition strategies, and a preferential enrichment of cluster-rooted and EM plants compared with AM plants. Nutrient exchanges among plants are potentially important in promoting plant coexistence in nutrient-poor soils.

Soil acidification and adaptations of plants and microorganisms in Bornean tropical forests

AbstractIn tropical forest ecosystems, a paradoxical relationship is commonly observed between massive biomass production and low soil fertility (low pH). The loss and deficiency of soil phosphorus (P) and bases generally constrain biomass production; however, high productivity on nutrient‐deficient soils of Bornean tropical forests is hypothesized to be maintained by plant and microorganism adaptation to an acidic soil environment. Proton budgets in the plant–soil system indicated that plants and microorganisms promote acidification to acquire bases, even in highly acidic tropical soils. The nitric and organic acids they produce contribute to the mobilization of basic cations and their uptake by plants. In response to soil P deficiency and the recalcitrance of lignin‐rich organic matter, specific trees and fungi can release organic acids and enzymes for nutrient acquisition. Organic acids exuded by roots and rhizosphere microorganisms can promote the solubilization of P bonded to aluminum and iron oxides and its uptake by plants from P‐poor soils. Lignin degradation, a rate‐limiting step in organic matter decomposition, is specifically enhanced in acidic organic layers by lignin peroxidase, produced by white‐rot fungi, which may solubilize recalcitrant lignin and release soluble aromatic substances into the soil solution. This dissolved organic matter functions in the transport of nitrogen, P, and basic cations in acidic soils without increasing leaching loss. In Bornean tropical forests, soil acidification is promoted by plants and microorganisms as a nutrient acquisition strategy, while plant roots and fungi can develop rhizosphere and enzymatic processes that promote tolerance of low pH.

Comparative analysis of Salmonella genomes identifies a metabolic network for escalating growth in the inflamed gut.

ABSTRACTThe Salmonella genus comprises a group of pathogens associated with illnesses ranging from gastroenteritis to typhoid fever. We performed an in silico analysis of comparatively reannotated Salmonella genomes to identify genomic signatures indicative of disease potential. By removing numerous annotation inconsistencies and inaccuracies, the process of reannotation identified a network of 469 genes involved in central anaerobic metabolism, which was intact in genomes of gastrointestinal pathogens but degrading in genomes of extraintestinal pathogens. This large network contained pathways that enable gastrointestinal pathogens to utilize inflammation-derived nutrients as well as many of the biochemical reactions used for the enrichment and biochemical discrimination of Salmonella serovars. Thus, comparative genome analysis identifies a metabolic network that provides clues about the strategies for nutrient acquisition and utilization that are characteristic of gastrointestinal pathogens.

Shoot Feeding as a Nutrient Acquisition Strategy in Free-Living Psylloids

Shoot feeding by sucking insects is accepted as an adaptation to feeding where plant nutrients are most concentrated and/or of higher quality. Psylloids are an important hemipteran taxon, most of which are free-living and comprise many shoot feeding species, whose nutritional ecology has been largely ignored. I conducted a longitudinal study of Ctenarytaina eucalypti (Maskell) and C. bipartita Burckhardt et al. (Aphalaridae) feeding on eucalypts to document how within-plant (ontogenic) variation in nutritional quality, in particular of free amino acids, determines host suitability and hence the distribution and abundance of nymphs. Nymphs were most abundant within developing apical buds but were not more abundant on branchlets of greater vigour (indicated by rate of extension). Nymphs could be found up to two (C. bipartita) to three (C. eucalypti) alternate leaf pairs distant from apical buds but infrequently and in low numbers; they were never found on older, fully expanded leaves. The position of a leaf on a branchlet (indicative of age) determined its nutritional quality. Younger leaves had higher water contents, lower chlorophyll contents and differed in amino acid (essential and non-essential) composition compared to older leaves. The abundance of C. eucalypti nymphs on expanding leaves and in buds was positively correlated with the concentrations of methionine, valine and threonine in E. globulus leaves at the same or comparable position on a branchlet. The abundance of C. bipartita nymphs was positively correlated with foliar leucine concentrations. Shoot feeding by these two psyllids facilitates access to more concentrated, better quality plant nutrients but may not entirely explain the adaptive significance of their behaviour. The humid microclimate created by the architecture of the hosts’ apical buds protects eggs and nymphs from desiccation and is suggested to have had a significant influence on the evolution of host utilisation strategies of psyllids within this genus.

Amoeba host‐Legionella synchronization of amino acid auxotrophy and its role in bacterial adaptation and pathogenic evolution

Legionella pneumophila, the causative agent of Legionnaires' disease, invades and proliferates within a diverse range of free-living amoeba in the environment, but upon transmission to humans, the bacteria hijack alveolar macrophages. Intracellular proliferation of L. pneumophila in two evolutionarily distant hosts is facilitated by bacterial exploitation of conserved host processes that are targeted by bacterial protein effectors injected into the host cell. A key aspect of microbe-host interaction is microbial extraction of nutrients from the host, but understanding of this is still limited. AnkB functions as a nutritional virulence factor and promotes host proteasomal degradation of polyubiquitinated proteins generating gratuitous levels of limiting host cellular amino acids. Legionella pneumophila is auxotrophic for several amino acids including cysteine, which is a metabolically preferred source of carbon and energy during intracellular proliferation, but is limiting in both amoebae and humans. We propose that synchronization of bacterial amino acids auxotrophy with the host is a driving force in pathogenic evolution and nutritional adaptation of L. pneumophila and other intracellular bacteria to life within the host cell. Understanding microbial strategies of nutrient generation and acquisition in the host will provide novel antimicrobial strategies to disrupt pathogen access to essential sources of carbon and energy.

Cell and Developmental Biology of Arbuscular Mycorrhiza Symbiosis

The default mineral nutrient acquisition strategy of land plants is the symbiosis with arbuscular mycorrhiza (AM) fungi. Research into the cell and developmental biology of AM revealed fascinating insights into the plasticity of plant cell development and of interorganismic communication. It is driven by the prospect of increased exploitation of AM benefits for sustainable agriculture. The plant cell developmental program for intracellular accommodation of AM fungi is activated by a genetically defined signaling pathway involving calcium spiking in the nucleus as second messenger. Calcium spiking is triggered by chitooligosaccharides released by AM fungi that are probably perceived via LysM domain receptor kinases. Fungal infection and calcium spiking are spatiotemporally coordinated, and only cells committed to accommodating the fungus undergo high-frequency spiking. Delivery of mineral nutrients by AM fungi occurs at tree-shaped hyphal structures, the arbuscules, in plant cortical cells. Nutrients are taken up at a plant-derived periarbuscular membrane, which surrounds fungal hyphae and carries a specific transporter composition that is of direct importance for symbiotic efficiency. An elegant study has unveiled a new and unexpected mechanism for specific protein localization to the periarbuscular membrane, which relies on the timing of gene expression to synchronize protein biosynthesis with a redirection of secretion. The control of AM development by phytohormones is currently subject to active investigation and has led to the rediscovery of strigolactones. Nearly all tested phytohormones regulate AM development, and major insights into the mechanisms of this regulation are expected in the near future.

Nitrogen and phosphorus interact to control tropical symbioticN2fixation: a test inInga punctata

Summary Symbiotic di‐nitrogen (N2) fixation is a critical biogeochemical process in tropical forests, yet it remains unresolved how fixation is controlled by the availability of soil nitrogen and phosphorus, two nutrients often considered limiting in terrestrial ecosystems. We examine whether individualN2‐fixing trees can overcome nitrogen and phosphorus constraints by employing different strategies of nutrient acquisition and use:N2fixation, phosphatase exudation, mycorrhizal symbiosis and changes in root–shoot ratio or tissue stoichiometry. We grew a common and widespreadN2fixer,Inga punctata, in a full factorial nitrogen and phosphorus addition experiment (each nutrient at three levels) and evaluated whether trees adjusted their strategies of nutrient acquisition to overcome limitation. N2fixation was controlled by nitrogen availability in phosphorus‐sufficient soils, but both fixation and plant growth were constrained by phosphorus in the unamended native phosphorus‐poor soils. Despite the investment in both extracellular phosphatases and mycorrhizal symbionts, plants were unable to overcome phosphorus limitation. Our findings support the hypotheses that: (i)N2fixation is proximately controlled by nitrogen availability, consistent with a facultative fixation strategy, and (ii)N2fixation andN2fixer biomass growth are ultimately constrained by soil phosphorus. We found no support for the hypothesis that fixers can overcome phosphorus limitation by trading fixedN2for soil phosphorus. Synthesis. This study provides new knowledge about how nitrogen and phosphorus interact to regulate tropicalN2fixation by examining a suite of strategies that plants may employ to overcome nutrient limitation. These findings, focused at the organismal level, have broader implications for biogeochemical controls at the ecosystem level in tropical forests.

Fuelling flight in a parasitic wasp: which energetic substrate to use?

1. Flight is an energy‐demanding behaviour in insects. In parasitic wasps, strategies of nutrient acquisition and allocation, resulting life‐history trade‐offs and relationships with foraging strategies and resource availability have received much attention. However, despite the ecological importance of dispersal between host and food patches, and the great impact energy diverted to flight should have on lifetime reproductive success, the eco‐physiology of flight in parasitoids is poorly understood.2. The objective of this study is to (i) identify the energetic resources used to fuel flight, and (ii) relate nutrient type and rate of utilisation to selective pressures in terms of resource availability posed by the environment.3. Using a flight mill and biochemical assays, we compared flight performance and nutrient dynamics during flight between two reproductive modes of the parasitoid Venturia canescens Gravenhorst, which is known to thrive preferentially in contrasted environments (i.e. natural vs. anthropogenic habitat), differing notably in host and food distribution.4. Biochemical analyses of different nutrient types showed that glycogen is the flight fuel used by this species, yet no significant differences in its dynamics in flight were found between the two reproductive modes.5. Results suggest that both glycogen quantity and flight performance are related to the diverging ecological conditions experienced by thelytokous and arrhenotokous strains.

Metagenome, metatranscriptome and single-cell sequencing reveal microbial response to Deepwater Horizon oil spill

The Deepwater Horizon oil spill in the Gulf of Mexico resulted in a deep-sea hydrocarbon plume that caused a shift in the indigenous microbial community composition with unknown ecological consequences. Early in the spill history, a bloom of uncultured, thus uncharacterized, members of the Oceanospirillales was previously detected, but their role in oil disposition was unknown. Here our aim was to determine the functional role of the Oceanospirillales and other active members of the indigenous microbial community using deep sequencing of community DNA and RNA, as well as single-cell genomics. Shotgun metagenomic and metatranscriptomic sequencing revealed that genes for motility, chemotaxis and aliphatic hydrocarbon degradation were significantly enriched and expressed in the hydrocarbon plume samples compared with uncontaminated seawater collected from plume depth. In contrast, although genes coding for degradation of more recalcitrant compounds, such as benzene, toluene, ethylbenzene, total xylenes and polycyclic aromatic hydrocarbons, were identified in the metagenomes, they were expressed at low levels, or not at all based on analysis of the metatranscriptomes. Isolation and sequencing of two Oceanospirillales single cells revealed that both cells possessed genes coding for n-alkane and cycloalkane degradation. Specifically, the near-complete pathway for cyclohexane oxidation in the Oceanospirillales single cells was elucidated and supported by both metagenome and metatranscriptome data. The draft genome also included genes for chemotaxis, motility and nutrient acquisition strategies that were also identified in the metagenomes and metatranscriptomes. These data point towards a rapid response of members of the Oceanospirillales to aliphatic hydrocarbons in the deep sea.

Using Plant Functional Traits to Explain Diversity–Productivity Relationships

BackgroundThe different hypotheses proposed to explain positive species richness–productivity relationships, i.e. selection effect and complementarity effect, imply that plant functional characteristics are at the core of a mechanistic understanding of biodiversity effects.Methodology/Principal FindingsWe used two community-wide measures of plant functional composition, (1) community-weighted means of trait values (CWM) and (2) functional trait diversity based on Rao’s quadratic diversity (FDQ) to predict biomass production and measures of biodiversity effects in experimental grasslands (Jena Experiment) with different species richness (2, 4, 8, 16 and 60) and different functional group number and composition (1 to 4; legumes, grasses, small herbs, tall herbs) four years after establishment. Functional trait composition had a larger predictive power for community biomass and measures of biodiversitity effects (40–82% of explained variation) than species richness per se (<1–13% of explained variation). CWM explained a larger amount of variation in community biomass (80%) and net biodiversity effects (70%) than FDQ (36 and 38% of explained variation respectively). FDQ explained similar proportions of variation in complementarity effects (24%, positive relationship) and selection effects (28%, negative relationship) as CWM (27% of explained variation for both complementarity and selection effects), but for all response variables the combination of CWM and FDQ led to significant model improvement compared to a separate consideration of different components of functional trait composition. Effects of FDQ were mainly attributable to diversity in nutrient acquisition and life-history strategies. The large spectrum of traits contributing to positive effects of CWM on biomass production and net biodiversity effects indicated that effects of dominant species were associated with different trait combinations.Conclusions/SignificanceOur results suggest that the identification of relevant traits and the relative impacts of functional identity of dominant species and functional diversity are essential for a mechanistic understanding of the role of plant diversity for ecosystem processes such as aboveground biomass production.

Harmful dinoflagellate blooms caused by Cochlodinium sp.: Global expansion and ecological strategies facilitating bloom formation

The past two decades have witnessed an expansion in the reported occurrences of harmful algal blooms (HABs) caused by the dinoflagellate Cochlodinium. Prior to 1990, blooms had been primarily reported in Southeast Asia, with South Korea alone reporting more than $100M USD in annual fisheries losses during the 1990s. Since then, time blooms have expanded across Asia, Europe, and North America, with recognition of multiple species and ribotypes that exhibit similar ecophysiological and harmful characteristics. Here, we summarize the current state of knowledge regarding taxonomy, phylogeny, detection, distribution, ecophysiology, life history, food web interactions, and mitigation of blooms formed by Cochlodinium. We review this recent expansion of Cochlodinium blooms and characterize the ecological strategies utilized by Cochlodinium populations to form HABs. Although Cochlodinium is comprised of more than 40 species, we focus primarily on the two HAB-forming species, C. polykrikoides and C. fulvescens, specifically describing their flexible nutrient acquisition strategies, inhibition of grazing by inducing rapid mortality in a diverse set of predators, and allelopathic inhibition of a broad range of competing phytoplankton. Finally, we summarize the available information on prevention, control, and mitigation strategies specific to this genus, and discuss pressing questions regarding this increasingly important HAB organism.

A Unique Resource Mutualism between the Giant Bornean Pitcher Plant, Nepenthes rajah, and Members of a Small Mammal Community

The carnivorous pitcher plant genus Nepenthes grows in nutrient-deficient substrates and produce jug-shaped leaf organs (pitchers) that trap arthropods as a source of N and P. A number of Bornean Nepenthes demonstrate novel nutrient acquisition strategies. Notably, three giant montane species are engaged in a mutualistic association with the mountain treeshrew, Tupaia montana, in which the treeshrew defecates into the pitchers while visiting them to feed on nectar secretions on the pitchers' lids.Although the basis of this resource mutualism has been elucidated, many aspects are yet to be investigated. We sought to provide insights into the value of the mutualism to each participant. During initial observations we discovered that the summit rat, R. baluensis, also feeds on sugary exudates of N. rajah pitchers and defecates into them, and that this behavior appears to be habitual. The scope of the study was therefore expanded to assess to what degree N. rajah interacts with the small mammal community.We found that both T. montana and R. baluensis are engaged in a mutualistic interaction with N. rajah. T .montana visit pitchers more frequently than R. baluensis, but daily scat deposition rates within pitchers do not differ, suggesting that the mutualistic relationships are of a similar strength. This study is the first to demonstrate that a mutualism exists between a carnivorous plant species and multiple members of a small mammal community. Further, the newly discovered mutualism between R. baluensis and N. rajah represents only the second ever example of a multidirectional resource-based mutualism between a mammal and a carnivorous plant.

A model of Ustilago maydis leaf tumor metabolism

Extensive progress has been made in the last years in unraveling molecular mechanisms of plant-pathogen interactions. Although the main research focus lies on defense and counter-defense mechanisms, some plant-pathogen interactions have been characterized on the physiological level. Only a few studies have focused on the nutrient acquisition strategies of phytopathogens. In a previous study, we analyzed how local infection of maize leaves by the tumor-inducing fungus Ustilago maydis affects whole plant physiology and were able to show that carbon and nitrogen assimilates are rerouted to the tumor. While the sink strength of infected emerging young leaves increases with tumor development, systemic source leaves exhibit elevated export of assimilates and delayed senescence to compensate for the altered sink-source balance. Here we provide new experimental data on the metabolization of these assimilates in the tumor and propose a model on their utilization in the infected tissue.

Genome analysis of Bifidobacterium bifidum PRL2010 reveals metabolic pathways for host-derived glycan foraging

The human intestine is densely populated by a microbial consortium whose metabolic activities are influenced by, among others, bifidobacteria. However, the genetic basis of adaptation of bifidobacteria to the human gut is poorly understood. Analysis of the 2,214,650-bp genome of Bifidobacterium bifidum PRL2010, a strain isolated from infant stool, revealed a nutrient-acquisition strategy that targets host-derived glycans, such as those present in mucin. Proteome and transcriptome profiling revealed a set of chromosomal loci responsible for mucin metabolism that appear to be under common transcriptional control and with predicted functions that allow degradation of various O-linked glycans in mucin. Conservation of the latter gene clusters in various B. bifidum strains supports the notion that host-derived glycan catabolism is an important colonization factor for B. bifidum with concomitant impact on intestinal microbiota ecology.