Nutrient-rich Particles Research Articles

Bacterial interactions on nutrient-rich surfaces in the gut lumen.

The intestinal lumen is a turbulent, semi-fluid landscape where microbial cells and nutrient-rich particles are distributed with high heterogeneity. Major questions regarding the basic physical structure of this dynamic microbial ecosystem remain unanswered. Most gut microbes are non-motile, and it is unclear how they achieve optimum localization relative to concentrated aggregations of dietary glycans that serve as their primary source of energy. In addition, a random spatial arrangement of cells in this environment is predicted to limit sustained interactions that drive co-evolution of microbial genomes. The ecological consequences of random versus organized microbial localization have the potential to control both the metabolic outputs of the microbiota and the propensity for enteric pathogens to participate in proximity-dependent microbial interactions. Here, we review evidence suggesting that several bacterial species adopt organized spatial arrangements in the gut via adhesion. We highlight examples where localization could contribute to antagonism or metabolic interdependency in nutrient degradation, and we discuss imaging- and sequencing-based technologies that have been used to assess the spatial positions of cells within complex microbial communities.

Environmental mechanism of capturing nutrient-rich particles by the lake bottom trap in a large, shallow lake

Bottom traps capture and preserve nutrient-rich mobile bottom sediments by forming a weak hydrodynamic environment. In this study, Lake Chaohu, a large shallow lake in China, was considered the research object, and the influence of trap at the bottom of the lake on the physical, chemical, and biological characteristics of sediments and water were analysed by combining on-site monitoring and laboratory analysis. The results showed that the hydrodynamic intensity was attenuated by more than 65% at the bottom of the trap compared with that of the upper surface of the water body under different weather conditions, forming an obviously weak hydrodynamic environment. The weak dynamic environment and large sedimentation rate at the bottom of the trap were beneficial to the sedimentation and storage of fine particles that adsorb nutrients, such as nitrogen and phosphorus, in the water. Owing to the increase in local water depth, a low-temperature and low-dissolved oxygen environment was formed inside the trap. The abundance and diversity of microorganisms in the sediments inside the trap were reduced, and the abundance of nitrifying and denitrifying bacteria in the sediment was reduced by approximately 50%, indicating an environment favourable for nitrogen accumulation in the sediment in the trap. Therefore, the environment inside the bottom trap is favourable for capturing the high nutrient-rich particulate matter in the water, which provides theoretical support for use of the lake bottom traps for controlling the endogenous pollution of shallow lakes.

Colonies of the marine cyanobacterium Trichodesmium optimize dust utilization by selective collection and retention of nutrient-rich particles

SummaryTrichodesmium, a globally important, N2-fixing, and colony-forming cyanobacterium, employs multiple pathways for acquiring nutrients from air-borne dust, including active dust collection. Once concentrated within the colony core, dust can supply Trichodesmium with nutrients. Recently, we reported a selectivity in particle collection enabling Trichodesmium to center iron-rich minerals and optimize its nutrient utilization. In this follow-up study we examined if colonies select Phosphorus (P) minerals. We incubated 1,200 Trichodesmium colonies from the Red Sea with P-free CaCO3, P-coated CaCO3, and dust, over an entire bloom season. These colonies preferably interacted, centered, and retained P-coated CaCO3 compared with P-free CaCO3. In both studies, Trichodesmium clearly favored dust over all other particles tested, whereas nutrient-free particles were barely collected or retained, indicating that the colonies sense the particle composition and preferably collect nutrient-rich particles. This unique ability contributes to Trichodesmium's current ecological success and may assist it to flourish in future warmer oceans.

Colonies of the Marine Cyanobacterium <i>Trichodesmium</i> Optimize Dust Utilization by Selective Collection and Retention of Nutrient-Rich Particles

Trichodesmium, a globally important, N2-fixing and colony-forming cyanobacterium employs multiple pathways for acquiring nutrients from air-borne dust, including the active collection of dust particles. Once concentrated within the colony core, dust can supply Trichodesmium with the limiting nutrients iron (Fe) and phosphorus (P). Studying particle collection by natural colonies, we recently documented a preference for Fe-rich over Fe-free particles. In this follow-up study we examined if colonies selectively collect P-rich particles. Over an entire bloom season, we incubated ~1 200 Trichodesmium colonies from the Red Sea with P-free CaCO3, P-coated CaCO 3 and dust. We utilized three discrete parameters to characterize the colony-particle interactions and integrated them to an index that describes the particle collection behavior over time. Colonies were found to preferably interact, center and retain P-coated CaCO3 in comparison to P-free CaCO3, suggesting that Trichodesmium can optimize its P-acquisition by selecting P-rich particles. In both current and former studies, colonies clearly favored dust over all other particles tested, while nutrient-free particles were barely collected or retained, indicating that Trichodesmium senses the particle composition and preferably collects nutrient-rich particles. This unique ability contributes to Trichodesmium's current ecological success and may assist it to flourish in future warmer oceans.

Culture-independent tracking of Vibrio cholerae lineages reveals complex spatiotemporal dynamics in a natural population.

Populations of the bacterium Vibrio cholerae consist of dozens of distinct lineages, with primarily (but not exclusively) members of the pandemic generating lineage capable of causing the diarrhoeal disease cholera. Assessing the composition and temporal dynamics of such populations requires extensive isolation efforts and thus only rarely covers large geographic areas or timeframes exhaustively. We developed a culture-independent amplicon sequencing strategy based on the protein-coding gene viuB (vibriobactin utilization) to study the structure of a V. cholerae population over the course of a summer. We show that the 26 co-occurring V. cholerae lineages continuously compete for limited space on nutrient-rich particles where only a few of them can grow to large numbers. Differential abundance of lineages between locations and size-fractions associated with a particle-attached or free-swimming lifestyle could reflect adaptation to various environmental niches. In particular, a major V. cholerae lineage occasionally grows to large numbers on particles but remain undetectable using isolation-based methods, indicating selective culturability for some members of the species. We thus demonstrate that isolation-based studies may not accurately reflect the structure and complex dynamics of V. cholerae populations and provide a scalable high-throughput method for both epidemiological and ecological approaches to studying this species.

High-resolution radiocarbon records trace episodes of Zoophycos burrowing

The unknown Zoophycos-producing organism potentially reworks marine sediments far deeper (up to >1 m) than common bioturbational mixing of the topmost sediment layer. The Zoophycos producer displaces planktonic foraminifera tests down to deep sediment levels hence, may seriously bias the faunal and isotopic composition and in particular, the radiocarbon age (14C) of the ambient host sediment. Here we present three high-resolution 14C records from sediment cores retrieved at intermediate water depths off Brazil, New Zealand, and Norway where Zoophycos burrows have biased 14C ages by 1000–5000 years. Based on closely spaced 14C ages and 14C plateau tuning we distinguish particular episodes with enhanced Zoophycos production that coincide with time spans of decreased sedimentation and thus, with probably reduced benthic nutrition. Off New Zealand, the actual burrowing activity was dated close to the Bølling/Allerød–Younger Dryas boundary. Displaced grains are traced from the ancient sediment surface of the Younger Dryas as far back as to the onset of Heinrich Stadial 1 and the terminal Last Glacial Maximum. These displaced 14C ages and similar 14C records obtained from two other sediment cores suggest that Zoophycos producers generally mount a burrowing campaign during times when environmental conditions are switching toward a starved sedimentation regime. During these tipping points Zoophycos spreiten probably serve as storage space for nutrient-rich particles foraged at the sediment surface and bioturbational mixed layer.

Changes in Sediment Fatty Acid Composition during Passage through the Gut of Deposit Feeding Holothurians: Holothuria atra (Jaeger, 1883) and Holothuria leucospilota (Brandt, 1835).

Sea cucumbers Holothuria atra and Holothuria leucospilota play an important role in the bioturbation of sediment in coral reef and rocky intertidal ecosystems. This study investigated changes in sediment fatty acid (FA) composition during gut passage in H. atra and H. leucospilota. The FA composition did not differ significantly between species. Comparison of FA composition in ambient sediment (AS), foregut (FG), midgut (MG), hindgut (HG), and faecal pellets (FPs) indicated that marked changes in FA composition occurred during passage through the gut of H. atra and H. leucospilota. Saturated fatty acids (SAFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), and branched fatty acids (BrFAs) were significantly higher in FG than in AS, suggesting that both species selectively ingested nutrient rich particles. Significant reduction of SAFAs, MUFAs, PUFAs, and BrFAs occurred in MD and HD, with complete elimination of most PUFAs in FPs. A decrease in PUFAs 20:5ω3, 18:4ω3, 22:5ω3, 22:6ω3, 18:2ω6, 18:3ω3, 18:3ω6, odd-numbered BrFAs, and MUFA 18:1ω7 indicated that algal detritus and bacteria were important part of diet. These results have implications for the fate of specific dietary FAs, especially ω3 and ω6, and the contribution holothurian FPs make to the FA composition of coral reef and rocky intertidal ecosystems.

Physiological and genomic characterization of two novel marine thaumarchaeal strains indicates niche differentiation.

Ammonia-oxidizing Archaea (AOA) are ubiquitous throughout the oceanic water column; however, our knowledge on their physiological and ecological diversity in different oceanic regions is rather limited. Here, we report the cultivation and characterization of two novel Nitrosopumilus strains, originating from coastal surface waters of the Northern Adriatic Sea. The combined physiological and genomic information revealed that each strain exhibits different metabolic and functional traits, potentially reflecting contrasting life modes. Strain NF5 contains many chemotaxis-related genes and is able to express archaella, suggesting that it can sense and actively seek favorable microenvironments such as nutrient-rich particles. In contrast, strain D3C is non-motile and shows higher versatility in substrate utilization, being able to use urea as an alternative substrate in addition to ammonia. Furthermore, it encodes a divergent, second copy of the AmoB subunit of the key enzyme ammonia monooxygenase, which might have an additional catalytic function and suggests further metabolic versatility. However, the role of this gene requires further investigation. Our results provide evidence for functional diversity and metabolic versatility among phylogenetically closely related thaumarchaeal strains, and point toward adaptations to free-living versus particle-associated life styles and possible niche differentiation among AOA in marine ecosystems.

Mucous contribution to gut nutrient content in American gizzard shad Dorosoma cepedianum.

This study developed and applied an approach to calculate the proportion of fish gut content composed of mucus secreted by the oropharyngeal cavity and gut. The amount of nitrogen in the contents of the foregut (oesophagus and gizzard) and the epibranchial organs of suspension-feeding American gizzard shad Dorosoma cepedianum was significantly higher than the nitrogen in the homogeneous food source. Using data collected from suspension-feeding experiments and the nitrogen content of D. cepedianum mucus, a series of equations illustrated that mucus constituted c. 10% of D. cepedianum foregut content and 12% of epibranchial organ content by dry mass. Future quantification of fish feeding selectivity and absorption efficiency can use this approach to take into account the contribution of fish mucus to the nutrients in the gut contents. This study supports the conclusion that suspension-feeding D. cepedianum in a heterogeneous environment selectively ingest nutrient-rich particles, even when gut nutrient content is adjusted to take into account the contribution of mucus.

Selective feeding on nutrient-rich particles by gizzard shad Dorosoma cepedianum does not involve mechanical sorting

Previous field and laboratory studies have concluded that suspension-feeding detriti - vorous fish such as gizzard shad Dorosoma cepedianum selectively ingest nutrient-rich particles using either mechanical sorting within the oropharyngeal cavity or behavioral selectivity within the environment, but none have distinguished between these hypothesized selection mecha- nisms. To determine whether mechanical selectivity occurs within the oropharyngeal cavity, giz- zard shad were fed particles of standardized size but different carbon and nitrogen content in homogeneous particle suspensions vs. non-homogeneous particle distributions. By comparing foregut and epibranchial organ contents with the particles available in a homogeneous suspen- sion, we demonstrated that the fish did not use mechanical selection for nutrient-rich particles. Previously published hypotheses for intraoral selection of nutrient-rich particles in gizzard shad using crossflow filtration or gustatory receptors were not supported. However, when particles with different nutrient content were allowed to settle in a heterogeneous distribution, the nutrients in the foregut and epibranchial organs were 1.5 times higher than those of particles in the water and 2.5 times higher than those of settled particles (p ≤ 0.0001). As a test of one potential behavioral mechanism of particle selection, disturbance of the sedimentwater interface resulted in signifi- cantly higher organic carbon (p = 0.01) and nitrogen (p = 0.001) within 1 to 2 cm of the bottom com- pared to the overlying water and the bottom sediment. Thus, future laboratory and field studies should focus on potential behavioral mechanisms of particle selectivity in detritivorous fish sus- pension feeding on non-homogeneous distributions of small particles (<< 1 mm).

Phytoplankton Chytridiomycosis: Fungal Parasites of Phytoplankton and Their Imprints on the Food Web Dynamics

Parasitism is one of the earlier and common ecological interactions in the nature, occurring in almost all environments. Microbial parasites typically are characterized by their small size, short generation time, and high rates of reproduction, with simple life cycle occurring generally within a single host. They are diverse and ubiquitous in aquatic ecosystems, comprising viruses, prokaryotes, and eukaryotes. Recently, environmental 18S rDNA surveys of microbial eukaryotes have unveiled major infecting agents in pelagic systems, consisting primarily of the fungal order of Chytridiales (chytrids). Chytrids are considered the earlier branch of the Eumycetes and produce motile, flagellated zoospores, characterized by a small size (2–6 μm), and a single, posterior flagellum. The existence of these dispersal propagules includes chytrids within the so-called group of zoosporic fungi, which are particularly adapted to the plankton lifestyle where they infect a wide variety of hosts, including fishes, eggs, zooplankton, algae, and other aquatic fungi but primarily freshwater phytoplankton. Related ecological implications are huge because chytrids can killed their hosts, release substrates for microbial processes, and provide nutrient-rich particles as zoospores and short fragments of filamentous inedible hosts for the grazer food chain. Furthermore, based on the observation that phytoplankton chytridiomycosis preferentially impacts the larger size species, blooms of such species (e.g., filamentous cyanobacteria) may not totally represent trophic bottlenecks. Besides, chytrid epidemics represent an important driving factor in phytoplankton seasonal successions. In this review, I summarize the knowledge on the diversity, community structure, quantitative importance, and functional roles of fungal chytrids, primarily those who are parasites of phytoplankton, and infer the ecological implications and potentials for the food web dynamics and properties. I reach the conclusion that phytoplankton chytridiomycosis represents an important but as yet overlooked ecological driving force in aquatic food web dynamics and network organization.

Modelling water erosion in the Sahel: application of a physically based soil erosion model in a gentle sloping environment

AbstractWater is a major limiting factor in arid and semi‐arid agriculture. In the Sahelian zone of Africa, it is not always the limited amount of annual rainfall that constrains crop production, but rather the proportion of rainfall that enters the root zone and becomes plant‐available soil moisture. Maximizing the rain‐use efficiency and therefore limiting overland flow is an important issue for farmers. The objectives of this research were to model the processes of infiltration, runoff and subsequent erosion in a Sahelian environment and to study the spatial distribution of overland flow and soil erosion.The wide variety of existing water erosion models are not developed for the Sahel and so do not include the unique Sahelian processes. The topography of the Sahelian agricultural lands in northern Burkina Faso is such that field slopes are generally low (0–5°) and overland flow mostly occurs in the form of sheet flow, which may transport large amounts of fine, nutrient‐rich particles despite its low sediment transport capacity. Furthermore, pool formation in a field limits overland flow and causes resettlement of sediment resulting in the development of a surface crust.The EUROSEM model was rewritten in the dynamic modelling code of PCRaster and extended to account for the pool formation and crust development. The modelling results were calibrated with field data from the 2001 rainy season in the Katacheri catchment in northern Burkina Faso. It is concluded that the modified version of EUROSEM for the Sahel is a fully dynamic erosion model, able to simulate infiltration, runoff routing, pool formation, sediment transport, and erosion and deposition by inter‐rill processes over the land surface in individual storms at the scale of both runoff plots and fields. A good agreement is obtained between simulated and measured amounts of runoff and sediment discharge. Incorporating crust development during the event may enhance model performance, since the process has a large influence on infiltration capacity and sediment detachment in the Sahel. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Structure, Formation, and Darkening Process of Albedo-reducing Material (Cryoconite) on a Himalayan Glacier: A Granular Algal Mat Growing on the Glacier

Dark-colored material (cryoconite) covering Himalayan glaciers has been reported to greatly accelerate glacier-melting by reducing surface albedo. Structure, formation, and the darkening process of the cryoconite on a Himalayan glacier were analyzed. The cryoconite was revealed to be a stromatolite-like algal mat, a product of microbial activity on the glacier. The granular algal mat contains filamentous blue-green algae (cyanobacteria) and bacteria, and grows on the ice by trapping mineral and organic particles. This structure seems to enable high algal production in nutrient poor glacial meltwater by gathering and keeping nutrient rich particles inside. The dark coloration of the mats promotes melt-hole formation on the ice (cryoconite holes), providing a semistagnant aquatic habitat for various algae and animals in the glacier. Optical and chemical analyses of the cryoconite strongly suggests that their high light- absorbency (dark coloration) is mainly due to dark-colored humic substances, residues from bacterial decomposition of the algal products and other organic matter. Our results strongly suggest that biological activity on the glacier substantially affects the albedo of the glacier surface. The structure of the algal mat seems to be important in the glacier ecosystem and biological process affecting glacier albedo.

Feeding Behaviour and Digestion Pattern in Stylonychia mytilusEhrenberg

Summary Stylonychia mytilus is a phagotrophic feeder with a strong discriminating sense of food selection. The inorganic and non-nutrient organic particles are rejected while as the organic nutrientrich particles are readily ingested. Among a variety of live food materials also, there is a preferential acceptance of specific prey organisms. The rate of uptake of food material is high in the initial phases of feeding. The log phase cells feed at a higher rate than the stationary phase cells. Controlled feeding experiments show that total digestion time increases proportionately with the number of ingested food organisms, though all the prey organisms become acid phosphatase positive within minutes of their ingestion. Experiments with cycloheximide inhibition show that Stylonychia possess a reserve pool of digestive enzymes sufficient to catabolize about 25 food organisms. The reservoir of digestive enzymes shows a slow turnover rate. Proteins other than lysosomal enzymes are involved in the process of ingestion; such proteins show countinuous turnover.