Particle-attached bacteria act as gatekeepers in the decomposition of complex phytoplankton polysaccharides

BACKGROUND

Marine microalgae (phytoplankton) mediate almost half of the worldwide photosynthetic carbon dioxide fixation and therefore play a pivotal role in global carbon cycling, most prominently during massive phytoplankton blooms. Phytoplankton biomass consists of considerable proportions of polysaccharides, substantial parts of which are rapidly remineralized by heterotrophic bacteria. We analyzed the diversity, activity, and functional potential of such polysaccharide-degrading bacteria in different size fractions during a diverse spring phytoplankton bloom at Helgoland Roads (southern North Sea) at high temporal resolution using microscopic, physicochemical, biodiversity, metagenome, and metaproteome analyses.

RESULTS

Prominent active 0.2-3 µm free-living clades comprised Aurantivirga, "Formosa", Cd. Prosiliicoccus, NS4, NS5, Amylibacter, Planktomarina, SAR11 Ia, SAR92, and SAR86, whereas BD1-7, Stappiaceae, Nitrincolaceae, Methylophagaceae, Sulfitobacter, NS9, Polaribacter, Lentimonas, CL500-3, Algibacter, and Glaciecola dominated 3-10 µm and > 10 µm particles. Particle-attached bacteria were more diverse and exhibited more dynamic adaptive shifts over time in terms of taxonomic composition and repertoires of encoded polysaccharide-targeting enzymes. In total, 305 species-level metagenome-assembled genomes were obtained, including 152 particle-attached bacteria, 100 of which were novel for the sampling site with 76 representing new species. Compared to free-living bacteria, they featured on average larger metagenome-assembled genomes with higher proportions of polysaccharide utilization loci. The latter were predicted to target a broader spectrum of polysaccharide substrates, ranging from readily soluble, simple structured storage polysaccharides (e.g., laminarin, α-glucans) to less soluble, complex structural, or secreted polysaccharides (e.g., xylans, cellulose, pectins). In particular, the potential to target poorly soluble or complex polysaccharides was more widespread among abundant and active particle-attached bacteria.

CONCLUSIONS

Particle-attached bacteria represented only 1% of all bloom-associated bacteria, yet our data suggest that many abundant active clades played a pivotal gatekeeping role in the solubilization and subsequent degradation of numerous important classes of algal glycans. The high diversity of polysaccharide niches among the most active particle-attached clades therefore is a determining factor for the proportion of algal polysaccharides that can be rapidly remineralized during generally short-lived phytoplankton bloom events. Video Abstract.

Plankton assessment across the distribution of West African hake and tuna based on eDNA metabarcoding

The richness of plankton communities determines the fish productivity in the ocean, including important resources that rely on extractive fisheries, such as hakes (genus Merluccius) and tunas (genus Thunnus). Their preys forage on zooplankton, and the latter feed on phytoplankton. Inventories of plankton communities for scientific advice to sustainable fishing are essential in this moment of climate change. Plankton is generally inventoried using conventional methodologies based on large water volumes and visual morphological analyses of samples. In this study, we have employed metabarcoding on environmental DNA (eDNA) samples extracted from small water volumes for plankton inventory from twelve distant sampling stations in the East Atlantic Ocean. Zones rich in hake and tuna prey were detected from eDNA, and multivariate multiple regression analysis was able to predict those zones from diatom-based indices and planktonic diversity based on functional groups. Salinity was negatively correlated with the proportion of diatoms in phytoplankton, highlighting expected impacts of current global change on marine plankton communities. The results emphasise the importance of the plankton richness for fish productivity and support the utility of environmental DNA as a tool to monitor plankton composition changes.

Dissolved storage glycans shaped the community composition of abundant bacterioplankton clades during a North Sea spring phytoplankton bloom

BACKGROUND

Blooms of marine microalgae play a pivotal role in global carbon cycling. Such blooms entail successive blooms of specialized clades of planktonic bacteria that collectively remineralize gigatons of algal biomass on a global scale. This biomass is largely composed of distinct polysaccharides, and the microbial decomposition of these polysaccharides is therefore a process of prime importance.

RESULTS

In 2020, we sampled a complete biphasic spring bloom in the German Bight over a 90-day period. Bacterioplankton metagenomes from 30 time points allowed reconstruction of 251 metagenome-assembled genomes (MAGs). Corresponding metatranscriptomes highlighted 50 particularly active MAGs of the most abundant clades, including many polysaccharide degraders. Saccharide measurements together with bacterial polysaccharide utilization loci (PUL) expression data identified β-glucans (diatom laminarin) and α-glucans as the most prominent and actively metabolized dissolved polysaccharide substrates. Both substrates were consumed throughout the bloom, with α-glucan PUL expression peaking at the beginning of the second bloom phase shortly after a peak in flagellate and the nadir in bacterial total cell counts.

CONCLUSIONS

We show that the amounts and composition of dissolved polysaccharides, in particular abundant storage polysaccharides, have a pronounced influence on the composition of abundant bacterioplankton members during phytoplankton blooms, some of which compete for similar polysaccharide niches. We hypothesize that besides the release of algal glycans, also recycling of bacterial glycans as a result of increased bacterial cell mortality can have a significant influence on bacterioplankton composition during phytoplankton blooms. Video Abstract.

Stress resistance for unraveling potential biopollutants. Insights from ballast water community analysis through DNA

In marine settings, anthropogenic disturbances and climate change increase the rate of biological invasions. Predicting still undescribed invasive alien species (IAS) is needed for preparing timely management responses. We tested a strategy for discovering new potential IAS using DNA in a trans-equatorial expedition onboard RV Polarstern. During one-month travel, species inside ballast water experienced oxygen depletion, warming, darkness and ammonium stress. Many organisms died but several phytoplankton and zooplankton survivors resisted and were detected through a robust combination of individual sampling, DNA barcoding and metabarcoding, new in ballast water studies. Ammonium was identified as an important influential factor to explain diversity changes in phytoplankton and zooplankton. Some species reproduced until the end of the travel. These species tolerant to travel stress could be targeted as potential IAS and prioritized for designing control measures. Introducing resistance to travel stress in biosecurity risk analysis would be recommended.

The Patient Assessment of Chronic Illness Care produces measurements along a single dimension: results from a Mokken analysis

Background

As the worldwide prevalence of chronic illness increases so too does the demand for novel treatments to improve chronic illness care. Quantifying improvement in chronic illness care from the patient perspective relies on the use of validated patient-reported outcome measures. In this analysis we examine the psychometric and scaling properties of the Patient Assessment of Chronic Illness Care (PACIC) questionnaire for use in the United Kingdom by applying scale data to the non-parametric Mokken double monotonicity model.

Methods

Data from 1849 patients with long-term conditions in the UK who completed the 20-item PACIC were analysed using Mokken analysis. A three-stage analysis examined the questionnaire’s scalability, monotonicity and item ordering. An automated item selection procedure was used to assess the factor structure of the scale. Analysis was conducted in an ‘evaluation’ dataset (n = 956) and results were confirmed using an independent ‘validation’ (n = 890) dataset.

Results

Automated item selection procedures suggested that the 20 items represented a single underlying trait representing “patient assessment of chronic illness care”: this contrasts with the multiple domains originally proposed. Six items violated invariant item ordering and were removed. The final 13-item scale had no further issues in either the evaluation or validation samples, including excellent scalability (Ho = .50) and reliability (Rho = .88).

Conclusions

Following some modification, the 13-items of the PACIC were successfully fitted to the non-parametric Mokken model. These items have psychometrically robust and produce a single ordinal summary score. This score will be useful for clinicians or researchers to assess the quality of chronic illness care from the patient's perspective.

Invasion trajectory of Pacific oysters in the northern Wadden Sea

Invasion trajectories of introduced alien species usually begin with a long establishment phase of low abundance, often followed by exponential expansion and subsequent adjustment phases. We review the first 26 years of feral Pacific oysters Crassostrea gigas around the island of Sylt in the Wadden Sea (North Sea, NE Atlantic), and reveal causal conditions for the invasion phases. Sea-based oyster farming with repeated introductions made establishment of feral oysters almost inevitable. Beds of mussels Mytilus edulis on mud flats offered firm substrate for attachment and ideal growth conditions around low tide level. C. gigas mapped on to the spatial pattern of mussel beds. During the 1990s, cold summers often hampered recruitment and abundances remained low but oyster longevity secured persistence. Since the 2000s, summers were often warmer and recruitment more regular. Young oysters attached to adult oysters and abundances of >1000 m-2 were achieved. However, peak abundance was followed by recruitment failure. The population declined and then was also struck by ice winters causing high mortality. Recovery was fast (>2000 m-2) but then recruitment failed again. We expect adjustment phase will proceed with mean abundance of about 1000 m-2 but density-dependent (e.g., diseases) and density-independent (e.g., weather anomalies) events causing strong fluctuations. With continued global warming, feral C. gigas at the current invasion fronts in British estuaries and Scandinavian fjords may show similar adjustment trajectories as observed in the northern Wadden Sea, and also other marine introductions may follow the invasion trajectory of Pacific oysters.

Depression as a systemic syndrome: mapping the feedback loops of major depressive disorder

BACKGROUND

Depression is a complex public health problem with considerable variation in treatment response. The systemic complexity of depression, or the feedback processes among diverse drivers of the disorder, contribute to the persistence of depression. This paper extends prior attempts to understand the complex causal feedback mechanisms that underlie depression by presenting the first broad boundary causal loop diagram of depression dynamics.

METHOD

We applied qualitative system dynamics methods to map the broad feedback mechanisms of depression. We used a structured approach to identify candidate causal mechanisms of depression in the literature. We assessed the strength of empirical support for each mechanism and prioritized those with support from validation studies. Through an iterative process, we synthesized the empirical literature and created a conceptual model of major depressive disorder.

RESULTS

The literature review and synthesis resulted in the development of the first causal loop diagram of reinforcing feedback processes of depression. It proposes candidate drivers of illness, or inertial factors, and their temporal functioning, as well as the interactions among drivers of depression. The final causal loop diagram defines 13 key reinforcing feedback loops that involve nine candidate drivers of depression.

CONCLUSIONS

Future research is needed to expand upon this initial model of depression dynamics. Quantitative extensions may result in a better understanding of the systemic syndrome of depression and contribute to personalized methods of evaluation, prevention and intervention.

Care plans and care planning in long-term conditions: a conceptual model

The prevalence and impact of long-term conditions continues to rise. Care planning for people with long-term conditions has been a policy priority for chronic disease management in a number of health-care systems. However, patients and providers appear unclear about the formulation and implementation of care planning. Further work in this area is therefore required to inform the development, implementation and evaluation of future care planning initiatives. We distinguish between 'care planning' (the process by which health-care professionals and patients discuss, agree and review an action plan to achieve the goals or behaviour change of most relevance and concern to the patient) and a 'care plan' (a written document recording the outcome of a care planning process). We propose a typology of care planning and care plans with three core dimensions: perspective (patient or professional), scope (a focus on goals or on behaviours) and networks (confined to the professional-patient dyad or extending to the entire care network). In addition, we draw on psychological models of mediation and moderation to outline potential mechanisms through which care planning and care plans may lead to improved outcomes for both patients and the wider health-care system. The proposed typology of care planning and care plans offered here, along with the model of the process by which care planning may influence outcomes, provide a useful framework for future policy developments and evaluations. Empirical work is required to explore the degree to which current care planning approaches and care plans can be described according to these dimensions, and the factors that determine which types of patients and professionals use which type of care plans.

Plankton-toxin interaction with a variable input nutrient

A simple model of phytoplankton-zooplankton interaction with a periodic input nutrient is presented. The model is then used to study a nutrient-plankton interaction with a toxic substance that inhibits the growth rate of plankton populations. The effects of the toxin upon the existence, magnitude, and stability of the periodic solutions are discussed. Numerical simulations are also provided to illustrate analytical results and to compare more complicated dynamical behaviour.

Numerical calculations of switched magnetic field gradients during magnetic resonance imaging

During magnetic resonance imaging (MRI) pulse-sequences the human body is exposed to switched magnetic gradient fields. These gradients become stronger and are switched faster for fast imaging. Effects resulting from these fields with trapezoidal waveforms are on the one hand sensory perception of induced currents and on the other hand muscular and cardiac stimulation. All three components of the current density induced by gradient pulse sequence were analysed in a high-resolution model of the human torso. The evaluation of the calculated data was performed thoroughly in the region of the heart muscle of the torso model to find out how different waveforms of the switched gradient field influence strength and direction of induced currents.

Psychosocial risk assessment: problems and prospects

Health and safety legislation now requires organizations to undertake risk assessments for psychosocial hazards in the workplace. Despite this, there is relatively little guidance on what constitutes a psychosocial risk assessment and how one should be conducted. The approaches that do exist are not without problems. This paper examines some of the difficulties with current approaches and looks at possible areas for development to improve understanding and performance in this important area of health and safety management.

Evaluation of an evolutionary model of self-preservation and self-destruction

According to deCatanzaro's mathematical model of self-preservation and self-destruction, staying alive actually may reduce inclusive fitness for an individual who is low in reproductive potential and, at the same time, poses such a burden to close kin that it costs them opportunities for reproduction. Predictions generated from this model were tested using 175 university students as subjects and variables constructed from a 164-item questionnaire. The criterion variables were separate measures of depression, hopelessness, and suicide ideation and behavior. The predictor variables derived from the model were separate measures of reproductive potential of the individual, the individual's perceived benefit or cost to kin, and reproductive potential of the individual's kin. As predicted, there were negative and significant bivariate correlations between each of the model-generated predictor variables and one or more of the criterion variables. Multiple regression analyses showed that benefit to kin was the best predictor of both depression and hopelessness. Discriminant analysis showed that reproductive potential of kin significantly differentiated suicide attempters from nonattempters. Overall, our results support and extend deCatanzaro's model and empirical findings.

Use of parenteral nutrition to maintain adequate nutritional status in hyperemesis gravidarum

A retrospective study was performed to demonstrate that safe parenteral nutrition (PN) support can be given during pregnancy. There has been some hesitation to use PN during pregnancy partly due to the unknown consequences of the lipid emulsions in the PN solution. Twenty-three women received PN including lipid daily but at varying stages of pregnancy. The regimen was based on individual calculated requirements plus 300 kcal for pregnancy. Approximately 50% of the nonprotein calories were provided by lipid. At delivery, no gross abnormalities of the placenta were seen. The majority of the women (52%) received PN during the first trimester of pregnancy. The mean duration of PN therapy was 2.7 weeks (SE +/- 0.4) with a range of 0.5 to 7.5 weeks, and the mean weight gain on PN therapy was 2.4 lb (SE +/- 0.5). The majority of the women (84%) were able to gain appropriate weight to maintain the pregnancy. Although there was a 20% incidence of prematurity and a 30% incidence of low birthweight, this was not significantly different from the control group of women matched for age and parity. It was concluded that PN can provide a safe means of maintaining adequate maternal nutrition and continued fetal growth during a period when oral intake is severely curtailed. The nutrition regimen should include lipid and should be customized to meet the specific needs of each individual.

Refractoriness of neurons mediating intracranial self-stimulation in the anterior basal forebrain

The post-stimulation excitability of neurons mediating electrical self-stimulation of the anterior basal forebrain was evaluated psychophysically in the rat. Rats with electrodes in the nucleus accumbens, caudate nucleus, lateral preoptic area, diagonal band, or anterior medial forebrain bundle pressed a lever to earn 0.5-s trains of conditioning (C) and test (T) pulse pairs. The C-T interval was systematically varied and the effectiveness of the T-pulse was estimated by measuring the frequency of pulse pairs required to sustain criterion responding. All sites tested demonstrated similar recovery; T-pulse effectiveness, normalized against the effect of the C-pulse, was lowest at delays of 0.4-0.8 ms and it rose monotonically until 5 ms when it achieved an effectiveness plateau of one. Increasing the current of the T-pulse by 50 or 60% failed to hasten recovery, suggesting that the recovery profiles primarily reflect the activation of neurons very soon after emergence from absolute refractoriness. Compared to lateral hypothalamic and ventral tegmental self-stimulation, the neurons that support self-stimulation in the ventral basal forebrain recover more slowly; recovery here is only about half done by the time lateral hypothalamic placements demonstrate complete recovery.

Cardiac arrhythmias. An update on identification and therapy

Cardiac arrhythmias result from conduction block, abnormal impulse formation, or a combination of both. The decision to treat arrhythmias depends on symptoms, hemodynamic problems, the presence or absence of organic heart disease, and the presence of malignant arrhythmias. Holter monitoring, treadmill exercise testing, and electrophysiologic stimulation can facilitate identification. Control involves correction of precipitating or contributing factors and selection of an appropriate antiarrhythmic drug or surgical technique.