Prokaryotic morphological features and maintenance activities governed by seasonal productivity conditions.

Prokaryotic maintenance respiration and associated metabolic activities constitute a considerable proportion of the total respiration of carbon to CO2 in the ocean's mixed layer. However, seasonal influences on prokaryotic maintenance activities in terms of morphological and metabolic adaptations at low (winter) and high productivity (summer) are still unclear. To address this, we examined the natural prokaryotic communities at the mesocosm scale to analyse the differences in their morphological features and gene expression at low and high maintenance respiration, experimentally manipulated with the specific growth rate. Here, we showed that morphological features including membrane blebbing, membrane vesicles and cell‒cell connections occurred under high productivity. Metabolic adaptations associated with maintenance activities were observed under low productivity. Several Kyoto Encyclopedia of Genes and Genomes categories related to signal transduction, energy metabolism, and translational machinery supported maintenance activities under simulated winter conditions. Differential abundances of genes related to transporters, osmoregulation, nitrogen metabolism, ribosome biogenesis, and cold stress were observed. Our results demonstrate how specific growth rate in different seasons can influence resource allocation at the levels of morphological features and metabolic adaptations. This motivates further study of morphological features and their ecological role during high productivity, while investigations of metabolic adaptations during low productivity can advance our knowledge about maintenance activities.

Microeukaryote community coalescence strengthens community stability and elevates diversity.

Mixing of entire microbial communities represents a frequent, yet understudied phenomenon. Here, we mimicked estuarine condition in a microcosm experiment by mixing a freshwater river community with a brackish sea community and assessed the effects of both environmental and community coalescences induced by varying mixing processes on microeukaryotic communities. Signs of shifted community composition of coalesced communities towards the sea parent community suggest asymmetrical community coalescence outcome, which, in addition, was generally less impacted by environmental coalescence. Community stability, inferred from community cohesion, differed among river and sea parent communities, and increased following coalescence treatments. Generally, community coalescence increased alpha diversity and promoted competition from the introduction (or emergence) of additional (or rare) species. These competitive interactions in turn had community stabilizing effect as evidenced by the increased proportion of negative cohesion. The fate of microeukaryotes was influenced by mixing ratios and frequencies (i.e. one-time versus repeated coalescence). Namely, diatoms were negatively impacted by coalescence, while fungi, ciliates, and cercozoans were promoted to varying extents, depending on the mixing ratios of the parent communities. Our study suggests that the predictability of coalescence outcomes was greater when the sea parent community dominated the final community, and this predictability was further enhanced when communities collided repeatedly.

Prokaryotic maintenance respiration and growth efficiency field patterns reproduced by temperature and nutrient control at mesocosm scale.

The distribution of prokaryotic metabolism between maintenance and growth activities has a profound impact on the transformation of carbon substrates to either biomass or CO2 . Knowledge of key factors influencing prokaryotic maintenance respiration is, however, highly limited. This mesocosm study validated the significance of prokaryotic maintenance respiration by mimicking temperature and nutrients within levels representative of winter and summer conditions. A global range of growth efficiencies (0.05-0.57) and specific growth rates (0.06-2.7 d-1 ) were obtained. The field pattern of cell-specific respiration versus specific growth rate and the global relationship between growth efficiency and growth rate were reproduced. Maintenance respiration accounted for 75% and 15% of prokaryotic respiration corresponding to winter and summer conditions, respectively. Temperature and nutrients showed independent positive effects for all prokaryotic variables except abundance and cell-specific respiration. All treatments resulted in different taxonomic diversity, with specific populations of amplicon sequence variants associated with either maintenance or growth conditions. These results validate a significant relationship between specific growth and respiration rate under productive conditions and show that elevated prokaryotic maintenance respiration can occur under cold and oligotrophic conditions. The experimental design provides a tool for further study of prokaryotic energy metabolism under realistic conditions at the mesocosm scale.

Co-occurrences enhance our understanding of aquatic fungal metacommunity assembly and reveal potential host-parasite interactions.

Our knowledge of aquatic fungal communities, their assembly, distributions and ecological roles in marine ecosystems is scarce. Hence, we aimed to investigate fungal metacommunities of coastal habitats in a subarctic zone (northern Baltic Sea, Sweden). Using a novel joint species distribution model and network approach, we quantified the importance of biotic associations contributing to the assembly of mycoplankton, further, detected potential biotic interactions between fungi-algae pairs, respectively. Our long-read metabarcoding approach identified 493 fungal taxa, of which a dominant fraction (44.4%) was assigned as early-diverging fungi (i.e. Cryptomycota and Chytridiomycota). Alpha diversity of mycoplankton declined and community compositions changed along inlet-bay-offshore transects. The distributions of most fungi were rather influenced by environmental factors than by spatial drivers, and the influence of biotic associations was pronounced when environmental filtering was weak. We found great number of co-occurrences (120) among the dominant fungal groups, and the 25 associations between fungal and algal OTUs suggested potential host-parasite and/or saprotroph links, supporting a Cryptomycota-based mycoloop pathway. We emphasize that the contribution of biotic associations to mycoplankton assembly are important to consider in future studies as it helps to improve predictions of species distributions in aquatic ecosystems.

Three Sisters With Heterozygous Gene Variants of CYP24A1: Maternal Hypercalcemia, New-Onset Hypertension, and Neonatal Hypoglycemia.

Gene variants of CYP24A1, which encodes the enzyme 24-hydroxylase, are a most unusual cause of maternal hypercalcemia. Loss-of-function mutations in CYP24A1 result in impaired dehydroxylation of active vitamin D (calcitriol). Secondary to this hypercalcemia, hypercalciuria and suppressed parathyroid hormone (P-PTH) can develop. These gene-variants are most often detected in children exposed to vitamin D prophylaxis. These children develop failure to thrive, hypercalciuria, hypercalcemia, and low PTH levels. CYP24A1 variants have also been reported in adults with hypercalcemia and recurrent urolithiasis. This report describes gestational hypercalcemia in two of three sisters with combined CYP24A1 heterozygous variants. METHODS: We retrospectively investigated medical files, clinical information, and calcium levels during and after pregnancy in three sisters giving birth to nine children. All three sisters were also tested genetically. RESULTS: Two sisters developed hypercalcemia during all seven pregnancies and late-onset hypertension during pregnancy. These sisters had two heterozygote variants in the enzyme CYP24A1: c1186C>T and c443T>C. A third sister had the c1186C>T variant and was normocalcemic. Of the seven children born to the two sisters with combined variants, four had hypercalcemia and five had hypoglycemia as neonates. In these mothers, calcium levels slowly normalized postpartum. In the affected neonates, calcium and blood glucose levels became normal within weeks. CONCLUSION: Combined variants of CYP24A1 caused long-standing gestational hypercalcemia and late-onset hypertension. In neonates, elevated serum calcium and hypoglycemia can be consequences necessitating prompt measures. CYP24A1 mutations should be considered in unexplained gestational hypercalcemia. Their combined effects during pregnancy have not been observed previously.

Importance of Bacterial Maintenance Respiration in a Subarctic Estuary: a Proof of Concept from the Field.

Bacterial respiration contributes to atmospheric carbon dioxide accumulation and development of hypoxia and is a critical, often overlooked, component of ecosystem function. This study investigates the concept that maintenance respiration is a significant proportion of bacterial respiration at natural nutrient levels in the field, advancing our understanding of bacterial living conditions and energy strategies. Two river-sea transects of respiration and specific growth rates were analyzed representing low- and high-productivity conditions (by in situ bacterial biomass production) in a subarctic estuary, using an established ecophysiological linear model (the Pirt model) estimating maintenance respiration. The Pirt model was applicable to field conditions during high, but not low, bacterial biomass production. However, a quadratic model provided a better fit to observed data, accounting for the maintained respiration at low µ. A first estimate of maintenance respiration was 0.58 fmol O2 day-1 cell-1 by the quadratic model. Twenty percent to nearly all of the bacterial respiration was due to maintenance respiration over the observed range of µ (0.21-0.002 day-1). In the less productive condition, bacterial specific respiration was high and without dependence on µ, suggesting enhanced bacterial energy expenditure during starvation. Annual maintenance respiration accounted for 58% of the total bacterioplankton respiration based on µ from monitoring data. Phosphorus availability occasionally, but inconsistently, explained some of the remaining variation in bacterial specific respiration. Bacterial maintenance respiration can constitute a large share of pelagic respiration and merit further study to understand bacterial energetics and oxygen dynamics in the aquatic environment.

Effect of Corticosteroids and Cyclophosphamide on Sex Hormone Profiles in Male Patients With Systemic Lupus Erythematosus or Systemic Sclerosis.

OBJECTIVE: Systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) are autoimmune diseases that predominantly affect female patients, and therefore fewer investigations have been conducted in men. The aim of this study was to analyze sex hormone levels in male patients with SLE and those with SSc, compared to matched controls, in relation to the use of corticosteroids and cyclophosphamide (CYC). METHODS: Sex hormone levels were measured in fasting blood samples from male patients with SLE (n = 71) and those with SSc (n = 29) and compared to population-based, age-matched male controls. Relevant hormone profiles were identified using cluster analysis. RESULTS: Male SLE patients had higher levels of luteinizing hormone (LH) (P < 0.0001) and more frequent bioactive testosterone deficiency (P = 0.02) than their matched controls. The current dosage of prednisolone correlated inversely with the levels of bioactive testosterone (r = -0.36, P = 0.03). Cluster analysis identified a subset of SLE patients with increased levels of follicle-stimulating hormone, LH, and prolactin as well as lower levels of bioactive testosterone (P < 0.0001) in relation to higher daily doses of prednisolone. In male SSc patients, levels of testosterone (P = 0.03) and bioactive testosterone (P = 0.02) were significantly lower than those in matched controls. Use of CYC during the previous year was associated with lower bioactive testosterone levels in both SLE patients (P = 0.02) and SSc patients (P = 0.01), after adjustment for age. CONCLUSION: The results of this study highlight the negative impact of corticosteroids on gonadal function in men with SLE. Furthermore, use of CYC during the year prior to study inclusion impaired bioactive testosterone levels in male patients with either SLE or SSc. Physicians should be more aware of the possibility of hypogonadism in male patients with autoimmune diseases. The need for hormonal supplementation remains to be formally evaluated in these patients.

Projected future climate change and Baltic Sea ecosystem management.

Climate change is likely to have large effects on the Baltic Sea ecosystem. Simulations indicate 2-4 °C warming and 50-80 % decrease in ice cover by 2100. Precipitation may increase ~30 % in the north, causing increased land runoff of allochthonous organic matter (AOM) and organic pollutants and decreased salinity. Coupled physical-biogeochemical models indicate that, in the south, bottom-water anoxia may spread, reducing cod recruitment and increasing sediment phosphorus release, thus promoting cyanobacterial blooms. In the north, heterotrophic bacteria will be favored by AOM, while phytoplankton production may be reduced. Extra trophic levels in the food web may increase energy losses and consequently reduce fish production. Future management of the Baltic Sea must consider the effects of climate change on the ecosystem dynamics and functions, as well as the effects of anthropogenic nutrient and pollutant load. Monitoring should have a holistic approach, encompassing both autotrophic (phytoplankton) and heterotrophic (e.g., bacterial) processes.

Increased microbial activity in a warmer and wetter climate enhances the risk of coastal hypoxia.

The coastal zone is the most productive area of the marine environment and the area that is most exposed to environmental drivers associated with human pressures in a watershed. In dark bottle incubation experiments, we investigated the short-term interactive effects of changes in salinity, temperature and riverine dissolved organic matter (rDOM) on microbial respiration, growth and abundance in an estuarine community. An interaction effect was found for bacterial growth, where the assimilation of rDOM increased at higher salinities. A 3 °C rise in the temperature had a positive effect on microbial respiration. A higher concentration of DOM consistently enhanced respiration and bacterial abundance, while an increase in temperature reduced bacterial abundance. The latter result was most likely caused by a positive interaction effect of temperature, salinity and rDOM on the abundance of bacterivorous flagellates. Elevated temperature and precipitation, causing increased discharges of rDOM and an associated lowered salinity, will therefore primarily promote bacterial respiration, growth and bacterivore abundance. Our results suggest a positive net outcome for microbial activity under the projected climate change, driven by different, partially interacting environmental factors. Thus, hypoxia in coastal zones may increase due to enhanced respiration caused by higher temperatures and rDOM discharge acting synergistically.

Combining culture-dependent and -independent methodologies for estimation of richness of estuarine bacterioplankton consuming riverine dissolved organic matter.

Three different methods for analyzing natural microbial community diversity were combined to maximize an estimate of the richness of bacterioplankton catabolizing riverine dissolved organic matter (RDOM). We also evaluated the ability of culture-dependent quantitative DNA-DNA hybridization, a 16S rRNA gene clone library, and denaturing gradient gel electrophoresis (DGGE) to detect bacterial taxa in the same sample. Forty-two different cultivatable strains were isolated from rich and poor solid media. In addition, 50 unique clones were obtained by cloning of the bacterial 16S rDNA gene amplified by PCR from the community DNA into an Escherichia coli vector. Twenty-three unique bands were sequenced from 12 DGGE profiles, excluding a composite fuzzy band of the Cytophaga-Flavobacterium group. The different methods gave similar distributions of taxa at the genus level and higher. However, the match at the species level among the methods was poor, and only one species was identified by all three methods. Consequently, all three methods identified unique subsets of bacterial species, amounting to a total richness of 97 operational taxonomic units in the experimental system. The confidence in the results was, however, dependent on the current precision of the phylogenetic determination and definition of the species. Bacterial consumers of RDOM in the studied estuary were primarily both cultivatable and uncultivable taxa of the Cytophaga-Flavobacterium group, a concordant result among the methods applied. Culture-independent methods also suggested several not-yet-cultivated beta-proteobacteria to be RDOM consumers.

Limited resolution of 16S rDNA DGGE caused by melting properties and closely related DNA sequences.

The phylogenetic affiliation of 91 operational taxonomic units, randomly sampled from three aquatic microcosm experiments, was investigated by two PCR based and one culture dependent method. The occurrence of multiple melting domains and poor coupling between Tm and DGGE retardation was demonstrated to cause poor resolution at the species level in PCR-DGGE analysis of microbial communities. We also showed that the problem of multiple melting domains was particularly prone for brackish water bacterioplankton in the Flavobacterium genus, providing characteristic band morphology for this genus. Banding patterns from DGGE analysis may therefore be misinterpreted in terms of the species richness in natural bacterial communities, when using commonly applied universal primers.

Salinity as a structuring factor for the composition and performance of bacterioplankton degrading riverine DOC.

Abstract The impact of salinity on the composition and functional performance (biomass production, growth efficiency and growth rates) of bacterial communities was investigated using batch cultures growing on dissolved organic carbon from a river draining into the Northern Baltic Sea. The cultures were adjusted to riverine or estuarine salinity levels and inoculated with bacteria from these two environments. Bacterial growth efficiencies differed in response to salinity and the origin of the inoculum. When salinity was adjusted to correspond to the salinity at the site where the inoculum was retrieved, growth efficiency was relatively high (11.5+/-2.6%). However, when bacteria were confronted with a shift in salinity, growth efficiency was lower (7.5+/-2.0%) and more of the utilized carbon was respired. In contrast, growth rates were higher when bacteria were exposed to a change in salinity. The composition of the bacterial communities developing in the batch cultures differed, as shown by 16S rDNA DGGE, depending on the origin of the inoculum and salinity. Reverse and direct DNA-DNA hybridization revealed salinity optima in the growth of specific bacterial strains as well as broader phylogenetic groups. Strains belonging to the alpha- and beta-Proteobacteria, Actinobacteria and gamma-Proteobacteria other than the genus Pseudomonas showed higher relative abundance under freshwater conditions, whereas strains of the genus Pseudomonas and the Cytophaga-Flavobacterium-Bacteroides group were favored by estuarine conditions. Generally, our results demonstrate functional changes associated with changes in community composition. We suggest that even moderate changes in salinity affect bacterial community composition, which subsequently leads to altered growth characteristics.

Phylogeny of culturable estuarine bacteria catabolizing riverine organic matter in the northern Baltic Sea.

The objective of our study was to isolate and determine the phylogenetic affiliation of culturable estuarine bacteria capable of catabolizing riverine dissolved organic matter (RDOM) under laboratory conditions. Additions of RDOM consistently promoted the growth of estuarine bacteria in carbon-limited dilution cultures, with seasonal variation in growth rates and yields. At least 42 different taxa were culturable on solid agar media and, according to quantitative DNA-DNA hybridizations, constituted 32 to 89% of the total bacterial number in the enriched treatments. Five species in the Cytophaga-Flexibacter-Bacteroides group and one in the gamma-proteobacteria phylogenetic group (Marinomonas sp.) were numerically dominant during the stationary phase of the RDOM-enriched dilution cultures but not in the control cultures. Four of the isolates in Cytophaga-Flexibacter-Bacteroides group were putatively affiliated with the genus FLAVOBACTERIUM: All dominating isolates were determined to be new species based on comparison to the current databases. The same group of species dominated independently of the season investigated, suggesting a low diversity of bacteria catabolizing RDOM in the estuary. It also suggested a broad tolerance of the dominating species to seasonal variation in hydrography, chemistry, and competition with other species. Taken together, our results suggest that a limited group of bacteria, mainly in the Flavobacterium genus, played an important role in introducing new energy and carbon to the marine system in the northern Baltic Sea.