| 1. |
- Broman, Elias, 1985-, et al.
(författare)
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Eutrophication induced early stage hypoxic ‘dead zone’ sediment releases nitrate and stimulates growth of archaea
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the Baltic Sea, two annual algal blooms occur in spring and summer. The bloom intensity is determined by nutrient concentrations in the water column, while the period depends on weather conditions. During the course of the bloom, dead cells sink to the sediment where their degradation consumes oxygen to create hypoxic zones (< 2 mg/L dissolved oxygen, referred to as ‘dead zones’). These zones prevent the establishment of benthic communities and result in fish mortality. The aim of the study was to determine how the sediment chemistry and microbial community composition changed due to phytoplankton biomass degradation by adding cyanobacterial or diatom biomass to sediment cores from an all-year round oxic coastal Baltic Sea bay. After biomass addition, some typical anaerobic microbial processes were observed such as a decrease in NO2-+NO3- in the sediment surface (0-1 cm) and iron in the underlying layer (1-2 cm). In addition, an increase in NO2-+NO3- was observed in the water phase in all incubations (including controls without addition of phytoplankton biomass). The combination of NO2-+NO3- diffusion from the sediment plus nitrification of the available NH4+ could not account for this increase. Potential nitrogen sources that could at least partially explain this discrepancy included microbial nitrogen fixation and cycling of nitrogen compounds from deeper layers of the sediment. Based on 16S rRNA gene sequences, the addition of diatom biomass caused minor changes in the relative abundance of microbial community members while cyanobacterial biomass caused a large increase in ferrous iron-oxidizing archaea. Considering that OTUs sharing lineages with acidophilic microorganisms were present, it was suggested that specific niches developed in sediment microenvironments. These findings highlight the importance of nitrogen cycling in oxic sediments and early microbial community changes in the sediment surface due to sinking phytoplankton before major hypoxia events occur. The release of nitrate into the water could potentially enhance algal blooms and facilitate the development of ‘dead zones’.
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| 2. |
- Broman, Elias, 1985-, et al.
(författare)
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Spring and Late Summer Phytoplankton Biomass Impact on the Coastal Sediment Microbial Community Structure
- 2019
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Ingår i: Microbial Ecology. - : Springer. - 0095-3628 .- 1432-184X. ; 77:2, s. 288-303
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Tidskriftsartikel (refereegranskat)abstract
- Two annual Baltic Sea phytoplankton blooms occur in spring and summer. The bloom intensity is determined by nutrient concentrations in the water, while the period depends on weather conditions. During the course of the bloom, dead cells sink to the sediment where their degradation consumes oxygen to create hypoxic zones (< 2 mg/L dissolved oxygen). These zones prevent the establishment of benthic communities and may result in fish mortality. The aim of the study was to determine how the spring and autumn sediment chemistry and microbial community composition changed due to degradation of diatom or cyanobacterial biomass, respectively. Results from incubation of sediment cores showed some typical anaerobic microbial processes after biomass addition such as a decrease in NO2− + NO3− in the sediment surface (0–1 cm) and iron in the underlying layer (1–2 cm). In addition, an increase in NO2− + NO3− was observed in the overlying benthic water in all amended and control incubations. The combination of NO2− + NO3− diffusion plus nitrification could not account for this increase. Based on 16S rRNA gene sequences, the addition of cyanobacterial biomass during autumn caused a large increase in ferrous iron-oxidizing archaea while diatom biomass amendment during spring caused minor changes in the microbial community. Considering that OTUs sharing lineages with acidophilic microorganisms had a high relative abundance during autumn, it was suggested that specific niches developed in sediment microenvironments. These findings highlight the importance of nitrogen cycling and early microbial community changes in the sediment due to sinking phytoplankton before potential hypoxia occurs.
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| 3. |
- Chapman, Joanne R., et al.
(författare)
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A Panel of Stably Expressed Reference Genes for Real-Time qPCR Gene Expression Studies of Mallards (Anas platyrhynchos)
- 2016
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- Determining which reference genes have the highest stability, and are therefore appropriate for normalising data, is a crucial step in the design of real-time quantitative PCR (qPCR) gene expression studies. This is particularly warranted in non-model and ecologically important species for which appropriate reference genes are lacking, such as the mallard-a key reservoir of many diseases with relevance for human and livestock health. Previous studies assessing gene expression changes as a consequence of infection in mallards have nearly universally used beta-actin and/or GAPDH as reference genes without confirming their suitability as normalisers. The use of reference genes at random, without regard for stability of expression across treatment groups, can result in erroneous interpretation of data. Here, eleven putative reference genes for use in gene expression studies of the mallard were evaluated, across six different tissues, using a low pathogenic avian influenza A virus infection model. Tissue type influenced the selection of reference genes, whereby different genes were stable in blood, spleen, lung, gastrointestinal tract and colon. beta-actin and GAPDH generally displayed low stability and are therefore inappropriate reference genes in many cases. The use of different algorithms (GeNorm and NormFinder) affected stability rankings, but for both algorithms it was possible to find a combination of two stable reference genes with which to normalise qPCR data in mallards. These results highlight the importance of validating the choice of normalising reference genes before conducting gene expression studies in ducks. The fact that nearly all previous studies of the influence of pathogen infection on mallard gene expression have used a single, non-validated reference gene is problematic. The toolkit of putative reference genes provided here offers a solid foundation for future studies of gene expression in mallards and other waterfowl.
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| 4. |
- Christel, Stephan, et al.
(författare)
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Acidithiobacillus ferrivorans SS3 presents little RNA transcript response related to cold stress during growth at 8 A degrees C suggesting it is a eurypsychrophile
- 2016
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Ingår i: Extremophiles. - : Springer Science and Business Media LLC. - 1431-0651 .- 1433-4909. ; 20:6, s. 903-913
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Tidskriftsartikel (refereegranskat)abstract
- Acidithiobacillus ferrivorans is an acidophilic bacterium that represents a substantial proportion of the microbial community in a low temperature mining waste stream. Due to its ability to grow at temperatures below 15 A degrees C, it has previously been classified as 'psychrotolerant'. Low temperature-adapted microorganisms have strategies to grow at cold temperatures such as the production of cold acclimation proteins, DEAD/DEAH box helicases, and compatible solutes plus increasing their cellular membrane fluidity. However, little is known about At. ferrivorans adaptation strategies employed during culture at its temperature extremes. In this study, we report the transcriptomic response of At. ferrivorans SS3 to culture at 8 A degrees C compared to 20 A degrees C. Analysis revealed 373 differentially expressed genes of which, the majority were of unknown function. Only few changes in transcript counts of genes previously described to be cold adaptation genes were detected. Instead, cells cultured at cold (8 A degrees C) altered the expression of a wide range of genes ascribed to functions in transcription, translation, and energy production. It is, therefore, suggested that a temperature of 8 A degrees C imposed little cold stress on At. ferrivorans, underlining its adaptation to growth in the cold as well as suggesting it should be classified as a 'eurypsychrophile'.
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| 5. |
- Christel, Stephan, et al.
(författare)
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RNA transcript sequencing reveals inorganic sulfur compound oxidation pathways in the acidophile Acidithiobacillus ferrivorans
- 2016
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Ingår i: FEMS Microbiology Letters. - : Oxford University Press (OUP). - 0378-1097 .- 1574-6968. ; 363:7
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Tidskriftsartikel (refereegranskat)abstract
- Acidithiobacillus ferrivorans is an acidophile implicated in low-temperature biomining for the recovery of metals from sulfide minerals. Acidithiobacillus ferrivorans obtains its energy from the oxidation of inorganic sulfur compounds, and genes encoding several alternative pathways have been identified. Next-generation sequencing of At. ferrivorans RNA transcripts identified the genes coding for metabolic and electron transport proteins for energy conservation from tetrathionate as electron donor. RNA transcripts suggested that tetrathionate was hydrolyzed by the tetH1 gene product to form thiosulfate, elemental sulfur and sulfate. Despite two of the genes being truncated, RNA transcripts for the SoxXYZAB complex had higher levels than for thiosulfate quinone oxidoreductase (doxDA genes). However, a lack of heme-binding sites in soxX suggested that DoxDA was responsible for thiosulfate metabolism. Higher RNA transcript counts also suggested that elemental sulfur was metabolized by heterodisulfide reductase (hdr genes) rather than sulfur oxygenase reductase (sor). The sulfite produced as a product of heterodisulfide reductase was suggested to be oxidized by a pathway involving the sat gene product or abiotically react with elemental sulfur to form thiosulfate. Finally, several electron transport complexes were involved in energy conservation. This study has elucidated the previously unknown At. ferrivorans tetrathionate metabolic pathway that is important in biomining.
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| 6. |
- Fridlund, Jimmy, et al.
(författare)
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A microbiological method for determining serum levels of broad spectrum β-lactam antibiotics in critically ill patients
- 2016
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Ingår i: Journal of Microbiological Methods. - : Elsevier BV. - 0167-7012 .- 1872-8359. ; 129, s. 23-27
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Tidskriftsartikel (refereegranskat)abstract
- Background Recent studies show that suboptimal blood levels of β-lactam antibiotics are present in intensive care unit (ICU) patients. A common reference method for assessing drug concentrations is liquid chromatography coupled with mass-spectrometry (LC-MS) which is highly accurate but rarely available outside reference centres. Thus, our aim was to develop a microbiological method for monitoring β-lactam antibiotic serum levels which could be used at any hospital with a microbiological laboratory. Methods The method was developed as a 96-well broth microdilution format to assess the concentrations of cefotaxime (CTX), meropenem (MER), and piperacillin (PIP). Patient serum containing antibiotics were diluted in suspensions of bacteria with known minimal inhibitory concentrations (MICs). Serum antibiotic concentrations were calculated by dividing the MIC with the dilution factor at which the serum inhibited growth of the bacterial suspension. Serum (n = 88) from ICU patients at four hospitals in south-east Sweden were analysed and compared to LC-MS analysis. Results The overall accuracy and precision for spiked samples and patient samples was within the pre-set target of ± 20.0% for all drugs. There was a significant correlation between the microbiological assay and LC-MS for the patient samples (CTX: r = 0.86, n = 31; MER: r = 0.96, n = 11; PIP: r = 0.88, n = 39) and the agreement around the clinical cut-off for CTX (4.0 mg/l), MER (2.0 mg/l) and PIP (16.0 mg/l) was 90%, 100% and 87%, respectively. Conclusion The microbiological method has a performance for determination of serum levels of meropenem, piperacillin and cefotaxime suitable for clinical use. It is an inexpensive method applicable in any microbiology laboratory.
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| 7. |
- Nilsson, Emelie, et al.
(författare)
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Genomic and Seasonal Variations among Aquatic Phages Infecting the Baltic Sea Gammaproteobacterium Rheinheimera sp. Strain BAL341
- 2019
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Ingår i: Applied and Environmental Microbiology. - : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 85:18, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge in aquatic virology has been greatly improved by culture-independent methods, yet there is still a critical need for isolating novel phages to identify the large proportion of "unknowns" that dominate metagenomes and for detailed analyses of phage-host interactions. Here, 54 phages infecting Rheinheimem sp. strain BAL341 (Gammaproteobacteria) were isolated from Baltic Sea seawater and characterized through genome content analysis and comparative genomics. The phages showed a myovirus-like morphology and belonged to a novel genus, for which we propose the name Barbavirus. All phages had similar genome sizes and numbers of genes (80 to 84 kb; 134 to 145 genes), and based on average nucleotide identity and genome BLAST distance phylogeny, the phages were divided into five species. The phages possessed several genes involved in metabolic processes and host signaling, such as genes encoding ribonucleotide reductase and thymidylate synthase, phoH, and rnazG. One species had additional metabolic genes involved in pyridine nucleotide salvage, possibly providing a fitness advantage by further increasing the phages' replication efficiency. Recruitment of viral metagenomic reads (25 Baltic Sea viral metagenomes from 2012 to 2015) to the phage genomes showed pronounced seasonal variations, with increased relative abundances of barba phages in August and September synchronized with peaks in host abundances, as shown by 16S rRNA gene amplicon sequencing. Overall, this study provides detailed information regarding genetic diversity, phage-host interactions, and temporal dynamics of an ecologically important aquatic phage-host system. IMPORTANCE Phages are important in aquatic ecosystems as they influence their microbial hosts through lysis, gene transfer, transcriptional regulation, and expression of phage metabolic genes. Still, there is limited knowledge of how phages interact with their hosts, especially at fine scales. Here, a Rheinheimera phage-host system constituting highly similar phages infecting one host strain is presented. This relatively limited diversity has previously been seen only when smaller numbers of phages have been isolated and points toward ecological constraints affecting the Rheinheimera phage diversity. The variation of metabolic genes among the species points toward various fitness advantages, opening up possibilities for future hypothesis testing. Phage-host dynamics monitored over several years point toward recurring "kill-the-winner" oscillations and an ecological niche fulfilled by this system in the Baltic Sea. Identifying and quantifying ecological dynamics of such phage-host model systems in situ allow us to understand and study the influence of phages on aquatic ecosystems.
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