Ragnar Johannsson

Ragnar Johannsson
Marine and Freshwater Research Institute | MRI · Aquaculture

PhD

About

57
Publications
15,629
Reads
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790
Citations
Citations since 2017
11 Research Items
303 Citations
2017201820192020202120222023010203040506070
2017201820192020202120222023010203040506070
2017201820192020202120222023010203040506070
2017201820192020202120222023010203040506070
Additional affiliations
January 2017 - present
Marine and Freshwater Institute of Iceland
Position
  • Head of Department
August 1994 - June 2003
Technological Institute of Iceland
Technological Institute of Iceland
Position
  • Head of Department

Publications

Publications (57)
Article
Full-text available
Marine sponges host bacterial symbionts with biotechnological potential, yet isolation of true sponge symbionts remains difficult due to their host dependency. Moreover, attempts to grow sponges for their pharmacologically-active compounds outside of their habitat often results in a shift of their microbial community. In this study we evaluate suit...
Article
Full-text available
The marine sponge Halichondria panicea inhabits coastal areas around the globe and is a widely studied sponge species in terms of its biology, yet the ecological functions of its dominant bacterial symbiont “Candidatus Halichondribacter symbioticus” remain unknown. Here, we present the draft genome of “Ca. H. symbioticus” HS1 (2.8 Mbp, ca. 87.6 % g...
Article
Full-text available
A Gram-stain-negative, motile, mesophilic, aerobic, rod-shaped bacterium, designated Hp12T, was isolated from a marine sponge in the intertidal zone off the coast of Seltjarnarnes (64° 16' N 22° 00' W), Iceland. Strain Hp12T grew optimally at 20-22 °C, at pH 7-8 and in the presence of 1-2 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene s...
Article
Full-text available
The furan fatty acid (F-fatty acid) content was determined in different marine sources as well as in commercially available marine oil products that claim to be health promoting. The five F-fatty acids typically representing the majority of F-fatty acids in fish, 9M5 (9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid), 9D5 (9-(3-dimethyl-5-pentylfuran-...
Article
ABSTRACT: Genetic interactions (i.e. hybridization) between wild and escaped Atlantic salmon Salmo salar from aquaculture operations have been widely documented, yet the ability to incorporate predictions of risk into aquaculture siting advice has been limited. Here we demonstrate a model-based approach to assessing these potential genetic interact...
Article
Full-text available
Marine sponges can harbour diverse bacteria that contribute to host metabolism and defence. Identifying these stable members of sponge bacterial communities remains a necessary step in understanding their ecological roles and underlying co-evolutionary processes. In this study, we applied high-throughput sequencing of 16S rRNA gene amplicons, ribos...
Technical Report
Full-text available
The West Nordic region holds promising opportunities to improve utilisation, sustainability and value from its biological resources. The region’s major bioresources available for biorefining and biotechnological applications are the focus of this report. It identifies valuable ingredients in the different resources, processing technologies which ar...
Article
Background Aquaculture represents a solution to the future world demand for healthy protein while challenges that require urgent solutions are emerging in feed production, such as the rising costs of feed protein and massive imports. From a European perspective, a large proportion of the protein demand is met with imported protein. This article wil...
Article
Full-text available
The marine genus Pseudoalteromonas is known for its versatile biotechnological potential with respect to the production of antimicrobials and enzymes of industrial interest. We have sequenced the genomes of three Pseudoalteromonas sp. strains isolated from different deep sea sponges on the Illumina MiSeq platform. The isolates have been screened fo...
Data
Native enzyme assays for β‐galactosidase and protease activity were carried out with aliquots of overnight cultures from the respective Pseudoalteromonas sp. isolates. β‐
Technical Report
Full-text available
There is an increasing demand for dairy and meat products on the global market. In the Nordic and Baltic Sea Region, there is already a considerable production of these products, which is expected to increase. At present, the production of dairy and meat products relies on large quantities of imported protein rich feed in the form of soy products f...
Article
Full-text available
Increased demand of fish in combination with overexploitation of the fish stocks of the oceans has led to an increased production of fish through aquaculture. Today, fishmeal is the main protein source in fish feed for most aquaculture species. However, fishmeal is soon expected to fall short of demand as its production is associated with environme...
Article
Full-text available
The aim was to develop a Quality Index Method (QIM) scheme for fresh tilapia fillets and evaluate the scheme in a shelf life study. Farmed tilapia fillets were stored at 1 and −1°C for up to 20 days, and changes during storage were observed with sensory evaluation using the QIM scheme and General Descriptive Analysis (GDA), total viable counts (TVC...
Data
Full-text available
Disclaimer: This is a version of an unedited manuscript that has been accepted for publication. As a service to authors and researchers we are providing this version of the accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proof will be undertaken on this manuscript before final publication of the Version of Record (Vo...
Article
A soft thermo-reversible protein gel was studied with respect to failure. Flow curves recorded at constant shear-rates revealed a dynamic yield stress σy, seen as a stress plateau below about 10 s−1. When a shear stress below σy was applied to fractured gels, they reformed after a time that increased with increasing stress and diverged at σy. Appli...
Article
Full-text available
Optimal packaging and storage conditions for fresh tilapia fillets were established by evaluating sensory and microbiological changes, as well as monitoring physicochemical properties. Nile tilapia (Oreochromis niloticus) farmed in recirculation aquaculture system was filleted, deskinned, and packaged in air and 50% CO2/50% N2 prior to chilling and...
Article
Functional and biochemical properties of fish protein hydrolysates (FPH) from blue whiting (BW) were studied. FPH (2.5%, 5%, 10%, and 15% degree of hydrolysis [DH]) were made from isolated proteins from headed and gutted BW with Alcalase 2.4 L. The properties of dried BW mince and protein isolate compared to 4 reference proteins (soy and milk prote...
Article
Fish protein isolates (FPI) from cod muscle were studied at pH 9 and 11. Thermo-reversible gels, stable at and below room temperature could be produced at both pH values. Application of low shear stress to the gels led to an initial elastic response followed by a power-law deformation (creep) at both pH. Above a critical shear stress gels fractured...
Article
Cod (Gadus Morhua) muscle proteins were solubilized using alkaline treatment of the muscle. Solutions of similar protein composition were obtained between pH 10.5 and 12.0, however, pH > 11 was required for optimal yield. Addition of salt (up to 0.25 M NaCl) did not affect protein yield or composition. Light scattering showed that a significant fra...
Article
Myosin was extracted from Atlantic Cod (Gadus morhua) using different methods resulting in small aggregates of pure myosin. These aggregates consisted of between 8 and 20 myosin molecules and were relatively stable at low temperatures (T<20 °C) in dilute (C<5 g/L) solutions containing 0.5 M KCl in the pH range 6.0–8.0. At higher concentrations prec...
Chapter
Full-text available
There are promising opportunities in the upgrading of marine by-products and underutilized fish by using mild processing techniques to convert them into protein and peptide ingredients both to improve yield in traditional seafood and to be used as nutraceuticals or in functional foods. Mild techniques like pH shift, fermentation, enzymatic hydrolys...
Article
This study aims to evaluate the performances of the membrane processes during the treatment of blue whiting peptide hydrolysates. Ultrafiltration with high molecular weight cut-off (MWCO) can be used for the separation between peptides and non-hydrolyzed pro-teins. A membrane of MWCO 20 kDa was tested on hydrolysates containing 11.4 g of peptides p...
Article
The formation of a transient network by α,ω-sodium sulfonato polyisoprene (α,ω-NaPIPS) and α,ω-lithium sulfonato polystyrene (α,ω-LiPSS) in toluene is studied using static and dynamic light scattering and dynamic mechanical analysis. It is shown that at low concentrations aggregates are formed with increasing molar mass and polydispersity as the po...
Article
Solutions of alpha,omega-sodium sulfonatopolyisoprene (alpha,omega NaPIPS) in toluene are studied using static and dynamic light scattering and dynamic mechanical analysis. At concentrations above 4 g/L, which is well below the overlap concentration of the polymer chains (C*), a transient network is formed characterized by a plateau modulus at high...
Article
The application of the time-resolved fluorescence quenching method (TRFQ) to study the structure and aggregation behavior of nonionic surfactant polyoxyethylene(4)lauryl ether (C(12)E(4)) in reverse micellar systems is presented. Solutions of different concentrations in three nonpolar solvents (cyclohexane, n-decane, and n-dodecane), at different w...
Article
Full-text available
Time-resolved fluorescence (TRF) of fluorescent and quencher probe molecules has been used to investigate the dynamics, mean size and polydispersity of oil-in-water (o/w) droplet microemulsions stabilised by a range of alkyloply(oxyethylene glycol ether) non-ionic surfactants. Close to the low-temperature (solubilisation) phase boundary of the micr...
Article
Time-resolved phosphorescence and triplet absorption quenching measurements were made to monitor the cluster structure on approach of phase separation, by increasing temperature, for AOT microemulsion systems in the L2 reversed droplet phase. The frequency and the activation energy of the droplet fusion is determined at different droplet sizes, wit...
Article
The size and polydispersity of AOT water/oil microemulsions were measured by time-resolved fluorescence quenching. From the measured volume polydispersity the radius polydispersity was derived and calculated. An average polydispersity of 15.7% was obtained. No trends in polydispersity values at different droplet sizes or different solvent chain len...
Article
The kinetics of triplet-state diffusional deactivation in bicontinuous phases of nonionic and ionic water-oil-amphiphile systems has been studied. The reactants (probes and quenchers) have been situated both in water domains, both in oil domains, or each in a separate domain of the bicontinuous phase. It is found that the reaction kinetics depends...
Article
Kinetic models for the deactivation of excited species by quenching in clusters of micelles are presented and tested experimentally by measurement of phosphorescence deactivation in clusters of AOT-water reversed micelles having an H2O/AOT molar ratio of 12.5 in dodecane. Models were devised for a random walk of quenchers in compact clusters, in op...
Article
Full-text available
The kinetics of diffusion-controlled deactivation processes is strongly affected by confinement of the reacting species in a space kept at molecular dimensions in at least one direction. In globular micelles the confinement is in all three dimensions, and the well-known kinetics is determined by a first-order rate constant representing the frequenc...
Article
Full-text available
Time-resolved fluorescence and phosphorescence quenching measurements were made to determine the structure and dynamical behavior of micelles in oil-continuous microemulsions stabilized by aerosol OT, (AOT). In particular water/AOT/dodecane and water/AOT/isooctane systems were studied. It was found that reversed micelles, or water droplets stabiliz...
Article
Full-text available
Time-resolved fluorescence and phosphorescence quenching measurements were made to determine the structure and dynamical behavior of micelles in oil-continuous microemulsions stabilized by aerosol OT, (AOT). In particular water/AOT/dodecane and water/AOT/isooctane systems were studied. It was found that reversed micelles, or water droplets stabiliz...
Chapter
Full-text available
Time-resolved fluorescence and phosphorescence quenching measurements were made to determine the size, n c , of possible micellar clusters and the aggregation number, N agg, of micelles in oil-continuous microemulsions stabilized by aerosol OT (AOT). In particular, water/AOT/dodecane and water/AOT/isooctane systems were studied. The decay curves fo...
Article
Full-text available
The use of light scattering for the investigation of proteins, protein aggregates, viruses and even DNA molecules has become widespread during the last couple of decades1. Extensive measurements of the aggregation and gelation of miscellaneous proteins have been done, with globular, easily isolated food proteins getting the most attention. In compa...
Article
Full-text available
Inngangur Í erindinu er reynt að svara því hvernig líftaekni muni gagnast íslenskum matvaelaiðnaði tengdum landbúnaði. Segja má að líftaeknin geti komið við sögu á tveimur meginsviðum – Annars vegar erfðataekni til nota við kynbaetur og svo hins vegar nýting líftaeknilegra afurða sem ég kýs að kalla svo. Þar er um að raeða ensím sem nýtast á marga...
Article
Thesis (doctoral)--Uppsala University, 1993. Includes bibliographical references (p. 35-38).

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Projects

Project (1)
Archived project
BluePharmTrain is a multi-disciplinary alliance of 17 European academic and industrial partners working in collaboration to train young scientists in multi-disciplinary aspects of blue biotechnology. It has been funded as a Marie Curie Initial Training Network that started at 1 September 2013 and will run till 31 August 2017. The focus of the project is on using marine sponges for the development of new pharmaceuticals. Marine sponges have been long since recognised as the most prolific source in the marine environment, presenting more than 7,000 bioactive molecules with the number of bioactive compounds discovered still increasing every year. In addition, sponges are known to host extremely diverse microbial communities that may account for up to half of the sponge’s body mass. Hence, the development of methods to obtain significant quantities of sponge-derived bioactives will most likely have high impact on exploitation of the biosynthetic capacities of sponges and their microbes. BluePharmTrain has the following key objectives: - Establish routines for the isolation of sponge-specific microorganisms by integrating novel high-throughput cultivation strategies and state-of-the-art genomics and transcriptomics. - Establish sponge cell cultures of target species by translating ecology into technology. - Develop heterologous expression tools for sponge-derived bioactives. - In addition, we aim to provide a fundamental understanding of the sponge holobiont. http://www.benthis.eu/en/bluepharmtrain/About.htm