The ability to grow on solid culture medium is a pre-requisite for a successful microbial genetic model organism. Skeletonema marinoi, a bloom-forming, planktonic marine microalga, is widely used in ecological, evolutionary and population genetics studies. We have tested and confirmed the ability of this common organism to grow on solid culture medium (agar) under experimentally manipulated conditions. We established a protocol for quantifying growth characteristics – length of lag phase, growth rate, maximum biomass yield – on agar medium. The procedure was tested under experimental
treatments and the resulting growth changes correlated with those observed in standard liquid culture. The ability to grow on solid medium broadens the use of S. marinoi as a molecular model, where agar is routinely used for various purposes (growth, selection, storage); and the possibility to quantify colony growth opens the way for high throughput, automated, or semi-automated phenotyping solutions.
Kourtchenko O, Rajala T, Godhe A (2018) Growth of a common planktonic diatom quantified using solid medium culturing. Scientific Reports. 8:9757 DOI:10.1038/s41598-018-28129-y.
Rickard Stenow defended his MSc thesis with distinction!
DIATOM RESTING STAGES ASSIMILATE NITROGEN IN ANOXIC CONDITIONS
Diatoms can survive for a century buried in oceanic sediment, during dark and anoxic conditions. It’s not previously known if the cells preform respiratory and/or assimilatory processes while they are resting. If they do it could have implications for the global nutrient circulation. Diatoms have been documented to perform dissimilatory nitrate reduction to ammonium (DNRA) using internal nitrate storages. In this project nitrogen assimilation, carbon assimilation and nitrogen driven respiration been investigated in resting cells of Skeletonema marinoi and Chaetoceros socialis. This was performed during dark anoxic conditions with either nitrate or ammonium as the available nitrogen source. This was done using stable isotopes during a 63 days long incubation period, by analyzing nitrogen and carbon redistribution, changes in POC/PON and survival rate of the resting cells. The assimilatory and dissimilatory processes were investigated using Secondary Ion Mass Spectrometry (SIMS). Nitrogen assimilation was significant in both treatments. No significant carbon uptake was detected. Denitrification was recorded in the nitrate treatment, no obvious electron acceptor was identified in the ammonium treatment to enable the assimilation of nitrogen. One of the S. marinoi strains showed significantly higher nitrogen assimilation in the nitrate treatment compared to the ammonium treatment. C. socialis did not survive the inoculation. Survival varied with S. marinoi strain, but overall survival was higher in the nitrate treatment. The inoculation was not axenic, and this could have impacted the results. This is the first study indicating nitrogen assimilation in resting diatoms. This will change our understanding of both the global nitrogen cycle and the dynamics controlling diatoms evolutionary processes.
The anchoring effect – long-term dormancy and genetic population structure
Lisa Sundqvist, Anna Godhe, Per R. Jonsson, Josefin Sefbom
Understanding the genetic structure of populations is key to revealing past and present demographic and evolutionary processes in a species. In the past decade high genetic differentiation has been observed in many microbial species challenging the previous view of cosmopolitan distribution. Populations have displayed high genetic differentiation, even at small spatial scales, despite apparent high dispersal. Numerous species of microalgae have a life-history strategy that includes a long-term resting stage, which can accumulate in sediments and serve as refuge during adverse conditions. It is presently unclear how these seed banks affect the genetic structure of populations in aquatic environments. Here we provide a conceptual framework, using a simple model, to show that long-term resting stages have an anchoring effect on populations leading to increased genetic diversity and population differentiation in the presence of gene flow. The outcome that species with resting stages have a higher degree of genetic differentiation compared to species without, is supported by empirical data obtained from a systematic literature review. With this work we propose that seed banks in aquatic microalgae play an important role in the contradicting patterns of gene flow, and ultimately the adaptive potential and population dynamics in species with long-term resting stages.
On November 24 Susanna Gross will defend her thesis ”Phenotypic and Genotypic responses in the planktonic diatom Skeletonema marinoi – Effects of Natural Processes and Anthropogenic Stressors”
Opponent is Dr Akira Kuwata from Tohoku national Fisheries Research Institute, Sendai, Japan
Many have been puzzled about large intra-specific genetic differentiation over small spatial scales in aquatic protists without any apparent dispersal barriers. We did a transplant experiment with two populations of common diatom from a fjord and the open sea and we found that both populations displayed significant higher fitness in their native water and they were also much more competitive in their native water compared to the foreign water. Read more on Environ Microbiol doi:10.1111/1462-2920.13372
Jonathan was born in December and has kept Sussi from the lab since then. However, after the summer she is back again!