Cyanolab publications in September/October 2016

In September and October 2016 Cyanolab contributed to five publications.

Research on CRISPR RNA endonucleases: In our article „Structural constraints and enzymatic promiscuity in the Cas6-dependent generation of crRNAs“ in Nucleic Acids Research we investigated two CRISPR-associated RNA endonucleases of the Cas6 family. Small RNA molecules generated by the activity of Cas6 enzymes are an essential element of all CRISPR-Cas systems in the recognition of invading phage DNA or other nucleic acids. However, many bacteria and archaea possess multiple systems and several Cas6 endonucleases. It is poorly understood what makes these enzymes able to keep their substrates apart from each other. We found that the enzymes Cas6-1 (Slr7014) and Cas6-2a (Slr7068) can, despite their sequence identity of only 16.5 %, recognize the respective non-cognate substrate in vitro but not in vivo. We further found that adjacent spacer sequences can interfere with the formation of the short hairpin element within the substrate RNA that is required for proper recognition. This work was supported by the German Research Foundation (DFG) program FOR1680 “Unravelling the Prokaryotic Immune System” and is a joint publication with the group of Rolf Backofen.

Two articles dealt with the regulation of gene expression in cyanobacteria: In “Awakening of a dormant cyanobacterium from nitrogen chlorosis reveals a genetically determined program” in Current Biology the genetic program is described that governs the awakening of a dormant bacterium from nitrogen chlorosis back to photosynthetically active life. This work was performed in collaboration with partners in Germany, the Czech Republic and Japan, led by Karl Forchhammer at the Institute of Microbiology at the University of Tübingen. The results have wide-ranging implications for the understanding of bacterial persistence and cellular aging. More information can be found also here.
In “CyAbrB2 contributes to the transcriptional regulation of low CO2 acclimation in Synechocystis sp. PCC 6803”, which appeared in Plant and Cell Physiology we studied the function of the transcriptional factor cyAbrB2 in the adjustment of primary carbon and nitrogen metabolism to photosynthetic activity under fluctuating environmental conditions.

Two publications targeted the adaptation of microorganisms to the marine environment: In “Trimethylated homoserine functions as the major compatible solute in the globally significant oceanic cyanobacterium Trichodesmium” in PNAS the chemical compound was identified and the biosynthetic pathway leading to it elucidated that assures robust survival under the osmotically harsh high salinity within the marine environment. Globally, substantial amounts of organic carbon are stored in this compound, homoserine betaine, as it contains three methyl groups and occurs in high intracellular concentrations. Thus, its sudden release during the demise of high-density surface blooms of Trichodesmium will impact the marine microbial community. This work was performed in collaboration with partners in Germany and Israel and was led by Martin Hagemann at the Life Sciences Institute of the University of Rostock. More (in German) can be found also here.

In our article „mdRNAseq analysis of marine microbial communities from the northern Red Sea”, which was published in Scientific Reports, we have employed Differential RNA-Seq to analyze the primary transcriptomes of a complex marine microbiome sample. This technique, not previously used for metatranscriptomics, is powerful for the simultaneous identification of transcriptional start sites (i.e., the suite of active promoters) and the analysis of gene expression at community-wide scale. We identified promoters active in situ for five different pico-planktonic organisms genera belonging to the three domains of life (the SAR11 clade of Alphaproteobacteria, Synechococcus cyanobacteria, Euryarchaeota, Thaumarchaeota, and Micromonas as an example for picoeukaryotic algae), showing the applicability of this approach to highly diverse microbial communities.