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The filamentous green alga Spirogyra pratensis is a member of the class Zygnemophyceae, also called conjugating green algae. The genus Spirogyra comprises 531 widely distributed, freshwater species. S. pratensis is characterized by unbranched filaments formed by cells longer than broad, with one or more typical helical chloroplasts. Spirogyra filaments can attach to solid substrates with the help of rhizoids. Like many Zygnemophyceae algae, Spirogyra also produces a sheath of mucilage. Recent phylogenomic work of Hess et al. (2022) has shown that the genus Spirogyra is separated from the order of Zygnematales and forms the sister clade of the Desmidiales. These findings have led to the proposition of the new order of “Spirogyrales”, which currently contains the genera Spirogyra and Sirogonium both belonging to the family of Spirogyraceae.

S. pratensis strain MZCH#10213 has been selected from the Microalgae and Zygnemophyceae Collection Hamburg for sequencing and elucidation of its genomic landscape because it is easy to grow and offers the possibility to control its life cycle under in vitro conditions. When cultivated on agar, conjugation channels (scalariform and lateral) followed by the formation of zygospores can easily be observed. S. pratensis MZCH#10213 is an emerging model system, easy to cultivate using liquid or solid media (C- or WHM-medium). Methods of transient genetic transformation are currently optimized. [Image credit: Klaus von Schwartzenberg]

The iron-containing porphyrin heme is of high interest for the food industry for the production of artificial meat as well as for medical applications, e.g. for anemia treatment. Recently, the biotechnological platform strain Corynebacterium glutamicum has emerged as a promising host for animal-free heme production. Beyond engineering of complex heme biosynthetic pathways, improving heme export offers significant yet untapped potential for enhancing production strains. In this study, a growth-coupled biosensor was designed to impose a selection pressure on the increased expression of the hrtBA operon encoding an ABC-type heme exporter in C. glutamicum. For this purpose, the promoter region PhrtB was replaced with that of the growth-regulating genes pfkA (phosphofructokinase) and aceE (pyruvate dehydrogenase), creating biosensor strains with a selection pressure for hrtBA activation. Resulting sensor strains were used for plate-based selections and for a repetitive batch f(luorescent)ALE using a robotics platform. Genome sequencing of isolated clones featuring increased hrtBA expression revealed three distinct mutational hotspots: (i) chrS, (ii) chrA, and (iii) cydD. Mutations in the genes of the ChrSA two-component system, which regulates hrtBA in response to heme levels, were identified as a promising target to enhance export activity. Furthermore, causal mutations within cydD, encoding an ABC-transporter essential for cytochrome bd oxidase assembly, were confirmed by the construction of a deletion mutant, which showed strongly increased hrtBA expression as well as increased cellular heme levels. These results further support the proposed role of CydDC as a heme transporter. Mutations identified in this study therefore underline the potential of biosensor-based growth coupling and provide promising engineering targets to improve microbial heme production.

Pangenome of Camellia sinensis

This ARC is based on the research of Mönchgesang et al. 2016, who performed a metabolite profiling of 19 Arabidopsis thaliana accessions. The natural variability of root metabolic patterns was analyzed between different accessions, with the result that plant-to-plant variability is greater than natural variation between accessions and non-biological variation between experimental batches.