Finally, after 4 years of work with dozens of cultivations and millions of sequenced reads, our paper about a CRISPRi library in the model cyanobacterium Synechocystis was published in Nature Communications. What is this story about? Cyanobacteria are promising hosts for biotech production of (fine) chemicals. They are particularly interesting because they can grow solely on CO2 and sunlight. However, the productivities are low, the implemented pathways often instable, and the adaptation to varying amounts of light or CO2 not fully understood. Our group created a ’library’ (a mixed pool) of thousands of mutants, each one equipped qith a CRISPR based gene repression system repressing one gene at a time. By cultivating this pool of mutants under low light, high light, and a lactate production condition, better adapted mutants were enriched over time, and worse adapted mutants depleted. By these means we were able to find a handful of genes improving growth, acid tolerance, or lactate productivity.