Phage susceptibility to a minimal, modular synthetic CRISPR-Cas system in Pseudomonas aeruginosa is nutrient dependent

CRISPR-Cas systems can provide adaptive, heritable immunity to their prokaryotic hosts against invading genetic material such as phages. It is clear that the importance of acquiring CRISPR-Cas immunity to anti-phage defence varies across environments, but it is less clear if and how this varies across different phages. To explore this, we created a synthetic, modular version of the type I-F CRISPR-Cas system of Pseudomonas aeruginosa. We used this synthetic system to test CRISPR-Cas interference against a panel of 13 diverse phages using engineered phage-targeting spacers. We observed complete protection against eight of these phages, both lytic and lysogenic and with a range of infectivity profiles. However, for two phages CRISPR-Cas interference was only partially protective in high nutrient conditions, yet completely protective in low nutrient conditions. This work demonstrates that nutrient conditions modulate the strength of CRISPR-Cas immunity and highlights the importance of environmental conditions when screening defence systems for their efficacy against various phages.