PT - JOURNAL ARTICLE AU - Xin-Ran Lan AU - Zhi-Ling Liu AU - Deng-Ke Niu TI - Bacterial CRISPR abundance jumps up at around 45°C AID - 10.1101/2021.05.25.445389 DP - 2021 Jan 01 TA - bioRxiv PG - 2021.05.25.445389 4099 - http://biorxiv.org/content/early/2021/05/25/2021.05.25.445389.short 4100 - http://biorxiv.org/content/early/2021/05/25/2021.05.25.445389.full AB - Although functioning for adaptive immunity, CRISPR-Cas systems are present in only 40% of bacterial genomes. In this study, we observed an abrupt transition of bacterial CRISPR abundance at around 45°C. Phylogenetic comparative analysis showed that the CRISPR abundance correlates with growth temperature only in temperature ranges around 45°C. The existence of a saltation point indicates that temperature unlikely determines the thermal distribution of CRISPR-Cas systems directly. We put forward a novel hypothesis referring to the predator effect on immune function previously observed in birds. At around 45°C, an abrupt decrease of cellular predators rapidly decreases bacterial mortality resulting from cellular predator grazing. Consequently, the relative contribution of viral lysis in bacterial mortality increases rapidly with temperature; mutants allocating more resources to the adaptive immunity would be favored. In temperature ranges where the abundance of cellular predators does not change with temperature, the temperature effect on CRISPR abundance would be negligible.Competing Interest StatementThe authors have declared no competing interest.