Bacterial CRISPR-Cas Abundance Increases Precipitously at Around 45°C: Linking Antivirus Immunity to Grazing Risk

Abstract

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.

Precipitous Increase of Bacterial CRISPR-Cas Abundance at Around 45°C

“…We thank Quan-Guo Zhang and Wen-Hong Deng for helpful discussions, Christine Pourcel and Pierre-Albert Charbit for technical support and the reviewers for helpful comments. This manuscript has been released as a Pre-Print at BioRxiv ( Lan et al, 2021 ).…”