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

Abstract

Although performing adaptive immunity, CRISPR-Cas systems are present in only 40% of bacterial genomes. We observed an abrupt increase of bacterial CRISPR-Cas abundance at around 45°C. Phylogenetic comparative analyses confirmed that the abundance correlates with growth temperature only at the temperature range around 45°C. From the literature, we noticed that the diversities of cellular predators (like protozoa, nematodes, and myxobacteria) have a steep decline at this temperature range. The grazing risk faced by bacteria reduces substantially at around 45°C and almost disappears above 60°C. We propose that viral lysis would become the dominating factor of bacterial mortality, and antivirus immunity has a higher priority at higher temperatures. In temperature ranges where the abundance of cellular predators does not change with temperature, the growth temperatures of bacteria would not significantly affect their CRISPR-Cas contents. The hypothesis predicts that bacteria should also be rich in CRISPR-Cas systems if they live in other extreme conditions inaccessible to grazing predators.

Investigating the Relationship between CRISPR-Cas Content and Growth Rate in Bacteria

“…Previous studies observed that bacterial CRISPR abundance is positively correlated with growth temperatures ( 16 – 19 ), with an abrupt jump at around 45°C ( 20 ). Here, we first compared the CRISPR-Cas contents and predicted minimal doubling times between thermophilic and mesophilic bacteria using the phylogenetic ANOVA method, phylANOVA ( 12 ).…”

Exploring the Frozen Armory: Antiphage Defense Systems in Cold-Adapted Bacteria with a Focus on CRISPR-Cas Systems

“…However, little is known about their occurrence and distribution in cold-adapted bacteria. Previous research has shown that temperature range is a strong predictor of CRISPR-Cas incidence, with increasing abundance observed with rising temperatures [36,37]. Yet, these studies have been limited by a small sample size of cold-adapted bacteria and analyzes of CRISPRs and Cas clusters individually.…”

Investigating the relationship between CRISPR-Cas content and growth rate in bacteria

“…Previous studies observed that bacterial CRISPR abundance is positively correlated with growth temperatures (6-9), with an abrupt jump at around 45°C (10). Here, using spacer abundance as the dependent variable, the minimal doubling time and the growth temperature as the independent variables, we performed multiple PGLS regression analyses.…”

“…CRISPR-Cas content and growth temperature. Previous studies observed that bacterial CRISPR abundance is positively correlated with growth temperatures (16)(17)(18)(19), with an abrupt jump at around 45C (20). We also examined the relationship between the CRISPR-Cas contents and optimal growth temperatures by controlling the minimal doubling time using 8 multiple PGLS regression analyses.…”

“…CRISPR-Cas content and growth temperature. Previous studies observed that bacterial CRISPR abundance is positively correlated with growth temperatures (16)(17)(18)(19), with an abrupt jump at around 45C (20). Here, we first compared the CRISPR-Cas contents and predicted minimal doubling times between thermophilic and mesophilic bacteria using the phylogenetic ANOVA method, phyloANOVA (12).…”