The genus Neisseria includes two pathogenic species, N. gonorrhoeae and N. meningitidis, and numerous commensal species. Neisseria species frequently exchange DNA with one other, primarily via transformation and homologous recombination, and via multiple types of mobile genetic elements (MGEs). Few Neisseria bacteriophages (phages) have been identified and their impact on bacterial physiology is poorly understood. Furthermore, little is known about the range of species that Neisseria phages can infect. In this study, we used three virus prediction tools to scan 248 genomes of 21 different Neisseria species and identified 1302 unique predicted prophages. Using comparative genomics, we found that many predictions are dissimilar from other prophages and MGEs previously described to infect Neisseria species. We also identified similar predicted prophages in genomes of different Neisseria species. Additionally, we examined CRISPR-Cas targeting of each Neisseria genome and predicted prophage. While CRISPR targeting of chromosomal DNA appears to be common among several Neisseria species, we found that 20% of the prophages we predicted are targeted significantly more than the rest of the bacterial genome in which they were identified (i.e., backbone). Furthermore, many predicted prophages are targeted by CRISPR spacers encoded by other species. We then used these results to infer additional host species of known Neisseria prophages and predictions that are highly targeted relative to the backbone. Together, our results suggest that we have identified novel Neisseria prophages, several of which may infect multiple Neisseria species. These findings have important implications for understanding horizontal gene transfer between members of this genus. IMPORTANCE: Drug-resistant N. gonorrhoeae is a major threat to human health. Commensal Neisseria species are thought to serve as reservoirs of antibiotic resistance and virulence genes for the pathogenic species N. gonorrhoeae and N. meningitidis. Therefore, it is important to understand both the diversity of mobile genetic elements (MGEs) that can mediate horizontal gene transfer within this genus, and the breadth of species these MGEs can infect. In particular, few bacteriophages (phages) have been identified and characterized in Neisseria species. In this study, we identified a large number of candidate phages integrated within the genomes of commensal and pathogenic Neisseria species, many of which appear to be novel phages. Importantly, we discovered extensive interspecies targeting of predicted phages by Neisseria CRISPR-Cas systems, which may reflect their movement between different species. Uncovering the diversity and host range of phages is essential for understanding how they influence the evolution of their microbial hosts.
The Repertoire of Minimal Mobile Elements in the Neisseria Species and Evidence That These Are Involved in Horizontal Gene Transfer in Other Bacteria