ИСТИНА

Defense systems of prokaryotes protect them against an invasion of foreign DNA. The most widely known defense systems are Restriction-Modification and CRISPR-Cas systems, dozens of new systems have been recently found [1]. Defense systems are often studied on WGS data and their distribution in real microbial communities has not been intensively studied yet. We found genes of known defense systems and phage capsid proteins in the World Ocean, using metagenomes of the Tara Oceans project [2] and revealed a relationship between ecological conditions and distribution of the defense genes. Homologs of R-M systems, CRISPR-Cas, and 13 other defense systems were found in 135 samples of the Tara Oceans project. Geographically adjacent samples did not demonstrate noticeable similarity by R-M system composition. Samples from the deep oceanic layer (> 200 m) possess more numerous and diverse set of the defense systems of each type as compared to the surface samples. At the same time, phage capsid proteins do not share this trend. It implies that the benefits of defense system usage could depend not only on phage concentration itself but also some environmental factors. The work was supported by Russian Foundation for Basic Research (RFBR) grant no 18-34-00860. Doron S, et al. (2018) Science. 359(6379). Sunagawa S, et al. (2015) Science. 348(6237):1261359.