Picocyanobacteria (mainly Synechococcus and Prochlorococcus) contribute significantly to ocean’s primary production. Toxin-Antitoxin (TA) systems present in bacteria and archaea are known to regulate cell growth in response to environmental stresses. However, little is known about the presence of TA systems in picocyanobacteria. This study investigated complete genomes of Synechococcus and Prochlorococcus to understand the prevalence of TA systems in picocyanobacteria. Using the TAfinder software, Type II TA systems were predicted in 27 of 33 (81%) Synechococcus strains, but none of 38 Prochlorococcus strains contain TA genes. Synechococcus strains with larger genomes tend to contain more putative type II TA systems. The number of TA pairs varies from 0 to 42 in Synechococcus strains isolated from various environments. A linear correlation between the genome size and the number of putative TA systems in both coastal and freshwater Synechococcus was established. In general, open ocean Synechococcus contain no or few TA systems, while coastal and freshwater Synechococcus contain more TA systems. The type II TA systems inhibit microbial translation via ribonucleases and allow cells to enter the “dormant” stage in adverse environments. Inheritance of TA genes in freshwater and coastal Synechococcus could confer a recoverable persister mechanism important to survive in variable environments.

微微蓝藻（主要是聚球藻和原绿球藻）对海洋的初级生产有重要贡献。已知存在于细菌和古细菌中的毒素-抗毒素 (TA) 系统可调节细胞生长以响应环境压力。然而，关于微蓝细菌中存在 TA 系统的情况知之甚少。本研究调查了聚球藻和原绿球藻的完整基因组，以了解 TA 系统在微微蓝藻中的流行。使用 TAfinder 软件，在 33 种 (81%)聚球藻菌株中的 27 种中预测了 II 型 TA 系统，但 38 种原绿球藻菌株中没有一种含有 TA 基因。聚球藻具有较大基因组的菌株往往包含更多推定的 II 型 TA 系统。在从各种环境中分离的聚球藻菌株中，TA 对的数量从 0 到 42 不等。建立了沿海和淡水聚球藻中基因组大小与推定 TA 系统数量之间的线性相关性。一般来说，公海聚球藻不含有或很少含有 TA 系统，而沿海和淡水聚球藻含有更多的 TA 系统。II 型 TA 系统通过核糖核酸酶抑制微生物翻译，并允许细胞在不利环境中进入“休眠”阶段。淡水和沿海聚球藻中 TA 基因的遗传 可以赋予一个可恢复的持久性机制，对于在可变环境中生存很重要。