A fundamental strategy of eukaryotic antiviral immunity involves the cGAS enzyme, which synthesizes 2′,3′-cGAMP and activates the effector STING. Diverse bacteria contain cGAS-like enzymes that produce cyclic oligonucleotides and induce anti-phage activity, known as CBASS. However, this activity has only been demonstrated through heterologous expression. Whether bacteria harboring CBASS antagonize and co-evolve with phages is unknown. Here, we identified an endogenous cGAS-like enzyme in Pseudomonas aeruginosa that generates 3′,3′-cGAMP during phage infection, signals to a phospholipase effector, and limits phage replication. In response, phages express an anti-CBASS protein (“Acb2”) that forms a hexamer with three 3′,3′-cGAMP molecules and reduces phospholipase activity. Acb2 also binds to molecules produced by other bacterial cGAS-like enzymes (3',3'-cUU/UA/UG/AA) and mammalian cGAS (2′,3′-cGAMP), suggesting broad inhibition of cGAS-based immunity. Upon Acb2 deletion, CBASS blocks lytic phage replication and lysogenic induction, but rare phages evade CBASS through major capsid gene mutations. Altogether, we demonstrate endogenous CBASS anti-phage function and strategies of CBASS inhibition and evasion.

真核抗病毒免疫的一个基本策略涉及 cGAS 酶，它合成 2',3'-cGAMP 并激活效应器 STING。多种细菌含有类 cGAS 酶，可产生环状寡核苷酸并诱导抗噬菌体活性，称为 CBASS。然而，这种活性仅通过异源表达得到证实。携带 CBASS 的细菌是否与噬菌体拮抗并共同进化尚不清楚。在这里，我们在铜绿假单胞菌中鉴定了一种内源性 cGAS 样酶，该酶在噬菌体感染期间产生 3',3'-cGAMP，向磷脂酶效应子发出信号，并限制噬菌体复制。作为响应，噬菌体表达抗 CBASS 蛋白（“Acb2”），该蛋白与三个 3',3'-cGAMP 分子形成六聚体并降低磷脂酶活性。 Acb2 还与其他细菌 cGAS 样酶 (3',3'-cUU/UA/UG/AA) 和哺乳动物 cGAS (2',3'-cGAMP) 产生的分子结合，表明对基于 cGAS 的免疫具有广泛的抑制作用。 Acb2 缺失后，CBASS 会阻止裂解性噬菌体复制和溶原性诱导，但罕见噬菌体通过主要衣壳基因突变来逃避 CBASS。总而言之，我们证明了内源性 CBASS 抗噬菌体功能以及 CBASS 抑制和逃避策略。